Abstract
Purpose :
Outer retinal tubulations (ORT) is an OCT finding believed to be the culmination of a Muller cell derived process along with photoreceptor degeneration and RPE disruption. Here we describe the incidence of ORTs in patients with neovascular age related macular degeneration (nAMD) and propose an alternate hypothesis for ORT formation.
Methods :
A retrospective chart review of new nAMD patients seen at a referral retina center. Initial baseline fluorescein and OCT images were reviewed and CNVs classified. Consecutive visits’ OCT images were analysed in chronological order.
Results :
147 eyes of 137 consecutive patients were included. The mean age at presentation was 81 years. Patients had a median of 15 visits (range 5-44) during the study period. Mean follow-up period was 24 months (range 5 – 52). 56 of 147 (38.1%) eyes developed ORT. In the ORT cohort the incidence of different types of CNV on initial OCT were: mixed membranes consisting of both a Type 1 and Type 2 element in 38 of 56 (67.9%) eyes, Type 2 membrane (no type 1 element) in 23.2%, and Type 1 membrane (no type 2 element) in 7.1%; in 1.8% of eyes no membrane could be identified on OCT. Together this means that 91.1% of eyes that developed ORT had an element of a type 2 membrane visible on OCT at initial presentation. In the ORT group the most common tissue underlying the ORT was scar-tissue–without-RPE (46.4%) followed by a-scar-on-top-of-RPE (23.2%). Intact-RPE was found in 17.9% of cases and RPE-atrophy and RPE-on-a-scar in 10.7% and 1.8% of cases respectively. Thus scar tissue was directly under the ORT in 69.6% of cases. In multivariate analysis membrane type and initial CNV size were identified as significant independent predictors of ORT development with mixed membranes (OR 20.9, 95% CI: 5.9-73.5, P<0.05) and type 2 membranes (OR 41.8, 95% CI: 8.5 – 205.6, P< 0.05) being associated with higher odds compared to type 1 membranes, and CNV sizes >1.5DA associated with higher odds (OR 4.8, 95% CI :1.4 -16.2, P<0.05) compared to CNV sizes =<1DA.
Conclusions :
Type 2 membranes and larger in size CNV are predictors of ORT development. Eyes that developed ORT had a high incidence of scar tissue directly underlying the ORT. We hypothesize that contraction of a type 2 CNV derived scar is the primary mechanical driver behind ORT formation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.