Correlation Between Visual Acuity, OCT-measured Thicknesses Of Retinal Layers, MfERG And MfONHC In Patients With Clinically Significant Diabetic Macular Edema (CSDME)

Abstract

Purpose: : To study correlations between visual acuity, optical coherent tomography (OCT)-measured thicknesses of retinal layers, multifocal electroretinography (mfERG), and multifocal optic nerve head component (mfONHC) in patients with CSDME.

Methods: : This pilot study included 12 patients (18 eyes) with CSDME due to type I or II diabetes. Data for the study are collected at one-time point, prior to the patients’ treatment. Quantitative analysis of the following parameters is performed: Cirrus HD-OCT-measured thicknesses of different retinal layers; the layers are measured on horizontal (180°) and vertical (90°) central scans, at 1000 µm ("central" location) and 2500 µm ("peripheral" location) away from the fovea, on both sides of the fovea on each scan; mfERG (VERIS^TM 5.2) 1st- and 2nd-order kernels’ amplitudes and implicit times; extent of the mfONHC loss. Data of 25 healthy age-matched subjects (41 eyes) are used as control. Correlations between the best-corrected visual acuity (BCVA), OCT measurements and mfERG parameters are analyzed. Data collection is in progress.

Results: : BCVA varied from 20/50 to 20/200. Mean (±St.Dev.) central retinal thickness was 421.9±72.6 µm. OCT measurements show a significant thinning of the retinal nerve fiber layer (RNFL): in the "central" location, mean (±St.Dev.) RNFL is 27.9±9.4 µm in CSDME and 34.7±8.8 µm in norm (p<0.05); in the "periphery" it is 34.1±14.1 µm in CSDME and 45.7±13.4 µm in norm (p<0.001). Larger thicknesses of the RNFL correlate with higher BCVA (r=0.62). Photoreceptor outer segment layer does not show changes in the CSDME (p>0.7). Other layers cannot be compared due to the edematous thickening. MfERG in CSDME shows significant depressions and large delays of N1 and P1 components of the 1st-order kernel and p1, n1, and p2 components of the 2nd-order kernel in all mf-eccentricities (p<0.001 for all comparisons). No clear correlation between the abnormalities of the 1st-order kernel and BCVA are seen. However, the 2nd-order kernel foveal traces are undetectable and mfONHC is completely lost when BCVA is 20/80 or lower.

Conclusions: : The observed correlations between the BCVA and RNFL loss, mfONHC loss and mfERG 2nd-order kernel abnormalities in CSDME may be suggestive for the degree of the RNFL atrophy to be responsible for the discrepancies between the BCVA and degree of macular edema. These findings may be useful for prognosis of outcomes of CSDME.

Keywords: diabetic retinopathy • edema • imaging/image analysis: clinical