Scanning Laser Tomography Retinal Thickness and Edema Maps in Normal & Diabetic Eyes

Abstract

Abstract: : Purpose: To present age–normative data for retinal thickness maps and edema maps derived from scanning laser tomography images (HRTII), and to demonstrate the utility of the algorithm with clinical examples and their comparisons with OCT. Methods: One hundred and forty–three normal individuals, distributed approximately evenly across a 50 year age span, were imaged with a second generation Heidelberg Retinal Tomograph (HRTII). At least three sets of HRT images were obtained for each subject. The retinal thickness estimates are derived from a two reflector impulse model (internal limiting membrane & retinal pigment epithelium) convolved with an estimate of the point spread function. The edema maps were generated using the Retina Module of the HRTII. Edeman index and thickness maps, and OCT3 thickness profiles were also obtained in 15 subjects with diabetes. Results: Retinal thickness maps in normal subjects increased with eccentricity from the fovea, in keeping with expected anatomical values. The average retinal thickness for the central 500 micron radius circle, centred on the fovea, was 238µm and the average edema index was 1.08. The average difference from baseline for three repeated measures in the central 500 microns zone was –0.03 for the edema index (Range –0.06 to –0.01; ±2SD 0.21–0.33) and was –3.35µm for retinal thickness (Range –4.90 to –1.20µm; ±2SD 39.80–53.20µm) in normal subjects. Corresponding data for the 15 subjects with diabetes was –0.23 for the edema index (Range 0.14 to 0.28; ±2SD 1.10–1.87) and was –19.1µm for the retinal thickness (Range –26.6 to –10.71µm; ±2SD 86.90–97.60µm). Good to excellent concordance between HRT and OCT images of each individual were observed. Specific cases at a single visit and over consecutive visits will be described to give insight into the clinical utility of the thickness estimates. Conclusions: Normative data is presented for both the new retinal thickness maps and for the edema index maps. In clinical examples, the thickness data was concordant with thickness profiles derived from the OCT. The impulse model is capable of giving repeatable thickness with HRT2 data.

Keywords: retina • clinical (human) or epidemiologic studies: systems/equipment/techniques • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)