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Bingyao Tan, Benjamin MacLellan, Erik Mason, Vivian Choh, Karen M Joos, Kostadinka K Bizheva; Non-linear changes in the pSTR and ERG responses of the rat retina to visual stimulation for different levels of elevated IOP. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6421.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the retinal response to visual stimulation at different levels of elevated IOP.
One group of eleven-week old male Brown Norway (n=6) rats were dark-adapted for at least 12 hours before isoflurane anesthesia. The IOP of the right eye was raised from 10 mmHg to 70 mmHg in steps of 20 mmHg using a vascular loop anterior to the equator of the eye. The left eye was left untouched and served as control. Corneas were anesthetized and pupils were dilated prior to collection of scotopic threshold responses (STRs) or full-field Electroretinography (ERG) from both eyes simultaneously. Measurements were conducted at baseline, all steps of elevated IOP and at recovery, thirty minutes after loop removal.
The pSTRs magnitude increased significantly from baseline IOP = 10 mmHg to 30mmHg (p<0.0001), and decreased by ~20 % for 50-mmHg (p=0.0002). As the IOP increased further to 60mmHg, pSTR amplitude decreased significantly (p=0.0496) relative to 50mmHg and was on average 9.4µV lower than the baseline, though not significantly (p =0.5903). The STR amplitude at 70-mmHg was significantly lower than the baseline (p=0.0063) and recovered to baseline within 30 min after the loop removal. In general, significantly larger implicit pSTR times (p=0.0010) were measured at higher IOP, however, there is no significant difference between the baseline and recovery measurement (p=1.0000).The ERG a-wave amplitude increased significantly (p<0.0001) from baseline to 30 mmHg and remained relatively constant up to 60mmHg, then sharply decreased to baseline for IOP= 70 mmHg. The ERG b-wave amplitude increased significantly from baseline and peaked 30 mmHg, then progressively declined to baseline until ~55 mmHg. For IOP of 60 mmHg and 70-mmHg, the b-wave magnitude was significantly lower than baseline (p = 0.0038 and p=0.0013, respectively).
Results from this study suggest that acute increase of the IOP can alter the normal retinal physiology, and provide better understanding of the mechanism of early degeneration in retinal ganglion cells induced by increased IOP.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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