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Published on: January 22, 2018
Clinical features of the retinopathy, globe enlarged (rge) chick phenotype
Fabiano Montiani-Ferreira1, Tong Li, Matti Kiupel
1Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA. ferreir9@cvm.msu.edu
Insights
This study details the autosomal recessive retinopathy, globe enlarged (rge) phenotype in chicks, revealing progressive vision loss and secondary globe enlargement. The rge defect causes severe visual impairment and unique electroretinographic changes in affected birds.
Area of Science:
- Ophthalmology
- Genetics
- Animal Models
Background:
- Autosomal recessive disorders can cause significant ocular abnormalities.
- Understanding genetic mutations is crucial for diagnosing and treating vision loss.
Purpose of the Study:
- To clinically characterize the autosomal recessive retinopathy, globe enlarged (rge) phenotype in chicks (Gallus gallus).
- To investigate the progression of visual impairment and ocular changes associated with the rge mutation.
Main Methods:
- Clinical examinations, ophthalmoscopy, tonometry, pachymetry, and ultrasonography were performed on rge/rge, rge/+, and +/+ chicks.
- Vision testing, electroretinography (ERG), and histopathology were utilized to assess visual function and retinal structure.
- A comprehensive suite of ophthalmic tools was employed to evaluate ocular parameters from hatch to 336 days of age.
Main Results:
- Rge/rge chicks exhibited progressive vision loss, becoming functionally blind by 30 days of age.
- Ocular changes included thickened corneas, hyperopia, shallow anterior chambers, and enlarged globes.
- Preliminary ERG showed elevated thresholds, altered a-wave and b-wave amplitudes, and absent oscillatory and c-waves.
Conclusions:
- The rge defect represents a unique progressive retinal dystrophy leading to severe visual deficit.
- Secondary globe enlargement occurs in parallel with retinal layer thinning.
- This chick model provides valuable insights into inherited retinal dystrophies and their clinical manifestations.
Abstract:
The purpose of the study reported here was to characterize the clinical aspects of the autosomal recessive retinopathy, globe enlarged (rge) phenotype in chicks (Gallus gallus). Rge/rge, rge/+ and +/+ chicks were studied from hatch to 336 days of age by general clinical examination, post-mortem examination, vision testing with an optokinetic device, ophthalmoscopy, biomicroscopy, tonometry, central corneal pachymetry, a-mode ultrasonography, infrared photoretinoscopy and photokeratometry. Additionally, preliminary electroretinographic and histopathologic investigations were performed. There is a variable degree of vision loss in rge/rge chicks at 1 day of age with further chicks losing vision over the next few weeks until all chicks become functionally blind by 30 days of age (although some optokinetic responses remain in some of the rge/rge chicks). Over the first few weeks of life rge/rge chicks develop thicker corneas with a larger radius, hyperopia, shallower anterior chambers and enlarged globes both radially and axially, compared to controls. A preliminary ERG study showed that 1 day old rge/rge chicks have an elevated response threshold, a lower amplitude a-wave with a markedly shallow leading slope, a lack of both oscillatory responses and c-waves and, at brighter flashes, an increased b-wave amplitude. Light microscopy revealed no gross retinal abnormalities in young chicks to account for the blindness. A thinning of all retinal layers developed in parallel with globe enlargement. The rge defect is a unique progressive retinal dystrophy that results in a severe visual deficit, abnormal electroretinographic waveforms, and secondary globe enlargement.
