Retrobulbar Blood Flow and Intraocular Pressure Analysis in Macular Edema Patients Treated With Focal Argon Laser Therapy

Abstract

Purpose: : There are several hypothetical mechanisms which explain how macular focal argon laser treatment reduces macular edema in diabetes. The purpose of this study was to investigate whether argon laser treatment influences intraocular pressure and the retrobulbar blood flow to the retina in patients with clinically significant diabetic macular edema.

Methods: : We performed a prospective pilot study on patients with clinically significant macular edema treated with focal argon laser therapy. Intraocular pressure and retrobulbar blood flow were measured using Goldmann applanation tonometry and Color Doppler Imaging before and 1 and 6 weeks after macular focal argon laser treatment. Blood pressure and visual acuity were also measured at baseline, 1 and 6 weeks after laser treatment. We report our preliminary results on 3 patients who have completed all study visits.

Results: : There was no consistent pattern of variation in intraocular pressure, blood pressure or visual acuity after focal laser treatment. However, retrobulbar blood flow changed in all patients seen as a decrease in the vascular Resistive Index (RI) of the ophthalmic artery (OA) one week after laser treatment. In 2 patients, the OA RI returned to the baseline levels 6 weeks after laser treatment. In the third patient, the RI continued to decline 6 weeks after treatment. Additionally, the RI of the central retinal artery (CRA) increased in 2 of the study eyes after 1 week, returning to near baseline levels after 6 weeks. The third patient had a decrease in the CRA RI after 1 week which remained stable after 6 weeks. The peak systolic and end diastolic velocities of the OA and CRA exhibited a more variable pattern following treatment. Temporal and nasal short posterior ciliary artery blood flow did not change in a consistent pattern following treatment.

Conclusions: : In this pilot study, macular focal argon laser treatment produced an acute decrease in vascular resistance in the ophthalmic artery 1 week after therapy. Intraocular pressure did not exhibit a similar change following argon laser treatment. The decrease in retrobulbar vascular resistance following argon laser treatment may be associated with localized thermal injury of retinal tissue independent of intraocular pressure.

Keywords: blood supply • edema • diabetes