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Functional Assessment of the Regional Distribution of Disease in a Cat Model of Hereditary Retinal Degeneration

¹ From the University Eye Hospital, Department II, Tübingen, Germany; and the ² Department of Medicine and Surgery, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden.

PURPOSE. To establish a method for the recording of multifocal electroretinograms (MF–ERGs) in animals under fundus control using a scanning-laser ophthalmoscope (SLO) and to analyze the spatial distribution of disease in a strain of Abyssinian cats with a recessively inherited rod-cone degeneration (ARCD).

METHODS. Four normal and 12 Abyssinian cats at four different clinical stages of ARCD were examined with the RETIscan MF–ERG system using 61 hexagonal elements within a visual field of approximately 30° radius. The stimulus pattern was generated by the green laser beam (515 nm) of a Heidelberg Engineering HRA SLO, whose power was reduced with a Schott long-pass filter allowing for simultaneous infrared fundus imaging.

RESULTS. Topographical recordings could be obtained in all animals except one in stage 4. Amplitudes were minimal at the optic disc and had a slight maximum at the area centralis. Implicit times had a tendency to lower values in the central region, most pronounced in progressed stages of ARCD. The clinical stages of ARCD correlated with a successive generalized loss of amplitude and a rise in implicit time. Without a decrease in retinal illuminance, topographical landmarks like the optic disc were no longer detectable, pointing to stray light as a possible cause.

CONCLUSIONS. It was demonstrated that topographical MF–ERG recordings can be obtained in an animal model under fundus control using SLO stimulation. The appearance of retinal landmarks was found to be dependent on sufficient attenuation of laser power. Because the changes in ARCD are more patchy than in human retinitis pigmentosa (RP), a generalized loss of function was detected. However, like in RP, the central area was found to retain a better function than the periphery, especially in later stages of the disease. In summary, fundus controlled methods like the one presented will greatly improve the reliability of MF–ERG in future research on glaucoma, transplantation studies, and evaluation of gene therapy.

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