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V. H. Wong, B. V. Bui, A. J. Vingrys; Effect of Acute Intraocular Pressure Challenge on Inner Retinal Function in Diabetic Rats. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2761.
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We consider whether the diabetic rat retina is more susceptible to acute intraocular pressure (IOP) challenge.
Electroretinogram (ERG) responses were measured in anaesthetized (60:5 mg/kg Ketamine:Xylazine) dark-adapted (>12 hours) adult Long-Evans rats 5 weeks following citrate buffer (n=6) or diabetes induction (streptozotocin, STZ, n=10, 65 mg/kg at 6 weeks of age, blood glucose: >15 mmol/L). Baseline IOP (mean±SEM) was measured using Tonopen. IOP challenge was produced with a staircase (10-100 mmHg, 5 mmHg increments every 3 min) after vitreal chamber cannulation. Non-cannulated eye acted as control. Blood pressure (mean±SEM) was measured using tail-cuff sphygmomanometer. At each IOP, dim and bright flash (-4.56, -1.72 log cd.s.m-2) ERGs were collected to give the scotopic threshold response (STR) and the rod b-wave, respectively. Amplitudes were expressed relative to baseline (%, 10 mmHg), and the change in function with IOP was described using a cumulative normal function. Non-parametric confidence limits (95% confidence limits, 2.5-97.5CL) for mean were bootstrapped. Two-tailed t-test was used to evaluate IOP and blood pressure at baseline.
Baseline IOP (control: 13.4±0.1 vs. STZ: 13.9±0.1 mmHg, P=0.68) and blood pressure (control: 118±15 vs. STZ: 114±5 mmHg, P=0.78) were similar. Cumulative normal functions fitted to the IOP-response revealed that the peak-to-peak amplitudes of the STR in STZ-treated animals returned a mean (60.4, CL 58.0-62.9 mmHg) that was significantly more sensitive to IOP challenge than control rats (69.3, CL 60.4-68.2) by ~9 mmHg. In contrast, the b-wave IOP-response was not different in diabetic rats (60.3, CL 58.0-62.7 mmHg) compared with controls (62.3, CL 60.0-64.5 mmHg).
Ganglion cell function in diabetic eyes was more affected by acute IOP challenge compared with controls. This was not the case for the ON-bipolar cell dominated b-wave. This indicates for a selective ganglion cell susceptibility to IOP challenge in diabetic eyes.
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