Does glaucoma medication influence the diameter of the retinal arteriole in the human eye? (A pilot study using the...

To investigate the potential in vivo influence of different topical glaucoma medications on the diameter of the retinal arterioles of healthy volunteers and glaucoma patients.

The diameter of one pre-selected retinal arteriole per eye was measured using the Retinal Vessel Analyser (RVA), an instrument developed for non-invasive clinical measurement of the diameter of the main retinal vessels. The instrument contains a video system, and the integrated software recognises the boundaries of the retinal vessels by detecting their light-transmission profile. The vessel diameter (in arbitrary units) is plotted against time (seconds) on a separate display screen. In Study I the vessel diameter was measured in 12 eyes of six healthy volunteers (age 21-26 years, mean age 24.0 years) on six occasions each separated by 14 days. In a double-masked fashion, each subject's right eye was treated with one of 5 glaucoma medications (brinzolamide 1%, timolol 0.5%, betaxolol 0.5%, brimonidine 0.2% or latanoprost 0.005%) and the left eye always received balanced salt solution. In Study II, one randomly selected eye of 16 patients (age 50-79 years, mean age 65.2 years) suffering from primary open-angle glaucoma controlled with topical monotherapy was investigated, in an unmasked fashion. Four patients were on betaxolol 0.5% treatment, six subjects were receiving non-selective topical beta receptor blockers and six subjects were being treated with once daily latanoprost 0.005%.

The coefficient of variation for the arteriole diameter in the healthy volunteers was less than 12% in each case. No significant post-treatment change of the diameter of the pre-selected arteriole was found for any topical medication investigated, either in the healthy volunteers (Study I) or in the patients suffering from glaucoma (Study II) (p>0.05, paired t-test). In addition, in Study I no difference was observed in the alteration of the arteriole diameter between the baseline and the hour 2 measurements when the values from the drug-treated and placebo treated eyes were compared (p>0.05, two-way ANOVA).

In the present investigations it was not possible to detect any statistically meaningful change of the arteriole diameter at two hours after the instillation of any of several topical antiglaucoma drugs widely used in clinical practice. Further investigations are necessary to clarify whether the lack of observed change is due to the lack of retinal vascular effects of the drugs investigated, or is due to an inability of the RVA instrument in practice to detect alterations between time-points separated by several hours.