Comparison of the modified Early Treatment Diabetic Retinopathy Study and mild macular grid laser photocoagulation strategies for diabetic macular edema

Abstract

Objective: To compare 2 laser photocoagulation techniques for treatment of diabetic macular edema: the modified Early Treatment Diabetic Retinopathy Study (ETDRS) direct/grid photocoagulation technique and a potentially milder (but potentially more extensive) mild macular grid (MMG) laser technique in which microaneurysms are not treated directly and small mild burns are placed throughout the macula, whether or not edema is present.

Methods: Two hundred sixty-three subjects (mean age, 59 years) with previously untreated diabetic macular edema were randomly assigned to receive laser photocoagulation by either the modified ETDRS (162 eyes) or MMG (161 eyes) technique. Visual acuity, fundus photographs, and optical coherence tomography measurements were obtained at baseline and at 3.5, 8, and 12 months. Treatment was repeated if diabetic macular edema persisted.

Main outcome measure: Change in optical coherence tomography measurements at 12-month follow-up.

Results: Among eyes with a baseline central subfield thickness of 250 microm or greater, central subfield thickening decreased by an average of 88 microm in the modified ETDRS group and by 49 microm in the MMG group at 12-month follow-up (adjusted mean difference, 33 microm; 95% confidence interval, 5-61 microm; P = .02). Weighted inner zone thickening by optical coherence tomography decreased by 42 microm in the modified ETDRS group and by 28 microm in the MMG group (adjusted mean difference, 14 microm; 95% confidence interval, 1-27 microm; P = .04); maximum retinal thickening (maximum thickening of the central and 4 inner subfields) decreased by 66 and 39 microm, respectively (adjusted mean difference, 27 microm; 95% confidence interval, 6-47 microm; P = .01), and retinal volume decreased by 0.8 and 0.4 mm3, respectively (adjusted mean difference, 0.3 mm3; 95% confidence interval, 0.02-0.53 mm3; P = .03). At 12 months, the mean change in visual acuity was 0 letters in the modified ETDRS group and 2 letters worse in the MMG group (adjusted mean difference, 2 letters; 95% confidence interval, -0.5 to 5 letters; P = .10).

Conclusions: At 12 months after treatment, the MMG technique was less effective at reducing optical coherence tomography-measured retinal thickening than the more extensively evaluated current modified ETDRS laser photocoagulation approach. However, the visual acuity outcome with both approaches is not substantially different. Given these findings, a larger long-term trial of the MMG technique is not justified.

Application to clinical practice: Modified ETDRS focal photocoagulation should continue to be a standard approach for treating diabetic macular edema.

Trial registration: clinicaltrials.gov Identifier: NCT00071773.

Figure 1

Flow chart showing visit completion and reasons for study discontinuation in the two treatment groups.

Figure 2

Resolution of edema in the two treatment groups at 3.5, 8, and 12 months for OCT measurements: A. Central subfield thickening: only includes eyes with at least 275 microns of thickness at baseline; resolution defined as central subfield < 250 microns and at least a 50 micron decrease. B. Weighted inner zone thickness: only includes eyes with at least 300 microns of thickness at baseline; resolution defined as < 285 microns and at least a 50 micron decrease. C. Maximum retinal thickening in the central subfield, or any inner subfield: only includes eyes with at least 75 microns of thickening at baseline; resolution defined as < 50 microns of thickening and at least a 50 micron decrease from baseline. D. Retinal volume: only includes eyes with volume at least 7.82 mm³ (3 standard deviations greater than normal) at baseline; resolution defined as thickening within 2 standard deviations of normal in each subfield and volume decreased at least 0.5 mm³. N refers to the number of eyes with edema on the measure at baseline and with a gradable OCT at the visit. Dark bars are mETDRS group and lighter bars are MMG group. P-values obtained using repeated measures least squares regression models adjusting for baseline values and accounting for the correlated data from subjects with two study eyes.