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Volume 20 Number 6 Reports 6. Ham WT Jr, Ruflblo JJ Jr, Mueller HA, Clarke AM, and Moon ME: Histologic analysis of photochemical lesions produced in rhesus retina by short-wavelength light. INVEST OPIITIIALMOL VIS SCI 17:1029, 1978. 7. Zuclich JA: Cumulative effects of near-UV induced corneal damage. Health Phys 38:833, 1980. Table I Measurement Technique Corneal diameter Central corneal thickness Anterior chamber depth Horizontal and vertical keratometry Pupil size Millimeter ruler Haag-Streit pachymeter Hagg-Streit pachymeter American Optical keratometer Millimeter ruler at ambient light Millimeter ruler in primary position A-scan ultrasonography Indentation technique with two weights on the Schiotz' tonometer Retinoscopy and manifest refraction Masked grading of external photographs on scale 0 - 4 + Palpebral fissure size Low ocular rigidity in patients with os- Length of globe Ocular rigidity teogenesis imperfecta. MURIEL I. KAISERKUPFER, LESSIE M C C A I N , JAY R. MARVIN J. PODCOR, CARL SHAPIRO, Sixteen patients with osteogenesis imperfecta (01) have undergone a thorough eye examination. These patients had statistically significantly lower ocular rigidity measurements than a group of normal oolunteers matched on age, sex, and, refractive error. In addition, the corneal diameter and. length of the eyeball was smaller in 01 patients than that in controls. Possible correlations of low ocular rigidity with biochemical changes in scleral collagen await further investigation. Osteogenesis imperfecta (01) is an inherited disease of bone affecting between 10,000 and 20,000 persons in the United States. OI is usually inherited as an autosomal dominant, but cases of sporadic or recessive inheritance have been reported. Given the variability in clinical and genetic expression, the term OI probably represents several clinically similar but genetically distinct disorders. Although blue sclera, along with fractures and deafness, have been identified as cardinal clinical features of OI, there has been poor correlation of the presence or absence of blue sclera with the other features of the disease.1' 2 This may be because of subjectivity in estimating the presence or absence of blue sclera as well as grading the color. A more quantitative assessment of the properties of sclera could be of value in determining the functional characteristics of this tissue in OI patients. The purpose of this presentation is to report the findings of a complete ocular evaluation of sixteen patients with OI as compared with age-, sex-, and refractive error-matched controls. Materials and methods. Sixteen patients with OJ ranging in age from 9 to 56 years underwent a complete ocular examination, including measurement of corneal diameter, corneal thickness centrally, anterior chamber depth, horizontal and vertical keratometry, pupil size, palpebral fissure Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017 Refractive error KUPFER, AND DAVID ROVVE. 807 Scleral color size, length of globe, ocular rigidity, refractive error, and scleral color. Table I presents the- techniques used for each of these measurements. These patients represented the broad clinical and genetic spectrum of OI. Each had a lifelong history of multiple fractures, compatible radiologic findings, and no chemical abnormality indicative of another cause for the brittle bone disease. Skeletal deformities, scoliosis, and hernias were associated findings. A control group consisted of 16 normal volunteers matched on age, sex, and refractive error to the patients with OI. All ages matched within 2 years. This control group also had the complete eye examination. For each variable, first the right eye then the left eye of each person was measured. Statistical analysis involved the paired t test and calculation of the intraclass correlation coefficient.' Results. Because each patient was matched to a control, the paired t test provided a sensitive procedure for identifying differences between the patient group and the control group. For each variable, a value for each person was determined by averaging the two eyes. The appropriateness of this averaging was investigated by the intraclass correlation coefficient, a measure of relatedness of the two eyes, which accounts for the variation in measurements between persons. An intraclass correlation coefficient close to 1 indicated similar measurements between eyes. Only two variables (length of globe for patients and corneal thickness for controls) had low (0.4) intraclass correlation coefficients. This indicated considerable variation between eyes (when compared with the variation between persons) and 808 Invest. Ophthalmol. Vis. Sci. June 1981 Reports Table II. Comparison of 0 1 patients and age-, sex-, and refractive error-matched controls (16 pairs)* Patients (N = 16) Controls (N = 16) Pair difference (patient — control) (N = 16) Variable Mean S.D. Mean S.D. Mean Pupil size (mm) Corneal diameter (mm) Horizontal keratometry (diopters) Vertical keratometry (diopters) Corneal thickness (mm) Anterior chamber (mm) Applanation tomometry (mm Hg) Palpebral fissure (mm) Length of globe (mm) Ocular rigidity (I" 1 ) 4.5 10.7 42.9 44.7 0.58 3.3 14.7 21.3 22.8 0.015 1.2 0.6 1.7 1.5 0.11 0.3 2.3 1.1 1.0 0.004 4.1 11.4 43.5 44.7 0.58 3.6 13.5 22.1 24. Of 0.020 1.2 0.5 1.8 2.0 0.02 0.5 2.5 2.0 1.6 0.006 0.4 -0.6 -0.6 0.0 0.00 -0.3 1.2 -0.8 -1.2t -0.005 S.D. 1.3 0.8 2.8 2.4 0.10 0.5 3.1 2.0 1.3 0.005 Significance level (two-sided p value) 0.23 0.007 0.39 0.99 0.97 0.05 0.14 0.13 0.003 0.001 * Values for each person were determined by averaging the measurements of the two eyes. t Length of globe for one control was unavailable; therefore calculations were based on a sample size of 15. Table III. Ocular rigidity and blueness of sclera in OI patients Ocular rigidity* Group 1. Blue sclera 0 to 2+ N = 7 Mean = 0.017 S.D. = 0.004 Group II. Blue sclera 3+ to 4 + N = 13 Mean = 0.014 S.D. = 0.003 p = 0.04 * Ocular rigidity value for a person is the average of the two eyes. thus suggests caution in averaging values from the eyes for these two variables. Therefore, with these cautions, we were satisfied in averaging eyes. Table II summarizes the comparison between the patient group and the control group by the paired t test with the average of the two eyes. The mean ocular rigidity value was significantly lower in the OI patients than that in the normal controls (p = 0.001). The corneal diameter was smaller in patients than that in controls (p = 0.007), and the A-scan for length of the globe indicated a small eye in patients as compared with controls (p = 0.003). No other values were significantly different between the two groups. We also compared the scleral color (with respect to blueness) to the ocular rigidity measurements of 12 of the 16 patients above and eight additional OI patients (Table III). The 20 OI patients were divided into two groups; group I had sclera graded blue from 0 to 2+ on external photographs, whereas group II had sclera graded blue from 3+ to 4+. In group 1 the average ocular rigidity was 0.017, and in group II it was 0.014. This difference Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017 in ocular rigidity was significantly different at p = 0.04 as determined by the Student's t test, although the correlation of ocular rigidity and blueness of sclera (R = 0.25) was not significantly different from zero (p = 0.29). Discussion. Ocular rigidity is a measurement of the distensibility of the coats of the eye when the cornea is indented with a weight, in this case a Schiotz tonometer. Low ocular rigidity is sometimes associated with myopia. Thus it was most important to have as controls normal volunteers matched not only for age and sex but also for refractive error. Because there was a highly significant difference between patients and controls, myopia does not seem to explain the low ocular rigidity in these patients. It was of particular interest that the eyes in OI patients tended to be smaller, as determined by A-scan ultrasonography, which showed a decreased corneal diameter and decreased overall globe length. Since a smaller eye requires less fluid to raise the intraocular pressure (IOP) the same amount as a normal-sized eye, the low ocular rigidity in OI patients is even lower than measured. If a small eye and a normal eye have the same elasticity of the ocular coats, the small eye will require less injected fluid than the large eye to produce the same elevation oflOP. In the OI small eyes the low ocular rigidity is indicated by the larger corneal indentations produced by the tonometer. Therefore the decreased ocular rigidity cannot be the result of the small eyeballs but rather is the result of increased distensibility of the ocular coats. Although these data demonstrate the increased extensibility of the sclera, they contain no information about the tensile strength of the ocular coats and Volume 20 Number 6 should not be interpreted to indicate that these eyes are more easily ruptured by internal pressure than are normal eyes. What can be concluded is that the decreased ocular rigidity and smaller eye may be related to the developmental aspect of the globe, reflecting an underlying biochemical abnormality in either the type of collagen produced or the ratio of aj and a2 chains in type I collagen. These determinations must await further investigation. We detected no correlation between ocular rigidity and blueness of sclera in patients with 01. This may be the result of a number of factors such as true independence between ocular rigidity and blue sclera, the difficulty of having a truly linear scale for blueness of sclera, or the small sample size. Efforts continue to improve the measurement of scleral color and to increase the sample size. From the Clinical Branch, National Eye Institute, National Institutes of Health, Bethesda, Md. (M.I.K., L.M., C.K.) Office of Biometry and Epidemiology, National Eye Institute, National Institutes of Health, Bethesda, Md. (M.J.P.), Clinical Center, National Institutes of Health, Bethesda, Md. (J.R.S.), and Department of Pediatrics, University of Connecticut, Farmington, Conn. (D.R.). Submitted for publication Dec. 19, 1980. Reprint requests: Muriel I. Kaiser-Kupfer, M.D., National Eye Institute, Building 10, Room 12S235, National Institutes of Health, Bethesda, Md. 20205. Key words: ocular rigidity, osteogenesis imperfecta, blue sclera REFERENCES 1. Bell J: Introduction. In The Treasury of Human Inheritance, Pearson K, editor. Vol. II. Anomalies and Diseases of the Eye. (Nettleship Memorial Volume). Part III. Blue Sclerotics and Fragility of Bone. London, 1928, Cambridge University Press. 2. Smith R, Francis MJA, and Sykes B: The eye and collagen in osteogenesis imperfecta. Birth Defects 13:563, 1976. 3. Snedecor GW and Cochran WG: Statistical Methods, ed. 6. Ames, Iowa, 1967, Iowa State University Press. Flicker: a "decay" effect after light deprivation. ANNE CHRISTAKE CORNWELL. The "decay" effect resulting from repetitive light stimulation at different flicker rates was investigated. Adult cats were visually deprived monocularly or binocularly for I or 2 weeks. The results showed a progressive decrease in the b-wave of the electroretinogram during the Reports later flashes in a train. The data are presented as percent of the initial response to a flash. In the control eye the b-wave stabilized rapidly after the initial flash in a train of stimuli. Partial recovery occuired after 1 week of normal stimulation. Monocular light deprivation over a brief period causes changes in the b-wave of the electroretinogram (ERG). The b-wave is decreased in amplitude to a single flash and wanes to a train of flashes. l~4 The deprived eye is sensitive to both the frequency and intensity of the stimuli. The b-wave of the nondeprived eye, however, does not show a similar progressive decrease. After the initial rapid rise in amplitude, it stabilizes to a constant fraction of the initial response at slow flicker rates. 5 Light deprivation for 1 week or longer clearly affects certain retinal response properties. These ERG changes reflect the sensitivity of the eye to restrictions of light input and the subsequent inability of the retina to sustain a normal response during flicker. A lack of resolution of intermittent light flashes was shown in the normal all-rod skate retina.(> A decreased ERG b-wave and reduced ganglion cell activity were recorded during flicker. In the cat, however, the retinal neural structures or their mechanism of action may differ. Cats have both cones and rods, although the latter predominate (rod-cone ratio = 10.5:1 in area centralis, 66:1 in periphery, and 100:1 in ora serrata).' It can be hypothesized from these findings that the normal activity of the photoreceptors in the cat retina may be disrupted by light deprivation and result in a "decay" effect during flicker. This decay effect after light deprivation was investigated in this study with different flicker rates. This would maximize the b-wave reduction in the deprived eye but would leave the normal eye virtually unaffected. The progressive decrease in b-wave amplitude during flicker was also studied, since this decay phenomenon is affected by the cumulative effects of light input. Materials and methods. The data are based on the averaged ERG b-wave from the right and left eye of two adult cats deprived monocularly for 2 weeks and of two cats deprived binocularly for 1 week. The ERG was recorded from both eyes simultaneously before and immediately after deprivation. Recovery was tested 1 week after the end of monocular deprivation. The procedure followed in the present study was previously described. 1 The monocularly deprived animals were anesthesized with pentobarbital (Nembutal) and were deprived of all light by means of a black plastic bulbous disc sutured to 0146-0404/81/060809+04$00.40/0 © 1981 Assoc. for Res. in Vis. and Ophthal., Inc. Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017 809