Abstract
Purpose: :
When myopic or hyperopic defocus is imposed on a growing eye with a spectacle lens, the eye compensates for the defocus and changes its rate of growth accordingly. We used plus and minus lens-wear to investigate the development of central and peripheral refractive error and associated eye shape changes in the guinea pig.
Methods: :
Guinea pigs wore a -4D (n=15), 0D (n=8) or +4D (n=16) spectacle lens on one eye from 8 days of age for ~12 days. At the end of the lens-wear period, refractive error was measured centrally and off-axis in the temporal and nasal fields in cyclopleged eyes using the crystalline lens margin as a reference. Animals were then anaesthetized, and on-axis ocular components were measured using high frequency ultrasound. Eyes were enuceulated immediately after death, and rapidly frozen and sectioned in the horizontal plane. Eye shape was analyzed from high-resolution images of the section with maximum lens thickness and relative to the center of the lens axes.
Results: :
Eyes wearing -4D lenses became centrally myopic (-4.6D) with ocular elongation (89µm) relative to their fellow eye, and myopic in temporal and nasal retina (-3.9D and -2.9D respectively). The ocular difference in animals wearing plano lenses was -1.1D; this myopia was not present after +4D lens wear which instead induced significantly more hyperopia than controls in central, temporal and nasal retina (0D, +0.3D and +0.4D respectively). Eye shape analysis showed highly significant correlations between on-axis in-vivo and in-vitro measures. The greatest ocular elongation after minus lens wear did not occur centrally, specifically about the optic nerve located ~10° temporal to the optic axis. The greatest inhibition in growth for eyes wearing +4D lenses occurred throughout the nasal retina, with the optic disk area resistant to shrinkage.
Conclusions: :
During the early development of myopia from minus lens wear, peripheral shrinkage does not occur. The eye initially elongates about the optic nerve, similar to that reported during form deprivation (Zeng G, McFadden SA. ARVO Abstracts, 2011 52:3923). During plus lens wear, maximum inhibition in growth occurs in the peripheral nasal retina with resistance to inhibitory growth at the optic nerve. This suggests not central retina, but the region around the optic nerve is prone to expansion in the early stages of scleral remodeling.
Keywords: myopia • refractive error development