Effect of Topical Latanoprost–Timolol Combined Therapy on Retinal Blood Flow and Circulation of Optic Nerve Head Tissue in Cynomolgus Monkeys

Abstract

Purpose: To evaluate the effects of topical latanoprost and timolol in combined therapy on retinal blood flow and tissue circulation in the optic nerve head (ONH) of the cynomolgus monkey. Methods: Latanoprost (30 μL, 0.005%) was instilled once daily and timolol (30 μL, 0.5%) twice daily for 6 days into 1 eye, and physiological saline into the other eye to serve as control. Blood velocity through retinal veins was determined using Kowa Laser Speckle Blood Flow Meter. The ONH tissue blood velocity (NB ONH) was determined using the Laser Speckle Tissue Circulation Analyzer. Retinal blood flow and NB ONH determinations were carried out before the first instillation and 4 hours after the first instillation on the 2nd experimental day, and the last instillation at the same sites at the same time of day. The intraocular pressure (IOP) was also measured periodically. Results: After the first instillation, on the 2nd experimental day, the retinal blood flow decreased compared with the baseline, but 6-day instillation caused no significant change from the baseline. Six-day instillation increased the NB ONH in the treated eyes by 10% from the baseline and by 7% from that in the fellow control eye. After 6-day instillation, the IOP was lowered by 7.8±2.7 mm Hg and 3.6±4.3 mm Hg in the treated and control eyes, respectively. Conclusions: Combined 6-day instillation of latanoprost once daily and timolol twice daily has no significant effect on the retinal blood flow, but significantly increases the ONH tissue blood velocity in monkey eyes. Jpn J Opthalmol 2000;44:227–234