Retinal Vasoactive Effects Resulting From the Use of Topical Mydriatic Agents

Abstract

Purpose: : To compare the vascular reactivity responses of the superior-temporal, and inferior-temporal, arterioles using 3 different mydriatic agents: 1% tropicamide (T); a combination of 0.8% tropicamide and 5% phenylephrine (TP); and 1% cyclopentolate (C).

Methods: : One randomly selected eye of each of 10 healthy volunteers (age 22.0±3.1, 6 females) was prospectively enrolled. Volunteers were examined at three visits. At visit 1, pupils were dilated using 1% tropicamide (T), at visit 2 using a combination of 0.8% tropicamide and 5% phenylephrine (TP) and at visit 3 using 1% cyclopentolate (C). At each visit, volunteers were connected to a sequential gas delivery circuit and an automated gas sequencer (RespirAct^TM, Thornhill Research Inc., Toronto, Canada) and underwent a gas provocation protocol consisting of 2 phases. Baseline was achieved with gas flow adjusted to provide a PETCO₂ of 38mmHg. Hyperoxia was achieved at a PETO₂ of 500mmHg with PETCO₂ clamped at 38mmHg. Four flow measurements were acquired of the superior temporal (STA) and of the inferior temporal arterioles (ITA), using the Canon Laser Blood Flowmeter (CLBF-100, Canon, Japan), at equivalent positions during each phase. Repeated measures ANOVA using JMP software (v. 8.0, SAS Inc., Cary, NC) was performed.

Results: : The vascular reactivity in terms of the diameter, velocity and flow response was the same when comparing the STA and ITA using T, TP or C. The vascular reactivity responses of STA diameter (p=0.8; T=13.7µm ± 3.5, TP=12.2 ± 6.7, C=12.3 ± 5.6) and ITA diameter (p=0.5; T=15.0µm ± 9.6, TP=11.1 ± 7.4, C=11.7 ± 4.6) were the same for the three mydriatic agents (i.e. across the 3 visits). The vascular reactivity responses of STA velocity (p=0.9; T=9.8mm/sec ± 4.7, TP=9.9 ± 6.3, C=9.9 ± 4.7) and ITA velocity (p=0.7; T=10.3mm/sec ± 5.3, TP=10.3 ± 3.0, C=8.8 ± 4.4) were also the same for the three mydriatic agents. The vascular reactivity responses of STA flow (p=0.9; T=4.4 ± 1.6µL/min, TP=4.2 ± 1.7, C=4.3 ± 1.2) and ITA flow (p=0.3; T=6.1µL/min ± 3.8, TP=4.6 ± 1.2, C=4.7 ± 0.8) were the same for the three mydriatic agents.

Conclusions: : The three mydriatic agents investigated in this study do not affect the retinal vascular reactivity response of the major arterioles to hyperoxia.

Keywords: blood supply • metabolism • retina