Ocular Component Development during Infancy and Early Childhood.

SIGNIFICANCE: The study fills an important gap by providing a longitudinal description of development of the major structural and optical components of the human eye from 3 months to nearly 7 years of age. Normative development data may provide insights into mechanisms for emmetropization and guidance on intraocular lens power calculation. PURPOSE: The purpose of this study was to describe the pattern of development of refractive error and the ocular components from infancy through early childhood. METHODS: Cycloplegic retinoscopy (cyclopentolate 1%), keratophakometry, and ultrasonography were performed longitudinally on between 162 and 293 normal birth weight infants at 0.25, 0.75, 1.5, 3, 4.5, and 6.5 years of age. RESULTS: Refractive error and most ocular components displayed an early exponential phase of rapid development during the first 1 to 2 years of life followed by a slower quadratic phase. Anterior and vitreous chamber depths, axial length, and crystalline lens radii increased at every visit. The crystalline lens thinned throughout the ages studied. The power of the cornea showed an early decrease, then stabilized, whereas the crystalline lens showed more robust decreases in power. The crystalline lens refractive index followed a polynomial growth and decay model, with an early increase followed by a decrease starting at 1 to 2 years of age. Refractive error became less hyperopic and then was relatively stable after 1 to 2 years of age. Axial lengths increased by 3.35 ± 0.64 mm between ages 0.25 and 6.5 years, showed uniform rates of growth across the range of initial values, and were correlated with initial axial lengths (r = 0.44, P < .001). CONCLUSIONS: Early ocular optical and structural development appears to be biphasic, with emmetropization occurring within the first 2 years of infancy during a rapid exponential phase. A more stable refractive error follows during a slower quadratic phase of growth when axial elongation is compensated primarily by changes in crystalline lens power.

Accommodation, acuity, and their relationship to emmetropization in infants.

PURPOSE: To evaluate the relationship between accommodation, visual acuity, and emmetropization in human infancy. METHODS: Defocus at distance and near (57 cm) was assessed using Mohindra and dynamic retinoscopy, respectively, in 262 normal birthweight infants at 3, 9, and 18 months of age. Preferential looking provided acuity data at the same ages. The spherical equivalent refractive error was measured by cycloplegic retinoscopy (cyclopentolate 1%). RESULTS: Univariate linear regression analyses showed no associations between the change in refractive error and defocus at distance or near. Change in refractive error was linearly related to the accommodative response at distance (R = 0.17, p < 0.0001) and near (R = 0.13, p < 0.0001). The ten subjects with the poorest emmetropization relative to the change predicted by the linear effects of their refractive error had higher average levels of hyperopic defocus at distance and near (p < 0.043). Logistic regression showed a decrease in the odds of reaching +2.00 diopter or less hyperopia by 18 months with increasing levels of hyperopia at 3 months, or if Mohindra retinoscopy was myopic combined with acuity better than the median level of 1.25 logMAR [area under the receiver operating characteristic curve = 0.78 (95% CI = 0.68 to 0.88)]. CONCLUSIONS: The level of cycloplegic refractive error was the best single factor for predicting emmetropization by 18 months of age, with smaller contributions from visual acuity and Mohindra retinoscopy. The lack of correlation between defocus and change in refractive error does not support a simple model of emmetropization in response to the level of hyperopic defocus. Infants were capable of maintaining accurate average levels of accommodation across a range of moderate hyperopic refractive errors at 3 months of age. The association between the change in refractive error and accommodative response suggests that accommodation is a plausible visual signal for emmetropization.

Axial growth and changes in lenticular and corneal power during emmetropization in infants.

PURPOSE: To evaluate the contribution made by the ocular components to the emmetropization of spherical equivalent refractive error in human infants between 3 and 9 months of age. METHODS: Keratophakometry in two meridians was performed on 222 normal-birthweight infant subjects at 3 and 9 months of age. The spherical equivalent refractive error was measured by cycloplegic retinoscopy (cyclopentolate 1%). Anterior chamber depth, lens thickness, and vitreous chamber depth were measured by A-scan ultrasonography over the closed eyelid. RESULTS: Both the mean and SD for spherical equivalent refractive error decreased between 3 and 9 months of age (+2.16 +/- 1.30 D at 3 months; +1.36 +/- 1.06 D at 9 months; P < 0.0001, for the change in both mean and SD). Average ocular component change was characterized by increases in axial length, thinning, and flattening of the crystalline lens, increases in lens equivalent refractive index, and decreases in lens and corneal power. Initial refractive error was associated in a nonlinear manner with the change in refractive error (R(2) = 0.41; P < 0.0001) and with axial growth (R(2) = 0.082; P = 0.0005). Reduction in hyperopia correlated significantly with increases in axial length (R(2) = 0.16; P < 0.0001), but not with changes in corneal and lenticular power. Decreases in lenticular and corneal power were associated with axial elongation (R(2) = 0.40, R(2) = 0.12, respectively; both P < 0.0001). CONCLUSIONS: Modulation in the amount of axial growth in relation to initial refractive error appeared to be the most influential factor in emmetropization of spherical equivalent refractive error. The associations between initial refractive error, subsequent axial growth, and change in refractive error were consistent with a visual basis for emmetropization. The cornea and crystalline lens lost substantial amounts of dioptric power in this phase of growth, but neither appeared to play a significant role in emmetropization.

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 > or =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 (R=0.002, p=0.48 and R=0.001, p=0.56, respectively). The two were only weakly correlated at 18 and 36 months (R=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 R for J0=0.0001; p=0.85) or the change in J0 (partial R 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.