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Lakshmi Priya Rajagopalan, Nimesh Bhikhu Patel, Kevin Ivers, Nripun Sredar, Suresh Viswanathan, Jason Porter, Ronald S Harwerth, Laura J Frishman; Early changes in structure and inner retinal function in experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4827. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relationships between structural and functional measures of glaucomatous neuropathy over the timecourse of experimental glaucoma in non-human primates.
Five macaque monkeys with unilaterally elevated intraocular pressure (IOP), induced by laser photocoagulation of the trabecular meshwork, were followed longitudinally using multifocal electroretinogram (mfERG) and optical coherence tomography (OCT). The stimulus display for mfERG, was a 35° X 34° array of 19 unstretched hexagons, each 7° across. The stimulus sequence consisted of five focal flashes followed by 25 dark frames repeating every 400ms. Global (averaged across all hexagons) and regional percent change in the experimental eye for the photopic negative response (mfPhNR), and retinal nerve fiber layer thickness (RNFLT), retinal ganglion cell inner plexiform layer thickness (GCIPLT) or optic nerve head (ONH) measures of minimum rim width, (MRW), and anterior lamina cribrosa surface depth (ALCSD) were compared longitudinally. Values in the experimental eye were considered to be reduced when the percent change exceeded the lower 95% confidence limit of the control eye values. The data were analyzed to model relationships between the local mfPhNR, peripapillary RNFLT, and macular GCIPLT.
In the experimental eyes, sectoral mfPhNR amplitude (corresponding to at least one of the six different sectors of the temporal RNFL) was the first measure to be reduced after elevation of IOP. Global mfPhNR amplitude changed next, concurrently with ONH structural measurements of global MRW and global ALCSD, and all of these changed prior to global or sectoral changes in RNFLT. For the control eye, local mfPhNR amplitude was linearly related to RNFLT and GCIPLT in the corresponding retinal regions (RNFLT, r>0.85, P<0.0001: GCIPLT, r>0.75, P<0.0001). In experimental eyes, the relationship showed an initial nonlinearity due to reductions in mfPhNR amplitude that preceded reductions in retinal thickness measures.
The onset of changes in mfPhNR and ONH measures (MRW and ALCSD) occurred prior to the onset of changes in RNFLT. These results suggest that mfPhNR and ONH parameters reflect early changes in the timecourse of glaucomatous neuropathy.
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