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Moe H. Aung, Moon K. Kim, Darin E. Olson, Peter M. Thule, Machelle T. Pardue; Early Visual Acuity Deficits in a Rat Model of Diabetic Retinopathy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5960.
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© ARVO (1962-2015); The Authors (2016-present)
Vascular abnormalities define clinical diabetic retinopathy (DR). However, studies increasingly suggest that neuronal dysfunction precedes retinal vascular changes. Previously, we reported delays in the scotopic ERG following 4 weeks of hyperglycemia in steptozotocin (STZ) treated rats and mice. Here we assess visual acuity in STZ rats and examine its correlations with cataract formation, retinal dysfunction, and duration of diabetes.
Retinal function (monthly dark-adapted ERGs), cataract formation (biweekly slit lamp exam), and visual acuity (weekly optokinetic tracking) was assessed longitudinally for 12 weeks in two groups of pigmented Long-Evans rats: control (n=8) and diabetic (n=8). Diabetes was induced by STZ injection (100 mg/kg, i.v) and confirmed through serially elevated blood glucose (>250 mg/dl). Only responses from the right eye were analyzed and compared between the two groups.
As early as 5 week post-STZ, diabetic animals exhibited an average 25% decreased visual acuity (Two-way RM ANOVA, p=0.005). Diabetic rats also exhibited significantly higher cataract score (indicating denser cataract formation) compared to controls (p=0.002), starting at 6 week post-STZ. Similar to our previous reports, the latency to a dim flash (0.02 cd sec/m2) of summed oscillatory potentials (OPs) was significantly delayed in diabetic rats compared to controls (p<0.001) as early as 4 week post-STZ. Importantly, the magnitude of all deficits significantly increased with the duration of diabetes (p<0.05). In contrast, both the amplitudes and implicit times of a-wave and b-wave did not consistently differ between control and diabetic animals. While none of the variables examined correlated with visual acuity in control rats, cataract score correlated most strongly with visual acuity changes among diabetic rats (Pearson correlation, r2 = 0.534, p<0.0001).
Diabetes markedly reduces visual acuity in STZ rat, as early as 5 week post-STZ. Although the visual defects may be related to previously reported retinal neuronal changes in STZ rats, such as inner retinal dysfunction, it is important to note that cataract formation may be another contributing factor to the deficit.
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