[Effect of panretinal photocoagulation on the ocular pulse curve]

Most studies on the effects of panretinal photocoagulation (PRPC) on ocular circulation are concerned with retinal circulation. In the present study, we examined the ocular pulse curve after PRPC and determined pulsatile ocular blood flow (an indicator of choroidal circulation) and ocular perfusion pressure.

In 10 patients with diabetes mellitus (8 with type II and 2 with type I; mean age 64 yrs) and severe, hitherto untreated, bilateral proliferative diabetic retinopathy, an intensive unilateral PRPC with 1500 argon laser burns (spot size: 500 mu) was performed in 2 sessions (interval: 3 wks). Before and-in 3-wk intervals-up to 9 wks after onset of treatment, an ocular pulse curve was recorded using oculo-oscillo-dynamography, and the following variables were determined: ocular pulsation amplitude (OPA), pulsatile ocular blood flow (POBF), systolic ophthalmic artery pressure (SOAP), and systolic ocular perfusion pressure (SOPP).

PRPC led to a reduction of OPA and POBF in relation to the untreated contralateral eyes. 3 wks after the 1st coagulation, the reduction averaged 20% (OPA) and 19.1% (POBF). The maximum reduction was found 9 wks after onset of treatment (6 wks after the 2nd coagulation) and amounted to 29.9% and 29.2%, respectively. The differences between photocoagulated and untreated eyes were highly significant on average (P < 0.01; ANOVA) as well as for the time course (P < 0.001). SOAP and SOPP were not changed significantly during PRPC.

OPA and POBF are determined by the cardiac cycle-related intraocular volume changes depending predominantly on choroidal blood flow. Thus, the reduction of POBF after PRPC is indicative of a lowered pulsatile choroidal blood flow. The morphological substrate is probably the choriocapillaries closure after photocoagulation described in the literature.