Retinal thickness variation in the diabetic patient measured by the retinal thickness analyser

Abstract

Aim: To evaluate the potential of the retinal thickness analyser (RTA) as an objective tool for assessment and follow up of diabetic macular oedema.

Methods: A prototype of the RTA that operates on the principle of laser slit biomicroscopy was used. Retinal thickness was obtained in 41 eyes of 41 diabetic patients. The clinical diagnosis was cystoid macular oedema (CMO) in 10 eyes, clinically significant macular oedema (CSMO) without retinal cysts in 21 eyes, and "dry" macula following grid pattern laser treatment in 10 eyes. The control group consisted of 46 eyes of age matched healthy volunteers.

Results: In normal eyes (46 eyes), the foveal thickness measured was 178 (SD 44) microns and the macular thickness around the fovea was 311 (51) microns. The eyes with CMO displayed the largest foveal thickening, 875 (287) microns (390% increase compared with normal values). The average thickness of the fovea in the non-cystoid CSMO group was 427 (175) microns (144% increase compared with normal fovea). The average thickness of the foveal centre in eyes judged as having "dry" macula after laser treatment was 315 (71) microns (77% increase compared with normal value and a 26% decrease in thickness compared with the CSMO eyes). Statistically significant differences were found in central thickness between these four groups (p = 0.0001). The average thickness at 500 microns surrounding the fovea was 566 (202) microns in the CSMO eyes compared with 311 (51) microns in normal eyes (80% increase). The "dry" macula group (after undergoing laser treatments) had an average thickness of 414 (94) microns (27% decrease compared with CSMO eyes and a 33% increase compared with eyes of healthy controls).

Conclusions: RTA is a system for quantifying macular thickness and imaging of macular pathology. The system can be a useful tool for diagnosis of macular diseases and for evaluation of the effect of treatment modalities.

Figure 1

Ten adjacent optical cross sections of the retina covering an area of about 2 × 2 mm. The separation of the white lines is proportional to the thickness of the retina at that location. In these images the inner limiting membrane is on the right (right arrow) and the retinal pigment epithelium is on the left (left arrow).

Figure 2

Three dimensional topographic presentation of the retinal thickness an area of the fovea, 2 × 2 mm, of a normal patient. The coloured scale represents the thickness in microns (µm) and the map represents the variation in thickness in and around the fovea.