Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study

Background-Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (R PE) and avoids damage to the neural retina. The initial results in this pro spective pilot study on various macular diseases are presented. Methods-12 patients with diabetic maculopathy (group I), 10 with soft druse n (group II), and four with central serous retinopathy (CSR) (group III) we re treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 mu s) of a green Nd:YLF laser (param eters; 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 mu m, energies: 70-100 mu J). Laser energy was based on the visibility of t est lesions on fluorescein angiography (50-130 mu J). Patients were examine d at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging. Results-After 6 months hard exudates disappeared in six out of nine patient s in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stabl e in all cases. None of the laser lesions was clinically visible immediatel y. After 1 day most lesions were visible as yellowish RPE depigmentation. A fter 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first wee k. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas. Conclusion-This study showed that subthreshold (RPE) photocoagulation is ef fective in some cases of diabetic maculopathy, drusens, and in CSR, Visibil ity of laser burns is not always necessary in the treatment of macular dise ases presented here, Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.