The Dry Eye Zone

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Abstract: BAK on healthy eyes

This is an interesting one.

Basically, you expose healthy eyes to BAC (BAK) for 12 weeks. They don't show any signs of dry eye (no information on whether they experienced symptoms). Density of their corneal Langerhans cells increases during treatment but goes back down after they're taken off.

Not sure what the implications are for either the dry eye crowd or the non dry eye crowd other than that people without dry eye who use a BAK-preserved Rx drop for short term probably don't have to worry about BAK. People with healthy eyes who have to take BAK for longer than 12 weeks (everyone with glaucoma that doesn't already have dry eye) on the other hand... and people with existing dry eye on the other hand...

Influence of benzalkonium chloride on langerhans cells in corneal epithelium and development of dry eye in healthy volunteers.
Curr Eye Res. 2010 Aug;35(8):762-9.
Zhivov A, Kraak R, Bergter H, Kundt G, Beck R, Guthoff RF.
Department of Ophthalmology, University of Rostock, Rostock, Germany. andyzhyvov@yahoo.com

PURPOSE: To investigate the influence of benzalkonium chloride (BAC) on corneal Langerhans cells (LCs) and on the development of dry eye.

METHODS: A randomized double-blind clinical trial was performed in 20 healthy volunteers. One eye of each subject was treated with a 0.01% BAC solution (and the fellow eye with a placebo solution) three times daily for 12 weeks. The distribution and density of LCs in the central and peripheral corneal epithelium were evaluated by in-vivo confocal laser-scanning microscopy (CLSM). The subjects were monitored for dry eye (subjective discomfort, slit-lamp biomicroscopy, tear film break-up time, Schirmer's test).

RESULTS: In the BAC group, compared with placebo, a marked increase in LC density was found in the central cornea at Week 6 and in the central and peripheral cornea at Week 12. LC density then decreased again in both zones after the end of treatment, falling toward (or even below) baseline levels. Significant changes in the LC count relative to baseline were found at Week 12 in the central and peripheral cornea in the BAC group as well as in the peripheral cornea in the placebo group. LC density in the BAC group increased more rapidly in the central than in the peripheral cornea. During therapy the BAC group showed no signs of dry eye.

CONCLUSION: 12-week application of a 0.01% BAC solution in healthy volunteers induces a significant increase in LCs in the central cornea at Week 12 without dry-eye changes. The return of LC counts toward (or even below) baseline levels just four weeks after the end of BAC administration demonstrates the rapid normalization of the inflammatory environment.
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