Corneal and Crystalline Lens Dimensions Before and After Myopia Onset

Abstract

Purpose To describe corneal and crystalline lens dimensions before, during, and after myopia onset compared to age-matched emmetropic values. Methods Subjects were 732 children 6 to 14 years of age who became myopic and 596 emmetropic children participating between 1989 and 2007 in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study. Refractive error was measured using cycloplegic autorefraction, corneal power using a hand-held autokeratometer, crystalline lens parameters using video-based phakometry, and vitreous chamber depth (VCD) using A-scan ultrasonography. Corneal and crystalline lens parameters in children who became myopic were compared to age-, gender-, and ethnicity-matched model estimates of emmetrope values annually from 5 years before through 5 years after the onset of myopia. The comparison was made without, then with statistical adjustment of emmetrope component values to compensate for the effects of longer VCDs in children who became myopic. Results Before myopia onset, the crystalline lens thinned, flattened, and lost power at similar rates for emmetropes and children who became myopic. The crystalline lens stopped thinning, flattening, and losing power within ±1 year of onset in children who became myopic compared to emmetropes statistically adjusted to match the longer vitreous chamber depths of children who became myopic. In contrast, the cornea was only slightly steeper in children who became myopic compared to emmetropes (<0.25 D) and underwent little change across visits. Conclusions Myopia onset is characterized by an abrupt loss of compensatory changes in the crystalline lens that continue in emmetropes throughout childhood axial elongation. The mechanism responsible for this decoupling remains speculative, but might include restricted equatorial growth from internal mechanical factors.

Lens power loss in early adulthood

“…The increase in axial thickness can be seen in the follow-up of the current study, and interestingly, although curvatures may be steepening slightly with age in these engineering students, the lens is losing power probably because of changes in its internal structure, as has been discussed before (Iribarren et al 2012). The fact that the lens seems to be losing more power in baseline emmetropes or hyperopes than in myopic subjects is possibly related to the changes seen in lens power loss during myopia development in previous studies (Iribarren et al 2012;Mutti et al 2012).…”

“…This loss of power compensates for axial elongation in eyes that remain nearly emmetropic during infancy and adolescence. But during school myopia development, the lens has been shown to alter its rate of lens power loss (Iribarren et al 2012;Mutti et al 2012). Three studies in selected groups developing myopia during early adulthood have reported prospectively on myopic shifts and biometry.…”

Heritability of Lenticular Myopia in English Springer Spaniels

“…Myopia, more specifically, is due to an elongation of the eye that becomes independent of compensatory changes in the crystalline lens at the onset of myopia. 1 The thinning, flattening, and loss of lens power typical of eyes that remain emmetropic over time abruptly stops at the onset of juvenile myopia. 1 A better understanding of the regulation of the relationship between axial elongation and crystalline lens power may provide novel insights into the development of canine and human refractive error.…”

“…1 The thinning, flattening, and loss of lens power typical of eyes that remain emmetropic over time abruptly stops at the onset of juvenile myopia. 1 A better understanding of the regulation of the relationship between axial elongation and crystalline lens power may provide novel insights into the development of canine and human refractive error. Naturally-occurring models for lenticular based myopia are lacking, making the study of human lenticular myopia more challenging.…”

Myopia, Just a Refractive Error?

“…Myopia is progressive; we are not born nearsighted, but it develops in the first decade of life and can progress into the teens and early 20s. 6 The mechanism seems to be multifactorial, involving both genetics and the environment. The key issue is can we control myopia progression?…”