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Lakshmi Rajagopalan, Nimesh Bhikhu Patel, Suresh Viswanathan, Ronald S Harwerth, Laura Frishman; Comparison of multifocal photopic negative response (mfPhNR) with structural and functional measures in experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5128.
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© ARVO (1962-2015); The Authors (2016-present)
To utilize the multifocal electroretinogram (mfERG) technique to assess local loss of function, as reflected by the mfPhNR, in a nonhuman primate model of experimental glaucoma and to compare the results with standard clinical structural and functional measures.
mfERGs, were recorded longitudinally (5-10 visits) in 3 macaques with unilateral elevated intraocular pressure (IOP) induced by laser photocoagulation of the trabecular meshwork. Optical coherence tomography (OCT) and standard automated perimetry tests were done concurrently. The mfERG (VERIS 4.1) stimulus display, 35° x 34°, was an array of 19 unstretched hexagons, each 7° across. For each hexagon the stimulus consisted of 5 bright frames, each occurring on 50% of the frame changes (75 Hz), followed by 25 dark frames, repeating every 400 ms for 7 min. Global and regional mfPhNR amplitudes were compared in experimental (Exp) and fellow control (Con) eyes using a repeated measure ANOVA corrected with a post hoc Tukey test. Relationships between local mfPhNR amplitude and corresponding sectoral retinal nerve fiber layer thickness (RNFLt), retinal ganglion cell/inner plexiform thickness (RGC/IPLt) and local subjective visual sensitivity (VS) were analyzed using linear regression for individual subject data.
Significant reductions in mfPhNR amplitudes occurred early after lasering in all Exp eyes, compared to fellow Con eyes (P<0.005, ANOVA). Local mfPhNR amplitudes were strongly correlated with corresponding sectoral RNFLt. The Pearson correlation coefficient r was >0.78 (P<0.0001) and 0.86 (P<0.0001) for Exp and Con eyes respectively. Similarly good correlations were seen between mfPhNR and RGC/IPLt; r >0.9 (Exp eye; P<0.0001) and 0.77 (Con eye; P<0.0001). Local mfPhNR amplitudes were correlated moderately with local VS; r >0.41 (Exp; P<0.001) and 0.42 (Con; P<0.001). Reductions in mfPhNR amplitude in Exp eyes that exceeded the test-retest variability in Con eyes, preceded parallel changes in corresponding sectoral RNFLt in two subjects (superior optic nerve head in one, and temporal in the other) and the reduction in macular RGC/IPLt in one subject.
The current findings indicate that the mfPhNR can be used as an additional tool to detect and monitor functional changes in primate eyes with elevated IOP.
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