Abstract
Background: In our ophthalmology outpatient department, routinely to observe the posterior segment of the eye and the fundus of the eye, we use various mydriatics such as atropine, cyclopentolate, and tropicamide for various indications. As there are a lot of mydriatics clinically used, taking much time for dilation, any add-on drug can be used for dilatation of pupils helping the underlying drugs for a better outcome. This study provides information regarding the effect of topical administration of gentamicin on horizontal pupillary diameter (HPD) over and above use of other mydriatics in rabbit’s eye. There are no similar studies in the past.

Aims and Objectives: The aim of this study was to evaluate the effect of gentamicin on the HPD of rabbit’s eye.

Materials and Methods: After taking the Institutional Ethics Committee clearance, 48 rabbits were taken into this study and were divided into 2 groups of 24 rabbits each. HPD was measured in both eyes before starting the experiment. Gentamicin eye drops were instilled in the right eye (test) and normal saline in the left eye (control) in both groups of 24 each. HPD was measured in both eyes after 30 min of instilling drops, and readings were noted. Thereafter, homatropine hydrobromide was instilled in both eyes in the first group (24 rabbits), and phenylephrine hydrochloride in the second group (24 rabbits). HPD in both eyes was measured every 5 min for 30 min.

Results: After 30 min of instilling gentamicin eye drops in the test eye, there was no change in HPD; however, after instilling a mydriatic agent (homatropine or phenylephrine), there was an early onset of mydriasis as well as marked mydriasis in test eye compared to control eye in both groups. Hence, the differences in HPD between both eyes (test and control eye) were statistically not significant (P = 0.083).

Conclusion: Topical application of gentamicin does not have a mydriatic effect, but it potentiates the mydriatic effect of homatropine and phenylephrine in rabbit’s eye.

Key words: Gentamicin; Homatropine; Phenylephrine; Pupillary Diameter; Rabbit’s Eye