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Zeinab Nasralah, Dennis L Gierhart, Alistair J. Barber; Changes in retinal thickness measured by spectral-domain optical coherence tomography in diabetic rats: effect of zeaxanthin. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4712.
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© ARVO (1962-2015); The Authors (2016-present)
Previous histology studies showed that 5-7 months of diabetes reduced the thickness of the inner retina in rodents. This study used spectral-domain optical coherence tomography (OCT) to measure retinal cell layer thicknesses in diabetic and control Long-Evans rats. The study also assessed visual function in the same animals. The effect of an anti-oxidant dietary supplement, zeaxanthin, on retinal thickness and visual function was also tested.
Young male Long-Evans rats were made diabetic by streptozotocin (STZ, 100 mg/kg, pH 4.5, i.v., n= 8) and compared to age-matched controls (CNT, n=10). All procedures were in accordance with the Penn State Hershey College of Medicine IACUC and the ARVO guidelines for use of animals in ophthalmology research. Zeaxanthin pellets (ZeaVision) suspended in water were given to half of the rats in both the CNT and STZ groups (200 mg daily oral gavage), beginning a week after diabetes induction. Spatial frequency threshold (SFT) and contrast sensitivity (CS) were measured using behavioral optokinetic testing (Optomotry) 10 weeks after diabetes induction. Retinal layer thicknesses were measured by OCT (Bioptigen) after 15-16 weeks of diabetes. Statistical analysis was by ANOVA with Newman-Keuls multiple comparisons test and p<0.05 was considered a significant difference.
A pilot study confirmed a 3-fold increase in liver zeaxanthin after one week of treatment. SFT and CS were significantly reduced (p<0.001, p<0.01, respectively) in both the STZ and zeaxanthin-fed STZ groups compared to CNT. The outer nuclear layers of the STZ and the zeaxanthin-fed STZ groups was significantly thicker compared to CNT (11.2% increase, p<0.01). The thickness of the inner plexiform layer was 11.7% smaller in the STZ group compared to CNT (p<0.05), while that of the zeaxanthin-fed STZ group was not significantly different from the CNT groups.
The significant swelling of the outer plexiform layer in diabetic rats may be due to edema. There was an associated reduction in both SFT and CS measures of visual function. Four months of diabetes caused thinning of the inner plexiform layer, indicating inner retina degeneration. Treatment with zeaxanthin prevented the degeneration of the inner plexiform layer despite its lack of effect on vision loss and outer retina swelling.
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