Optical Coherence Tomography and Multifocal Electroretinography in Diabetic Macular Edema: A Neurovascular Relation With Vision.

BACKGROUND AND OBJECTIVES: To evaluate retinal neuropathy in patients with diabetic macular edema (DME) with multifocal electroretinograph (mfERG), and to evaluate the simultaneous impact of retinal neuropathy and vasculopathy on visual acuity in subtypes of DME.

PATIENTS AND METHODS: This prospective, controlled, investigative study conducted at a tertiary eye care center of Northern India included 79 eyes of 50 treatment-naïve patients with DME (Group 1), 94 eyes of 50 diabetic patients without diabetic retinopathy (Group 2), and 100 eyes of 100 normal volunteers as controls. Comprehensive ocular evaluation along with mfERG and optical coherence tomography (OCT) were performed for all patients. N1 and P1 mfERG waveforms in the two central-most rings of macula were evaluated for amplitudes and implicit time. OCT was used to sub-classify types of DME and evaluate macular thickness, ellipsoid zone (EZ), and external limiting membrane (ELM) disruption. Best-corrected visual acuity (BCVA) relative to other variables was the primary outcome measure. The three groups were compared for all the parameters inclusive of OCT and mfERG patterns. Further, OCT subtypes of DME were analyzed for mfERG waveform patterns.

RESULTS: All mfERG values were significantly lower in Group 1 and Group 2 as compared to Group 3 (P < .05). BCVA strongly correlated with central macular thickness, EZ, and ELM disruption scores in Group 1 (P = .001), but correlated modestly with mfERG waveform amplitudes in Group 1 patients with intact EZ and ELM only. BCVA correlated with mfERG amplitudes in patients with neurosensory detachment, but not in those with cystoid macular edema.

CONCLUSIONS: Neural changes set in before the clinical changes related to vasculopathy manifest in diabetic patients. Neuroretinopathy in patients with DME affects all retinal layers symmetrically in early stages, but impacts the middle retinal layers severely in advanced disease form. BCVA correlates with electrophysiological changes till the time morphological features are visible when stronger correlation is seen with anatomical disruption. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:626-631.].