Two time point versus 4 time point data acquisition in aqueous humor flow rate determinations by fluorophotometry.

ABSTRACT

PURPOSE: To establish the validity of a fluorophotometric protocol based on 2 time points to facilitate aqueous humor flow rate calculations in minimally cooperative species. MATERIALS AND METHODS: A standard canine fluorophotometry protocol was followed in 6 dogs. Fluorescein concentrations were obtained at 4 time points 5, 6, 7, and 8 hours after topical application of 3 drops of 10% fluorescein. At the 5- and 8-hour time points, each animal was scanned 4 times. Fluorophotometric parameters were calculated using (1) the first 5-hour scan, the 6- and 7-hour scans, and the first 8-hour scan (ie, the "4 pt method"); and (2) using only the average of the 4 scans obtained at 5 hours and the average of the 4 scans obtained at 8 hours (ie, the "2 pt method"). Parameters calculated using each method were compared using paired t tests. RESULTS: There were no statistically significant differences between the 2 methods of parameter acquisition (P>0.05 for all parameters). CONCLUSIONS: When fluorophotometric aqueous humor flow rate calculations are needed in species for which acquisition of fluorescein concentrations at >2 time points is difficult, using data obtained at 2 widely spaced points provides reasonably accurate estimates of flow rate provided multiple scans are performed at each of those 2 time points.