The lowering of the intraocular pressure and the retinal venous pressure by cyclophotocoagulation

Purpose: To measure whether cyclophotocoagulation (CPC) can reduce not only intraocular pressure (IOP) but also retinal venous pressure (RVP) in glaucoma patients. Patients and methods: This retrospective study included 36 eyes of 23 patients with primary open angle glaucoma in whom RVP was measured before and after CPC. In 13 patients both eyes were included in the study and in 10 patients only one eye. Instruments: Applanation tonometry. Measurement of RVP: Slow inflation of a pad lateral to the cornea under observation of the retinal veins (IOPstim, IMEDOS Health GmbH, Jena, Germany). When a venous pulse appears, measurement of the IOP. CPC by IRIS Medical OcuLight SLx diode laser (Iridex Corporation, California, USA). Fifteen spots applied at the inferior 270 degrees. Results: Pressures are measured in mmHg (median (Q1; Q3); before surgery: IOP = 19.0 (18.0;21.5); RVP = 25.5(23.0;28.5) (p < 0.0001) (Wilcoxon test, N = 23: averaging of measured values for binocularity). At follow-up 14.3 (11.9;16.1) weeks later: IOP 14.0 (13.0;17.0); RVP = 17.7 (16.0;20.0) (p < 0.0001). The median IOP decreased by -5.0 (-7.5; -2.0), the median RVP by -7.8 (-11.0; -4.7) (P < 0.01). Both the IOP and the RVP were significantly smaller in the median. The correlation between the magnitude of the pressure-drop in RVP and IOP was low (R² = 0.21). Conclusion: Both IOP and RVP are significantly reduced by CPC, RVP is more reduced than IOP. Apart from the direct physical effect of IOP lowering on retinal vessels this behaviour may also be caused by a relaxation of the lamina cribrosa with less stress on passing structures like nerve fibers but also on blood vessels.