Choroidal thickness in normal eyes measured using Cirrus HD optical coherence tomography

Abstract

Purpose: To examine choroidal thickness and area in healthy eyes using spectral-domain optical coherence tomography (SD-OCT).

Design: Retrospective, observational case series.

Methods: Thirty-four eyes (34 subjects), with no retinal or choroidal disease, underwent high-definition raster scanning using SD-OCT with frame enhancement software. Choroidal thickness was measured from the posterior edge of the retinal pigment epithelium to the choroid/sclera junction at 500-microm intervals up to 2500 microm temporal and nasal to the fovea. The central 1-mm area of the choroid was also measured, along with foveal thickness of the retina. All measurements were performed by 2 independent observers. Statistical analysis was used to correlate inter-observer findings, choroidal thickness and area measurements with age, and choroidal thickness with retinal foveal thickness.

Results: The 34 subjects had a mean age of 51.1 years. Reliable measurements of choroidal thickness were obtainable in 74% of eyes examined. Choroidal thickness and area measurements had strong inter-observer correlation (r = 0.92, P < .0001 and r = 0.93, P < .0001 respectively). Area had a moderate negative correlation with age (r = -0.62, P < .0001) that was comparable to the correlation between mean subfoveal choroidal thickness and age (r = -0.61, P < .0001). Retinal and choroidal thickness were found to be poorly correlated (r = -0.23, P = .18). Mean choroidal thickness showed a pattern of thinnest choroid nasally, thickening in the subfoveal region, and then thinning again temporally. Mean subfoveal choroidal thickness was found to be 272 microm (SD, +/- 81 microm).

Conclusions: Choroidal thickness can be measured using SD-OCT high-definition raster scans in the majority of eyes. Choroidal thickness across the macula demonstrates a thin choroid nasally, thickest subfoveally, and again thinner temporally, and a trend toward decreasing choroidal thickness with age.

FIGURE 1. Choroidal thickness measurements on Cirrus HD-OCT high definition 1 line raster scans

(Top) Demonstration of normal choroidal thickness measured at 500 μm intervals, up to 2500 μm temporal and nasal to the fovea. Perpendicular lines were drawn from posterior edge of the retinal pigment epithelium to the choroid/sclera junction using Cirrus HD-OCT software. (Bottom) Central 1 mm cross-sectional area of choroid measured using ImageJ analysis software; outlined area is 0.32 mm².

FIGURE 2. Graph of mean macular choroidal thickness in normal eyes

Mean thickness at each of the 11 locations measured at 500 μm (0.5 mm) intervals temporal (T) and nasal (N) to the fovea (F).

FIGURE 3. Cirrus HD-OCT 1 line raster scans demonstrating poor visualization of posterior choroid/sclera junction

Example OCT images from two different subjects with (Top) 2+ NSC and (Bottom) a PCIOL respectively in which full choroidal thickness could not be assessed and measurements could not be performed.