Quantification of Early and Intermediate Age-related Macular Degeneration Using OCT "en face" Presentation

Early and intermediate age-related macular degeneration (AMD) results in drusen deposits under the retinal pigment epithelium (RPE). These early stages of AMD exhibit different risks of progressing to late AMD. To date, early AMD has been classified and quantified by fundus photography. This does not appear to be sensitive enough for clinical trials studying the impact on drusen. SD-OCT with two-dimensional rendering of the segmented slices analysed allows for en face imaging of the drusen. The present trial studied the potential of quantifying early and intermediate AMD by en-face optical coherence tomography (OCT).

Thirty-one eyes of 29 patients in different stages of early and intermediate AMD were studied. To this end, fundus photographs (Kowa VX-10i, Kowa, Tokyo, Japan) and en-face OCT images (RTVue XR Avanti, Optovue, Inc., Fremont, CA, USA) were taken. First, different segmentation levels (6 µm underneath the RPE, on the RPE, 6 µm and 9 µm above the RPE) and different layer thicknesses (5 µm, 10 µm, 20 µm and 30 µm) were analysed to determine the best segmentation for visualising drusen. Drusen were marked manually and their number and surface area calculated. This analysis was then compared with the standardised drusen analyses on fundus photography. Additional changes in early and intermediate AMD such as pigment epithelial detachments (PEDs) and subretinal drusenoid deposits (SDD) as well as small atrophies were also documented and compared.

The best segmentation for delineating the drusen on the en-face OCT images was found to be a segmentation 6 µm underneath the RPE with a slice thickness of 20 µm. Comparison of drusen quantification on en-face OCT images with the standardised drusen analysis on fundus photography revealed particularly good similarity. Other changes in early and intermediate AMD, such as PEDs, SDD and small atrophies, were easier to assess on the en-face OCT images.

The analysis and quantification of drusen from en-face OCT images with 20 µm segmentation at 6 µm underneath the RPE allows differentiated quantification of various drusen characteristics. Moreover, other changes in early and intermediate AMD can also be analysed. In future observational and clinical trials, this could help quantify drusen.