Topography of diabetic macular edema with optical coherence tomography

Abstract

Objective: This study aimed to develop a protocol to screen and monitor patients with diabetic macular thickening using optical coherence tomography (OCT), a technique for high-resolution cross-sectional imaging of the retina.

Design: A cross-sectional pilot study was conducted.

Participants: A total of 182 eyes of 107 patients with diabetic retinopathy, 55 eyes from 31 patients with diabetes but no ophthalmoscopic evidence of retinopathy, and 73 eyes from 41 healthy volunteers were studied.

Intervention: Six optical coherence tomograms were obtained in a radial spoke pattern centered on the fovea. Retinal thickness was computed automatically from each tomogram at a total of 600 locations throughout the macula. Macular thickness was displayed geographically as a false-color topographic map and was reported numerically as averages in each of nine regions.

Main outcome measures: Correlation of OCT with slit-lamp biomicroscopy, fluorescein angiography, and visual acuity was measured.

Results: Optical coherence tomography was able to quantify the development and resolution of both foveal and extrafoveal macular thickening. The mean +/- standard deviation foveal thickness was 174 +/- 18 microns in normal eyes, 179 +/- 17 microns in diabetic eyes without retinopathy, and 256 +/- 114 microns in eyes with nonproliferative diabetic retinopathy. Foveal thickness was highly correlated among left and right eyes of normal eyes (mean +/- standard deviation difference of 6 +/- 9 microns). Foveal thickness measured by OCT correlated with visual acuity (r2 = 0.79). A single diabetic eye with no slit-lamp evidence of retinopathy showed abnormal foveal thickening on OCT.

Conclusions: Optical coherence tomography was a useful technique for quantifying macular thickness in patients with diabetic macular edema. The topographic mapping protocol provided geographic information on macular thickness that was intuitive and objective.

Figures

Figure 1

A, radial spoke pattern of six optical coherence tomograms. B, retinal thickness is computed automatically from the inner and outer retinal boundaries (purple) for each optical coherence tomogram. Arrows indicate the center of the fovea, which is chosen either to lie at fixation (denoted by an “F”) or at a location determined by a feature recognition algorithm (denoted by an “R”). C, macular thickness is displayed as a false-color topographic map and as numeric averages over several regions covering the macula. The three circle radii are 500μm, 1 disc diameter, and 2 disc diameters. The false-color map for a prototypical healthy eye is shown on the left. Mean ± standard deviation thickness in micrometers is reported for the population of healthy eyes on the right.

Figure 2

Histogram of foveal thickness in eyes with diabetic retinopathy averaged over a 500-μm radius disc and stratified by results from slit-lamp biomicroscopic analysis. CSME = clinically significant macular edema. The maximum normal foveal thickness observed is indicated by a vertical bar placed at 216 μm. Eyes to the right of this bar were considered abnormally thickened by optical coherence tomography.

Figure 3

Right versus left average foveal thickness in healthy eyes (left) and in eyes with diabetes but no evidence of retinopathy (right). Dashed lines indicate the maximum foveal thickness observed for normal eyes (216 μm). Solid lines demarcate a strip within which the difference between left and right foveal thickness was less than 2 standard deviations away from the mean difference in normal subjects (±24 μm). One normal and three diabetic eyes (A–C) showed a suspicious difference between right and left foveal thickness. In two of these eyes (A,B), the larger foveal thickness was greater than the maximum observed for normal eyes.

Figure 4

Foveal thickness averaged over eyes with the same visual acuity correlates linearly with visual acuity on a logarithmic scale. The numbers in parentheses indicate the number of eyes averaged for each Snellen visual acuity. Error bars denote standard error. MAR = minimum angle of resolution.

Figure 5

Case 1. Macular edema and exudate not clinically significant. A, fundus photograph showing severe extmfoveal exudate. B, fluorescein angiography showing late leakage surrounding the fovea. C, cross-sectional optical coherence tomograms showing retinal thickening and intraretinal hard exudate. D, optical coherence tomography topographic map displaying extrafoveal macular thickening.

Figure 6

Case 2. Cystoid macular edema before and after treatment. A, hindus photograph showing hard exudate inferior to the fovea. B, fluorescein angiogmphy showing diffuse leakage in the superior macula. C, large central cysts and intraretinal hard exudate are observed on optical coherence tomography (OCT). D, OCT topographic map displays increased macular thickness throughout the macula, especially in the area of fluorescein leakage. E, OCT topographic map obtained 4 months after focal laser photocoagulation showing a decrease in macular thickness.

Figure 6

Case 2. Cystoid macular edema before and after treatment. A, hindus photograph showing hard exudate inferior to the fovea. B, fluorescein angiogmphy showing diffuse leakage in the superior macula. C, large central cysts and intraretinal hard exudate are observed on optical coherence tomography (OCT). D, OCT topographic map displays increased macular thickness throughout the macula, especially in the area of fluorescein leakage. E, OCT topographic map obtained 4 months after focal laser photocoagulation showing a decrease in macular thickness.

Figure 7

Case 3. Development and resolution of clinically significant macular edema. A, fundus photograph showing areas of hard exudate and hemorrhage temporal and inferior to the fovea. B, optical coherence tomography topographic map showing clinically significant macular thickening, which is most prominent temporal to the fovea. C, 8 months later, the macular thickening has increased substantially. D, 5 months after focal laser photocoagulation, the edema is almost completely resolved in the central fovea.

Figure 8

Case 4. Extrafoveal resolution of clinically significant macular edema. A, fundus photograph. B, optical coherence tomography shows mild clinically significant macular thickening and severe macular edema inferotemporal to the fovea. C, (2, 2 months after grid laser treatment, the inferotemporal edema has begun to resolve, but the central thickening persists. D, the central thickening has resolved 10 months after laser treatment.

Figure 9

Case 5. Minimal clinically significant macular thickening. A, fundus photograph showing dot and blot hemorrhages but no clinically significant macular edema. B, optical coherence tomography showing abnormal foveal thickening and edema both superotemporal and nasal to the fovea.