The relationship between perifoveal capillary ring alterations and visual acuity in diabetic retinopathy

Background / Aim. To investigate the impact of diabetic macular ischemia (DMI) on visual acuity (VA) through the analysis of perifoveal capillary network in various stages of diabetic retinopathy (Non Proliferative Diabetic Retinopathy-NPDR and Proliferative Diabetic Retinopathy-PDR). Methods. Qualitative and quantitative analysis of 143 angiograms of patients with different stages of diabetic retinopathy was performed. The degree of macular ischemia was assessed by the analysis of 2 parameters: perifoveal capillary ring i.e. Foveal avascular zone (FAZ) outline irregularity and capillary loss. Finally, a comparison was made between the degree of macular ischemia with the best corrected visual acuity, depending on macular thickness. Results. In the eyes with mild and moderate NPDR, without significant macular thickening, no statistically significant decrease of visual acuity, caused by macular ischemia, was noticed (p=0.81). Opposite, in subgroup with severe NPDR and PDR, without significant macular thickening, statistically significant difference was presented among eyes with moderate and severe macular ischemia comparing to eyes with lower grades of macular ischemia (p=0.021, p=0.018). In eyes with moderate NPDR and mild macular ischemia, the increase in macular thickness resulted in a statistically insignificant decrease in visual acuity compared to eyes with normal macular thickness (p=0.088). But in eyes with severe NPDR, any pathological increase in macular thickness caused a statistically significant decrease in visual acuity, regardless of the degree of macular ischemia (p=0.018-0.040). A similar relationship was also found in eyes with PDR (p=0.017-0.042). In eyes with statistically significant decrease of visual acuity, the most of the examined eyes (98%) had FAZ outline irregularity in nasal perifoveal subfield. Conclusion. In the absence of significant macular thickening, destruction of one-half of the perifoveal capillary network or greater is associated with reduced VA. The location of macular ischemic changes in the nasal parts of the perifoveal capillary ring plays a crucial role in its effects on visual function.