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NV Rangaswamy, LJ Frishman, SM Saszik, DC Hood, RS Harwerth; Effect of Experimental Glaucoma and Pharmacological Suppression of Inner Retinal Activity on the Naso-temporal Asymmetries in Oscillatory Potentials in the Primate Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2170.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the effects of pharmacological suppression of inner retinal activity with the effects of experimental glaucoma on the naso-temporal asymmetries of oscillatory potentials in the slowed multifocal (mf)-ERG. Methods: Mf-ERGs were recorded differentially between DTL electrodes on the 2 eyes of anesthetized (Ketamine; 20-25 mg/kg/hr and Xylazine 0.8 mg/kg/hr) adult monkeys (Macaca mulatta). Recordings were made before and after intravitreal injection of TTX (n=3; 4.8-7.6 µM vitreal concentration), or TTX and NMDA (n=4; 1.4-6.4mM), or after laser- induction of monocular experimental glaucoma (n=6). The stimulus display consisted of 103 equal-sized hexagons within 17 of the fovea. The m-sequence was slowed by 100ms or 200ms to elicit OPs. OPs in the frequency range of 90-300 Hz were extracted. Results: In control eyes OPs were largest in the central retina, especially in the central three horizontal rows of hexagons that included the fovea and optic nerve head. OP amplitudes were quantified for these central hexagons by calculating the root mean square of the extracted responses. OP amplitude was consistently larger in the temporal retina than in the nasal retina. After suppression of spiking activity with TTX, or of inner retinal activity with TTX/NMDA, the OP amplitude was reduced everywhere, and the naso-temporal difference in amplitude was practically eliminated. In eyes with experimental glaucoma when mean deviation of visual field losses measured with behavioral static perimetry (Goldmann III white stimuli) were worse than -6dB, reductions in OP amplitude and loss of naso-temporal differences were similar to those after removal of inner retinal activity. To assess timing differences in nasal and temporal retina, cumulative energy was calculated as the sum of the squared deviations from the mean for each extracted OP. In the control animals, the time corresponding to 50% cumulative energy occurred earlier for the nasal retina than for the temporal retina and this asymmetry in timing was diminished or eliminated after blockade of inner retinal activity. It also was reduced when the mean deviation of field losses in eyes with experimental glaucoma was worse than -6dB. Conclusion: The naso-temporal asymmetries of mf-OPs related to inner retinal spiking activity are diminished in experimental glaucoma.
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