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OCULAR ACCOMMODATION Studies of amplitude, insufficiency, and facility training in young school children Bertil Sterner Department of Ophthalmology Institute of Clinical Neuroscience Göteborg University 2004 ii ISBN 91-628-5989-7 © Bertil Sterner Department of Ophthalmology Institute of Clinical Neuroscience Göteborg University Sweden Printed by Vasastadens Bokbinderi AB iii Till minne av min far Nils och min bror Ulf iv v ABSTRACT The purpose of this thesis was to establish the sufficiency of the ocular accommodation and to characterize accommodative problems and related symptoms among otherwise healthy young school children. The purpose was also to evaluate an accommodative facility training technique by studying the effect of the training on relative accommodation. Children from a junior level school were invited to participate in an examination of the accommodative function which was then compared to expected age levels. Children aged 9–13 years, referred by School Health Care for near work-related problems and complaining of headaches, blurred vision, asthenopia, loss of concentration, and avoidance of near activity, were also studied. Only children with reduced negative relative accommodation (NRA) and positive relative accommodation (PRA) and/or very slow accommodative facility were included. The subjects used an accommodative facility training technique until they reported that the symptoms had disappeared. The results showed lower amplitudes than expected in a large group of children and not equivalent to the expected age values. More than one third of the children reported subjective symptoms at near. The incidence of subjective symptoms emerged at the age of 7.5 years and there was significant discrimination ability between low amplitude and subjective symptoms. In all of the trained children the symptoms gradually decreased and finally disappeared during the training period. The data showed a significant increase, despite some individual variations, in both mean NRA and mean PRA among all children characterized with accommodative infacility due to an impaired relative accommodation. Accommodation is not as sufficient in young children as expected. Subjective symptoms emerge at the age of 7.5 years and there is a clear relation between accommodative parameters and these subjective symptoms. Clear standards for diagnosing an accommodative dysfunction need to be further refined. The results also indicate that accommodative facility training is an effective method resulting in loss of symptoms and that it also has a real effect on the relative accommodation in patients with impaired relative accommodation. Because accommodative dysfunctions may result in subjective symptoms, it is of great importance to identify this dysfunction to prevent unnecessary near vision problems. vi APPENDED PAPERS This work is based on following papers: Paper I. Sterner B., Gellerstedt M., Sjöström A. The amplitude of accommodation in 6–10-year-old children – not as good as expected! (Accepted for publication, Ophthalmic and Physiological Optics). Paper II. Sterner B., Gellerstedt M., Sjöström A. Accommodative insufficiency, subjective symptoms, and reference values for young school children. (Submitted). Paper III. Sterner B., Abrahamsson M., Sjöström A. (1999). Accommodative facility training with a long term follow up in a sample of school aged children showing accommodativedysfunction. Documenta Ophthalmologica 99: 93–101. Paper IV. Sterner B., Abrahamsson M., Sjöström A. (2001). The effects of accommodative facility training on a group of children with impaired relative accommodation - a comparison between dioptric treatment and sham treatment. Ophthalmic and Physiological Optics. 21: 470-476. The papers are reproduced with kind permission from Kluwer Academic Publishers and Blackwell Publishing. vii ABBREVIATIONS AC/A C CA CNS cpm D DA NRA NRM PC PRA PRM SD TA Accommodative convergence/accommodation Convergence Convergence accommodation Central nervous system Cycles per minute Diopter Prismatic diopter Dark accommodation Negative relative accommodation Negative relative movement Point of convergence Positive relative accommodation Positive relative movement Standard deviation Tonic accommodation viii ix TABLE OF CONTENTS INTRODUCTION .................................................................................... 1 The mechanism of accommodation.................................................. 1 Neural pathways ............................................................................... 3 Accommodative measurements........................................................ 6 Stimuli to accommodation ........................................................ 6 Amplitude of accommodation................................................... 6 Facets of accommodation ......................................................... 8 Accommodative measurements............................................... 13 Accommodative dysfunction .......................................................... 14 Presbyopia .............................................................................. 14 Dysfunction ............................................................................ 15 Asthenopia.............................................................................. 16 Accommodative therapy................................................................. 19 OBJECTIVES ........................................................................................ 21 SUBJECTS ............................................................................................. 23 METHODS ............................................................................................. 25 RESULTS ............................................................................................... 27 DISCUSSION ......................................................................................... 31 CONCLUSIONS..................................................................................... 37 FUTURE STUDIES................................................................................ 38 ACKNOWLEDGMENTS ...................................................................... 39 REFERENCES ....................................................................................... 41 APPENDED PAPERS (I - IV) x B. STERNER. OCULAR ACCOMMODATION. 1 INTRODUCTION The mechanism of accommodation Accommodation is the ability of the eye to change the refractive power of the lens and automatically focus objects at various distances on the retina. The accommodative process, which involves the accommodative apparatus illustrated in Figure 1, includes contraction of the ciliary muscle, which releases the tension on the zonular fibers, allowing the elastic lens capsule to increase its curvature, especially that of the front surface. Along with these changes, an increase in the thickness of the lens, a decrease in its equatorial diameter, and a reduction in pupil size take place (Brown, 1972) (Figure 2). Figure 1. The accommodative apparatus. Accommodation is measured in diopters (D), which is the reciprocal of the fixation distance. Thus, if the fixation distance is 1 m, the accommodation is said to be 1 D; if it is 0.5 m or 0.33 m, the accommodation is 2 D or 3 D, respectively. The furthest distance at which an object can be seen clearly is called the far point (punctum remotum). In order to see such an object the eye is in a state of rest, the ciliary muscle is relaxed, and the refractivity is at minimum. 2 B. STERNER. OCULAR ACCOMMODATION. Figure 2. Schematic picture of the lens and the ciliary muscle when relaxed during ”distance” vs accommodated during ”near” vision. When maximum accommodation is in force, the nearest point which the eye can see clearly is called the near point (punctum proximum). The difference between the refractivity of the eye in the two conditions – when at rest with minimal refraction, and when fully accommodated with maximal refraction – is called the amplitude of accommodation. In order to accurately perform visually guided daily tasks, it is necessary for the accommodative system to be dynamic, fast, and precise to ensure a wellfocused image on the retina. It has been known for over 50 years that, under certain conditions, accommodative activity in the eyes may act as a stimulus which produces a change in the relative position of the visual axes as a response (Morgan, 1944a). When the angle formed by the visual axes increases this is called convergence, and when it decreases, we call this divergence. In addition, with fixation at near pupillary constriction, miosis occurs (Jampel, 1959; Von Noorden, 1985). The synkinetic association between accommodation, convergence, and miosis during fixation at near may be termed the near vision complex or near response. The accommodative act is normally accompanied by a change in convergence because of the synkinetic association between the ciliary muscle and the medial recti muscle (of the eye) (Duke-Elder. 1971). An accommodative stimulus acts as a trigger which excites innervational mechanisms for convergence. This response of convergence due to the accommodation constitutes accommodative convergence. However, due to B. STERNER. OCULAR ACCOMMODATION. 3 the synkinetic association, a stimulus for convergence can also provoke an accommodative impulse called convergence accommodation. Neural pathways The afferent pathways that stimulate accommodation and the light reflex emanate from retinal receptors. Impulses are propagated through the nervus opticus, the chiasma, and the tractus opticus to corpus geniculatum laterale. The pupillomotoric nerves involved in the light reflex, unlike the visual pathways, project without any synaptic connections in corpus geniculatum laterale directly to nucleus pretectale and to the EdingerWestphal nucleus (Figure 3). Following nervus oculomotorius, the efferent signals travel via ganglion ciliare into musculus sphincter pupillæ (Walsh and Hoyt 1969a). The afferent sensory visual pathways have a synapse in corpus geniculatum laterale and proceed to the primary visual cortex. Figure 3. Neural pathways involved in the light reflex and accommodation. Pathways and areas in the CNS (central nervous system) that are related to accommodation and vergence eye movements as described by Gamlin (2002) are schematically illustrated in Figure 4. Pathways to areas that are known to be, or based on anatomical studies or electrophysiological studies believed to be related to accommodation and vergence eye movements are also illustrated. 4 B. STERNER. OCULAR ACCOMMODATION. Figure 4. Schematic illustration of neural pathways involved in the control of accommodation and vergence eye movements in CNS. Pathways to areas that are known to be, or based on anatomical studies or electrophysiological studies believed to be related to accommodation and vergence eye movements, are shown with solid lines. The pathways and areas that remain to be identified are shown with dotted lines and question marks. The efferent pathways, both parasympathetic and sympathetic fibres, involved in the accommodative process as described by Richter et al. (2000) are illustrated in Figure 5. B. STERNER. OCULAR ACCOMMODATION. 5 Figure 5. Illustration of the efferent pathways, both parasympathetic and sympathetic fibres, involved in the accommodative process. The major innervation to the ciliary muscle is parasympathetic and originate in the Edinger-Westphal nucleus. The fibres follow Nervus oculomotorius and synapse in the ciliary ganglion. Most of the postganglionic parasympathetic fibres travel to the ciliary muscle via the short ciliary nerves, but some of them (14) also travel with the long ciliary nerves. A direct pathway of uncertain functional significance (11) to the internal eye structures from the EdingerWestphal nucleus is also illustrated. The sympathetic innervation of the ciliary muscle starts in the diencephalon and travels caudally down to the lower cervical and upper thoracic segments to synapse in the ciliospinal centre of the spinal cord. From there, second-order neurones leave the cord by the last cervical and first thoracic ventral roots; these preganglionic fibres run up the cervical chain to synapse in the cervical ganglion. The third-order neurones continue up the sympathetic carotid plexus and enter the eye, either with the trigeminal nerves first division (following the nasociliary division) or independently, where they join the long and short ciliary nerves, in the latter instance passing through the ciliary ganglion without synapse (Richter et al., 2000). 6 B. STERNER. OCULAR ACCOMMODATION. Accommodative measurements Stimuli to accommodation The characteristics of effective accommodative stimuli are central to our understanding of the accommodative system. There are a number of different accommodative stimuli which stimulate accommodation to a varying degrees (Sivak & Bobier, 1978; Kruger & Pola, 1985; McLin Jr et al., 1988; Comerford & Thorn, 1990; Siderov & Johnston, 1990; Rosenfield et al., 1991; Gray et al., 1993; Mathews & Kruger, 1994; Rosenfield & Cohen, 1995; Kruger, Aggarwala et al. 1997; Kruger, Mathews et al., 1997): • • • • • • Blur of the object Proximity of the target Changing target size Chromatic abberation Convergence of the eyes Spatial frequency These are all different stimuli to accommodation, with blur of the object having the greatest impact as an accommodative stimulus, though dependent on visual acuity (White & Wick, 1995). However, an important implication is the completely different character of these accommodative stimuli, which can act together as well as individually. The inherent differences between the stimuli therefore require that different methods be used to describe them. Amplitude of accommodation The ability to accurately focus a visual target at varying distances exists to some extent from birth (Banks, 1980a), but improves rapidly in the first 3–6 months of life (Banks, 1980b; Howland, 1982–83; Hainline et al., 1992; Bobier et al., 2000). It is belived that a small child is normally able to focus from infinity down to a distance close to the eyes because of a high level of accommodative amplitude. However, accommodation and convergence are not evidently automatically linked from the start (Hainlineet al., 1992). In 1912, Duane presented his result on the accommodative amplitude among 1000 subjects aged 8 to 70 years. The given data are still commonly used as normality for accommodative amplitude in relation to age. A B. STERNER. OCULAR ACCOMMODATION. 7 formula based on Duane’s data, (minimum amplitude = 15 – 0.25 · age, expected amplitude = 18.5 – 0.3 · age, and maximum amplitude=25–0.4·age), predicts the range of accommodative amplitude expected at a given age (Hofstetter, 1950) (Figure 6). Because there were only 35 eyes between 8 to 12 years of age the reliability of this “normality” for these ages has been discussed (Turner, 1958; Wold, 1967; Kragha, 1986). Based on this formula, a 3 year old child is expected to have an average accommodative amplitude of 17.6 D. A study by McBrien and Millodot(1986) shows different data on accommodative amplitude linked to ametropia among 18-22-year-old subjects (i.e., late-onset myopes: mean10.77D; earlier-onset myopes: mean 9.87 D; emmetropes: mean 9.28D; and hyperopes: mean 8.63 D). This is an issue to consider in discussing the normality of the accommodative amplitude. Figure 6. The classic diagram from Duane (1912) showing the relation between age (x-axis) and accommodative amplitude in diopters (y-axis), with each dot representing the maximum amplitude of accommodation in an individual eye at a given age. The straight line is a plot of the prediction formula (expected amplitude= 18.5 – 0.3 · age) by Hofstetter (1950). 8 B. STERNER. OCULAR ACCOMMODATION. Facets of accommodation The accommodative function is normally explained, although insufficiently, by describing the accommodative amplitude and its dioptric value. However, the accommodative function is more complicated than that. The accommodative system is complex; the different facets of the accommodative function, beside the amplitude, are described and explained elsewhere in the literature (Rouse et al., 1984; Wick & Hall, 1987; Michaels, 1987; Rosner & Rosner, 1989; Von Noorden & Avilla, 1990; Ebenholtz, 1991; Miwa & Tokoro, 1993). Different facets of the accommodative function, together with accommodative amplitude, are listed below: • • • • • Tonic accommodation Lag of accommodation Convergence accommodation Accommodative facility Relative accommodation These facets differ greatly from each other with regard to function. They require different methods of examination and they are not explained by the same dioptric values; nor is a unified system of measurement used for their dioptric results. Each of the accommodative facets listed above is described below. However, in this thesis, I will concentrate on the amplitude of accommodation, accommodative facility, and relative accommodation with regard to function, method of examination, and expected dioptric value. In the case of failure of function, associated symptoms will be described. Tonic accommodation Tonic accommodation (TA), or dark accommodation (DA) (Tsuetaki&Schor, 1987; Rosner & Rosner, 1989; Ebenholtz, 1991; Rosenfield et al., 1992; Chiu & Rosenfield, 1994; Rosenfield et.al., 1994), is the passive state of accommodation in the absence of a stimulus, that is, when the eye is either in complete darkness, or when it is looking at a bright empty field (open-loop). One method of measuring the open-loop is by using an objective infrared optometer (Gray et al., 1998). B. STERNER. OCULAR ACCOMMODATION. 9 Lag of accommodation The amount by which the accommodative response of the eye is less than the dioptric stimulus to accommodation is defined as accommodative lag (Rouse et al., 1984; Wick & Hall, 1987; Goss & Zhai, 1994). Clinical measurement of accommodative lag at near is typically done using dynamic retinoscopy. This is an objective method in which the patient views a near point target, while the examiner adjusts the lens power, uses a “skia ladder”, or his or her distance from the patient. Convergence accommodation Convergence accommodation is normally described by the ratio between convergence accommodation and convergence, or the CA/C ratio (Morgan, 1944a). The ratio is a measure of the effect of a change in convergence on accommodation. It is expressed as the change in accommodation (in D) for each change in convergence (in prism D) (Tsuetaki & Schor, 1987). Accommodative facility Accommodative facility is the ability to rapidly change the refractive power of the lens to various focus distances (Wick & Hall, 1987) while maintaining a requisite angle of convergence (binocular) or eliminating the influence of convergence (monocular). This ability is important when changing fixation from near to distance, and back again. Clinically, accommodative facility can be measured using lenses that stimulate (minus) or inhibit (plus) accommodation. Any combination of lens power can be used for evaluation, but empirical testing has indicated that ±2.00 D is a reasonable choice (McKenzie et al., 1987). The testing procedure uses ±2.00 D lens pairs mounted in a flipper frame. A “flipper” is a holder with two minus lenses and two plus lenses (Figure 7). Figure 7. Flip lenses. 10 B. STERNER. OCULAR ACCOMMODATION. The subject focuses through one pair of lenses at an object at near distance (40 cm). When the object is clearly focused, a flip is quickly performed to the other lens pair and the subject focuses through them. This is then repeated and the number of cycles completed in 1 minute (cpm) is recorded as the accommodative facility. Normative data on monocular as well as binocular accommodative facility have been collected on both adult pre-presbyopic populations (Zellersetal., 1984; Siderov & Diguglielmo, 1991) and young school children (Hennessey et al., 1984; Scheiman et al., 1988; Jackson&Goss,1991a) (Table 1). In the study by Siderov&Diguglielmo(1991), adults between 30 years and 42 years of age showed a mean and SD for the ±2.00 flip task of 1.2 ±2.1 cpm binocularly. Another study, by Zellers et al. (1984), of adults aged 18–30years, had a mean and SD for the binocular ±2.00 flip task of 7.72±5.15 cpm. Two studies of young school children aged 6–12 reported means and SDs on the binocular ±2.00 flip task. Results were 5.0 ±2.7 cpm in one study (Jackson & Goss, 1991a), and 3.83 ±2.5 cpm in another (Scheiman et al., 1988). One reason for the lower mean cpm in this age group, as compared with the results for 18–30-year-olds, may be the difference in instructional sets. Instead of the subjects holding the flip lens, as with the adult groups, the examiner held it. One also has to consider possible differences with respect to the age and the time necessary for saying “clear” (Kedzia et al. 1999). Table 1. Binocular accommodative facility in cpm (mean ± SD) using ±2.00 D flip lenses. Age 6-12 years Jackson & Goss Scheiman et al. Zellers et al. Siderov & Diguglielmo Age 18-30 years Age 30-42 years 5.0 ± 2.7 3.83 ± 2.5 7.72 ± 5.15 1.2 ± 2.1 The monocular (Rouse et al., 1989) and binocular (Rouse et al., 1992) accommodative facility rates have previously been studied in an attempt to establish normative data and cutoff values which differentiate symptomatic from asymptomatic subjects (McKenzie et al., 1987; Garcia et al., 2000). The 1-minute testing method appears reliable if the initial rate is lower than 3 cpm. For patients whose initial rate is between 3 cpm and 8cpm, extended testing (i.e., 1–2 minutes’ additional testing) may be needed to arrive at an accurate diagnosis. B. STERNER. OCULAR ACCOMMODATION. 11 Relative accommodation The total amount of accommodation, which can be exerted while the convergence of the eyes is fixed, is called relative accommodation (Morgan, 1944a). This can be either positive relative accommodation (PRA) or negative relative accommodation (NRA). The PRA is the amount of accommodation in excess of the accommodation needed for convergence and the NRA is the amount of accommodation below that of convergence (Gettes, 1957) (Figure 8). Figure 8. The relation between positive relative accommodation (PRA), negative relative accommodation (NRA), and the point of convergence (PC). The dotted lines in the Figure describe the point the accommodation is focused to when a plus lens (for NRA) or a minus lens (for PRA) is added without changing the convergence stimuli. The positive relative movement (PRM) and negative relative movement (NRM) describe the direction of the different dioptric focus change movements of the PRA and the NRA in relation to the PC. Hung & Ciuffreda (1994) describe how relative accommodation is measured. In assessing accommodative flexibility, with a constant convergence stimulus and under binocular fusion, the accommodative stimulus was binocularly decreased. This is done by starting with positive lenses and continuing in +0.25 D steps over the distance correction, with the vergence stimulus (at 40 cm) held constant, until the first slight sustained blur is subjectively noted by the patient. The decreased amount of accommodative stimulus at this point is referred to as the NRA value. Back to distance correction, and if the accommodative stimulus is now increased binocularly with negative lenses in –0.25 D steps until the first slight sustained blur is again noticed, the increased amount of accommodative stimulus at this point is referred to as PRA. 12 B. STERNER. OCULAR ACCOMMODATION. Means for NRA and PRA in 800 subjects all of whom had an accommodative amplitude of 5.00 D or more, have been presented in Goss& Zhai (1994), to be +2.00 ±0.50 D and –2.37 ±1.12 D, respectively. In the same study, 1000 school children from first to twelfth grade had a mean NRA of +1.75 ±0.56 D and a mean PRA of –2.37 ±1.00 D. An important question at this point is what happens with the NRA/PRA value if we add prismatic diopter ()? Is it possible, for example, to increase the NRA value if we add base in prism? We know by hearsay that 6 with prismatic base in will increase the NRA value by approximately +0.50 D, but could not find any evidence in the literature for this relation. Due to the near vision complex, a certain portion of convergence is linked when accommodation is in force. The relation between the dioptric change of the accommodation and the prismatic change of the convergence is called the accommodative convergence/accommodation (AC/A) ratio. The AC/A ratio describes how much accommodative convergence is activated by an accommodative change of 1 D. In Table 2, the relationship between high, normal, and low AC/A ratios and the different convergence stimuli is described. Table 2. The relation between the AC/A ratio and the convergence stimuli when accommodation is changed by ± 2.00 D. AC/A “High” “Normal” “Low” AC/A ratio (/D) >5 3 to 5 <3 Convergence stimuli () >±10.0 ±6.0 to ±10.0 <±6.0 The normal range of the AC/A ratio is between three and five. Values above five are considered to denote excessive accommodative convergence and values below three an insufficiency (von Noorden & Avilla, 1990). In individuals with high AC/A ratio the larger convergence stimuli induced by the changed accommodation may affect the measured threshold of the PRA and/or the NRA if the fusional vergence is at its limit. If a prismatic lens is added in front of the eye, thereby changing the convergence stimuli, a change in accommodation will be expected. If we add a base in prism in front of the eye the convergence stimuli will change to a point further away from the eye. As a result, the PRA value will decrease and the NRA value will increase. 13 B. STERNER. OCULAR ACCOMMODATION. The correlation of PRA with prismatic base in blur at near distance is to be expected because the amount of PRA a person can exert may be limited by his or her negative fusional vergence capability (i.e., divergence with fusion at the same stimuli). There is a similar correlation between NRA with near base-out blur because NRA may be limited by the amount of available positive fusional vergence (i.e., convergence with fusion at the same stimuli) (Jackson & Goss, 1991b). Tests for PRA and NRA are very helpful in determining accommodative dysfunction (Weisz, 1983). A low NRA reveals accommodative spasticity; a very low PRA on the other hand, suggests that the focusing system may be prone to tiring after concentrated near work. Accommodative measurements The different accommodative components listed above require different methods of measuring accommodative ability and yielding dioptric results. There is no method in use that describes the complete accommodative function or even some of the functions put together, nor do we use the same measuring system for the different dioptric results. Since there is no method to combine the results of various accommodative components, we need to find out whether any existing method can be useful in identifying an accommodative dysfunction of any kind. The following tests are in use: Amplitude tests: Donders push-up method: This makes use of a RAF ruler (Figure 9). Figure 9. Instrument for measuring the closest focus distance in diopters (D), the RAF ruler. Sheard´s (1957) method: Here, minus lenses are added at far distance, monocularly or binocularly, until blur at distance occurs. 14 B. STERNER. OCULAR ACCOMMODATION. Facility tests: ±2.00 D flip lens test: This is used to measure the exertion and relaxation change of the accommodation in cpm (see also page 9, ”accommodative facility”, Figure 7). Relative accommodation: In this test, changing the accommodative stimulus assesses the accommodative flexibility. Objective tests: Dynamic retinoscopy: This is used to establish the degree of lag of accommodation (Leat & Gargon, 1996). Infrared optometers, e.g., a power refractor: These are used to examine the eyes for defects of refraction. Miscellaneous tests: Binocular cross cylinder at near distance: With this, the magnitude of the dioptric reading addition is established while the subject focuses a near distance object. Comparing cycloplegic and manifest refraction: This is done to objectively look for refractive differences (e.g., accommodative spasm or latent hyperopia) using retinoscopy. Accommodative dysfunction Presbyopia The ability to accommodate slowly deteriorates through life and during the fifth decade of life insufficient accommodative ability becomes a manifest problem for the emmetrope. The amplitude of accommodation has decreased to a level of approximately 4 D (Koretz & Handelman, 1988) and focusing at normal reading distance either requires longer arms or proper optical aids. This condition is called presbyopia (Duane, 1912) and the decrease of the accommodative amplitude continues until the amplitude of accommodation almost reaches 0 D. The development of presbyopia is not well understood, and there are theories that attempt to explain its mechanism (Bito, 1988; Fisher, 1988; Atchison, 1995; Beers & Van der Heijde, 1996). Although presbyopia means “vision of old age”, its onset can rarely be chronologically defined because it varies with coexisting ametropia, illumination, target size and B. STERNER. OCULAR ACCOMMODATION. 15 distance, the effect of drugs, arm length, geographic latitude, and psychological factors (Michaels, 1987). Dysfunction The accommodative system at young age is fairly flexible and resistant to fatigue (Berens & Sells, 1944). However, in clinical practice, accommodative dysfunction occurs among pre-presbyopic patients. Often patients complain of symptoms that appear when doing near distance work. The refractive status can be emmetropic or slightly ametropic but this is not always in relation to the patients’ complaints. There is, as mentioned previously, no simple standard procedure for examination of the accommodative system including all its facets. Because of the lack of such method, and the fact that we do not have any simple method to treat accommodative problems, the accommodative system is not routinely examined. Still it is of great importance to identify a dysfunction so that unnecessary near vision problems may be prevented. It is essential to identify any accommodative deficiencies in young individuals as soon as possible after school start. Because the focusing system of the eyes has a contribution in the learning process (Flax, 1970; Sucher & Stewart, 1993), any accommodative deficiency can make it unnecessarily difficult for the child to read and develop in school. If the child does not prevent his or her difficulties to accommodate he or she may always harbor a dislike for near distance work. Therefore, we need to find a simple and easy-to-use method that identifies and diagnoses an accommodative dysfunction. It can be difficult to group accommodative dysfunctions because the boundaries are often unclear. However, clinically it is useful to separate anomalies of accommodation into one of five distinct syndrome categories (Walsh & Hoyt, 1969b; Duke-Elder, 1971): • • • • • Insufficiency of accommodation Infacility of accommodation Fatigue of accommodation Spasm of accommodation Paresis of accommodation These five syndromes all constitute different accommodative disorders, with a different impact on the accommodative function (Table 3). 16 B. STERNER. OCULAR ACCOMMODATION. Asthenopia Different symptoms associated with accommodative dysfunction are also listed in Table 3. Asthenopia is a term used to describe eyestrain or symptoms associated with the use of the eyes (Millodot, 1986). In Figure 10, the most common causes of eyestrain are illustrated. Table 3. Diagnostic criteria with respect to accommodative dysfunction, and the incidence of related findings and symptoms. • •• Occasional incidence Frequent incidence Diagnosis Insufficiency of accommodation Fatigue of accommodation Spasm of accommodation Paresis of accommodation Infacility of accommodation Reduced relative accommodation Reduced accommodative facility Associated symptoms * •• Reduced ciliary muscle function • • • •• • •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• Reduced accommodative amplitude * Asthenopia, blur, headaches, diplopia, accommodative facility problems, photophobia, and reading problems are the most frequently reported symptoms indicating accommodative dysfunction (Hoffman and Rouse, 1980; Daum, 1983a; Hennessey et al. 1984). 17 B. STERNER. OCULAR ACCOMMODATION. Accommodative insufficiency Accommodative infacility Accommodative fatigue Accommodative paresis Accommodative spasm Uncorrected hypermetropia Concentration difficulties Uncorrected astigmatism Uncorrected presbyopia Dyslexia Asthenopia Neurological reasons Hysteria Aniseikonia Improper illumination Heterophoria Latent nystagmus Retinal/eye disease Musculus rectus medialis dysfunction Ocular inflammation, pain in the eye, dry eye Figure10. Illustration of different causes of asthenopia. Insufficiency of accommodation is a condition in which the amplitude of accommodation is chronically below the lower limits of the expected amplitude of accommodation for the patient’s age (VonNoordenetal.,1973; Daum, 1983b). Morgan (1944b), in describing various diagnostic criteria, states that insufficiency of accommodation occurs when the accommodative amplitude is reduced by more than 2 D below Duane’s expected values for age (1912). Daum (1983b) uses a criterion on 2 D below Hofstetter’s equation for the minimum amplitude by age. However, there is no consensus regarding the criteria for making the diagnosis. In a recent study (Cacho et al. 2002) a summary of nine different studies of insufficiency was given, all with different criteria. Most of the criteria contained the equations presented by Hofstetter (1950). Symptoms include headache, asthenopia, inability to focus on near objects or to sustain clear vision for a reasonable period of time. A study on nine children aged 9–16 years (Matsuo & Ohtsuki, 1992) with low accommodative amplitude in both eyes reports that the subjects had severe complaints of asthenopia, diplopia, and difficulty in reading. The clinical recognition of accommodation insufficiency is important in preventing unnecessary frustration in young school children (Chrousos et al., 1988). 18 B. STERNER. OCULAR ACCOMMODATION. Infacility of accommodation is the condition in which the ability to rapidly change accommodation from far to near distance is failing, or in which a rapid change of accommodation induces symptoms such as asthenopia, headache, and blur (Hennessey et al., 1984). It differs from accommodative insufficiency in that clear vision is eventually achieved (Michaels, 1987). Diagnostic criteria for accommodative infacility are an NRA and PRA of < ±1.75 D (Morgan, 1944b; Hennessey et al., 1984) and/or a facility test using the ±2.00 D flip test showing 1 SD below the mean of 3 cpm (Hennessey et al., 1984). If changing fixation from distance to near takes more than 1 second an abnormal condition is likely to be present (Daum, 1983a). Fatigue of accommodation is described as the inability of the ciliary muscle to maintain contraction while viewing a near target with a resulting shift in accommodation toward the far point (Pigion & Miller, 1985; Owens & Wolf-Kelly, 1987; Schor & Tsuetaki, 1987). Spasm of accommodation is a constant or intermittent involuntary and inappropriate ciliary contraction (Rutstein et al., 1988; Goldstein & Schneekloth, 1996). It may be unilateral or bilateral. Symptoms include distance and/or near blur, visual distortion, a drawing or pulling sensation, and possibly intermittent or persistent diplopia (Michaels, 1987). Also, a dynamic retinoscopy shows a lag of <±0.00 D (Rouse et al., 1984). The most common cause for paresis of accommodation is topical cycloplegia, whether deliberate or inadvertent. Such palsy is generally unilateral, transient, and evident from a patient’s history (Michaels, 1987; Mutti et al., 1994). Accommodative paresis can also be functional owing to weakness or fatigue of the ciliary muscle (Duke-Elder, 1971). However, a person’s ability to perform a nearpoint task may be impaired due to the accommodative syndromes listed above if, for example, his or her accommodative facility is deficient despite having sufficient accommodative amplitude (Hennessey et al., 1984). It is therefore essential to identify the exact cause of accommodative dysfunction in order to alleviate symptoms, improve accommodation efficiency, and decide on the type and extent of treatment. B. STERNER. OCULAR ACCOMMODATION. 19 Accommodative therapy Accommodative dysfunction is not an uncommon visual anomaly and the symptoms generally occur during the performance of nearpoint tasks (Daum, 1984). Dysfunctions of accommodation, which have been treated by optometric intervention, are usually clinically classified as those dysfunctions mentioned previously, namely accommodative insufficiency, accommodative spasm, accommodative fatigue, and accommodative infacility (Suchoff & Petito, 1986), with insufficiency and infacility as the most frequent forms of dysfunction (Daum, 1983a). After ruling out neurologic, pharmaceutical, or general health causes, the treatment of a dysfunction is generally a plus lens addition or orthoptic exercise (Hoffman, 1982; Bobier & Sivak, 1983; Cooper et al., 1987). In cases of accommodative insufficiency, treatment consists of either providing proper distance refractive correction, a plus add for near, or both (Goss, 1992), or orthoptic exercises aimed at strengthening the accommodative or vergence mechanisms, such as “push-up” training or flip lens training (Daum 1983b). A plus lens addition is recommended in cases of an excessive lag in accommodation, very low PRA (< –1.5 D), difficulty in performing the minus lens part of the ±2.00 D facility test, or fatigue during the facility test (Weisz, 1983). The prescription can be in the form of either normal reading glasses or a bifocal solution. Orthoptic excercise is indicated when there is spasticity in the accommodative system or the accommodative system is poorly controlled (Cooper et al., 1987). It is also indicated if the patient cannot clear the initial plus lens flip on the ±2.00 D or if the NRA is low (i.e., <+1.5 D). Orthoptic excercise is a sequence of activities individually prescribed and monitored by the examiner to develop efficient visual skills and processing. One particular method in orthoptic excercise is the flip lens technique. A “flipper”, as described previously, is a holder with two minus lenses and two plus lenses (Figure 7). The subject focuses through one pair of lenses at an object at near distance (40 cm). When the object is clearly focused, a flip is quickly performed to the other lens pair and the subject focuses through this. The process is then repeated. There is scientific and clinical evidence to support the efficacy of using facility therapy techniques to “strengthen” or improve accommodative function (Wold et al., 1978; Liu et al., 1979; Weisz, 1979; 20 B. STERNER. OCULAR ACCOMMODATION. Levineetal.,1985; Hung et al., 1986; Rouse, 1987; Ciuffreda & Ordonez, 1998;Sterner et al., 1999; Ciuffreda, 2002). B. STERNER. OCULAR ACCOMMODATION. 21 OBJECTIVES Overall aim The aims of the present work have been firstly to study how sufficient the accommodation functions in otherwise healthy children and to identify and characterize symptoms related to accommodation. Secondly, to evaluate an accommodative facility training technique in children with impaired relative accommodation. It is important to ascertain how accommodation functions in younger ages, how to identify a dysfunction, and to evaluate treatment, before conclusions can be drawn about other groups such as visually impaired pre-presbyopes with accommodative dysfunction. Specific aim: Paper I The knowledge regarding accommodation in younger ages is rather limited. An extrapolation of Duane’s data using Hofstetter’s age amplitude formula suggests high amplitude of accommodation in younger ages. This could perhaps explain why younger children are in some extent neglected due to the expectation of sufficient accommodative ability. Such extrapolation may therefore give a false impression because accommodative dysfunctions among school children at any age might create near working related problems. The aim of this study was to describe accommodation in junior level school children and to compare these data with both Duane’s data and Hofstetter’s equations. Specific aim: Paper II The occurrence of subjective symptoms related to accommodative dysfunction at near among otherwise healthy young school children is not fully investigated. The aim of this paper was to study the relation between subjective symptoms at near to the accommodative function in terms of the amplitude and of the relative accommodation. A secondary aim was to explore adequate reference values. Specific aim: Paper III The specific aim of this study was to examine the effect of flip lens training on the accommodative function in a group of children with accommodative dysfunction and symptoms such as asthenopia, headache, blurred vision, and avoidance of near activity. Another aim was to study whether flip lens training increases accommodative facility, and to establish whether it may have long term positive effects on the subjects’ asthenopia and related problems. 22 B. STERNER. OCULAR ACCOMMODATION. Specific aim: Paper IV The aim of Paper IV was to further study the effect of accommodative facility training on relative accommodation. As part of the study, a comparison was made between traditional dioptric flipper treatment and a sham flipper treatment to establish whether it was the treatment as such that affected the subjects’ accommodative performance or whether the additional care giving of the children had an influence. 23 B. STERNER. OCULAR ACCOMMODATION. SUBJECTS Paper I & II A junior level school in the Göteborg area was chosen at random and all the children at this school were invited to freely and voluntary participate in the study. There were 136 children in the age range 6-10 years. The examination took place at school, and informed consent was obtained from the parents. Among all the 136 children, 28 declined participation, and 31 did not answer the invitation. Seventy-seven children were enrolled and all, except for one boy who did not turn up, were examined. After examination, four children were excluded due to a high astigmatism. Thus the study included 72 children, 43 boys (mean age 8.1 years) and 29 girls (mean age 8.3 years). Paper III Altogether 38 children aged 9–13 years were selected for this study. The children were referred by School Health Care for near work-related problems and for complaints of headaches, blurred vision, asthenopia, loss of concentration, and avoidance of near activity. We included only children with reduced NRA and PRA and/or a very slow accommodative facility. (Table 4 shows the values of the NRA and the PRA among the children in this study compared to the diagnostic criteria for accommodative infacility from Morgan, 1944b). Table 4. Mean relative accommodation (± SD) before training and for controls compared to the values presented by Morgan (1944b) as the diagnostic criteria for accommodative infacility. Mean NRA Mean PRA Before training Controls Morgan, 1944b + 1.25 ± 0.4 D - 1.3 ± 1.0 D + 2.0 ± 0.2 D - 3.9 ± 1.3 D < + 1.75 D < - 1.75 D Before entering the children into the training program, their accommodation, cycloplegic refraction, and visual acuity at distance (decimal notation) were examined. In all children, binocular vision, stereopsis, and motility were tested by an orthoptist. All the parameters were in normal range. All of the 38 children in the study were interviewed by telephone before the long-term follow-up examination 2 years after the conclusion of accommodative facility training. 24 B. STERNER. OCULAR ACCOMMODATION. Normative data were established using 24 voluntary controls aged 9–13 years. Paper IV Thirteen Swedish children, five girls and eight boys aged 9–11 years, were included in the study. They were referred by the same inclusion criteria as used for the children in Paper III. B. STERNER. OCULAR ACCOMMODATION. 25 METHODS Paper I Accommodative amplitude measurements was performed with Donder’s push-up method using a R.A.F. Near Point Rule (Figure 9), a rod with a movable target and metrics as well as dioptric markings, placed on the childs forehead. The child had distance correction in place and the movable target was slowly moved towards the child along the ruler until the child reported blurring and the dioptric result were then recorded. Determinations were made both monocular as well as binocular, and all measurements were repeated three times and the average distance was recorded in diopters. For comparisons, Hofstetter’s equations for minimum, expected, and maximum amplitude by age was calculated (minimum = 15 - 0.25 · age, expected=18.50.3·age, and maximum = 25 - 0.4 · age (Figure 11)). Figure 11. The same diagram as Figure 6, from Duane (1912), now including plots from the three prediction formulas (minimum amplitude = 15 - 0.25· age, expected amplitude = 18.5 - 0.3 ·age, and maximum amplitude = 25 - 0.4 ·age) by Hofstetter (1950). 26 B. STERNER. OCULAR ACCOMMODATION. Paper II A questionnaire containing four different questions linked to four different subjective symptoms (headache, asthenopia, floating text, facility problems) was used. The amplitude of accommodation and the relative accommodation were recorded. The relative accommodation, both positive and negative, was measured using the method described in Hung & Ciuffreda (1994). Paper III and IV To establish relative accommodation, both positive and negative, we used the method described in Hung & Ciuffreda (1994), same as in paper II. For accommodative facility training, the children were requested to use a dioptric flipper (Figure 7). A high compliance was demanded. Therefore, the children as well as their parents were given wide instructions before the onset of the treatment and the compliance was monitored after every examination. As far as could be determined the children were in compliance with the prescribed treatment. After careful instructions the training was done by each child at home following a protocol. An optometric examination was performed every second week to ensure high compliance. In Paper IV the children in the sham group started with 2weeks of training with plano lenses instead of dioptric lenses. After these 2weeks with plano lenses they changed to dioptric lenses and continued the training. If a subject showed a hypermetropia, plus lenses were prescribed after the first or second optometric examination for proper progression of the accommodative facility training. The necessity of correcting this grade of hypermetropia might be questionable due to the training effect. However, since they are symptomatic it is irresponsible not to correct them apart from the training effect. To correct this amount of ametropia is also what is recommended in the literature when to correct a hypermetropia in symptomatic individuals (O´Leary and Evans, 2003). The training continued until the subjects reported that the symptoms were gone. The Committee for Ethics at The Sahlgrenska Academy, Göteborg University, Sweden, approved the studies. B. STERNER. OCULAR ACCOMMODATION. 27 RESULTS Paper I The result showed lower accommodative amplitude than expected in a large group of children and not equivalent to the expected age values. Especially monocular measures which revealed an average difference from Hofstetter’s expected of –3.60 D (-4.5, -2.8) (right eye) (p<0.001) and –3.50 D (-4.4, -2.7) (left eye) (p<0.001). The binocular measures were higher; nevertheless, the average difference from the expected line was –0.80 D (-1.7, +0.1) (p = 0.072). Therefore, we found statistically significant differences between our monocular data and that from Hofstetter’s equations. The average difference of the binocular observations was not statistically significant. Paper II More than one third of the children (34,7%) reported at least one symptom when doing near work and the most frequent reported symptom was asthenopia (26,4%). The subjective symptoms emerged at the age of 7.5 years and the relation between different accommodative parameters to subjective symptoms was significant. The discrimination ability between the amplitude of accommodation, both monocular and binocular, was significant (right eye p = 0.013, left eye p = 0.019, and binocular p = 0.004), and the monocular amplitude was in average approximately two diopters lower in the symptom group compared to the group without symptoms. Regarding binocular amplitude the average difference was approximately three diopters. Also NRA showed significant discrimination ability (p=0.008) but there were no statistical significances regarding PRA (p>0,20). A table with different diagnostic reference values for accommodative insufficiency in terms of sensitivity, false positive rate and positive predicting value is presented as an assistance for the possibility to link the reference values to a risk for consequences for the patient. Paper III Symptoms such as headache and asthenopia, gradually decreased in all 38 children and finally disappeared during the training period. The length of the training period varied from 3 weeks to 25 weeks, with the training period being less than 8 weeks for the majority of children. Mean NRA as well as mean PRA increased during treatment. However, the post-training results for both NRA and PRA were significantly lower than the data on the controls. In other words, there was a statistically significant increase in both NRA (p<0.0001) and PRA (p < 0.0001) during the 28 B. STERNER. OCULAR ACCOMMODATION. training period although both the parameters PRA and NRA were significantly lower than the results obtained among the controls (viz. p = 0.024 for NRA and p < 0.0001 for PRA). The results from the facility tests is exemplified in Figure 12 (a, b). The time was measured when changing from the PRA value to the distance correction (a) and from the distance correction to the NRA (b) both before and after the training period. The result from the distance correction to the PRA and from the NRA to the distance correction is not illustrated in figures, but the trend was approximately the same. A follow-up examination was performed 2 years after the final examination. None of the children had any dioptric training during the time that elapsed from the conclusion of training to the follow-up examination. Both NRA and PRA were almost the same at the conclusion of training as at the follow-up examination and none of the children had regained any symptoms. Paper IV In the sham group, flipper treatment was divided into three periods, with an initial 2 weeks of (accommodative facility) training using a plano lens flipper as the sham treatment. This sham period had no effect on the symptoms (i.e., headaches, asthenopia, blurred vision) of the patients. In the following 2 weeks a ±2.00 D flip lens set was used and by the end of this period some symptoms had vanished. The period of accommodative facility training was extended until all of the patients were free from symptoms. This extended period starting in the fifth week of training varied with each case. There was a decrease in both mean NRA and mean PRA during the first period of training while the patients used plano lenses. This decrease was recovered in some of the patients during the next 2 weeks when a ±2.00 D flipper was used. The traditional treatment group who started their training with a ±2.00 D flip lens showed an increase in their mean relative accommodation at each examination. Their symptoms vanished by the end of the training period. The results show that the first weeks of dioptric training in the sham group as well as the traditional group showed an effect of the dioptric training, and the training had an effect for the whole of the training period in all subjects. In concordance with this is the fact that the plano lens flipper did not have any positive effect on either mean NRA or mean PRA in any 29 B. STERNER. OCULAR ACCOMMODATION. Facility in seconds from PRA value to distance correction 35 Number of children 30 25 20 Before training After training 15 10 5 0 1 5 10 15 20 25 30 35 40 45 50 Time in seconds Facility in seconds from distance correction to NRA value 35 Number of children 30 25 20 Before training After training 15 10 5 0 1 5 10 15 20 25 30 35 Time in seconds Figure 12. To present the result from the accommodative facility measurements, in terms of quickly changing the accommodation from exertion to relaxation, the time was measured when changing from the PRA value to the distance correction (above) and from the distance correction to the NRA (below), both before (filled staples) and after (open staples) the training period. 30 B. STERNER. OCULAR ACCOMMODATION. patient in the sham group. It is, however, difficult to explain why the PRA value actually decreased during the sham period for all the patients in the sham group. If there are any placebo effects we should in fact expect an increase instead of a decrease in the relative accommodation values during the sham period. Our data show a significant increase in both mean NRA and mean PRA in both the sham group and the non-sham study group during the dioptric training despite some individual variations in the results. B. STERNER. OCULAR ACCOMMODATION. 31 DISCUSSION The knowledge of how the neuronal accommodative complex functions are in some aspects still limited. In young persons the accommodation is expected to be flexible and powerful without any closer control of its sufficiency. In 1912, Duane stated according to his measurements, that the amplitude of accommodation is high at young ages. Furthermore, Berens & Sells (1944) stated that in young ages the accommodative system is quite flexible and resistant to fatigue. Even though this is old data it is still what we normally believe about ocular accommodation. If a person shows subjective symptoms when reading, a control of the accommodative function is therefore not always the primary function that is taken under consideration in an examination. However, accommodative dysfunction does occur among pre-presbyopic patients in clinical practice. These patients often complain of symptoms that appear when doing near distance work. The refractive status can be emmetropic or slightly ametropic, but this is not always in relation to the patients’ complaints. There is no simple standard procedure including all the accommodative facets for examination of the accommodative system. The accommodative system is not routinely examined because of the lack of such method, and in addition to the presumption mentioned above. We used Donders’ push-up method to establish the amplitude of accommodation. Even though it solely measures the amplitude of accommodation it is commonly the method used to diagnose any abnormality of accommodation. The results from Paper I showed lower amplitude of accommodation than expected among a considerable number of children. Whether these children also suffered from subjective symptoms at near that might be related to insufficient accommodation was examined in Paper II. The results imply that there is a need for clinical routines for examining the accommodative function as part of the ophthalmic or optometric examination. To expect that young children should possess high amplitudes of accommodation perhaps inhibits practitioners from making careful measurements of the accommodative amplitude, which Donders (1864) pointed out as fundamental in making a diagnosis. Unnecessary near vision problems may be prevented if a dysfunction is identified. For example, it is essential to identify and possibly treat any accommodative deficiencies in young individuals as soon as possible after school start. Since the focusing system of the eyes contributes to the learning process (Flax, 1970; Sucher and Stewart, 1993) any accommodative deficiency can make it unnecessarily difficult for the child 32 B. STERNER. OCULAR ACCOMMODATION. to read and develop in school. If the child does not alleviate or reduce his or her difficulties of accommodation he or she may always harbor a dislike for near distance work. In Paper II a questionnaire for identifying subjective symptoms related to accommodation was used. The questionnaire contained four different questions related to four different symptoms that, according to previous studies (Hoffman and Rouse, 1980; Daum, 1983a; Hennessey et al. 1984), are the most frequent related subjective symptoms to an accommodative dysfunction. Using these questions we were able to identify subjective symptoms in a considerable group of children studied. Asthenopia and headache were the most frequent symptoms in these children. The questionnaire did not give any information about grade or intensity of each symptom. A qualitative evaluation of the symptoms might therefore further refine the linkage to an accommodative dysfunction. A follow up would be necessary to be able to study whether symptoms remains or disappear without treatment over time for these children,. That would also give information of what happens with the accommodative ability over time. There were no subjective symptoms before the age of 7.5 years. This is probably due to the increasing demand on their near sight at school at these ages and symptoms will probably not appear until then. Children below the age of 7.5 years with low accommodative amplitude who are not yet frequent readers may develop subjective symptoms later due to their low amplitude. There was a significant relationship between different accommodative parameters and subjective symptoms, especially “asthenopia” and “headache”. The amplitude of accommodation was of no use in diagnosing the less frequent symptoms “floating text” and “facility problems”. This does not necessarily imply that there is no relationship between amplitude and these symptoms. It is likely that the relation between symptoms and questions is not obvious to the children or that the non-significance is due to the limited sample size and the low frequency of these symptoms. We need to have clear standards for defining accommodative insufficiency (AI) and suitable choices of reference values to identify children with risk of developing an AI. If we have a low reference value we will probably miss many cases with AI that will benefit from treatment but there will be less cases of false positive. On the other hand, if we increase the reference B. STERNER. OCULAR ACCOMMODATION. 33 value we will have a better sensitivity even though we will obtain some cases with sufficient accommodation without causing symptoms. A longitudinal follow up of the children in this study would of course facilitate the decision of suitable reference values. A table is presented (Table 7 in Paper II) which shows the different levels of sensitivity and positive/negative prediction values from four different reference values for children aged 7.5 to 10 years in this cross-sectional study. It can be discussed which value to choose but the value close to the lower quartile could be suitable. Then there will be a sufficient positive predicting value and a reasonable number of cases of false positive. Possibly the prediction could be improved by performing a follow-up to capture more persisting and clinically more relevant symptoms. The patients included in Paper III and IV were selected from among children with problems at school related to near work. It was found that all of the selected patients had reduced relative accommodation and the majority of them had a slow accommodative facility. None of the patients could be classified as having the syndrome called convergence and accommodative insufficiency as described by Von Noorden et al. (1973). The studies in Paper III and IV were performed to investigate the possibility of increasing or improving accommodative function as being the probable main problem of these patients. We therefore tried to accomplish three goals: firstly, to quantitatively examine the effect of accommodative facility training on relative accommodation; secondly, to determine whether symptoms (headache, blur, asthenopia) disappeared with increased accommodative facility; and thirdly, to establish whether the dioptric training had any long-term effects. Accommodative insufficiency and accommodative facility training have been discussed in the optometric literature mainly during the past few decades (Hennessey et al., 1984; Daum, 1983b; Cooper et al., 1983; Cooper et al., 1987; Rouse, 1987; Chrousos et al., 1988; Russel & Wick, 1993; Ciuffreda, 2002), predominantly with regard to pre-presbyopic patients (Zellers et al., 1984; Cooper et al., 1987; Russel & Wick, 1993). The close relationship between accommodative deficiency and related visual symptoms, such as blurred vision, asthenopia, loss of concentration, and avoidance of near activity, has been pointed out. Among the findings listed by Hoffman & Rouse (1980), as indicative of accommodative difficulties when associated with symptoms, we focused on two items: a NRA and PRA of <±1.75 D, and a ±2.00 D flipper test result, measured monocularly and binocularly, of <12 cpm. 34 B. STERNER. OCULAR ACCOMMODATION. The proposed relationship between restricted relative accommodation and symptoms was in concordance with our findings. The results of these studies support to some degree the idea that a PRA and a NRA of <±1.75 D (Morgan, 1944b; Hennessey et al., 1984) are related to the presence of symptoms (i.e., headache, blurred vision, asthenopia, loss of concentration, and avoidance of near work). Our studies show that accommodative facility training can increase both positive and negative relative accommodation in selected patients, as well as relieve them of their symptoms. The studies also clearly indicate that there is a long-term effect of accommodative facility training using a dioptric flip lens technique. However, it is not clear from our studies whether the relief of symptoms was linked to an increase in relative accommodation or to an improvement of the accommodative facility, or both. We also do not know whether further accommodative training would have further increased the accommodative function. The fact that all the children became free from subjective symptoms after training might be discussed in relation to the knowledge from medical treatment in terms of rate of success; that it is not successful in all patients. However, the phenomenon of training is improvement, which also was the object in this study. As a group, the children’s accommodative function was not normalized, but improved enough to release all the children from their subjective symptoms Since the question has been posed whether it is the actual use of dioptric training that causes an increase in relative accommodation or whether unspecific training and caring can lead to such increase we studied the effect of sham treatment in seven patients given such treatment before the dioptric training. The findings clearly indicated that short-term sham treatment, if anything, had a negative effect on relative accommodation and no observable effect on symptoms. The lack of a positive effect of the sham treatment with plano lenses strongly suggests that the therapeutic effect of dioptric treatment of the accommodative facility is linked to the effect of the ±2.00 D flip lenses. The focus of this study was to examine changes in relative accommodation in relation to treatment. The fact that the effect on the relative accommodation of 2 weeks of dioptric training following the sham treatment was as marked in this group of patients as it was in the traditional training group starting directly with dioptric training further links the positive effect on relative accommodation to the use of the ±2.00 D flip lenses. B. STERNER. OCULAR ACCOMMODATION. 35 The fundus examination in an ophthalmologic examination of the eye, gives the examiner much information needed for proper diagnosis. Sometimes the examiner observes that the optic disc shows abnormalities, which indicates further examinations. The abnormality can be due to an abnormal fundus morphology, which in some cases may influence the visual function. Preliminary observations (Hellström et al. in preparation) suggest that children with impaired relative accommodation in many cases also have optic disc abnormalities and/or peripapillary pigmentation (Figure 13). a. b. Figure 13. Fundus photographs of (a) a 13-year-old girl with impaired relative accommodation demonstrating an optic disc with peripapillary pigmentation, and (b) a 13-year-old girl from a control group without any peripapillary pigmentation. The etiology of these optic disc abnormalities is not yet fully understood. However, these findings suggest involvement of congenital factors at least in some cases of impaired relative accommodation. Information about the natural history of accommodative dysfunction in children is lacking, and we do not know whether an insufficient accommodation spontaneously improves with age. However, our clinical experience is that an accommodative infacility lasts for years even though the effect of maturation cannot be excluded from the present study design. The facility training had a positive effect on both mean PRA and mean NRA as well as the symptoms, and offers the possibility of at least shortening the period of symptoms and withdrawal from near work at school at a stage in schooling that is academically important. The results, in terms of the dioptric treatment, in this study is in agreement with results reported previously in the literature (Daum, 1983b; Cooper et al., 1987; Siderov, 1990; Russel & Wick, 1993; Ciuffreda, 2002), although accommodative insufficiency has been more commonly reported in pre- 36 B. STERNER. OCULAR ACCOMMODATION. presbyopic individuals than in school children (Hennessey et al., 1984; Cooper et al., 1987; Russel & Wick, 1993; Scheiman et al., 1996). The result further raises the question whether the facility training method is a useful method for other aspects of the ophthalmologic practice, such as in diagnosing and training an accommodative dysfunction among visually impaired children (Woodhouse et al., 1993; Leat, 1996). An accommodative impairment can in some cases be hidden in an incorrect interpretation of eye disease and associated symptoms. The contact person of the child may conclude that the child’s difficulties in performing near work are the result of eye disease instead of being due to an accommodative impairment. B. STERNER. OCULAR ACCOMMODATION. 37 CONCLUSIONS The ocular accommodation in young children is not as sufficient as we expect. Young school children may have an insufficient accommodative ability that causes subjective symptoms when reading. These symptoms have shown to emerge in these children from the age of 7.5 years. Further studies which follow children over time to see if low accommodative amplitude generates subjective symptoms and to prove causality are highly desirable. This study has also characterized a group of children with impaired relative accommodation. They were relieved of subjective symptoms as a result of dioptric training and they improved both their NRA and PRA. The training intensity and spacing of training sessions over a considerable period still need further evaluation in order to optimize the training and the diopter value of the lenses. It is essential to identify accommodative dysfunction in order to alleviate symptoms, improve accommodation efficiency, and decide on the type and extent of treatment. It is also of utmost importance for a direct and successful treatment that children with accommodative dysfunction be properly diagnosed and that other ophthalmologic problems be excluded. 38 B. STERNER. OCULAR ACCOMMODATION. FUTURE STUDIES • A longitudinal follow up study is designed which will give us information on the stability of accommodation over time in the children included in paper I and II. Such a follow-up will also give information on whether the symptoms remain or disappear without treatment over time and facilitate the decision of suitable reference values. • A study on accommodation in visually impaired children and how the results from the present studies can be translated to these children has started. B. STERNER. OCULAR ACCOMMODATION. 39 TACKORD (Acknowledgments in Swedish) Bland alla de personer jag vill tacka för all den hjälp och allt det stöd jag fått i arbetet med denna avhandling, vill jag börja med att sända ett stort tack till Maths Abrahamsson, min förste handledare som tyvärr gick bort alldeles för tidigt. Med optimism och uppmuntran kryddat med allehanda skämt och anekdoter var han den förste att introducera och intressera mig för forskning. Tack Maths, för allt du gav. Anders Sjöström, som utan att tveka tog mig under sina vingar som ny handledare. Fastän Maths och jag hade bollat olika idéer om projekten som ej hann bli nedtecknade satte sig Anders snabbt in i arbetet och ytterligare hjälpte mig att utveckla och förbättra projekten. Tack Anders, för all din tid och för allt ditt jobb och för att du med sådan smittande entusiasm bistått mig till att slutföra avhandlingsarbetet. Tack också för att du lärt mig hur man tillagar en äkta “WildWest Dinner”. Johan Sjöstrand, min bihandledare, för din kunskap och klokhet som jag och vi andra på avdelningen alltid kan få luta oss mot och få hjälp av och för att du alltid är så positiv och glad. Martin Gellerstedt, min medförfattare, för ett gott samarbete och excellent statistisk rådgivning. Ulf Stenevi, Ann Hellström och Bertil Lindblom, för intressanta och givande kommentarer, och ett särskilt tack till Ann för värderingen av ögonbottenbilderna. Jörgen Thaung och Zoran Popovic, för att ni alltid är så snälla och hjälpsamma med allehanda ting och i synnerhet när det kört ihop sig med datorn. Ni är brillianta! Melanie Baumann, för din ortoptiska expertis. Stefan Michélsen, för givande diskussioner och råd kring optik och optometri. Eva Berglund och Anki Nyberg, för er hjälp med många administrativa saker. 40 B. STERNER. OCULAR ACCOMMODATION. Alla kollegor och vänner på och runt sektionen för oftalmologi och särskilt Gunilla Magnusson, Josefin Ohlsson, Karin Sundelin, Madeleine Zetterberg, Lada Kalaboukhova, Alf Nyström, Gunilla Brunnström, Ulla Kroksmark och Maria Kræmer, för er vänskap och generositet i att dela erfarenheter av att vara forskarstudent och för många trevliga fikapauser. Alla mina kollegor och vänner på Syncentralen i Göteborg och ett särskilt tack till min före detta chef, Lisbeth Axelsson-Lindh. Min mamma Lena, min brorsdotter Martina, min brorson Anton, och alla mina vänner, för alla glada tillrop. Ulrica, min hustru, för all din kärlek och allt ditt stöd. Du är bäst! Slutligen vill jag tacka alla de barn som deltagit i studierna. Jag tackar också för ekonomiskt stöd från (i alfabetisk ordning): Föreningen De Blindas Vänner; Medicinska forskningsrådet (Anslag nr 02226); Optikerförbundet; Sigvard & Marianne Bernadottes Forskningsstiftelse för Barnögonvård; Stiftelsen Handlanden H Svenssons fond för blinda och synsvaga; Stiftelsen Karl Simsons Fond; Stiftelsen Kronprinsessan Margaretas Arbetsnämnd för synskadade; Stiftelsen Solstickan; Stiftelsen Sunnerdahls Handikappfond; och Synoptik-Fonden. B. STERNER. OCULAR ACCOMMODATION. 41 REFERENCES Atchison DA. (1995) Accommodation and presbyopia. Ophthalmic Physiol Opt. Jul;15(4):255–72. Banks MS. (1980a) The development of visual accommodation during early infancy. Child Dev. Sep;51(3):646–66. Banks MS. (1980b) Infant refraction and accommodation. Int Ophthal Clin. 20(1):205–32. Beers AP, Van der Heijde GL. 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