Subthreshold Macular Laser Treatment

Abstract

The conventional continous wave (CW) laser photocoagulation, applied either as focal or grid pattern, using green argon laser (514 nm) was shown by the Early Treatment Diabetic Retinopathy Study (ETDRS) to reduce the risk of moderate vision loss (3 lines or more on the ETDRS chart) by 50% and has been the standard of care for DME (diabetic macular edema) since the mid-80s¹. Although the ETDRS demonstrated that focal/grid photocoagulation improves visual outcome in DME, it should be emphasized that the benefit was in reducing the frequency of visual loss and not in improving visual acuity. More than 3 lines (> 15 letters) of improvement in 3 years has been reported to be only 3% by the ETDRS report². Moreover, conventional laser treatment may be associated with significant destruction of retinal tissue, and heat conduction to the nerve fiber layer and photoreceptors may result in the irreparable thermal destruction. This may cause side effects such as loss of macular sensitivity on microperimetry, progressive enlargement of laser scars towards the fovea, choroidal neovascularisation, epi-submacular fibrosis, iatrogenic foveal coagulation, increased macular edema and central visual acuity loss^3-6. With anti-VEGF therapy while untoward effects of laser were overcome, it has also been shown to stabilize and increase vision in a significant proportion of patients^7,8. Nevertheless macular laser is still a choice of therapy because of the following reasons: