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왗your lab focus 왘 CE Update [generalist | management/administration and training] Eyes on the Lab Paulus T.V.M. de Jong, MD, PhD1, FRCOphth, Bouke C.H., de Jong, MD2, P. Stoutenbeek, MD3, Kevin L. Peterson, MD4 Netherlands Ophthalmic Institute, Department, the Academic Medical Center, Amsterdam, and the Department of Epidemiology and Biostatistics, Erasmus University, Rotterdam, the Netherlands; 2Division of Infectious Diseases and Geographic Medicine, Stanford University, Stanford, CA; 3private practice in Winterswijk, the Netherlands; 4San Joaquin County Public Health Services, Stockton, CA 1The After reading this article, the reader should understand the effects of common visual problems related to performing or interpreting laboratory tests and how to solve the problems. Generalist 0104 exam questions and corresponding answer form are located after the “Your Lab Focus” section, p 535. 왘 Basic eye structure and function is explained and related to how it affects performance in the laboratory 왘 Age-related changes in the eye and their effects on performance of laboratory work are explained 왘 Different visual defects are explained, and what can be done to correct them are explained A well functioning visual system is an important asset for coping in daily life. Humans can operate without any visual information, as is exemplified by the number of blind people functioning well in professions not typically associated with the blind, including law, medicine, and others.1 However, most people will be depressed and seriously handicapped initially when they lose important visual information, especially in the acute phase. The visual system is said to provide about three quarters of all sensory information to the human brain.2 The aim of this article is to highlight the relevant physiologic visual functions in the normal working population, with an emphasis on those in laboratories. We will review common disorders of these functions associated with aging or disease and comment on results of a small survey among laboratory workers. Physiologic Properties of Vision Giving a definition of vision or seeing is not easy. Dorland3 has no entry for the latter but defines vision as: “The special sense by which objects in the external environment are perceived by means of light they give off or reflect, which stimulates the photoreceptors in the retina; called also sight.” Webster’s Dictionary4 has as a single entry for “see”: “To get knowledge or an impression of, through the eyes and the sense of sight.” The Oxford English Dictionary5 writes for “see”: “To perceive (light, color, external objects and their movements) with the eyes, or by the sense of which the eye is the specific organ.” One definition of vision is: “Observing with the eyes.” We would define vision as: “Interpreting with our brain images or phenomena perceived with our eyes.” There are 3 major steps in perception: detection, awareness, and identification or recognition.2 In order to see an object, we use various visual cues such as size, form, texture, and edge sharpness, as well as its contrast with its surroundings. The most important physiologic properties of the visual system, as well as the changes in them, arise while aging or in disease states. These properties are given in [T1], together with a ranking of 1 to 5 with regard to their value in everyday life. We will discuss the modalities in [T1] and try to identify where these visual properties might specifically interfere with usual laboratory work. Visual Acuity Visual acuity (VA) is the reciprocal of the smallest angle in minutes of arc under which a person can discriminate a © contour or can, in physical terms, resolve spatial differences in luminance. In essence, VA is a measure for and is the counterpart to contrast sensitivity using strong contrasts, in practice 1:10, the contrast or luminance ratio of normal black print on white paper. Contrast can be defined as (L/L`–1) in which L is the luminance of an object and L` that of its surroundings1 However, VA and contrast sensitivity tests with various low contrasts do a poor job of predicting how well a person functions on a day-to-day basis. High contrast tests do only a slightly better job, but nevertheless they are often used in the form of Snellen acuity charts. Snellen VA is determined with high contrast letters or symbols that in various forms have been used in ophthalmology for over 100 years to express someone’s VA. A Snellen VA of 20/20 or 1.0 (in decimal notation) thus points to the ability to discern 2 objects separated by 1 minute of arc. A new unit for VA is the log MAR (Minimum Angle of Resolution) corresponding to minus the logarithm of the VA. The majority of the working population has a Snellen VA of 1.0 or higher, sometimes even as high as 2.5. The distance should not really matter when expressing VA because VA is defined by the angle of vision and thus distant and near VA should be the same. There are situations, however, such as impaired accommodation, or pupil diameters varying between 5 mm when looking nearby and 8 mm for far away, which hamper near vision more than distant vi- laboratorymedicine> september 2001> number 9> volume 32 519 왗your lab focus 왘 Estimate of the Importance of Visual Modalities for Daily Functioning on a 5-Point scale. T1 1. Very important for daily functioning 2. Of average importance 3. Of minor importance 4. Important for special occupations only 5. In general unimportant or hard to determine The lower the number the more important the physiologic properties are or the more inconvenient the disturbances. Physiologic properties of vision Importance Distant visual acuity 1 Near visual acuity 1 Intact central visual field within 30 degrees 1 Single vision in a 1-eyed person 1 Single vision binocular 2 Depth perception monocular 2* Ametropia (correctable with glasses or contact lenses) 3 Intact accommodation 3 Color discrimination 4 Vision in twilight 4 Stereoscopic vision or stereopsis 4** Disturbances in vision due to aging or disease Visual agnosia 1 Metamorphopsia 2 Oscillopsia 2 Presbyopia 3 Photophobia 3 Glare 3 Hemeralopia 4 Anisometropia and aniseikonia 4 Asthenopia 5 Dyschromatopsia 5 * Monocular depth perception depends on many different cues.12 Among them are static ones, such as the size of retinal image that is inversely proportional to the distance. Thus the longer the distance, the a) more perspective convergence b) finer the surface structures, c) more crowding of nearby images, d) more partial covering of images by neighboring ones, e) smaller the shade and light angle effects, e) more blurring and blue haze due to atmospheric light dispersion, f) higher and closer to the horizon the image, and g) more reduced influence of accommodative convergence. Dynamic cues for monocular depth perception include movement parallax, optic flow (the continuous and systematic changes in retinal image) due to movement of an image in against the texture of the surface, and radial movement (objects becoming smaller or larger, respectively, by moving away from or toward the observer; important in estimating time to collision in traffic or parachute diving). Monocular depth perception is, of course, quite important in daily life but difficult to measure in an overall way. Because it will be rare for someone with good visual acuity to have no monocular depth perception, this was arbitrarily ranked as 2. 520 **The median stereopsis for the population lies at about 40 seconds of arc. This means that with an interpupillary distance of 65 mm, one can estimate a difference in depth of 3 mm at 1 m distance, 2 m at 25 m, and nothing at 300 m.12 sion. Given the relative importance of near vision in many modern professions, it has become customary to specify requirements for near vision separately. The relative importance of near VA is also reflected in the AMA Guides to the eval- uation of permanent impairment.6 In these guides, impaired near vision was considered to be twice as important as impaired far vision during the time between 1925 and 1941. In 1955 this rule was reestablished. Possibly during the laboratorymedicine> september 2001> number 9> volume 32 interim, a war-time change of rules was instituted in order to obtain more recruits or snipers. With regard to minimum standards for VA, a rule of thumb is that a person with VA of 0.3 in the better eye, if neces- © 왗your lab focus 왘 in that way. The cones in the retinal center are necessary for obtaining a good VA as well as intact color vision. That is why macular degeneration, in which the retinal cone receptors degenerate, is nearly always associated with VA loss and often with decreased color vision. The rods, predominant in the peripheral retina, do not contribute to color perception but are important for our VF and for seeing under mesopic or scotopic circumstances such as twilight or moonlight. [F1] Anatomic Lesson by Rembrandt. See Figs 5, 7, and 8 for comparison with visual distortions due to various eye disorders. sary with normal reading addition, can read normal small print on paper and can perform administrative and routine laboratory functions. Pathologists can compensate a loss of VA by using higher magnification while performing microscopy, provided they have a sufficient width of their visual field (VF; see below) without too many small paracentral VF defects or scotomata. In performing an autopsy or while dissecting subtle tissue structures, however, one might miss cues with a suboptimal VA [F1]. Similarly, a technician embedding and sectioning samples for electron microscopy might be challenged by a VA lower than 0.3, at the very least requiring more time in order to perform as well. When assessing if someone can perform a task, one should also keep in mind that in many countries people depend on the ability to drive a car in order to get to work, and this implies meeting the legal requirement of a VA of 0.5. The necessity to reach the work-place, of course, holds for all aspects of vision (eg, VA, VF, absence of diplopia) that are discussed here. An irony behind some of our last remarks is that there is not much hard evidence for these statements. One would have to compare car drivers, lab technicians, or pathologists with good and poor vision according to well-defined end points in their daily performance; this is often not possible, and in the case of drivers on public roads, this would probably be illegal. In order to obtain a good VA, the visual system from the tear film on the cornea, through the optic media and the retina, to the brain areas past the primary visual cortex, must function well. The optic media are those clear parts of the eye through which the light must pass in order to reach the retina. The most common turbidities are in the lens (cataract) and vitreous body (floaters) that may create glare and irritating obfuscations while performing light microscopy. For good VA, one needs a more-or-less normal central part of the retina, the macula (lutea), and its center, the foveola. In [F2] the relation between VA, density of cones, and degrees of excentricity from the foveola is given in a graph projected onto the macula. Many amblyopic (also called lazy eyed) subjects fixate outside the foveola and, thus, cannot achieve full VA © Issues Related to Refraction Not wearing appropriate corrective lenses is the main cause of decreased VA in the Western population over age 55. Of 7,983 subjects aged 55 years and over from the Rotterdam Study, 20% needed no glasses to achieve their best visual acuity and, thus, are called emmetropic, assuming that they did not need to use their accommodation. The remainder was ametropic (refractive error present), 20% of the whole cohort was over 0.5 diopter myopic (near sighted; minus lenses necessary) and the remaining 60% was over 0.5 diopter hypermetropic (farsighted; plus lenses needed). Myopia up to 4 diopters may be handy in daily lab work because those individuals will typically not require reading glasses, assuming, of course, they do not have astigmatism, the condition in which the asymmetric curvature of the cornea requires glasses with what is called “cylinder.” Whereas myopic subjects cannot bring distant objects into sharp focus, young hypermetropic subjects have to use their accommodation in order to see sharply at a distance. The necessity to accommodate comes at a cost, however, and may lead to complaints of fatigue, squinting,or headache. As accommodative power wanes with age-related stiffening of the lens in people over 40, bifocals or reading glasses may become necessary. Wearing glasses while performing laboratory work generally creates no problems and even has a protective effect against particles or squirting fluid. However, glasses may be hampering during microscopy, while fogging may occur going from a cold room such as a mortuary or walk-in refrigerator into a humid, warm environment. laboratorymedicine> september 2001> number 9> volume 32 521 왗your lab focus 왘 522 People with astigmatism over 1.5 to 2 diopters who are troubled by glasses during light microscopy may wish to try hard or toric soft contact lenses. For some people, these contacts may be annoying during microscopy because the border of the lens distorts the retinal image or because they do not blink enough while concentrating on their task. Moreover, one should keep in mind that contact lenses, in particular soft ones, are the main cause of serious corneal ulcers nowadays. Given the potential chemical and biological contaminants in the lab environment, the utmost hygiene is indicated, and contacts should be left out if there is any redness of the eye. It is common to speak of high anisometropia when the difference in refractive error between both eyes of a subject is over 2 diopters. In general, this creates no problems, and with microscopy one can usually adjust the oculars individually. This is best done with about 20× magnification to decrease depth of focus. However, greater than 4 diopters anisometropia can create unequal sizes of the images on both retinas of a subject, so called aniseikonia, and the brain cannot fuse both images into a single image. This disturbing phenomenon can be corrected by wearing contacts instead of glasses or, in case this is not feasible, by prescribing a corrective lens for only the least ametropic eye. Lab work nowadays is hardly feasible without the use of computers. Most people read a book or the newspaper at 40 to 50 cm distance and look at a computer at 70 to 80 cm. This means that the reading glasses one uses for computer work should be 1 diopter weaker than those used for reading printed material. As one requires a stronger reading addition with advancing age, keeping old reading glasses for looking at the computer may work quite well. Accommodation is the ability of the eye to change its focus and, thus, to see sharply both near and far. The accommodative power is about 13 diopters at age 10 years and decreases by about 1.5 diopter for each 5 years. Thus at age 40, only about 5 diopters accommodative power is left, which typically [F2] Image of macula lutea of the right eye as seen on direct ophthalmoscopy. Black blur on the right is the temporal border of the optic disc. The “a” in the word "water" marks exactly the center of the foveola. The white concentric circles denote the foveola, the fovea, the parafovea and the perifovea, from the center outwards respectively with their outer radius from the center of the foveola 175 m (35' of arc), 925 m (3.1E), 1.425 mm (4.75E), and 2.925 mm (9.75E). Five micrometers equal one minute of arc. The outer circle is more or less the boundary of the macula lutea. Examples of the maximum visual acuity that can be obtained at any point on the retina eccentric to the foveola are given only in the upper right quadrant by the white curve, but this holds for the whole macula. The steep drop of number of cones per mm2 in relation to eccentricity to the foveola is similarly shown in the lower left quadrant. The minimum central visual field necessary to read is indicated by the white ellipse around the text "the water w. (From Trauzettel-Klosinski20) will not allow an emmetropic person to focus nearer than 20 cm (100/5) away. After this age, subjects typically need progressively stronger reading glasses, a phenomenon called presbyopia. When an older lab worker needs to look repeatedly at various distances, such as when alternatively reading, computer data entry, and perhaps helping visitors at a desk, this may become cumbersome when it calls for different glasses. Multifocal or trifocal glasses or monovision (1 eye wears contacts or a glass for near work, the second eye for distance) might be a solution. Visual Field The monocular VF is that solid angle that an immobile eye in an immobile head can oversee. The functional VF is the field covered by rotating head and eye. The VF is of great importance to prevent a subject bumping into obstacles on the sidewalk or the road, but also in the office or at home. Loss of the peripheral VF beyond the central 10E to 15E is called tunnel or barrel laboratorymedicine> september 2001> number 9> volume 32 © vision. One can experience what a person with this disorder can see by looking through a slightly opened fist in front of each eye. Thus, one can imagine that a subject with barrel vision might not want to walk with a jar of picric acid or radioisotopes in a lab where people tend to move chairs or cabinets. Visual fields are examined with perimeters, formerly mostly manually handled with moving (kinetic) stimuli of various intensities and sizes as in the Goldmann perimeter. In the majority of perimeters, these stimuli are offered to a single eye of a subject while that eye is fixating a central point in the perimeter bowl. Nowadays, mostly automated static perimeters are used in which on 1 point in the visual field the luminance of the test object is raised until the stimulus is seen. The light sensitivity thus measured on different locations in the retina may vary and in the foveola up till 10.000 times or 4 log units. Just as in audiometry 0.1 log unit is 1 decibel (dB) and, thus, VF loss is quantita- 왗your lab focus 왘 [F3] Dependency of visual acuity (VA) on luminance levels. The abscissa indicates the luminance in cd/m2, the ordinate gives the visual acuity in decimals. Note the steep drop in VA between 2 and 100 cd/m2. On top the transition between scotopic cone vision and photopic rod vision is indicated together with the corresponding luminance strata. The indicated objects that may be seen by a normal person give an idea about the tremendous range of sensitivity of the human visual system. (Courtesy J.J. Vos) tively expressed both in dB units and in extent of the scotoma expressed in degrees. Although some laws require a 120° VF for driving a car, in daily practice, most people can function well with a central field of 30E. For VF angles up to 30E 1 degree corresponds to 1 cm at 57 cm (arms length) distance. The width of someone’s VF in cm can be calculated with: VF angle × cm distance/57. Thus a person with a central VF remnant of 15E has at 10 meters a VF width of 15 × 1,000/ 57 = 2.63 m. Subjects with a VF smaller than 5E to 10E often automatically compensate by making scanning movements with their eyes and head. For the VF to be intact, we need (apart from a normal optic nerve and higher visual pathways) the peripheral retina where mostly the rod photoreceptors are situated. Although the VA derived from the peripheral retina is poor [F2], the VF is indispensable in activities of daily life such as driving. Thus, the World Health Organization considers someone to be blind, even with full VA, when the remaining central VF is smaller than 10 degrees.7 The same peripheral © retina with the rods is necessary for twilight vision. Night and Twilight Vision Visual acuity very much depends on ambient lighting. This is most clearly expressed in [F3]. Luminance levels are usually divided in photopic, mesopic, and scotopic ranges and at a luminance below 100 cd/m2 the VA drops fast. In mesopic conditions, people cannot read any more. In the lab this means that people working in a dark room will have a problem reading small print, particularly laboratorymedicine> september 2001> number 9> volume 32 523 왗your lab focus 왘 [F4] Dark adaptation curve for normal subjects. After looking in a white light for 7 minutes (bleaching the visual pigments in the retina), a test light with increasing intensity is flashed every 30 to 60 seconds till observed. The hatched area is the normal curve with a break point around 10–3cd/m2 where cone adaptation ends and rod adaptation takes over. Objects to be seen at various luminance levels are mentioned at the right. (Courtesy J.J.Vos) 524 if they have defective night vision as often happens with age or in patients with retinitis pigmentosa. Older people not only need more time to adapt to mesopic conditions [F4], but they also do not reach the same level of sensitivity. In other words, their dark adaptation curve ends too high. These persons not only have trouble in dark rooms but often find driving through tunnels difficult if the change from sunshine to tunnel darkness is too abrupt. Another common disorder in which subjects will need much longer dark adaptation times than their healthy peers is age-related maculopathy in which the macular area of the retina degenerates. Single Vision. Single vision (the opposite of diplopia, or double vision) is quite important for daily functioning. Most adults with acute diplopia (eg, due to diabetic ocular muscle paresis) can only read the ophthalmologist’s office chart with a patch on 1 eye. Imagine driving and not knowing which oncoming car is real or being in the lab and puzzling over which laboratorymedicine> september 2001> number 9> volume 32 © of the 2 test tubes should be filled. Small children cope with double vision by suppressing 1 visual image or by amblyopia. After age 7 to 9 years, amblyopia cannot be treated effectively; its prevalence is about 4% in the population. The suppression mechanism, however, is not effective in adults. In stereoscopic vision, the small differences in the images of both eyes due to the interpupillary distance of about 60 mm are used to advantage. Nearly everyone acutely losing VA in 1 eye will need up to 6 months adaptation time before ordinary actions, such as pouring tea 왗your lab focus 왘 [F5] Picture of Rembrandt's anatomical lesson as seen by a person with monocular diplopia due to cataract. in a teacup and gently and smoothly replacing it in a saucer. Finer tasks may take even longer adaptation times. Also misjudging the curb, the last step of a staircase, or the garage door at the far side of the driver are notorious. Also monocular diplopia may occur! Individuals with only 1 eye can experience diplopia eg, due to uncorrected astigmatism, cataract [F5] or corneal deformities. Because a 2-eyed subject can wear an occluder in case of diplopia, double vision in a monocular case is much more debilitating than in someone with 2 eyes. Color Discrimination. In the US, 8% to 10% of males have an X-linked, inherited color vision defect. About 5% of the defects are the common green (also called deutan) range. The red range deficiency is called a protan defect. In females, the prevalence is about 0.3%.8 The cone and rod photoreceptors share the same chromophore 11-cis-retinal but differ in protein component, the opsin. The genetics are far more complicated than previously thought, in that the red and green opsin genes are next to each other and are identical for about 98% of the structure. Most subjects with a red deficiency lack the red opsin gene, but have 2 green ones. The opposite holds for the subjects with a green deficiency.8 Several reports on subjective problems in daily life of subjects with varying degrees of color vision impairment leave no doubt that deficient color perception may create difficulties. Examples are selecting clothes or accessories, fruits or vegetables, and recognizing sunburn or the color of cooked meat.9 One can appreciate the handicap of partially color blind people by comparing detection of a bird in a tree through a black and white view finder on a video camera versus through a colored one. In general, most persons with a red-green deficiency perform well in daily life. They are banned from some occupations, sometimes more on historical than realistic grounds. During World War I it was necessary for a pilot about to land to discern the difference between a green grass field and a brown freshly ploughed area. But that does not justify the present day regulation that disqualifies pilots who have some red-green deficiency. Nowadays, there is a development © to try to adapt the job to a person. With modern means, this is often possible for workers with a color anomaly. Thus, it should not be a problem to come to an international regulation that, for instance, 10 years from now all red (alarm) and green (safe) lights in new planes and boats should be changed to orange and blue or violet. This would solve problems for about 8% of the male population who are now excluded. An example of adjusting the job to the electrician is the replacement in Europe of green and red electrical wires with brown and blue ones. In the lab and for physicians, defective color vision may be a handicap. Physicians with a severe congenital color vision deficiency had more trouble properly reading color blocks on a blood glucose test stick.11 Green fluorescent microscopy might be another example. “Color weak” surgeons sometimes have more difficulty telling arterial from venous bleeding. Similarly, pediatricians judging the color of a baby or ophthalmologists detecting a shallow retinal detachment by subtle changes in red may be challenged by moderate degrees of color blindness. A periodic acid–Schiff or Gram stain may create problems for a protanomalous person in the lab. Disturbances in Vision That May Influence the Practice of Laboratory Medicine The most prevalent pathologic change in the visual system for daily work probably is amblyopia, which often hampers stereo vision. Most visual functions eg, VA, contrast sensitivity, and retinal sensitivity for light gradually wane with aging. A small survey by questionnaire among 50 subjects working in a laboratory setting revealed that up to 14% had some difficulties with their visual tasks. The most common complaint was poorer vision in dim light. This can be expected from data showing up to 10 fold retinal sensitivity loss in aging and some diseases. However, none of the laboratory professionals surveyed felt that this influenced their overall performance in the lab. laboratorymedicine> september 2001> number 9> volume 32 525 왗your lab focus 왘 [F6] Decrease in visual acuity with increasing age. Each dot represents a study of visual acuity at various ages (Courtesy J.J. Vos and Verriest.21). 526 We have discussed the physiologic properties of vision earlier in this article. There is often insufficient knowledge about the gradual decline of these properties and their function in daily life, as well as about the many possibilities for subjects with visual handicaps to perform tasks with low vision aids or in special facilities. The visual changes, mainly due to aging, will be briefly discussed together with the results of the survey among lab personnel. It is not feasible to discuss all kinds of ophthalmic diseases in this article. However, it is hoped that the reader may find some help for estimating the functional consequences of an eye disorder could hamper working in the lab. image. These defective stimuli may lead to lack of maturation and/or abnormal development of the monocular and binocular visual system. Even after early (from age 6 months) and proper treatment, only one third of the amblyopic children will later achieve some binocular vision. Given the prevalence of amblyopia, one may expect that 2% to 4% of all lab workers will have 1 eye with lower VA and poor stereopsis. This does not in itself mean that they cannot do their jobs well, apart from tasks that require good stereo vision. It does require special care, eg, shatterproof glasses where there is a Amblyopia Amblyopia is a defect in monocular vision caused by insufficient visual stimuli during early development. In general, the defect results from the failure of the image to be focused on the retina, as in congenital cataract or strong hypermetropia. Amblyopia can also be caused by asymmetric images with regard to size or location on the retina of each eye, so that the brain cannot fuse them into a single laboratorymedicine> september 2001> number 9> volume 32 © 왗your lab focus 왘 [F7] Anatomic lesson of Rembrandt as probably seen by a subject with metamorphopsia due to exudative age-related maculopathy. [F8] Central scotoma in same picture as [F7] due to a (disciform) scar in fovea. The central scar is a common endstage of retinal hereditary or inflammatory (eg, toxoplamosis) retinal degenerations. Note blurred peripheral picture because this image falls outside central 5 degrees around the foveola [F2]. risk of flying particles, given that their overall VA is dependent on their better eye and because the better eye of an amblyopic person seems to be more often involved in injuries than the poorer one. Aging The eye continues to mature after birth and most visual functions are only fully developed around age 30, when they start declining again.13 This has best been inves- © tigated for VA, contrast sensitivity, glare, color vision, dark adaptation, and extent of the VF and should be understood when considering operating motor vehicles as well as for face recognition.14 We will discuss these aspects respectively. Visual acuity [F6] gradually reaches its peak with a mean acuity of 1.6 around age 15 years and gradually decreases to 0.3 by age 90; senescent decline in VA may start after age 40.13 There is controversy whether this deterioration occurs due to central or a retinal neuronal process dysfunction or optic changes in the eye itself, and a pragmatic solution is to look first for the latter.13 The obvious ocular causes are diminishment of pupillary diameter in older age and increasing lens opacities. The size of the lens’ central nucleus, 2.6 mm thick and 6.8 mm in diameter, allows light through an 8-mm-wide pupil to pass differently through the lens margin. It has been shown that the pupillary diameter decreases by about 40% from age 20 to age 90, which causes a reduction in light reaching the retina by a factor of 2. The reduction in lens transparency over the years adds another factor of 2, so that there is a net 4fold loss in luminance at the retina. Depending on individual differences, this may even go up to a factor of 10 or 1 log unit, and this means that elderly people need much more light to obtain a good VA and to see details. More light decreases the pupillary diameter, again reducing the retinal luminance but improving depth of focus and point spread function of the eye. The intensity of the light source should be an initial question to older people who complain that they can no longer read. Contrast sensitivity is comparable to VA. The difference is in measuring Snellen acuity when maximum contrast is used while testing spatial resolution, while in sensitivity tests spatial resolution is fixed, and a range of lower contrasts is tested. Contrast sensitivity also reaches its peak at age 30 and decreases by about 10% per decade.13 This decrease is not due to variation in retinal illumination as described above, but possibly due to neuronal processes. Thus, in slight optic neuritis, eg, due to multiple sclerosis, contrast sensitivity is reduced earlier than VA. An important age-related pathologic process resulting in laboratorymedicine> september 2001> number 9> volume 32 527 왗your lab focus 왘 Shortened Questionnaire About Visual Functions for Laboratory Staff Yes No ? 12. As far as I know I have good/ no good binocular stereo vision/ don't know 44 2 2 13. I can judge distances well/ poorly/ don't know 45 2 3 14a. The visual field is that solid angle (or part of the environment) that a subject can see with one immobile, nonrotating eye without turning the head. As far as I know I have no/a visual field defect NA NOA 2 50 14b. As far as I know I have a visual field defect in my right eye/left eye/both eyes 14c. The defects are within/ outside the central 30 degrees 15. I have as far as I know normal color vision yes/no I have most difficulty in discriminating red colors/ green colors/cannot specify 16. We need relatively fast dark adaptation to see sufficiently in twilight. I never felt/felt seeing less in twilight than my comrades/peers. From age (decade strata) on. 48 2 36 10 4 Questions related to laboratory work 17. Years experience in laboratory work: stratified in < 5 y and in climbing decades. <5y 5 < 15 15 < 25 25 < 35 35 < 45 > 45 528 9 14 13 12 1 1 18. Do you estimate that you experience more problems than your peers in one of the following items? If so, could you fill in to which previous questions your problems seem to be related? If you never perform these tasks, please write n.a. after the boxes. A. Performing autopsies B. Examining tissue specimens C. Dissecting tissue fragments <1 cm3 D. Preparing tissues for cutting, mounting, etc E. Using the (ultra)microtome F. Mixing chemicals or preparing special stains with delicate colors eg, PAS G. Examining slides under 40×, 50-100×, 110-200×, 210-400× magnification H. Examining slides with fluorescent staining I. Working in a room with dim light such as may be necessary for question H 7 3 6 3 2 43 37 38 35 26 9 5 11 19 1 1 1 3 2 18 29 1 3 3 47 42 3 2 1 43 2 4 ?, answered: do not know NA, not applicable NOA, no answer laboratorymedicine> september 2001> number 9> volume 32 © T2 왗your lab focus 왘 severe reduction of contrast sensitivity is age-related macular degeneration. Glare is a subjectively irritating perception of bright or poorly directed light and can be divided into discomfort glare and disability glare. Only in the latter case does it obstruct vision, but in both cases it hampers the performance of a task. The most common cause of glare is an early cataract. [F5]. Examples of glare encountered daily are light around a computer or television screen placed in front of a window, a traffic light without a shield to keep away the light from the sky around it, sunlight scattered by a dirty windshield, or the lights of oncoming traffic at night. Glare may also be disturbing with light reflected off water or shiny surfaces. In the lab, glare sources might include the backlighting of a microscope or a lightbox for looking at gels. Apart from subjects with early cataracts, those with a retinal degenerative disease often complain about glare from surfaces or fluorescent light tubes. Color discrimination seems to decrease with aging. This is primarily in the blue-violet range and thought to be mainly due to yellowing of the lens. This is why evaluators of the purity of diamonds are not usually over 35 years old (unless they have had a successful cataract extraction) and that painters have been known to be shocked at their paintings’ colors after a cataract extraction. It is unlikely that this age-related form of reduced color vision will create many problems in the laboratory. Dark adaptation is the property of the visual system that allows sensitivity to light to increase as luminance decreases [F4]. With aging, the absolute threshold of light perception, as measured with a dark adaptation curve, rises. Even when corrected for smaller pupil diameter and increased lens opacity, as done in an experimental setting, the retinal sensitivity under both photopic and scotopic circumstances decreases with aging.16 The former decreases roughly 0.04 log units per decade, the latter by 0.08 log u. In daily work a subject does not usually have the pupil and lens corrections, that have been used experimentally. On average, a 60-year-old subject will have a dark adaptation level that is 3 times or nearly 0.5 log unit higher than a young person and this could be bothersome while driving to work as well as in mesopic circumstances, such as a room used for fluorescent microscopy. In older subjects sensitivity loss may be tenfold or 1 log unit. Moreover dark adaptation usually is measured at locations 10E to 12E eccentric to the foveola. We found, however, that subjects with pathologically lowered dark adaptation levels due to a disorder called retinitis pigmentosa also need a factor 10 more light to discern contrasts in a microscope. This shows that not only excentric but also foveal sensitivity is reduced in these subjects. The visual field sensitivity decreases at a rate of about 0.7 dB per decade up to about age 50 years.17,18 After that period, the VF loss rate amounts to 2 dB per decade,18 although some authors found this only occurred after age 70 years. The extent of the VF decreases while aging. Older drivers, especially those over age 60 years, recognize highway signs at 65% to 75% of the distance as compared with those under 25 years.19 There are, of course, many more (visual) reasons why driving ability is diminished in the elderly, although they meet the official requirement for driving licensing of VA > 0.5 in the better eye. There is, however, a general consensus that most older drivers compensate for their deficits. Many avoid driving at night or in bad weather and may drive slower under certain circumstances. It is clear that a person depending on a personal car to commute to work has less freedom in this matter. Face recognition is another declining capacity above age 60, partly independent from VA.14,15 It may be that slowing of cerebral processes makes the complicated task of face recognition more time consuming. Although not life threatening, unless one is not cordial enough when greeting some thug’s friend, it is often mentioned as socially embarrassing. It seems that contrast sensitivity plays a relatively greater role in face recognition than VA. Subjects with age-related maculopathy often complain about not recognizing friends. In the early stages of age-related maculopathy prolonged readaptation after a blinding light source is one of the first complaints. In the late, exudative stage, metamorphopsia or distortion of the image is quite dis- © turbing [F7], while at the final stage with a central scar in the fovea a central scotoma remains [F8]. Reactions to Questionnaire on Visual Performance in Laboratory Work In order to try to gain an impression about the extent to which VA, accommodation, stereo vision, judging distances, VF extent, color vision, and dark adaptation might influence laboratory work, a questionnaire was designed and circulated to individual pathologists and chairpersons of departments with a request to distribute them. The first 11 questions were meant for demographic data and to estimate the respondent’s visual capacities and refraction. Of the 50 respondents, 33 were male, 5 older than 55 years of age, 1 had no driver’s license, 25 needed glasses for driving of which 24 were myopic, and 12 respondents were presbyopic. The answers to the remaining questions are given in [T2]. Initially, the majority of the respondents seemed to have little difficulty in their laboratory work. Fourteen percent felt that they had more visual problems than their peers in their work, but only 1 of these 7 respondents mentioned to which aspect of vision this was related: congenital cataract. One male respondent felt that he performed on 7 of 9 items worse than his peers, without mentioning why. Two subjects with color vision problems mentioned no problems with their laboratory work. Surprisingly, most of the problems (20% of the responders) were mentioned with regard to twilight vision. None of them, however, indicated that it impaired their functioning in the laboratory. As no reliable information was obtained how many questionnaires had been handed out, the response rate was unknown. The sampling was not random. Thus, interpretation of this small set of mostly anonymously obtained historic data should be approached with caution. Among the many confounders that could be mentioned would be that people either do not know, or do not admit, their deficiencies. In a recent study , it was found that 5.6% of 6250 Caucasian subjects aged 55 and over from a population study had VF loss in at least 1 eye. Of course, the age range was laboratorymedicine> september 2001> number 9> volume 32 529 왗your lab focus 왘 Glossary 530 Accommodation: The ability of the eye to change its focus and, thus, to clearly see objects both near and far. Age-related maculopathy: Degeneration of the macular area of the retina. Amblyopia: Impairment of vision without detectable organic lesion in the eye. Ametropic: Having a discrepancy between the size and refractive powers of the eye, so that images are not focused properly on the retina, resulting in hypertropia, myopia, or astigmatism. Aniseikonia: A condition in which the ocular image of an object seen by one eye is different in size and shape from the image seen by the other eye. Anisometropia: Having a difference in the refractive power of two eyes. Astigmatism: A condition resulting from unequal curvature of the refractive surface of the eye: a point of light cannot be brought to a point focus on the retina, but is spread over a more or less diffuse area. Central field: Field of vision that is clear and unobstructed. Diopter: A unit of refractive power of lenses, which is the reciprocal of the focal length. Diplopia: The perception of 2 images in a single object. Sometimes called double vision. Emmetropic: A state of correlation between the refractive system of the eye and the axial length of the eyeball so that rays of light enter the eye parallel to the optic axis, focusing exactly on the retina. Fixation: Direction of the eye to an object so its image falls on the fovea centralis, the depression in the center of the macula where vision is most acute. Foveola retinae: A small depression in the floor of the fovea centris (in the macula lutea, the area of clearest vision) devoid of rod cells but containing rod-like elongated cones. Hypermetropic (hyperopia): The error of refraction that causes rays of light entering the eye parallel to the optic axis to focus behind the retina. The eyeball is too short from front to back to accommodate the refraction. The condition is popularly called farsightedness. Luminance: The light-emitting intensity of a given surface viewed from a given direction. Macular degeneration: Degeneration of the lutea, including the retinal cone receptors. Mesopic: Descriptive of vision at intermediate light levels, such as at twilight. Monovision: Different lenses (external or contact lenses) are worn for each eye: one for near vision, one for distance. Myopic: Defect in which the focal point for light rays from a distant object is in front of the retina when the accommodative muscles are relaxed. Optic media: The clear parts of the eye through which light passes to hit the retina. Photopic: Pertaining to vision in the light, in which an eye is said to become light-adapted. Presbyopia: Hyperopia and impairment of vision caused by advancing years or old age. It is dependent on the diminution of the power of accommodation from loss of elasticity of the crystalline lens, causing the near point of distinct vision to be farther from the eye. Protanomalous: A form of dichromasy characterized by retention of a sensory mechanism for only blue and yellow color, with diminished ability to perceive red, green and their derivatives. In addition, the condition causes a loss of luminance and shift of brightness and hue curves toward the short-wave end of the spectrum. Protonopia is an X-linked genetic trait that affects about 1% of males. Retinal cone: A visual cell that serves light and color vision and visual acuity. Retinal rods: Rod-like cells in the retina specialized for night and peripheral vision. Their density is greatest around the fovea and decreases toward the retinal periphery. Retinitis pigmentosa: A group of diseases — often hereditary — that are marked by progressive loss of retinal response, retinal atrophy, attenuation of retinal vessels, and clumping of the pigment, with contraction of the field of vision. Scotoma: An area of lost or depressed vision within the visual field, surrounded by an area of less depressed or normal vision. Scotopic: Night vision or adaptation of vision to dark conditions. Single vision: A single image formed of an object seen with both eyes. Snellen acuity charts: Use of Snellen test types, in which the person looks at alternate red and green letters, with the sound eye covered with a red glass. If the green letters are read, the acuity can be determined. Named for Hermann Snellen, a Dutch ophthalmologist, 1834-1908. Toric: Shaped like a torus, a generally doughnut-shaped cylinder with the radius at one end larger than the other. Visual acuity: Clarity of vision, measured as the reciprocal of the smallest angle in minutes of arc that permits the person to discriminate a contour. Visual field: The entire area that can be seen while the eye is fixed on a target in the direct line of vision. laboratorymedicine> september 2001> number 9> volume 32 © 왗your lab focus 왘 different from the present study group but it remains possible that 1 in 3 people with VF defects were not aware of them. This has also be seen with color vision deficits.9 Whether people are not aware of their deficits because they never really compared their performance with their peers, or whether they simply do not wish to acknowledge them, is not known. There will also often be socio-economic differences between countries. While in the Netherlands, employers are obliged to offer a certain percentage of jobs to physically impaired employees, in countries with less protection against employment discrimination, people may tend to hide their problems to avoid dismissal or other adverse treatment at the workplace. We should consider these findings to be preliminary, given the limitations of the current study. In conclusion, of the many difficulties that may arise in the visual system, few were reported to cause problems among the 50 laboratory workers who answered our survey. Acknowledgements Thanks to JJ Vos, PhD, and D Baer, MD for comments. Thanks to AA Put for his excellent art work in the modifications of the anatomical lesson and in other illustrations. Rembrandt’s Anatomical Lesson courtesy of Royal Cabinet of Paintings, Mauritshuis, The Hague, The Netherlands. 1. Wainapel SF, Bernbaum M. The physician with visual impairment or blindness. Arch Ophthalmol: 1986;404:498-502. 2. Fankhauser F. Goldmann-Ged@chtnisvorlesung. Lichtempfindung und Sehorgan. Klin Mbl Augenheilk. 1997;210:231-255. 3. Dorland’s Illustrated Medical Dictionary. 28th ed. Philadelphia, PA: Saunders; 1998. 4. Webster’s New 20th Century Dictionary of the English Language, unabridged. 2nd ed. Williams Collins; 1980. 5. The Oxford English Dictionary. 2nd ed. Vol 14. Oxford, England: Clarendon Press; 1989. 6. AMA Guides to the Evaluation of Permanent Impairment. 4th ed. Chicago, IL: American Medical Association; 1993. 7. ICD-10. WHO, Geneva 1992. Vol 1, 457-8. 8. Neitz M, Neitz J. Molecular generics of color vision and color vision defects. Arch Ophthalmol. 2000;118:691-700. 9. Steward JM, Cole BL. What do color vision defectives say about everyday tasks? Optom Vis Sci. 1989;66:288-(2)95. 10. Loop MS, Crossman DK. High-color sensitivity in macaque and humans. Vis Neurosci 2000;17:119-(1)25. 11. Campbell JL, Spalding JA, Mir FA, et al. Doctors and the assessment of blood glucose testing sticks: does colour blindness matter? Br J Gen Pract. 2000;50:393-(39)5. 12. Walraven J, Kooi FL. Revision of Visual Standards for the Netherlands Royal Navy: Binocular Depth Perception Reconsidered. TNO Human Factors Research Institute; Soesterberg, the Netherlands: 1999:9-10. Report TM-99-A062. 13. Weale RA. Effects of senescence. In: Kulikowski; JJ, Walsh V, Murray IJ, eds. Limits of Vision. London, England: Macmillan; 1991: 277-285. Cronly-Dillon, J, ed. Vision and Visual Dysfunction; vol 5. 14. Kline DW. Light, Ageing and Visual Performance. In: Vision and Visual Dysfunction. Ed: J.CronlyDillon. Vol 16. The susceptible visual apparatus. Chapt. 10, 150-161. MacMillan London 1991. 15. Rubin GS, Munoz B, Bandeen-Roche K, et al. Monocular versus binocular visual acuity as measures of vision impairment and predictors of visual disability. Invest Ophthalmol Vis Sci. 2000;41:3327-3334. 16. Jackson GR, Owsley C. Scotopic sensitivity during adulthood. Vision Res. 2000;40:2467-2473. 17. Johnson CA, Adams AJ, Lewis RA. Evidence for a neural basis of age-related visual field loss in normal observers. Invest Ophthalmol Vis Sci. 1989;30:2056-2064. 18. Lachemmayr BJ, Kojetinsky S, Ostermaier N, et al. The different effects of aging on normal sensitivity in flicker and light-sense perimetry. Invest Ophthalmol Vis Sci 1994;35:2741-2748. 19. Sivak M, Olson PL, Pastalan LA. Effect of driver’s age on night time legibility of highway signs. Hum Factors. 1981;23:59-64. 20. Trauzettel-Klosinski S, Teschner C, Tornow R-P, et al. Reading strategies in normal subjects and in patients with macular scotoma, assessed by two new methods of registration. Neuroophthalmology. 1994;14:15-30. 21. Verriest G. Leeftijd en zien [Age and vision]. Eindhoven, the Netherlands; 1979. 531 © laboratorymedicine> september 2001> number 9> volume 32 ©