Elise Harb

Characteristics of Accommodative Behavior During Sustained Reading in Emmetropes and Myopes

Accommodation has long been suspected to be involved in the development of myopia because near work, particularly reading, is known to be a risk factor. In this study, we measured several dynamic characteristics of accommodative behavior during extended periods of reading under close-to-natural conditions in 20 young emmetropic and stable myopic subjects. Accommodative responses, errors, and variability (including power spectrum analysis) were analyzed and related to accommodative demand and subject refractive error. All accommodative behaviors showed large inter-subject variability at all of the reading demands. Accommodative lags and variability significantly increased with closer demands for all subjects (ANOVA, p<0.05). Myopes had significantly greater variability in their accommodation responses compared to emmetropes (ANOVA, p<0.05) and had larger accommodative lags at further reading distances (unpaired t test p<0.05). Power spectrum analysis showed a significant increase in the power of accommodative microfluctuations with closer demands (ANOVA, p<0.05) and with increasing myopia at the closest reading demand (ANOVA, p<0.01). The difference in the stability of the accommodative behavior between individuals with different refractive states suggests a possible relationship between variability in accommodation and the development of myopia.

Imposed anisometropia, accommodation, and regulation of refractive state.

Purpose. To determine the effects of imposed anisometropic retinal defocus on accommodation, ocular growth, and refractive state changes in marmosets. Methods. Marmosets were raised with extended-wear soft contact lenses for an average duration of 10 weeks beginning at an average age of 76 d. Experimental animals wore either a positive or negative power contact lens over one eye and a plano lens or no lens over the other. Another group wore binocular lenses of equal magnitude but opposite sign. Untreated marmosets served as controls and three wore plano lenses monocularly. Cycloplegic refractive state, corneal curvature, and vitreous chamber depth were measured before, during, and after the period of lens wear. To investigate the accommodative response, the effective refractive state was measured through each anisometropic condition at varying accommodative stimuli positions using an infrared refractometer. Results. Eye growth and refractive state are significantly correlated with the sign and power of the contact lens worn. The eyes of marmosets reared with monocular negative power lenses had longer vitreous chambers and were myopic relative to contralateral control eyes (p < 0.01). Monocular positive power lenses produced a significant reduction in vitreous chamber depth and hyperopia relative to the contralateral control eyes (p < 0.05). In marmosets reared binocularly with lenses of opposite sign, we found larger interocular differences in vitreous chamber depths and refractive state (p < 0.001). Accommodation influences the defocus experienced through the lenses, however, the mean effective refractive state was still hyperopia in the negative-lens–treated eyes and myopia in the positive-lens–treated eyes. Conclusions. Imposed anisometropia effectively alters marmoset eye growth and refractive state to compensate for the imposed defocus. The response to imposed hyperopia is larger and faster than the response to imposed myopia. The pattern of accommodation under imposed anisometropia produces effective refractive states that are consistent with the changes in eye growth and refractive state observed.

Factors associated with macular thickness in the COMET myopic cohort.

Purpose. To determine whether macular thickness is associated with ethnicity, gender, axial length (AL), and severity of myopia in a cohort of young adults from the Correction of Myopia Evaluation Trial (COMET). Methods. Eleven years after their baseline visit, 387/469 (83%) subjects returned for their annual visit. In addition to the protocol-specific measures of spherical equivalent refractive error (SER) and AL, high-resolution macular imaging also was performed with optical coherence tomography (RTVue). From these scans, full-thickness values for the central (1 mm), parafoveal (1 to 3 mm), and perifoveal (3 to 5 mm) annular regions were calculated. Gender, ethnicity, AL, and SER were examined for associations with macular thickness using univariate and multivariable linear regression analyses. Results. In the 377 subjects with usable data (mean age = 21.0 ± 1.3 years), the mean SER ± SD was −5.0 ± 1.9 D and mean AL was 25.4 ± 0.9 mm. Mean foveal thickness was 252.0 ± 20.1 &mgr;m in the center, 315.6 ± 14.0 &mgr;m in the parafovea, and 284.4 ± 12.9 &mgr;m in the perifovea. In the best-fit multivariable model that adjusted for gender, ethnicity, and AL, females had significantly thinner maculas than males for all three regions (p < 0.0001), with the largest difference in the center (12.8 &mgr;m, 95% confidence interval: 9.2 to 16.4). The effect of ethnicity was strongest in the central fovea, with African-Americans, Asians, Hispanics, and mixed ethnic groups having thinner maculas than whites (all p values < 0.005). Increased AL was significantly associated with slightly thicker central foveas (p = 0.001) and thinner parafoveal (p = 0.02) and perifoveal (p < 0.0001) regions. Conclusions. In this ethnically diverse cohort of moderate and high myopes, females and African-Americans were found to have the thinnest central foveas. Whether such thinning in the macula as a young adult is a risk factor for future disease remains to be determined.

Visual activity and its association with myopia stabilisation

To evaluate the association between outdoor and nearwork activities at baseline and myopia stabilisation by age 15 in the Correction of Myopia Evaluation Trial (COMET).