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Y. Sauve, B. Lu, S. Wang, R.D. Lund; Correlation of Full Field Corneal Electroretinogram (ERG) with Retinal Thresholds Recorded from the CNS in Rodent Retinal Degeneration and Rescue . Invest. Ophthalmol. Vis. Sci. 2003;44(13):485.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine how ERG parameters correlate with retinal threshold responses, in pigmented Royal College of Surgeons (RCS) rats, with and without therapeutic intervention. Methods: Dark-adapted ERG responses and focal retinal sensitivity, recorded from the superior colliculus, were studied in three groups of dystrophic RCS rats, under ketamine-xylazine anesthesia: 1- untreated; 2- with subretinal injections of the human RPE cell line, ARPE19, at 23 days post-natal (P23); and 3- with sham injections of medium alone. Congenic RCS rats served as non-dystrophic controls. Corneal ERG responses were collected under standard conditions. Visual thresholds were determined (with 0.02 cd/m2 background illumination) by recording multi-unit responses from at least 15 sites, evenly spread across the superior collicular map. Results: In untreated dystrophic rats, ERG function developed normally but started to decline abruptly at P27. Three weeks later (P51), the a-wave had reduced to the criterion amplitude of 10µV, while the b-wave persisted with progressively declining amplitude until about P100. Four weeks post-operatively (P51), although transplantation failed to sustain an a-wave, the b-wave amplitude was greater than in sham-operated rats. This difference was maintained up to at least P150. Threshold responses recorded across the visual field first showed elevation over controls at P27 and this continued over several months, with high threshold responses still recorded at P150 and beyond at a time when an ERG b wave could no longer be recorded. Sham injections resulted in a small area of reduced threshold response, but rats with transplants showed as much as a quadrant of rescued retina. The b-wave amplitude was proportional to the area of preserved thresholds (best correlation obtained using 2.5 log threshold elevation as a cut-off). Interestingly, in untreated rats, the time course of b-wave degradation (from P27 to P100) was best fitted with the waning of visual field area when using the same cut-off: less than 2.5 log threshold elevation. By P180-200, b-waves persisted in animals with transplants for which more than 50% of the visual field area had less than 2.5 log elevation in thresholds. Again, this cut-off led to the best correlation between b-wave occurrence and the extent of visual field preservation. Conclusion: Persistence of the ERG b-wave can be used to predict the area of visual field preservation recorded in the CNS with threshold levels of 2.5 log or better.
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