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SM Petersen-Jones, PM Hocking, F Montiani Ferreira; Clinical and Electroretinographic Features of the rge Chicken Phenotype . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3493.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To characterize the clinical, electroretinographic and histopathological features of a unique autosomal recessive retinal dystrophy with secondary globe enlargement (rge) in the chicken. Methods: We have established a breeding flock of chickens that suffer from an autosomal recessive retinal dystrophy (rge) that leads to blindness. Homozygous normal, heterozygous carrier and homozygous mutant chicks were examined weekly from hatch. Vision was assessed using an opticokinetic device. Ophthalmic examinations were performed including ultrasonic measurement of corneal thickness and axial globe length, and intraocular pressure measurement. Scotopic and photopic electroretinograms were recorded on embryos and chicks using a LKC UTAS-E 3000. Eyes were processed for light microscopy at various ages, including the embryonic stage. Results: The affected birds were blind by 5 weeks post hatch. The globes of affected birds enlarged and axial length became significantly greater than the controls at 4 to 5 weeks post hatch. The mean IOP was not significantly higher in affected birds at any time suggesting that the globe enlargement was not secondary to glaucoma. Globe enlargement in chicks secondary to a variety of visual deprivations is a well-recognized phenomenon. The ERG waveform of the homozygous affected birds developed abnormally and later than the control animals (from 19th to 20th embryonic day). The ERG a- and b- wave thresholds were significantly different (increased) in affected birds. The a-wave was significantly smaller in the affected birds at the time of hatch. The latency of the b-wave was also increased. The ERG of affected birds slowly deteriorated with increasing age, with the a- and b-waves decreasing in amplitude and increasing in latency. The development of the ERG of the heterozygous carriers was comparable to the normal controls. The loss of vision was not accompanied by gross changes in retinal architecture or loss of photoreceptors. Thinning of retinal layers developed in parallel with the globe enlargement, but became apparent after vision loss. An ultrastructural study is being performed to detect morphological changes that would explain the ERG changes and loss of vision in affected birds. Conclusion: Electroretinography suggests that the photoreceptors of the rge chicken never develop normal function. A slow deterioration in ERG traces occurs with age. The affected birds develop globe enlargement accompanied by vision loss at 4 to 5 weeks of age.
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