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Algis J. Vingrys, Jason Charng, Christine T. Nguyen, Andrew I. Jobling, Bang V. Bui; The Effect of Repeated Intracameral Injection on Young and Old Rat Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):164.
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This study was undertaken to consider whether young and old eyes show the same susceptibility to repeated intracameral injection with and without intraocular pressure (IOP) elevation.
Baseline electroretinograms (ERG) were measured in 3-month (Y) and 18-month (O) old Sprague-Dawley rats (n=16 each group). Following baseline assessment, eyes were randomly assigned to undergo anterior chamber cannulation (30G) with IOP set to 15 mmHg (sham) or elevated (IOP) to 60 mmHg for 60 minutes. Four repeated cannulations were induced, each separated by a week and ERGs were measured after each cannulation. Waveforms were analysed for photoreceptoral (amplitude, RmP3 and sensitivity, S), bipolar cell (amplitude, Vmax and sensitivity, 1/K) and ganglion cell mediated waveforms (pSTR). Data are expressed as a percentage change relative to pre-treatment baselines and analysed using 2-way ANOVA. Week 4 tissue was harvested for quantitative PCR for the inflammatory marker CX3CR1.
There was no significant difference between sham and IOP treated eyes for all ERG parameters analyzed (p>0.05). As such these groups were collapsed to determine the intracameral injection effect. Intracameral injections resulted in greater dysfunction in older eyes compared to their younger counterparts for photoreceptoral (RmP3: Y -6 ± 2 vs O -12 ± 2%, p=0.02) bipolar cell (Vmax: Y 2 ± 4% vs O -16 ± 2%, p<0.001) and ganglion cell (pSTR: Y-6 9% vs O -25 ± 5%, p<0.01) mediated amplitude. Younger rats exhibited an upregulation of phototransduction (S: Y 11 ± 3% vs O -5 ± 5, p<0.01) and bipolar cell sensitivity (1/K: Y 42 ± 13%, -24 ± 6% p<0.01) whereas older animals showed no change or a significant decrease. Gene expression of CX3CR1 was significantly increased in both sham and IOP treated eyes. This effect was greater in older eyes (Y 62 ± 11% vs O 101 ± 11%).
Repeated intracameral injection produces permanent retinal dysfunction in older eyes. Younger eyes resist this change by upregulating sensitivity of outer retinal responses to maintain normal retinal output.
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