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V. C. Fan, C. V. Koonapareddy, D. Chen, T. T. Du, P. A. Asbell; Simplified Technique of Fluorophotometry for Corneal Permeability Evaluation in Humans. Invest. Ophthalmol. Vis. Sci. 2007;48(13):803.
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Fluorophotometry was first used 1963 to study permeability in animal studies. In 1997, McNamara et al. measured corneal epithelial permeability using two in vivo methods - a single drop fluorescein to quantify the coefficient of corneal permeability and the eye bath method. The first method demonstrated substantial variability between measurements. The second method had several clinical limitations. In lieu given past difficulties, we have modified the Fluorophotometry technique to develop a simple non-invasive method to measure corneal permeability and present our repeatability findings.
After obtaining IRB approval, we varied all elements of the technique (fluorescein concentration, fluorescein concentration, time to irrigation, timing of scans, etc.) to determine the simplest, most repeatable technique. .Fourteen healthy adult, right eyes were scanned with the Fluorotron Master (Ocumetrics Inc, Mountain View, CA). On the first day, two baseline fluorometric scans of the right eye were taken using the Fluorotron Master. 15 µL 2.0% fluorescein was then instilled using a calibrated pipette in the lower conjunctival sac. After thirty seconds, topical 0.5% proparacaine ophthalmic solution was given followed by 10 ml rinse using a balanced saline washout. Two immediate washout Fluorophotometry scans were taken. Fifteen minutes after the instillation of fluorescein, two more fluorphotometry scans were taken. Peak corneal florescence values (PCFV) was measured by fluorophotometry, which is an indicator of corneal epithelial permeability.
The baseline mean corneal readings in 14 eyes of patients was 16.24 (SD=3.12) on day 1, compared to 16.93 (SD=3.93) on day 2 in healthy volunteers. The immediate post-rinse mean corneal reading was 312.02 (SD=390.52) on day 1, compared to 388.63 (SD=557.88) on day 2. The 15 minute post-rinse mean corneal readings was 102.15 (SD=97.30) on day 1, compared to 107.24 (SD=122.94) on day 2. Using a paired, 2-sided t-test, the differences were determined not to be statistically significant (P-value > 0.05).
Utilizing a new, simplified technique, results were found repeatable to measure fluorescein penetration into the cornea. Further research with a larger sample size and increased number of clinical visits will help us validate the repeatability of our results and technique. A simplified technique to measure corneal permeability will prove useful to quantifying ocular surface disease such as dry eyes and follow changes in new treatments and provide an objective metric for end points in clinical trials.
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