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Erin Gwen Sieck, Robert Enzenauer, Michelle Pedler; EFFECT OF INDUCED REFRACTIVE ERROR ON ELECTRORETINOGRAMS. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4884.
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Prior studies have noted decreased amplitudes in myopic patients compared to age related controls in electroretinograms (ERGs). However, these studies did not account for any retinal degeneration commonly associated with myopia. In refractive error, there is an optical defocus of light that we hypothesized would decrease recorded amplitudes in the absence of retinal pathology.
Ten otherwise healthy rabbits were selected for our study. Refractive error was induced by placing Proclear Cooper VisionTM contact lenses with powers of -10D, +10D, -20D and +20D. Control ERGs were performed with no contact lenses first. The rabbits were then randomized into receiving varied strengths of contact lenses and ERGs were repeated. Six rabbits received +10 or -10D and four received +20D or -20D as a higher impact on ERGs with increasing refractive error was anticipated. ERGs were preformed by standard protocol, with 20 minutes of dark adaption prior to scotopic testing. A total of three ERGs were preformed per rabbit per eye.
Step 1 of the ERG was analyzed for the dark adapted scotopic response as rods predominate in rabbit retinas. Comparing control ERGs to ERGs preformed with contact lenses, there was a statistically significant decrease in amplitudes using the two tailed paired t-test in 3 of the 4 groups of induced refractive errors. There was no difference of implicit times in both induced myopia or hyperopia. The greatest reduction in amplitude occurred with +20D induced myopia (n=4), with p=0.021 (95% CI 5.5 to 54.5). Induced myopia with +10D (n=6) noted significant decrease in amplitude, p=0.049 (95% CI 0.14 to 27.36). Lastly, induced hyperopia with -20D lens (n=4) also was found to significantly decrease amplitude, p=0.048 (95% CI 0.11 to 19.9). Induced hyperopia with -10D lens (n=6) was found to cause no statistically significant change, p=0.82.
ERGs remain a mainstay in visual prognosis. Based on our small study, both induced hyperopia and myopia decrease recorded amplitudes as predicted. It appears that there may be a relationship between decreasing amplitudes and increasing power of refractive error. Consequently, knowledge of high refractive errors would be important in considering abnormal ERG results.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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