Global vs Local Stereopsis in the Early Diabetic Retinopathy

Purpose: To compare the stereoacuities measured by TNO and titmus tests, in patients with diabetes with early retinopathies and those without diabetes.Methods: In this study, 110 participants (55 with diabetes mellitus, and 55 age-matched controls) were recruited from a retina subspecialist clinic in Qazvin, Iran, from September 2016 to March 2017. The stereo-acuities were measured following subjective refraction by Titmus and TNO tests at 40 cm according to their instruction manuals. The appropriate near corrections were worn when needed. The picture of the retina was acquired by Spectralis Heidelberg Retina Angiograph and Optical Coherence Tomography (HRA+OCT). In case of retinopathy, its grading was determined by the Early Treatment Diabetic Retinopathy Study (ETDRS) classification. Patients with diabetes whose retinal exam revealed no background retinopathy or only microaneurysms (very mild diabetic retinopathy) in the worse eye were enrolled in this study. Results: The mean stereoacuity measured by TNO in diabetic and non-diabetic groups were 211.6±124.3 and 67.1±37.8, respectively. The mean stereo-acuities measured by Titmus in diabetic and non-diabetic groups were 44.9±7.6, 40.0±0.0, respectively. The differences between the means of the two groups were statistically significant for two tests (P<0.05). The correlation between duration of disease and stereo findings was statistically significant for TNO (r= 0.38, P=0.004) and it was not statistically significant (r=0.235, P=0.084) for Titmus. Conclusion: The global pathway of stereopsis is damaged in patients with diabetes with no background retinopathy or very mild diabetic retinopathy. The difference in severity of damage to local and global pathways in patients with diabetes indicates that there may be different underlying mechanisms for these two pathways