Fluorophotometry in contact lens research : The next step

Fluorophotometry can be used to quantify changes in epithelial permeability (Pdc), corneal pH, and tear exchange (T95; time to deplete 95% of a fluorescent dye from beneath a contact lens) associated with contact lens wear. Using fluorometric procedures, we present previously reported data in order to review the effects of contact lens wear on Pdc and pH. We also introduce a new method for measuring tear exchange beneath a soft contact lens and present preliminary data. Pdc was assessed on 32 subjects after 1 h of closed-eye soft contact lens wear. Stromal pH was assessed on 21 subjects wearing lenses with a range of different oxygen transmissibilities (Dk/L). T95 was assessed on 7 subjects who wore disposable lenses. Pdc estimates were derived by measuring the rate at which topically applied fluorescein crossed the epithelial barrier from the tears; corneal pH was quantified by alternately exciting a fluorescein-loaded cornea with two wavelengths of blue light and calculating the fluorescence intensity ratio (490/450 nm), which is pH-sensitive; and the T95 was estimated by applying 2 microliters of FITC-Dextran to the posterior surface of a soft contact lens and the monitoring the exponential decay of dye under the lens. On average, 1 h of closed-eye contact lens wear caused a 41% increase in Pdc compared to the control eye. Corneal pH varied directly with a decrease in Dk/L. On average the T95 under contact lenses (mean = 29 min) was slow compared to normal rates with no lens (approximately 5 min). Fluorophotometry can be used to quantify some interesting effects associated with contact lens wear, and the use of these techniques may provide new information about the impact of contact lens wear on corneal structure and function.