Retinal Blood Flow and Perfusion Pressure Analysis in Patients With Clinically Significant Macular Edema Treated With Focal Argon Laser Therapy

Abstract

Purpose: : Clinically significant macular edema (CSME) is the leading cause of visual loss in patients with non-proliferative diabetic retinopathy. The EDTRS studies demonstrated the benefit of focal argon laser treatment with a 50% reduction in moderate visual loss of treated eyes. The purpose of this study was to investigate the effects of argon laser treatment on ocular perfusion pressures and retinal blood flow in patients with diabetic macular edema. This may help to elucidate the mechanism by which focal laser treatment reduces macular edema.

Methods: : We performed a preliminary prospective study on patients with clinical and angiographic evidence of CSME. These patients were subsequently treated with focal argon laser therapy. Retinal blood flow was measured using Heidelberg retinal flowmetry at baseline, 1 and 6 weeks post laser treatment. Ocular (2/3 MAP - intraocular pressure) and diastolic (diastolic blood pressure-intraocular pressure) perfusion pressures were also assessed at baseline, 1 and 6 weeks after laser treatment.

Results: : We report preliminary results on 3 patients (mean age 57, all male) who have completed all study visits. Blood flow assessment revealed that all 3 patients had a decrease in the percent of zero blood flow pixels in the supratemporal quadrant of the retina one week after treatment. Retinal blood flow values returned to baseline after 6 weeks. The ocular and diastolic perfusion pressures in the study eye were concurrently decreased in 2 patients one week post laser treatment. One patient experienced an increase in the ocular perfusion pressure one week after treatment. Ocular perfusion pressure and diastolic perfusion pressures returned to baseline values in 2 patients after 6 weeks. One patient experienced a further decline in diastolic perfusion pressure 6 weeks post argon laser treatment.

Conclusions: : In this pilot study, ocular and diastolic perfusion pressures demonstrated a trend of transient reduction one week after macular laser treatment with values returning to baseline levels at 6 weeks duration. Retinal blood flow and ocular perfusion pressures appear to respond in a parallel fashion following treatment. Ocular blood flow changes may be related to the mechanism by which argon laser treatment reduces capillary leakage. However, it may also reflect a response to localized retinal injury and subsequent compensatory alterations in the studied blood flow parameters.

Keywords: diabetic retinopathy • laser • blood supply