The role of central retina in chicks during form deprivation myopia

Abstract

Purpose: This study aimed to examine if the central retina plays any role in the development of form deprivation myopia in chicks.

Methods: Chicks (n=6-7) wore either central diffuser lenses (plano lens with either 4 or 6 mm diameter diffuser zone at the centre; C4/6mm FD) or full field diffuser lenses (full FD) in front of their right eyes for 7 days . Plano lenses were mounted to their left eyes as control. Refractive errors were measured both on-axis (centrally) as well as 45 degrees off-axis nasally and temporally by retinoscopy. The axial ocular dimensions were also measured by a high-resolution A-scan ultrasound system respectively before and after 7 days of lens wear.

Results: All treated eyes had significant changes of both central refractive errors (C4mm FD vs control: -3.21± 0.57 vs -0.71 ± 0.23; C6mm FD vs control: -5.50 ± 0.83 vs -2.16 ± 0.42; Full FD vs control: -17.50 ± 0.99 vs -1.14 ± 0.34; mean changes [D] ± SEM, independent-samples t-test, p<0.01 for all groups) and vitreous chamber depth (C4mm FD vs control: 0.48 ± 0.02 vs 0.38 ± 0.02; C6mm FD vs control: 0.53 ± 0.04 vs 0.35 ± 0.04; Full FD vs control: 1.02 ± 0.09 vs 0.31 ± 0.04; mean changes [mm] ± SEM; independent-samples t-test, p<0.05 for all groups) after 7 days of lens wear. The refractive errors in temporal retina and nasal retina also became myopic when compared with the control eyes. The myopic shift in the central refractive error of the treated eyes was due primarily to the increase in vitreous chamber depth. The interocular differences of both central refractive error and the vitreous chamber depth increased with the size of central form-deprived retina.

Conclusions: Form depriving the central retina with different sizes of diffuser produced graded responses in terms of myopic growth even in the presence of normal peripheral vision. The magnitude of myopia induced in both central and peripheral retina increased with the size of central diffuser. Apparently, central retina also plays a significant role in form deprivation myopia in chicks. The graded response of myopia may be due to integration between retinal regions that received opposing optical inputs.

Keywords: 605 myopia • 511 emmetropization