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T. Li, C. Wahl, H.C. Howland; The Effects of Alternatingly Covering the Eyes, or the Pineal Gland and Eyes of Chicks Raised Under Constant Light . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1977.
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Purpose: The effects (flattened corneas, shallow anterior chambers, hyperopia) of raising chicks (Gallus Gallus domesticus) in constant light (CL) can be mitigated by periodically covering the eye(s) or pineal gland. We wished to see if these CL effects can be blocked by alternatingly covering each eye or alternatingly covering the eyes and the pineal gland in 12 hr periods.Methods: Groups of chicks were raised under one of 6 conditions: 12/12 light/dark conditions (N); constant light only (CL); CL with both eyes covered 12 hours per day (BEC); CL with pineal glands covered 12 hr/day (HC); CL with alternating eyes covered (AEC) and CL with alternating pineal and eye covers (AHE) for up to 2 weeks of age. The covers applied to the different eyes in AEC group and to eyes and pineal glands in AHE group were 180° in counterphase. Using IR autorefraction, keratometry, and "A" scan ultrasound, we measured refraction, corneal radius of curvature, anterior chamber depth, lens thickness and vitreous chamber depths. Intraocular pressures (IOPs) were also determined using a "Tonopen" twice or four times a day at the end of the experiment. Results: CL effects could be significantly prevented by alternating eye covers and alternating pineal and eye covers (p<0.0001). There were no significant differences in refraction among groups N, BEC, HC, AEC, and AHE (p>0.05). As in normal birds, the IOPs in groups BEC and HC always significantly different by about 4 mm Hg between day and night (ps<0.0001). However, these diurnal rhythms in IOPs in groups AEC and AHE disappeared with the treatments (ps>0.05). Conclusions: The CL effects on the eye growth, except IOPs, can be protected by alternating eye covers or alternating eye and pineal gland covers. These results indicate that the each eye and pineal gland has a local oscillator which is not strongly coupled to the others, and therefore any single one is sufficient to protect against most CL effects.
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