6th session: OCT

Volumetric optical coherence tomography for macular edema
Glenn J. Jaffe (Durham)
Purpose: Optical coherence tomography (OCT) is a useful
ancillary test to diagnose and manage a variety of retinal disorders.
It is particularly useful
for characterizing
macular diseases. Here, the volumetric OCT technique (VOCT) to manage
patientswith macular edema is described.
Methods: Volumetric OCT is a term used to denote the
data obtained from the Retinal Thickness Map or Fast Macular Thickness
Map scan modes. To perform
VOCT, 6 radial scans, approximately 6 mm in length, centered on the
fovea are done to produce a series of “optical sections” through
the cortical vitreous, retina, RPE and choroid. 100 – 256 points
are sampled along the length of each radial scan. The retinal thickness
at each of these points
is calculated by measuring the distance between the retinal pigment
epithelial layer and the nerve fiber layer. The typical volumetric scan
obtained in this manner includes an area in the posterior pole bounded
by the major
temporal vascular arcades, the optic nerve, and a point equidistant
to the foveal center on the temporal side of the fovea. These scans
are reconstructed to form an interpolated surface contour map of the
retina that indicates
the retinal thickness at various points in the posterior pole.
Results: Data obtained from VOCT include 6 cross sectional
radial macular images, a measurement of mean (± SD) central foveal
thickness, a measurement of average thickness in the central, and 8
paracentral macular
regions, and a measurement of volume under the area enclosed by the
surface map. Measurements are quite reproducible, and retinal thickness
measurements correlate well with leakage observed on fluorescein angiography
and qualitative thickness analysis of stereoscopic fundus photographs.
The quantitative and morphological data obtained from VOCT are extremely
useful to evaluate and monit the course of macular edema. Typical clinical
situations for which this test may be appropriate include cystoid macular
edema caused by uveitis, retinal degenerative diseases, drug toxicity,
macular edema associated with diabetic retinopathy, and macular edema
associated with choroidal neovascularization. Artifacts can be produced
by operator error, hazy media, inner and outer retinal boundary misidentification
by the software.
Conclusions: VOCT is a very useful, non-invasive method
to evaluate eyes with macular edema, and to determine response to therapy.
This technique provides morphological and quantitative
data that are not readily obtained with alternative techniques such
as fluorescein angiography and stereo fundus photography.
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