Tear normalization test provides new way of diagnosing dry eye

The test is quick, inexpensive, reliable, and highly sensitive and specific.

Issue: May 1, 2005

ByRobert Latkany, MD

Dry eye symptoms affect an estimated 80 million Americans and are a common reason for patients to seek help from an eye care professional. However, many eye care professionals remain unfamiliar with the scope of the problem and underdiagnose dry eye syndrome, blepharitis and related tear film disorders. This is hardly a surprise.

Currently, the diagnosis of dry eyes is made on the basis of a variety of characteristic historical features and exam findings. It is fair to say that there is little correlation between signs and symptoms in patients with dry eyes; without an objective test, practitioners who are not already familiar with the range of presentations consistent with dry eyes are bound to overlook some cases. One clinical test for dry eyes, Schirmer’s test, appears to miss many patients with clear symptoms and signs of dry eye, including abnormal tear breakup time, fluorescein or rose bengal staining, or decreased blink rates. Other patients have no symptoms at all but have variable clinical signs and an abnormal Schirmer’s test.

What the field has lacked is a quick, inexpensive and reliable screening test for dry eyes that is both highly sensitive and specific compared to the gold standard test, the complete evaluation by a dry eye specialist.

Study

Many of our patients complain of blurry vision, especially in dry environments or after prolonged visual tasks. They present to the office dissatisfied with currently available over-the-counter artificial tear drops and are looking for alternative therapy. I decided to evaluate what type of an effect these over-the-counter artificial tears had on visual acuity and how long it lasted.

At the Ocular Tear Film Society meeting in Puerto Rico in 2004, we presented findings on the effect of artificial tears on visual acuity in dry eye patients. We found that artificial tears consistently improved the visual acuity of dry eye patients (P < .001);="" however,="" the="" effect="" lasted="" less="" than="" 4="" minutes.="" clinically,="" this="" was="" a="" satisfying="" study="" to="" perform;="" most="" patients="" exclaimed="" “wow”="" when="" they="" noticed="" the="" improvement="" in="" vision.="">

After contemplating this obvious positive effect of artificial tears on uncorrected and best corrected near and distance visual acuity in dry eye patients, we hypothesized that the artificial tears may function by “normalizing” a dry eye patient’s “abnormal” tear film. It has been shown in prior studies that artificial tears reduce ocular aberrations present in dry eye patients. So perhaps temporarily “normalizing” the surface irregularities in dysfunctional tear film patients by instilling artificial tears improves the optic properties of the anterior surface of the cornea, thereby improving visual acuity.

This visual acuity improvement was not specific to a particular brand of tears. We found that all non-viscous artificial tears tested, including Refresh and Refresh Plus (Allergan), Moisture Eyes (Bausch & Lomb), MiniDrops (Optics Therapy) and TheraTears (Advanced Vision Research), had one thing in common — they temporarily improved visual acuity in dry eye patients.

The test

We then designed a prospective study to evaluate the effect of tears on the visual acuity of patients with a clinical diagnosis of dry eyes compared to the visual acuity of those without a clinical diagnosis of dry eyes. If patients with dry eyes were to have improved vision with instillation of tears but those without dry eyes did not, perhaps that data could be harnessed to create a new test for dry eyes: the tear normalization test, or TNT.

There would be several potential benefits to a test such as this. It is inexpensive, a technician can perform the test without difficulty, it can be done in every eye doctor’s office, and it is clinically satisfying to hear, “Wow, what was that?” from patients. The tear normalization test can even be performed at home if the patient instills the artificial tear and then focuses on a previously distant blurry object. If the object becomes more clear, then the patient may have dry eye. The tear normalization test would be less irritating to patients than having a filter paper placed in the eye or having the nose stimulated with a cotton tip applicator.

An additional benefit of the tear normalization test is that it should detect both types of dry eyes, aqueous tear deficiency and evaporative dry eyes. Studies have already shown that aqueous tear deficient patients have baseline surface irregularities and their vision improves with artificial tear drops. Evaporative dry eye patients usually complain of fluctuating vision during prolonged visual tasks (ie, staring at a Snellen vision chart). So both types of dry eyes should be detected using the tear normalization test.

Results

Preliminary results of a prospective study of 80 eyes, 40 with dry eyes and 40 without dry eyes, indicate that although patients with dry eyes had an improvement in vision with instillation of tears, those without dry eyes also had a modest but statistically significant improvement in visual acuity. At the time of this article submission, our team was still evaluating the test properties of these data using ROC curve analysis and preparing for formal manuscript submission.

A study comparing the test properties of the tear normalization test to Schirmer’s tests, tear breakup time, tear meniscus height and dry eye questionnaires may be in order. Other tests that evaluate tear osmolarity may be accurate, but because of their expense, they are not as readily available. Future tests may need to look at contrast sensitivity rather than high-contrast Snellen visual acuity testing, as this may better apply to everyday life activities.

See how the TNT works in your practice. Start by checking the patient’s uncorrected distance vision in each eye before any other drops are placed in the eyes and before any slit lamp examination is performed. After the vision is recorded, add a drop of a non-viscous artificial tear into each eye and immediately recheck the vision starting at the highest line read incorrectly on the Snellen visual acuity chart. Then, re-record the vision. You may have to wait for the patient’s tear film to “normalize,” which can be up to 20 seconds after drop instillation in some patients. You should also watch for excessive blinking after tear drop instillation as this may “squeeze” the added tear drop out of the eye.

For Your Information:

Robert Latkany, MD, is director and founder of the Dry Eye Clinic, New York Eye & Ear Infirmary, and director and founder of the Center for Ocular Tear Film Disorders. He can be reached at 115 East 57th St., 10th Floor, New York, NY 10022; 212-832-2020; e-mail: relief@dryeyedoctor.com; Web site: www.dryeyedoctor.com. Dr. Latkany has no financial interest in any of the products mentioned in this article.