"Light" versus "classic" laser treatment for clinically significant diabetic macular oedema

Abstract

Aim: To compare the effectiveness of "light" versus "classic" laser photocoagulation in diabetic patients with clinically significant macular oedema (CSMO).

Methods: A prospective randomised pilot clinical trial in which 29 eyes of 24 diabetic patients with mild to moderate non-proliferative diabetic retinopathy (NPDR) and CSMO were randomised to either "classic" or "light" Nd:YAG 532 nm (frequency doubled) green laser. "Light" laser treatment differed from conventional ("classic") photocoagulation in that the energy employed was the lowest capable to produce barely visible burns at the level of the retinal pigment epithelium. Primary outcome measure was the change in foveal retinal thickness as measured by optical coherence tomography (OCT); secondary outcomes were the reduction/elimination of macular oedema on contact lens biomicroscopy and fluorescein angiography, change in visual acuity, contrast sensitivity, and mean deviation in the central 10 degrees visual field. Examiners were masked to patients' treatment.

Results: 14 eyes were assigned to "classic" and 15 were assigned to "light" laser treatment. At 12 months, seven (50%) of 14 eyes treated with "classic" and six (43%) of 14 eyes treated with "light" laser had a decrease of foveal retinal thickness on OCT (p = 0.79). A comparison of reduction/elimination of oedema, visual improvement, visual loss, change in contrast sensitivity, and mean deviation in the central 10 degrees showed no statistical difference between the groups at 12 months (p>0.05 for all groups).

Conclusions: This study suggests that "light" photocoagulation for CSMO may be as effective as "classic" laser treatment, thus supporting the rationale for a larger equivalence trial.

Figure 1

Case report, right eye. Clinically significant macular oedema before and after “classic” laser treatment. (A) Fundus photograph. (B) Fluorescein angiography shows late leakage surrounding the fovea. (C) OCT retina thickness map shows severe diffuse macular thickening. (D) Red-free photograph immediately after “classic” laser treatment demonstrates multiple, ETDRS level grey-white burns applied to the areas of fluorescein leakage. (E) Fundus photograph 1 year after treatment shows multiple laser scars associated with several areas of hyperpigmentation. (F) Late phase fluorescein angiogram obtained 1 year after treatment demonstrates only minimal residual leakage temporal to the fovea. (G) OCT retina thickness map at 1 year shows a significant decrease in foveal thickening with minimal residual thickening temporal to the fovea. (H) “Total deviation” display of the central 10° visual field before (left) and 1 year after laser treatment (right). A mean deviation (MD) decrease from −5.4 dB to −3.45 dB and six scotomata (focal losses greater than 5 dB, indicated by circles) mostly located on the nasal hemifield can be observed at 1 year.

Figure 2

Case report, left eye. Clinically significant macular oedema before and after “light” laser treatment. (A) Fundus photograph. (B) Fluorescein angiography reveals areas of focal and diffuse leakage. (C) OCT retina map demonstrates severe diffuse macular thickening. The topographic pattern of retinal thickening was very similar to the other eye. (D) Immediate post-“light” laser treatment photograph demonstrates barely visible laser lesions. (E) and (F) Fundus photograph and late phase fluorescein angiogram obtained 1 year after treatment show very faint laser scar and significant reduction in fluorescein leakage. (G) 1 year after “light” laser treatment the oedema is almost completely resolved in the central fovea and residual thickening temporal to the fovea is present. (H) “Total deviation” display of the central 10° visual field before (left) and 1 year after laser treatment (right). A mean deviation (MD) decrease from −5.9 dB to −3.6 dB and two scotomata (focal losses greater than 5 dB, indicated by circles) both located on the nasal hemifield can be seen at 1 year.