Purpose
To investigate the correlation of outer retinal layers (ORL) thickness and visual acuity (VA) in patients with diabetic macular edema
Methods
Consecutive patients presented with diabetic macular edema seen at the retina clinic of The University of Hong Kong were recruited for Optical Coherence Tomography (OCT) assessment. The outer retinal layers (ORL) thickness was defined as the distance between external limiting membrane (ELM) and retinal pigment epithelium (RPE) at the foveal center. The correlations between total retinal thickness, ORL thickness and visual acuity were assessed.
Results
78 patients with diabetic macular edema were recruited. The mean age was 58.1 years (+/- 11.5 years) and their mean visual acuity measured with Snellen Chart was 0.51 (+/- 0.18). The correlation coefficient between total retinal thickness and visual acuity was 0.34 (p<0.001) whereas the correlation coefficient was 0.65 (p<0.001) between outer retinal layers thickness and visual acuity.
Conclusions
Outer retinal layers thickness represents the total length of photoreceptor inner segments and outer segments, which consists of mitochondria for energy production and disks of photoreceptors with opsin for photons absorption. This measurement has important implication in the integrity of photoreceptors. We found that outer retinal layers thickness correlates better with vision than total retinal thickness. Its correlation with visual acuity is comparable to the photoreceptor outer segment (PROS) length with a theoretically higher repeatability. To conclude, outer retinal layers thickness is a novel optical coherence tomography parameter that correlates well with vision in the assessment of diabetic macular edema. Further studies shall be conducted to assess the potential of outer retinal layers thickness to be the long term visual prognostic factor for patients with the diabetic macular edema.