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Y. Liu, C. F. Wildsoet; The Effect of Iridectomy on Ocular Development and Accommodation in Chickens. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1719.
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© ARVO (1962-2015); The Authors (2016-present)
Surgical iridectomy provides a fixed, enlarged pupil, a potentially useful tool for experimental myopia studies. However, a previous in vitro study reported loss of accommodation in iridectomized (ID) chick eyes. Here we report on an equivalent in vivo study.
Unilateral IDs were performed through a 1.5 mm limbal incision on 27 White-Leghorn chicks (age range 12-54 days). At least 5 days after surgery, both ID eyes and their fellows (controls) were measured before (baseline), and at timed intervals after instillation of 2 drops of 0.4% topical nicotine solution, using retinoscopy for refractions, high frequency A-scan ultrasonography for axial dimensions, and a customized Topcon wavefront analyzer for corneal curvature.
There was no difference between ID and control eyes at any age, in either baseline refraction (-0.13±0.98D, p=0.22) or corneal curvature (0.32±1.25D, p=0.08), although there were small but statistically significant differences in anterior chamber depth (ACD; -0.09±0.017mm), lens thickness (LT; 0.056±0.012 mm), and vitreous chamber depth (VCD; -0.079±0.026mm) (p<0.005). Nicotine induced accommodation in both eyes at all ages, the maxima decreasing with age, from 24.73±0.85 to 5.84±0.97D from 22 to 54 days. Corneal steepening accounted for between 27 and 42% of induced accommodation, less in older chicks and there was no significant difference between ID and control eyes, either in terms of refractive or corneal curvature changes (p=0.32). Nicotine induced a significant decrease in ACD, a smaller decrease in VCD and an increase in LT (ID vs. Control: -0.14±0.053, -0.24±0.32mm, ACD; -0.051±0.075, -0.051±0.040mm, LT; 0.24±0.076, 0.26±0.066mm, VCD); all effects decreased significantly with increasing age and the difference between ID and control eyes was significant for ACD (p=0.045).
The use of iridectomy to enlarge the pupil in myopia studies is supported by findings of near normal nicotine-induced accommodation and only small biometric changes, which likely reflect reduced mechanical support of the lens and secondary growth of VCD in compensation.
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