Update and critical appraisal of combined timolol and carbonic anhydrase inhibitors and the effect on ocular blood flow in glaucoma patients

Comparison of intraocular pressure, blood pressure, ocular perfusion pressure and blood flow fluctuations during dorzolamide versus timolol add-on therapy in prostaglandin analogue treated glaucoma subjects

Objective: To compare the effects of dorzolamide and timolol add-on therapy in open-angle glaucoma (OAG) patients previously treated with prostaglandin analogue (Pg), by evaluating fluctuations in the intraocular (IOP), blood (BP), ocular perfusion pressures (OPP) and retrobulbar blood flow (RBF) parameters. Methods: 35 OAG patients (35 eyes), 31 women (88.6%) age 63.3 (8.9) years were evaluated in a 3 month randomized, cross-over, single-masked study. During the experiments BP, heart rate, IOP and OPP were assessed 4 times per day (8–12–16–20 h). RBF was measured twice per day (8–20 h) using Color Doppler imaging in the ophthalmic (OA), central retinal (CRA), nasal (nSPCA) and temporal (tSPCA) posterior ciliary arteries. In each vessel, peak systolic velocity (PSV) and end-diastolic velocity (EDV) were assessed and vascular resistance (RI) calculated. Results: Both add-on therapies lowered IOP in a statistically significant manner from 15.7 ± 2.4 mmHg at latanoprost baseline to 14.9 ± 2.2 mmHg using dorzolamide (p < 0.001) and 14.2 ± 1.9 mmHg using timolol (p < 0.001). The IOP lowering effect was statistically significant at 20 h, favoring timolol as compared to dorzolamide (1.4 ± 2.4 vs. 0.2 ± 2.1 mmHg), (p < 0.05). Dorzolamide add-on therapy showed smaller IOP (2.0 ± 1.4), SPP (13.3 ± 7.9), systolic BP (13.5 ± 8.7) and diastolic BP (8.4 ± 5.4) fluctuations as compared to both latanoprost baseline or timolol add-on therapies. Higher difference between morning and evening BP was correlated to decreased evening CRA EDV in the timolol group (c = −0.41; p = 0.01). With increased MAP in the morning or evening hours, we found increased evening OA RI in timolol add-on group (c = 0.400, p = 0.02; c = 0.513, p = 0.002 accordingly). Higher MAP fluctuations were related to impaired RBF parameters during evening hours-decreased CRA EDV (c = −0.408; p = 0.01), increased CRA RI (c = 0.576; p < 0.001) and tSPCA RI (c = 0.356; p = 0.04) in the dorzolamide group and increased nSPCA RI (c = 0.351; p = 0.04) in the timolol add-on group. OPP fluctuations correlated with increased nSPCA RI (c = 0.453; p = 0.006) in the timolol group. OPP fluctuations were not related to IOP fluctuations in both add-on therapies (p < 0.05). Conclusions: Both dorzolamide and timolol add-on therapies lowered IOP in a statistically significant fashion dorzolamide add-on therapy showed lower fluctuations in IOP, SPP and BP. Higher variability of daytime OPP led to impaired RBF parameters in the evening.