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Lakshmi Priya Rajagopalan, Nimesh Bhikhu Patel, Kevin M Ivers, Nripun Sredar, Hope M Queener, Jason Porter, Ronald S Harwerth, Laura J Frishman; Longitudinal evaluation of structural and functional changes in the optic nerve head and inner retina in experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze the structural and functional changes in the optic nerve head (ONH) and inner retina using spectral domain optical coherence tomography (SD-OCT), adaptive optics scanning laser ophthalmoscope (AOSLO) and multifocal electroretinogram (mfERG) in a primate model of experimental glaucoma (EG).
Five monkeys with unilaterally elevated intraocular pressure (IOP), induced by laser photocoagulation of the trabecular meshwork, were followed longitudinally using SD-OCT, AOSLO and mfERG. ONH parameters (mean anterior lamina cribrosa surface depth [ALCSD], mean minimum rim width [MRW]]) and global (g) and sectoral(s) retinal nerve fiber layer thickness (RNFLT) were quantified using semi-automatically segmented SD-OCT images. ALCS pore parameters (mean pore area, elongation, nearest neighbor distance) were quantified globally, from images acquired at each time-point using AOSLO. The mfERG stimulus 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 (g) and sectoral (s) multifocal photopic negative response (mfPhNR) and the temporal retinal multifocal oscillatory potentials (mfOPs) were measured. Longitudinal measurements and the effects of cumulative IOP insult on the structural and functional measures were analyzed for the EG eyes.
The relation between cumulative IOP and the structural and functional measures was described using an exponential function. The rate of change for RNFLT was more than 8 fold slower than for ALCSD, and at least 4 fold slower than for MRW and the two mfERG measures. In the EG eye, MRW and ALCSD were the first structural parameters to show a significant change relative to control eye, followed by ALCS pore parameters, then s-RNFLT and finally g-RNFLT. For the functional measures, reductions in amplitude of g-mfPhNR, s- mfPhNR and mfOPs occurred at similar times on average. Over all, the ONH parameters tended to change before the mfERG and ALCS pore parameters, and the g-RNFLT was the last to change.
These findings indicate that changes in the optic nerve head structure, and in the inner retinal function evaluated using mfERG, can be detected prior to nerve fiber loss in experimental glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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