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Akshay Gurdita, Karen M Joos, Bingyao Tan, Yunwei Feng, Kostadinka K Bizheva, Daphne L McCulloch, Vivian Choh; The effects of isoflurane and ketamine:xylazine on the scotopic threshold response (STR) in albino rats with elevated intraocular pressure (IOP).. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6428.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the scotopic threshold response (STR) of acute, moderately-elevated intraocular pressure (IOP) in the retinas of Sprague Dawley rats under isoflurane or ketamine:xylazine (kx) anesthesia.
Two group of rats, isoflurane anesthetized (n=9) and kx anesthetized (n=6) underwent acute IOP elevation to 35 mmHg using a vascular loop around the treated eye anterior to the equator, for one hour, while the other eye served as a control. Binocular STRs were recorded prior to loop wear, 45 minutes into the IOP elevation, and 45 minutes after removal of the loop.
The positive STR (pSTR) amplitude was greater with kx than with isoflurane and increased during IOP elevation with both anesthetics. For isoflurane anaesthetized rats, peak pSTRs (mean ± S.D.: 61.2 ± 39.9 μV) were greater than those before loop wear (6.4 ± 6.4 μV; p<0.0001) and those after loop removal (10.1 ±7.5 μV; p<0.0001) with no significant difference in pSTR between the pre- and post-wear conditions (p=1.000). For control eyes, pSTR amplitudes did not change over the course of the experiment (p=1.000 for all comparisons). In kx-anesthetized animals, pSTR amplitudes during loop wear (158.5 ± 81.7 μV) were also greater than those before loop wear (58.3 ± 37.9 μV, p<0.0001). However, post-loop pSTR amplitudes remained elevated and were not significantly different from those during loop wear (126.4 ± 62.2 μV, p=0.1347) and were also larger than pre-loop values (p=0.0007). The control eye for the kx anesthetized rats also changed over the course of the experiment, with post loop pSTR amplitudes larger than those prior to loop wear (compare 115.5 ± 55.3 μV vs 58.4 ± 34.6 μV, respectively; p=0.0028).
IOP elevation to 35 mmHg is associated with an increase in the pSTR response irrespective of the anaesthetic used. Additionally, although kx anesthesia resulted in larger pSTR amplitudes, the anaesthetic was associated with a significant systemic increase in the control eye pSTR amplitude. Thus, the anesthesia used may be important in electrophysiological studies that depend on consistent control eye values over the time course of the experiment.
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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