Photocoagulation uses light to create a thermal burn in retinal tissue. When energy from a strong light source is absorbed by the retinal pigment epithelium (RPE) and is converted into thermal energy, coagulation necrosis occurs with denaturation of cellular proteins as temperature rises above 65°C.
Since the Diabetic Retinopathy Study (DRS), the source of light for photocoagulation has evolved from using a diffuse Xenon arc to using well-focused laser in the treatment of proliferative diabetic retinopathy. Presently, laser retinal photocoagulation is a therapeutic option in many retinal and eye conditions.
Effective retinal photocoagulation requires an unobscured view of the retinal tissue for light to be absorbed by pigment in the target tissue. In retinal tissue, light is absorbed by melanin, xanthophyll or hemoglobin. Melanin absorbs green, yellow, red and infrared wavelengths; xanthophyll (in the macula) absorbs blue but minimally absorbs yellow or red wavelengths; hemoglobin absorbs blue, green and yellow with minimal red wavelength absorption.
Indications for retinal photocoagulation include the following:
Panretinal photocoagulation (PRP) for neovascular proliferative diseases such as proliferative diabetic retinopathy, sickle cell retinopathy, and venous occlusive diseases (see image below)
Panretinal photocoagulation in venous occlusive eye diseases. Image courtesy of National Eye Institute, National Institutes of Health.
Focal or grid photocoagulation for macular edema from diabetes or branch vein occlusion (see image below)
Focal or grid photocoagulation in macular edema from diabetes or branch vein occlusion. Image courtesy of National Eye Institute, National Institutes of Health.
Treatment of threshold and high-risk prethreshold retinopathy of prematurity
Closure of retinal microvascular abnormalities such as microaneurysms, telangiectasia and perivascular leakage
Focal ablation of extrafoveal choroidal neovascular membrane
Creation of chorioretinal adhesions surrounding retinal breaks and detached areas
Focal treatment of pigment abnormalities such as leakage from central serous chorioretinopathy
Treatment of ocular tumors
Treatment of the ciliary body to decrease aqueous production for glaucoma