Effect of tropicamide on ocular blood flow in the rabbit

Does pupil dilation influence subfoveal choroidal laser Doppler flowmetry?

PURPOSE

The aim of this study was to assess (i) whether pupil dilation with tropicamide influences subfoveal choroidal blood flow, as assessed by continuous laser Doppler flowmetry (LDF) and (ii) if this is the case, whether the effect is due to a haemodynamic response of the drug-induced dilation.

METHODS

Following the instillation of one drop of 1% tropicamide in one eye of 18 healthy, nonsmoking volunteers (age 20-25 years), the subfoveal choroidal LDF parameters (Vel, Vol and ChBF) were recorded during 30 min, at 3-min intervals under two paradigms: through an artificial pupil (4 mm diameter) placed in front of the cornea (P1) and without this artificial pupil (P2).

RESULTS

Tropicamide increased the pupil diameter from 3.3 ± 0.4 mm (mean ± SD) to 8.3 ± .4 mm. Full dilation was reached at ~24 min. During this period of time, linear regression analysis demonstrated that none of the LDF parameters varied significantly (p > 0.05), either under P1 or P2. Based on a group of 12 subjects, the smallest (%) change in the mean value of ChBF (ChBFm ) that would be detectable (sensitivity of the method, S) was found to be 2% for P1 and 6% for P2. The average coefficient of variation of ChBFm based on eight measurements during dilation was greater for P2 than for P1 by a factor of approximately 2.

CONCLUSION

Tropicamide had no significant influence on the subfoveal choroidal LDF parameters measured by continuous LDF during pupil dilation. Furthermore, pupil dilation did not affect ChBFm by more than the calculated minimum percentage change of 6% detectable with our method.

The effect of acetazolamide on different ocular vascular beds

PURPOSE

To assess the effect of acetazolamide (AZ) on different ocular vascular beds.

METHODS

In a prospective study, 32 healthy volunteers (16 male, 16 female) with a mean age of 23.9 ± 3.3 years (20-39 years) were included. Before and after intravenous administration of 1,000 mg AZ (single dose), ocular microcirculation parameters were measured every 20 min for 2 h. Retinal vessel diameters (VD) were measured by the retina vessel analyzer, blood flow (BF) in the neuroretinal rim by the laser doppler flowmeter according to Riva, and the parapapillary retinal BF by the scanning laser Doppler flowmeter. Additionally, the Langham ocular blood flow system was used to determine the ocular pulse amplitude (OPA) and the pulsatile ocular blood flow (pOBF). The measurements were correlated with systemic blood pressure (BP), ocular perfusion pressure (OPP), capillary base excess parameters and serum AZ levels.

RESULTS

Arterial and venous VD were significantly increased by about 4-5% each. Papillary BF increased significantly about 40%. Parapapillary retinal flow dropped significantly about 19% (120 min). OPA and pOBF showed no statistically significant changes. BP showed no significant changes, and OPP was significantly increased. There were no correlations with pH or systemic perfusion parameters.

CONCLUSIONS

AZ leads to a dilatation of retinal VD, to an increase of BF in the optic nerve head, and to a decrease of parapapillary retinal BF. The different BF changes in different vascular beds might be due to different regulatory mechanisms, steal effects, or different distributions of the carbonic anhydrase.

Effects of adrenergic and cholinergic antagonists on diameter of nasolacrimal drainage system

BACKGROUND

To determine the effect of an adrenergic and a cholinergic antagonist on the diameter of the lumen of the nasolacrimal drainage system.

METHODS

The asymptomatic side of 38 patients (29 women, nine men) with unilateral stenosis/obstruction of the nasolacrimal drainage system was studied. The tear meniscus height (TMH) of the asymptomatic side was normal, and the lacrimal drainage system was patent as revealed by dacryocystography. The nasolacrimal drainage system of the asymptomatic side was infused with 100 mul of 0.01% bunazosin hydrochloride, a selective alpha-1 adrenergic antagonist, or 100 mul of 0.4% tropicamide, a muscarinic and cholinergic antagonist. Dacryocystography was performed to determine the diameter of the lumen of the nasolacrimal drainage system before and after the antagonists.

RESULTS

Bunazosin reduced the diameter of the lumen significantly, and the changes were more marked in the nasolacrimal duct (NLD), especially the middle and the lower regions. The diameter of the lumen of the lacrimal sac was not changed significantly. In contrast, tropicamide did not cause any significant change in the diameter of the lumen of the nasolacrimal drainage system.

CONCLUSIONS

The alterations of the size of the lumen of the nasolacrimal drainage system, especially the NLD, by an adrenergic antagonist suggest that the lumen diameter is under continuous sympathetic tone, and the parasympathetic tone is weak.

Does topical phenylephrine, tropicamide, or proparacaine affect macular blood flow?

The acute effect of topical phenylephrine HCl 10%, tropicamide 1% and proparacaine HCl 0.5% on macular capillary blood flow was studied in six healthy human volunteers using the blue field simulation technique. This technique provides a method for quantifying the velocity of leukocytes flowing in one's own retinal macular capillaries. Patients adjusted the velocity of computer simulated leukocytes moving on a CRT screen to match that of their own entoptically perceived leukocytes before instillation of each of the tested preparations and for 35 minutes immediately thereafter A 5% NaCl solution was used as a control. We found no significant difference in leukocyte velocity between the control drop and any of the tested drugs. With the six subjects tested, the calculated average minimum percentage change in leukocyte velocity detectable with this technique (P less than 0.05, paired t-test) was 9%. None of the tested drugs affected macular leukocyte velocity, and presumably blood flow, by more than this amount.