Choroidal thickness and volume mapping by a six radial scan protocol on spectral-domain optical coherence tomography

Purpose: To report a 6 radial scan protocol, which simply generates a topographic map of choroidal thickness and volume on a commercial spectral-domain optical coherence tomography (SD-OCT) device. We analyzed the features of the resulting choroidal maps in healthy eyes.

Design: Prospective, noncomparative case series.

Participants: Eighty eyes from 40 healthy volunteers who visited the healthcare clinic of Hanyang University Hospital from December 2010 to February 2011.

Methods: All participants underwent a 6 radial scanning protocol using an SD-OCT device. In a single session, the device produces 6 high-resolution averaging B-scan images. For segmentation of the choroid layer, the reference lines of the retinal boundary (internal limiting membrane-retinal pigment epithelium) were adjusted to the choroidal boundary (retinal pigment epithelium-choroid/sclera junction) in each of the 6 radial B-scans. A topographic map of choroidal thickness and volume was automatically generated by built-in software according to the Early Treatment Diabetic Retinopathy Study (ETDRS) layout. A statistical analysis was conducted to compare the choroidal thickness and volume measurements for each ETDRS subfield.

Main outcome measures: An ETDRS-style topographic map of choroidal thickness and volume.

Results: The mean time required for segmentation adjustment was 167.4±15.8 seconds. The mean choroidal thickness of all ETDRS subfields was 285.9±53.0 μm, and the mean total choroidal volume of the entire ETDRS area was 7.72±1.2 mm(3). The nasal outer macula area was significantly smaller than any other ETDRS subfield (P<0.05) except for the adjacent superior and inferior outer macula subfields. Refractive error was correlated with choroidal thickness in all ETDRS subfields. Age was also correlated with choroidal thickness for almost all of the ETDRS subfields except for the temporal inner, nasal outer, and temporal outer macula areas. The total choroidal volume was correlated with the refractive error and age.

Conclusions: A 6 radial scan protocol, using a commercial SD-OCT device, enables the production of reliable choroidal thickness and volume maps with an ETDRS layout. By using this protocol, more comprehensive choroidal evaluation is possible in clinical practice or research.