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James Ver Hoeve, Charlene Kim, Carol Rasmussen, Christopher Murphy, Brian Christian, T Michael Nork; Electrophysiologic Correlates of RNFL Thickness in Experimental Glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):794.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relationship between electrophysiologic measures of retino-cortical function and structural measures of retinal nerve fiber layer thickness (RNFLT) in non-human primates with experimentally-induced glaucoma (EG).
Six female cynomolgus monkeys underwent laser scarification of the trabecular meshwork in one eye that resulted in chronic ocular hypertension (OH). At the time of assessment, OH had been present > 2 years. Recordings included full-field electroretinograms (FFERGs) to scotopic and photopic luminance intensity series, 30 Hz flicker, and flash-visual evoked potentials (FVEPs). Transient pattern ERG (PERGs) and pattern VEPs (PRVEPs) were recorded to checker-board stimuli of two check sizes reversing at a rate of 4/s. Animals were anesthetized with ketamine and dexmedetomidine. Pupils were dilated for FFERG. Eyes were refracted for viewing distance for PERG and PVEP recordings. Measures of RNFLT were obtained from each eye using automated and manual segmentation routines from two commercially-available sdOCT instruments (Cirrus™ and Spectralis™).
RNFLT in the EG eye averaged 42-52% of the fellow eye across instruments and segmentation methods. No differences in the amplitudes of the a- and b-wave for the FFERG scotopic and photopic series, oscillatory potentials, nor the P50-like PERG, were noted between EG and fellow eyes. The amplitudes of the FFERG photopic negative response (PhNR), the PERG N95-like wave, and FVEP and PRVEP were significantly reduced in the EG eyes of all six animals. There was a significant linear relationship between RNFLT and the amplitude of the PhNR, FVEP, N95 and PRVEP waves, accounting for 75, 66, 69, and 47 percent of the variance in RNFLT, respectively, using manual segmentation (all p’s < .001). Automatic segmentation by the Spectralis™ or the Cirrus™ instruments resulted in only a small reduction in size of the correlation between RNFLT and PhNR, FVEP, N95, and PRVEP.
Non-invasive electrophysiologic responses associated with retinal ganglion cell function (PhNR, FVEP, N95, PRVEP) have a strong linear relationship to RNFLT as assessed by sdOCT. The structural and functional deficits observed in animals with long-standing OH suggest that these associations likely remain stable over time.
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