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HD-OCT thickness maps best confirm RNFL defects in eyes with early glaucoma
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Thickness maps generated with high-definition spectral-domain optical coherence tomography proved more useful than other maps in identifying retinal nerve fiber layer defects in glaucomatous eyes, according to a study.
Investigators evaluated the accuracy of clock-hour, deviation and thickness maps created with the Cirrus HD-OCT (Carl Zeiss Meditec) in detecting retinal nerve fiber layer (RNFL) defects previously identified in red-free fundus photographs.
The study included 295 eyes with early glaucomatous RNFL defects; a control group comprised 200 healthy, age-matched eyes. Mean patient age was 50.6 years in the glaucoma group and 49.7 years in the control group.
Visual acuity, refractive error, IOP, slit lamp biomicroscopy, fundus photos, visual fields and RNFL measurements were assessed.
Among the 295 defects observed in glaucomatous eyes, 83 defects were misidentified in the clock-hour map, 27 were misidentified in the deviation map and none were misidentified in the thickness map.
Disclosure: The study authors report no relevant financial disclosures.
Perspective
Back to TopDonald L. Budenz, MD, MPH
Considerable emphasis has been placed on the deviation and probability maps of spectral-domain OCT printouts with relatively little emphasis on the total thickness map. To date, most clinicians have been treating the RNFL thickness map like the graytone printout on a visual field; that is, using it to look for patterns but not necessarily diagnostic information. In the paper by Hwang and colleagues, the authors demonstrate that ignoring the thickness maps may result in a missed opportunity for identifying RNFL defects. This study only applies to focal, rather than diffuse, RNFL thinning, which represents only 50% of photographically demonstrable RNFL thinning in glaucoma, however. Diffuse thinning of the RNFL may be the earliest sign of glaucoma and this is very difficult to see on red-free photographs and also difficult to demonstrate using OCT, since the average RNFL thickness has a wide range of normal values.
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