Abstract
Purpose :
Subretinal drusenoid deposits (SDD) are extracellular deposits found internal to the retinal pigment epithelium (RPE). The rod intercept time (RIT) is significantly delayed in eyes with SDD and so they are presumed surrogate markers of rod dysfunction. As RIT is usually tested at 5 degrees inferior to fovea, this study assessed whether RIT delay and SDD are due to localised OCT changes in the outer retina in the rod-rich juxtafoveal (JF) area (1500µm, to align with 5 degrees that covers the RIT test area) or whether these represent diffuse retinal pathology
Methods :
51 patients were stratified into 3 groups: control with normal macula and AMD with and without SDD. The best corrected visual acuity (BCVA), low luminescence visual acuity (LLVA) and RIT were compared. Using ImageJ, localised changes at 1500µm nasal and temporal to fovea measured on OCT included the distance between external limiting membrane (ELM) and retinal pigment epithelium (RPE), separation of RPE from the Bruch’s membrane (BM) and choroidal thickness (CT). For diffuse changes, total macular volumetric measurements of outer nuclear layer (ONL) and RPE-BM complex were measured using Heidelberg Spectralis algorithm. In addition, subfoveal CT (SFCT) was measured as foveola is rod-free. These structural changes were compared in the 3 patient groups and in those with RIT ≤ 12.5 minutes versus >12.5 minutes.
Results :
We included 10 controls, 16 AMD eyes with no SDD and 26 with SDD. Worst BCVA and RIT were observed in the SDD group (p<0.0001) but not LLVA (p=0.058). The only local JF change at 1500µm that was consistently significant was JF CT thinning (nasal, p=0.0005; temporal, p=0.0003). SFCT thinning was also observed, this was considered as diffuse choroidal thinning. There was also an overall reduction of both local thickness of ELM-RPE and total macular ONL volume and an increase in RPE-BM macular volume in the SDD group (p>0.05), signifying diffuse macula change. Delayed RIT was associated with CT in the JF area and diffuse increase in RPE-BM macular volume (p = 0.025).
Conclusions :
SDD is a surrogate marker of diffuse outer retina and choroid pathology and not due to any specific localised change. Delayed RIT is also explained by diffuse disease of the outer retina and choroid.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.