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G. A. Cull, B. Fortune, G. A. Cioffi, C. F. Burgoyne; Changes in Retinal Function After Onset of Experimental Glaucoma or Optic Nerve Transection in Non-Human Primates. Invest. Ophthalmol. Vis. Sci. 2008;49(13):717.
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To compare functional changes after onset of experimental glaucoma (EG) with those occurring after optic nerve transection (ONT).
Functional assessment included slow-sequence multifocal electroretinography (mfERG, 7F), transient pattern-reversal ERG (PERG) and photopic full-field ERG with red flashes on a blue background to elicit a robust photopic negative response (PhNR). Recordings were obtained in both eyes under ketamine-xylazine anesthesia at baseline and weekly after laser treatments to induce chronic intraocular pressure (IOP) elevation (N=2) or after surgical ONT (N=2) in rhesus macaque.
In EG eyes, IOP was elevated to 32±12 mm Hg above fellow control eyes. Functional changes were present during the first week of IOP elevation: amplitudes of mfERG high frequency components (HFC) had become 40% smaller than those of fellow control eyes, while the low-frequency features (N1 and P1) declined to a lesser extent (-15% and -11% of control eye, respectively). The PERG N95 amplitude was 77% smaller than control, while the P50 amplitude was 28% smaller than control. For the full-field photopic ERG, the PhNR amplitude was 34% smaller than control, while the a-wave and b-wave amplitudes were 0.5% larger and 8% smaller, respectively. Within 1 week of ONT, the mfERG HFC amplitudes had become 59% smaller than control, while the low-frequency features, N1 and P1, were 28% and 40% smaller than control, respectively. The PERG N95 amplitude was 59% smaller than control and the P50 was 68% smaller than control. The PhNR amplitude had become 42% smaller than control, while the photopic a-wave and b-wave amplitudes were 1% larger and 6% smaller than control, respectively. The average interocular amplitude differences during baseline recordings were: 7%, 8% and 5% for the mfERG HFC, N1 and P1, respectively; 3% and 5% for PERG N95 and P50, respectively; 25%, 18% and 7% for the PhNR, a-wave and b-wave, respectively.
In the non-human primate eye, similar functional changes were present during the first week of detectable IOP elevation in EG and within the first week of surgical ONT. Functional changes were consistent with damage to retinal ganglion cells, though there were also indications of mild outer retinal functional changes in both groups. The capability to detect altered function was similar across ERG techniques.
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