Washington, DC-An unstable tear film can decrease functional visual acuity and may be the primary target for treatment of dry eye, said Kazuo Tsubota, MD, at World Cornea Congress V.
Dr. Tsubota, professor of ophthalmology, Tokyo Dental College, Ichikawa-Shi, Chiba, Japan, has been working to develop tools for measuring functional visual acuity and tear film stability. The Functional Visual Acuity Meter (FVAM, Nidek) measures visual acuity after patients keep their eyes open for periods of 10 to 30 seconds. Dr. Tsubota explained this test was designed to simulate daily vision tasks involving gazing.
"In traditional acuity testing, patients can blink as often as they like and so can regenerate the tear film on the ocular surface. However, there are a number of vision tasks in daily living where blink is suppressed, such as when driving, reading, or working at the computer. Under those conditions, an unstable tear film associated with dry eye can cause poor-quality vision," he said.
"Therefore, we are certain the decrease in visual function we observed is due to the effect of an unstable tear film," Dr. Tsubota said.
Various modalities exist that can improve tear film stability, including instillation of artificial tears or topical cyclosporine 0.05% (Restasis, Allergan) as well as placement of punctal plugs.
In other studies, Dr. Tsubota demonstrated the benefits of treatment modalities for improving functional visual acuity and indices measured with the TSAS.
He has also worked to create an animal model of an unstable tear film that could be used to study the effects of dry eye treatments.
"Developing an animal model of this type is difficult because blink frequency cannot be reduced in mice by asking them to keep their eyes open and they do not do computer work," Dr. Tsubota jested.
Recognizing that humans keep their eyes open in situations where they are trying to stabilize the body to maintain balance, Dr. Tsubota placed laboratory rats on a jogging board constructed from a plastic pipe and used a fan to blow low-humidity air onto their faces for an added desiccating effect.
His studies showed that animals subjected to that situation had a decreased blink frequency and developed tear dynamics and ocular surface changes. After being placed on the jogging board for 7.5 hours/day for 5 days (to simulate the human situation of daily work at a computer monitor), significant changes were recorded in Schirmer score and tear clearance. In addition, fluorescein staining revealed that the unstable tear film led to punctuate keratopathy similar to that seen in humans with dry eye.