Comparison of Three Outflow Facility Measurement Techniques in Healthy Subjects Treated With Prostaglandin Analogues

Abstract

 

Abstract:

 

To compare three different methods of estimating outflow facility, in the same subjects treated with prostagladin analogues and placebo. Thirty healthy adult subjects were studied in a double–masked, placebo–controlled, randomized, paired comparison, 4–session crossover study. Bimatoprost, latanoprost, travaprost or placebo was administered to the left eye once a day for 7 days, with a minimum washout period of 4 weeks between sessions. Tonographic outflow facilities were measured by Schiotz tonography and pneumotonography (4 minutes). The aqueous humor flow rate and fluorophotometric outflow facility were measured by fluorophotometry (Toris. Ophthalmology 1993;100:1297). Intraocular pressure (IOP) was measured by pneumatonometry. Each treatment group was randomly assigned as group A, B, C or D to avoid any potential bias in analyzing the measurement methods. Analysis of variance was used to detect differences amongst the groups. To test the relationship of IOP and outflow facility, we calculated the correlation coefficient between IOP and 1/C (1/outflow facility) (linear relationship in Goldmann equation). The mean baseline IOP was 16.6 ± 3.0 mmHg in the study eye. Mean IOP was different amongst the groups after treatment (p=0.03). Aqueous production rate amongst the groups were not different (p=0.70). All three methods of measuring outflow facilities yielded different values and the fluorophotometric technique had consistently higher outflow facilities than the other two (p<0.001). The correlation coefficients of 1/C and IOP were; Schiotz; 0.43 (p<0.001); Pneumatonography; 0.038 (p=0.78); Fluorophotometrry; 0.29 (p=0.029). The table summarizes the results (mean ± SD).

 

 

^{Three of the four treatments appear to lower IOP, but none has a significant effect on aqueous flow rate. Measured outflow facilities differ amongst the 3 techniques. Outflow facilities from Schiotz and fluorophotometric methods provide better correlation to the IOP than outflow facility from pneumotonography method.}

 

 

Keywords: clinical (human) or epidemiologic studies: systems/equipment/techniques • aqueous • outflow: trabecular meshwork