SIZING UP the Tear Film

A new multimodal imaging system will help researchers develop new protocols to objectively assess and treat tear film abnormalities.

BY JAMES V. AQUAVELLA, MD

More than five million Americans older than 50 are estimated to have dry eye disease, and tear film abnormalities exist in up to 10% of the population. Environmental conditions and factors, such as frequent computer use, exacerbate symptoms in patients with an unstable tear film and dry eye symptoms. Although we see these conditions frequently in our patients, it is essential for us to understand what is happening with the tear film to accurately diagnose and treat these conditions.

The three-layered film (lipid, aqueous and mucus) protects the eye, and the precorneal tear film that remains after blinking helps maintain visual quality. Defects in components of the tear film or its breakup may cause the symptoms patients complain of and adversely affect visual quality.

Although current diagnostic methods do not allow us to objectively evaluate the tear film, we hope new technology will yield important answers for treating these patients.

Inexact Science

Patient reports of their symptoms yield subjective results. When you ask patients with dry eye symptoms to describe how they feel, you will receive a variety of descriptions. Some patients may say their eyes burn or sting, whereas others com plain of a foreign body sensation. Some are articulate, whereas others are poor historians.

Unfortunately, diagnostic tests also fall short in helping us to understand tear film dynamics. When using subjective assessments, such as Schirmer's test, tear film breakup time and tear film osmolari ty and staining of the conjunctiva with fluorescein, rose bengal or lissamine green stain, we introduce an element into the eye that disturbs the tear film.

Wavefront sensing spots (left) identify the tear film breakup pattern, which is then reconstructed as a wavefront aberrometry map (right).

Currently, ophthalmologists have no other option but to rely on these tests; however, my colleagues and I are using new technology to assess dynamic changes in the tear film under normal and unfavorable environmental conditions. Using this evidence-based approach, we hope to provide a new metric to better understand, examine and treat these patients with more concrete guidelines.

Objective Data

Our noninvasive, real-time, multimodal imaging system assesses the dynamics of the tear film, using highly sensitive, specially designed ocular-surface optical coherence tomography, wavefront sensors and ellipsometry that simultaneously obtain multiple images per second of the ocular sur face. This is used within an environmental chamber, where we can control humidity, temperature and air flow in order to stress the ocular surface.

With the OCT component, which captures cross-sectional images, we can evaluate the thickness of the tear film, the tear volume and the upper and lower lid meniscus. Wavefront sensors enable us to measure aberrations caused by abnormalities in the tear film. This technology allows us to determine where the tear film is beginning to break up between blinks and measure the visual acuity of the eye. With wavefront analysis, we can assess changes in the quality of the image projected to the retina at any given instant. At the same time, the ellipsometer, relying on light reflected from the surface of the cornea and tear film, measures the thickness of the lipid layer, which prevents tear evaporation, as well as its refractive index. As we simultaneously measure all of these parameters, we're also recording the number of times the patient blinks, and we can record and monitor what happens if we change the temperature, increase or decrease the air flow or decrease evaporation by increasing the humidity.

Within this closed chamber, Dr. Aquavella's team can modify the humidity, temperature and air flow to induce a variety of ocular surface conditions when testing dry eye patients.

Clinical Benefits of Research

Information generated from this system takes weeks to analyze, and our future research is planned over the next 10 years. Clinical ophthalmologists will not have this system, but we hope it will yield a number of benefits to clinicians and their patients.

First, we hope our findings will help us develop new markers to guide assessments, simplifying the diagnosis and making it more objective. This technology will find correlations between the symptoms the patient describes and what is actually happening on the surface of the eye. This information will help to streamline the diagnostic process, indicating which assessments are most accurate. It also will enable physicians to ask those questions that indicate what is really happening on the surface of the eye.

Second, we anticipate that this research will guide treatment. When we prescribe over-the-counter tear substitutes, our recommendations are not based on scientific data. We often advise patients to choose the product that works best for them from the dozens of available products. Using our environmental chamber, however, we have found that there really is a difference between products, and certain patients respond better to specific compounds. Furthermore, some products may actually worsen the tear film. We hope to categorize which products work best for which patients.

The system also will allow us to objectively determine the effect of anti-inflammatory modulators, such as cyclosporine and steroids, and their effect on the tear film between blinks.

Our technology may help companies that develop these treatments. Drug development is a tremendously expensive process that requires a huge investment of human and fiscal resources. In testing these compounds in our environmental chamber early in the process, we hope to help channel energies and investments where they will be most effective. Thus, we hope this will reduce both the cost and time for products to reach the market. In addition, this research may lead to new technology or to tests that ophthalmologists can use in their practices that are substitutes for our technology.

Furthermore, with the data that we generate, we can explore even minor details, such as how the tear film is affected when a person looks at a computer, as compared with a movie screen, or when a patient gazes down. We know that, if you look straight ahead or look up, the eyes open more widely, whereas they close a bit more when you look down. This information may help us to instruct patients with dry eye where they should place a computer monitor or how they should hold a book to minimize symptoms.

Looking Ahead

Although our research has just begun to produce results, we are optimistic that this technology will yield important answers for clinicians. An understanding of tear film dynamics is essential for us to optimally diagnose and treat dry eye conditions and to develop new medications to treat patients with tear film abnormalities. OM

Dr. Aquavella is a professor of ophthalmology at the Flaum Eye Institute at the University of Rochester, New York. He has no financial interest in any products mentioned in this article.