Purchase this article with an account.
T Michael Nork, Charlene B Y Kim, Alexander W. Katz, Carol A Rasmussen, James N Ver Hoeve; Effect of Hemiretinal Endodiathermy Axotomy (HEA) and Experimental Glaucoma (EG) on the Multifocal Electroretinographic (mfERG) Early Waveforms in Rhesus Macaques. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5874.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To determine if mfERG supranormality in EG is an effect of intraocular pressure (IOP) elevation and not due to the loss or absence of retinal ganglion cells (RGCs).
Six rhesus macaques underwent a series of baseline mfERG recordings. Endodiathermy spots were placed along the inferior 180° next to the optic nerve margin in the right eyes. mfERG recordings were obtained in each animal at regular intervals following HEA. 140 days after HEA (in 3 animals) and 95 days after HEA (in another 3 animals), laser trabecular meshwork destruction (LTD) was performed in the right eyes. mfERG recordings were obtained again at intervals during the epoch of elevated IOP, which varied from 137 to 235 days. The stimulus consisted of 241 unstretched elements subtending a total angle of ± 44° with the VERIS 4.9™ fast m-sequence. First-order kernel (K1) waveform root-mean-square determinations were done for two 7 hexagon groupings—one located in the superior (non-axotomized) macula and the other in the inferior (axotomized) macula.
At 3 months, there was marked thinning of the inferior nerve fiber layer as measured by optical coherence tomography. IOPs were not significantly different in the HEA eyes compared to baseline. There were no changes in K1 in N1 and P1 (9-35 ms) amplitudes compared to baseline in either the axotomized or non-axotomized portions of the macula for the 6 animals taken as a group. Following LTD, mean IOP in HEA eyes rose to 46 ± 8 vs 20 ± 2 mmHg (SD) in the fellow eyes. Three of the 6 animals showed a supranormal mfERG early waveform response to elevated IOP in both the axotomized and non-axotomized regions of the retina. For these 3 supranormal responders, the mean OD/OS ratios in the inferior (HEA) maculas were 1.04 ± 0.04, 1.14 ± 0.05 and 1.51 ± 0.07 for the baseline, HEA and elevated IOP epochs respectively. The respective ratios for the non-axotomized maculas were 0.99 ± 0.03, 1.02 ± 0.04 and 1.45 ± 0.05.
In animals in which supranormality occurs, while there is a mild (but significant) increase in the early mfERG K1 waveforms following axotomy, most of the increase occurs in response to elevated IOP. This study shows that supranormality is not secondary to RGC loss and, thus, may indicate outer retinal injury due to other factors, such as ischemia.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only