Patching fellow eyes during subjective night does not prevent disruption to minus lens compensation in constant light-reared chicks

Abstract

Purpose: This study re-examined an earlier claim that monocular patching during subjective night (i.e. patched at the usual time that night would occur) in the chicks reared in continuous lighting (CL), offered unpatched eyes some protection from the ocular effects of CL. It also examined whether this monocular patching protected unpatched eyes against the disruptive effect of CL on compensation to minus lenses.

Methods: Hatchling White-Leghorn chicks were reared in either constant or diurnal lighting conditions (n=28) for 2 weeks. Some CL chicks had their right eyes patched every night during the entire study. Lenses of either +10 or -10D power were fitted to the unpatched eyes of some patched chicks at the beginning of the second week. Retinoscopy, IR photo-keratometry and high-frequency A-scan ultrasonography were used to track refractions, corneal radius of curvature and ocular axial dimensions respectively; data were collected on experimental days 0, 7, 9 and 14.

Results: The patched eyes were completely protected from the ocular growth effects of CL, i.e. accelerated posterior segment (vitreous chamber) growth and inhibited anterior segment growth. Although the unpatched eyes showed no protection from the anterior chamber effects of CL, they were completely protected from the effects of CL on vitreous chamber growth. Nonetheless, the response to the -10D lenses was disrupted in unpatched eyes, which responded in the wrong direction for compensation (+5.5+/-0.25D more hyperopic than no lens-unpatched eyes). The response to the +10D lenses was preserved (+9.25+/-0.25D more hyperopic than no lens-unpatched eyes).

Conclusion: These data provide further support for local control of emmetropization, as reflected in compensatory lens responses, but point to additional influences on eye growth as reflected in CL-induced ocular changes.

Figure 1

a) Anterior chamber (AC) depth, lens thickness (LT), vitreous chamber (VC) depth, retinal thickness (RT), choroidal thickness (CT), scleral thickness (ST) shown as stacked bar graph; b) refractive error (RE), c) AC depth and d) VC depth plotted as means ± s.e.m., after 2 weeks under normal diurnal lighting (NLNL), continuous light without patching (CLCL) and monocular patching during the subjective night (CLp-no lens) (R_p, patched eyes; L_p, fellow unpatched eyes). Data normalized to baseline values.

Figure 2

Means ± s.e.m. for a) refractive error (RE), b) vitreous chamber (VC) depth, c) optical axial length (OL), d) corneal radius of curvature (CR), e) lens thickness (LT), and f) choroidal thickness (CT), plotted for 7 day lens wearing period, after further normalizing the prenormalized data to day 7 values. Data for Lp eyes with plus lenses (CL_p-plus), minus lenses (CL_p-minus), and no lens (CL_p-no lens) from patched CL group shown; also eyes with plus lenses (CL-plus) and minus lenses (CL-minus) of CLCL group from a previous study (Padmanabhan, Shih and Wildsoet 2007).