Purpose:
Recent studies have reported choroidal thickness measurements based on FD-OCT images. Lamina fusca is the natural anatomical outer boundary of the choroid. Unfortunately, lamina fusca is not always clearly visible in OCT images. The goal of this study is to assess the difference between lamina fusca boundary and posterior vessel boundary.
Methods:
This is a retrospective case review study. Horizontal 20° B-Scan images, acquired with RTVue FD-OCT (Optovue, Fremont,CA), through the center of the fovea for each study eye were reviewed. The inclusion criteria were age over 18 and sufficient choroid image contrast to visualize choroid vessels. Total 96 eyes of 96 subjects were included, consisting of 38 non-pathology eyes, 28 drusen eyes, 22 wet AMD eyes, and 8 CNV eyes. The eyes were divided into 3 categories based on the characteristics of the choroid-sclera junction: SCS (suprachoroidal space visible as a dark strand), LF (lamina fusca visible as a bright strand), and PVC (only posterior vessel cavity boundary visible). For eyes in SCS and LF, 2 sets of choroid thickness measurements were performed in the center based on PCV boundary and SCS or LF boundaries respectively.
Results:
The distributions (Mean, SD, Min, Max) of the study eyes were (61.9, 15.7, 28, 86) for age, (-3.68D, 4.71D, -17.00D, +3.00D) for refraction, and (185µm, 95µm, 30µm, 399µm) for average choroid thickness. Of the 96 study eyes, 50% (48 eyes) were in the PVC category in which neither LF nor SCS was observed, 35% (34 eyes) were in the LF category, and 15% (14 eyes) were in the SCS category. SCS was not observed in the non-myopic healthy eyes. Of the 48 eyes in the PVC category, 20 eyes had thin atrophic choroid due to either myopia or retinal pathology. For the 48 eyes in either the SCS or the LF categories, choroid thickness measurement differed by 26.9 µm on average, ranged from 8 to 85 µm in individuals, between different boundaries.
Conclusions:
Suprachoroid space may be associated with myopia or retinal pathology. Choroid thickness measurement could be affected by boundary criteria. Posterior vessels boundary is the best method in 50% cases, but presence of suprachoroidal space must be remembered. A common posterior boundary definition may be beneficial.