Abstract
Purpose:
To evaluate en face spectral-domain optical coherence tomography (SD-OCT) findings of outer retina in patients with diabetic macular edema (DME).
Methods:
Fifty-five eyes were classified according to OCT features of DME: diffuse retinal thickening (DRT), cystoid macular edema (CME), and serous retinal detachment (SRD). SD-OCT scans were obtained using the Macular Cube 512 x 128 scan of the Cirrus HD-OCT (Carl Zeiss, Dublin, CA, USA). The scanned data were processed using embedded tools of advanced visualization. A partial thickness OCT fundus images of the ellipsoid zone (EZ), the external limiting membrane (ELM), and the outer nuclear layer (ONL) were generated by setting the region of interest to a 20-㎛ thick layer, which was parallel and adjacent to the retinal pigment epithelium. The en face EZ reflectivity of 6mm and 1mm ETDRS subfield was analyzed with the mean gray value calculated by ImageJ software (version 1.46, National Institutes of Health, Bethesda, MD). The percentile of the en face ONL exudate area and reflectivity and circularity of the edematous space were also calculated for each type.
Results:
EZ reflectivity of both 6mm and 1mm ETDRS subfield was significantly correlated with visual acuity in all subtypes (DRT: r=-0.477, p=0.020; CME: r=-0.412, p=0.036; SRD: r=-0.524, p<0.001; respectively). Disrupted EZ was gradually restored over time following intravitreal ranibizumab injection. 42 eyes (76.3%; DRT: 17.3%; CME: 44.6%; SRD: 75.2%) had disrupted both ELM and EZ in en face images and 31 eyes (56.3%; DRT: 13.7%; CME: 56.2%, SRD: 80.9%) in cross-sectional images at baseline. Agreement between en face and cross-sectional image was fair at baseline (κ = 0.355). ONL exudate area at baseline was not significantly different between subtypes while the area at 12 months was greater in CME type (6.18%) than in DRT (4.25%) and SRD type (1.91%). Reflectivity of the edematous space was greater in CME (39.22±3.14) and SRD type (39.68±2.78) than in DRT type (33.45±3.59) in en face image.
Conclusions:
En face EZ reflectivity of ETDRS subfield significantly correlated with visual acuity in all subtypes. Disrupted integrity of ELM and EZ at baseline was frequently found in SRD type and en face image showed comparable agreement with cross-sectional image. En face ONL exudate area significantly increased in CME types.