November 2009




The implications for interferometry

by Matt Young EyeWorld Contributing Editor


A deteriorated lipid layer thickness (LLT) could lead to severe dry-eye symptoms, a new study has found. “Approximately 3 of 4 patients reporting severe symptoms have relatively thin lipid layers of 60 nm or less, whereas approximately 3 of 4 patients without symptoms have relatively thick lipid layers of 75 nm or more,” according to study co-author Donald R. Korb, O.D., clinical professor, School of Optometry, University of California, Berkeley, Calif. The study was published online in July in Cornea. The study also has implications for interferometry, which could now be of some clinical use, according to the study authors.

New meaning for LLT

Dr. Korb and colleagues analyzed 102 female and 35 male patients presenting consecutively for routine eye examinations. They completed the Standard Patient Evaluation of Eye Dryness (SPEED) questionnaire and had their LLT evaluated using the Ocular Surface Interferometer (OSI, Kolis Scientific, Morrisville, N.C.).

“For patients with severe dry eye symptoms, 74% had an LLT ≤60 nm (relatively thin). Conversely, 72% of patients with no dry eye symptoms had an LLT of ≥75 nm (relatively thick),” Dr. Korb noted. “Furthermore, a linear regression of LLT and SPEED score reveal a significant linear relationship (as LLT increases, SPEED score decreases).”

Dry-eye symptoms, in other words, significantly increase the chances of having a thin lipid layer and vice versa. “LLT seems to correlate better to symptoms, especially severe symptoms, than other reported correlations with objective clinical tests for dry eye disease,” Dr. Korb reported. “Because dry eye is not based solely upon LLT or upon any other single factor, a thick lipid layer does not preclude the presence of dry eye symptoms and dry eye symptoms do not ensure that the LLT is severely reduced,” Dr. Korb reported. “The high-resolution images and high color rendition provided by the new OSI results in a metric of LLT, which seems to correlate better with symptoms, especially severe symptoms, than other reported correlations with objective clinical tests for DED [dry eye disease].”

A device like the OSI, therefore, could see more clinical usage than interferometry predecessors. “In the recent past, there have been 3 commercially available instruments using interferometry to assess lipid layer characteristics, none of which are currently available for purchase in the United States,” Dr. Korb noted.

Here’s a little bit about how the OSI works, according to Dr. Korb: After the interferometer aligns, a portion of the cornea corresponding to a region about 1 mm above the inferior tear film meniscus to slightly below the inferior papillary margin is illuminated. The illuminated area should be limited to about 2.5 mm in height and 5 mm in width. This provides an appropriate area to observe without causing patient discomfort or reflex tearing. Interference patterns are viewed on a color monitor to evaluate and quantify LLT. “Interferometry has already been shown to be effective in evaluating the use of warm compresses, meibomian gland expression, eyedrops, ointments, and punctal plugs in a more controlled setting,” Dr. Korb noted. “The benefits of using a commercially available interferometer in a clinical setting are that it provides a noninvasive objective test, which is technician friendly, takes only 2–3 minutes to perform on both eyes, and does not consume practitioner time.”

Although William B. Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami, has not used interferometry, he said there might be a clinical niche for it. “If you have a thin layer of lipid, you have evaporative dry eye,” Dr. Trattler said. “That thin layer of lipid won’t lock in the tears.” Because interferometry could measure the quality of tears and the lipid layer, one might get a sense of how a patient’s dry eye manifests, he said. Whether interferometry is embraced in future clinical practice also depends on how easy it is to interpret, he said. “Operation of the prototype interferometer (OSI) required similar skills to those for the use of an autorefractor or topographer,” Dr. Korb noted in his study. “The time for measurement of LLT was 2–4 minutes. The grading of LLT was readily learned by the technicians. No physician time would have been required in clinical practice.”

If a patient does have evaporative dry eye, such as a form of blepharitis like meibomian gland dysfunction, there are plenty of treatments available, Dr. Trattler said. These include warm compresses, topical azithromycin, and lid scrubs.

“There are a lot of good options for patients with these abnormalities,” Dr. Trattler said.

Editors’ note: This study was supported in part by Kolis Scientific (Morrisville, N.C.). Dr. Trattler has no financial interests related to his comments.

Contact information

Korb: 617-426-0370,
Trattler: 305-598-2020,

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