Nina E. Friedman

Ocular component data in schoolchildren as a function of age and gender.

Purpose. To describe the refractive error and ocular components of a large group of school-aged children as a function of age and gender. Methods. In this report, we describe the refractive error and ocular components of 2583 school-aged children (49.3% girls, overall mean [±SD] age 10.0 ± 2.3). Measurement methods included cycloplegic autorefraction, autokeratometry, videophakometry, and A-scan ultrasonography. For statistical comparisons across gender and age, a critical point of &agr; = 0.005 was used to assess significance because of the large sample size and the large number of comparisons made. Results. Of these 2583 children, 10.1% were myopic (−0.75 D or more myopia in both meridians), and 8.6% were hyperopic (+1.25 D or more hyperopia in both meridians). As would be expected, there was a significant effect of age on refractive error (spherical equivalent, p < 0.0001), toward less hyperopia/more myopia. There was no significant difference in the average refractive error between girls and boys (p = 0.0192). Girls had steeper corneas than boys (0.74 D steeper in the vertical meridian and 0.63 D steeper in the horizontal meridian, p < 0.0001). There were no significant differences in corneal power with age (p = 0.16). Both older age and male gender were significantly associated with deeper anterior chambers (p < 0.0001 for both). The crystalline lens showed significant thinning with age (p < 0.0001), however, there was no significant difference in the lens thickness between girls and boys (p = 0.66). Both Gullstrand lens power and calculated lens power showed significant effects of age and gender (p < 0.0001 for both). Girls, on average, had Gullstrand lens powers that were 0.28 D steeper and calculated lens powers that were 0.80 D more powerful than boys. Axial length also showed significant effects of age and gender (p < 0.0001 for both). Girls’ eyes were, on average, 0.32 mm shorter than those of boys. Conclusions. These cross-sectional data show a general pattern of ocular growth, no change in corneal power, and crystalline lens thinning and flattening between the ages of 6 and 14 years. Girls tended to have steeper corneas, stronger crystalline lenses, and shorter eyes compared with boys.

Initial cross-sectional results from the Orinda Longitudinal Study of Myopia.

Background. Although investigations of human refractive error development and normal ocular growth have been conducted for the last 50 years, no previous study of refractive error and the ocular components has measured all the ocular components. Methods. The Orinda Longitudinal Study of Myopia was initiated to characterize the development of refractive error and normal eye growth in a sample of predominantly Caucasian children ages 6 to 14 years. Results. Crosssectional results from 530 children ages 5 to 12 years in the 1st, 3rd, and 6th grades are presented. Conclusions. This samples refractive error decreased toward emmetropia with age from an average of +0.73 D at age 6 years to an average of +0.50 D by age 12 years. Between the ages of 6 and 12 years, the vitreous chamber elongated (by 0.52 mm) and the crystalline lens power decreased (by 1.35 D); surprisingly, the crystalline lens thinned by 0.14 mm during this same time period

Refractive astigmatism and the toricity of ocular components in human infants.

Purpose. Many studies have characterized astigmatism in infancy, but few have been longitudinal or contained ocular component data. This study characterized the frequency, orientation, and longitudinal change with age of infant astigmatism. Additional factors investigated were the influence of early astigmatism on emmetropization and its relation to corneal and lenticular toricity. Methods. Three hundred two infants were enrolled in the study. Of these, 298 provided data for at least one visit at 3 ± 1 months, 9 ± 1 months, 18 ± 2 months, and 36 ± 3 months. Testing included cycloplegic retinoscopy (cyclopentolate 1%), video-based keratophakometry, and ultrasonography over the closed eyelid. Results. Astigmatism ≥1.00 DC was common at 3 months of age (41.6%) but decreased in prevalence to 4.1% by 36 months (p < 0.0001). The most common orientation was with-the-rule at 3 months (37.0% compared with 2.7% for against-the-rule) but against-the-rule at 36 months (3.2% compared with 0.9% for with-the-rule). Most of the change in the average value of the horizontal/vertical component of astigmatism (J0) occurred between 3 and 9 months (−0.26 ± 0.36 D; p < 0.0001) with no significant change between 9 and 36 months (−0.05 ± 0.36 D; p = 0.09). Spherical equivalent refractive error was not correlated with J0 at 3 and 9 months (R2 = 0.002, p = 0.48 and R2 = 0.001, p = 0.56, respectively). The two were only weakly correlated at 18 and 36 months (R2 = 0.06 for each age, p < 0.0001, p = 0.0002, respectively). Changes in spherical equivalent between 3 and 9 months were unrelated to either the initial value of J0 (partial R2 for J0 = 0.0001; p = 0.85) or the change in J0 (partial R2 for change in J0 = 0.0031; p = 0.31). Across all the ages, corneal toricity was with-the-rule, and lenticular toricity was against-the-rule (produced by the toricity of the posterior lens surface). The cornea and anterior lens surface became more spherical with age, contributing to the shift away from with-the-rule refractive astigmatism. Toricity of all the refractive surfaces became less variable with age. Conclusions. Consistent with many reports, astigmatism was common in early infancy but decreased in prevalence with age, particularly when with-the-rule in orientation. The reduction in percentage of infants with astigmatism appeared to be caused by decreases in the toricity of the cornea and the anterior lens combined with decreases in the variability of corneal and lenticular surfaces. Astigmatism in infancy appeared to be unrelated to emmetropization of spherical equivalent refractive error.

Corneal Changes in Schoolchildren

Videokeratography (TMS-1) data from the right eyes of 788 children between the ages of 6 and 14 years, examined in 1994 as part of the Orinda Longitudinal Study of Myopia, were analyzed using the Fast Fourier Transform (FFT) to quantify corneal power, toricity, and toricity axis. Cross-sectional analysis showed no statistically significant age trend for these parameters. Conversely, longitudinal analysis of data for 387 of these children, first measured in 1991, showed a statistically significant decrease in corneal power. Corneal toricity did not change significantly over this 3-year period, although there was a minute but statistically significant clockwise axis shift. From this we conclude that in the elementary and junior high school years—during which period axial length is known to increase—corneal flattening continues, but corneal toricity is stable.

Repeatability of corneal topography measurement in keratoconus with the TMS-1

Purpose. The purpose of this study was to report the test–retest variability of simulated indices derived from the TMS-1 topography instrument (Tomey Technology, Waltham, MA) in keratoconus subjects enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Methods. Four images were taken at an initial visit and at a repeat visit several weeks later. From these images, 17 indices were simulated from published formulas. Mixed-model analysis was used on test–retest data from the TMS-1 videokeratography instrument during the baseline year. This analysis yields estimates of within- and between-visit variability. Results. Repeatability analysis revealed that within-visit standard errors were 1.0 to 5.9 times greater in keratoconus eyes than in normal controls when two images were analyzed from each visit. These values changed only slightly when more images were used. The ratio of between-visit standard errors of the indices were nearly equally greater than normal controls for (0.9–4.6 and 0.9–4.3) two images per eye and all images per eye, respectively. Conclusions. These results suggest that the repeatability of simulated indices derived from TMS-1 topography in keratoconus subjects is poorer than in normal controls.

Quantifying corneal toricity from videokeratography with Fourier analysis.

BACKGROUND Fourier analysis can be used to quantify corneal toricity from videokeratography data. This study measures the repeatability of Fourier-derived toricity values in normal adult corneas. METHODS The Topographic Modeling System (TMS) was used to model the corneas of 29 subjects on two occasions, and Fourier analysis applied to the data. Repeatability of Fourier-derived toricity values between sessions was examined, and 95% limits of agreement were established. RESULTS The 95% limits of agreement between sessions for the Fourier method were -0.02 +/- 0.16 diopters (D) and -0.5 +/- 5.7 degrees for toricity amount and axis, respectively. CONCLUSIONS The Fourier method yields highly repeatable toricity values and thus provides a sensitive means of detecting longitudinal toricity change in normal corneas.