A New Corneal Epithelium Dehydration Rate Measurement Technique

Abstract

Purpose: : To develop a safe, non-invasive, non-contact, continuous in vivo method to measure the corneal epithelium dehydration rate caused by surface evaporation and to compare the effectiveness of a viscoelastic (CP, Cornea Protect®, Croma GmbH) at preventing corneal dehydration to that of BSS+ (BSS Plus®, Alcon Inc).

Methods: : Experiments were carried out on 10 (Age < 6 months, Weight ~ 2Kg) New Zeeland White rabbits were used. Rabbits were anesthetized by intramuscular injection; the OS was covered with a patch to prevent dehydration and the animal was immediately positioned under the operation microscope (OPMI) with the OD facing upward. A lid speculum was inserted without touching the cornea. Half the rabbits received CP in the OD and BSS+ in the OS and vice versa for the other half. Both eyes were monitored through the OPMI for 20 minutes, and a video recording and digital timer controlling a camera were triggered to produce a DVD as well as high resolution digital images (14 MPixels, 2:3) every 5 seconds. The OPMI magnification was set at 7x and sharply focused on the cornea by the surgeon who decided when it was necessary to apply either CP or BSS+. Specialized LabVIEW software was designed to analyze the reflection of the co-axial illumination of the OPMI. The software tracked and characterized the shape of the corneal reflection which became distorted as the surface of the epithelium dehydrated; characterization was accomplished by fitting an ellipse to the reflection.

Results: : The ellipse axis ratio was found to decrease initially after each application of either CP or BSS+, and then to increase linearly as the epithelium began to dehydrate (p < 0.001) for eyes treated with BSS+ only. Eyes treated with BSS+ required 7-8 applications to maintain sufficient corneal hydration during the 20 minute test period, while those treated with CP required 1-2 applications. The rate of dehydration differed significantly (p < 0.043) between CP and BSS+.

Conclusions: : The shape of the corneal reflection is strongly correlated with the hydration state of the epithelium. Corneas treated with CP remain hydrated significantly longer than corneas treated with BSS+.

Keywords: imaging/image analysis: non-clinical • cornea: tears/tear film/dry eye • cornea: basic science