The Importance of TBUT in Contact Lens Wearers
Traditionally used to evaluate dry eye therapy, tear breakup time also can point the way to contact lens success.
By Michael D. DePaolis, OD, FAAO

There's no question the tear film is vital to the eye's health and comfort. The proof is in the problems that ensue when the normal tear film is disrupted -- the discomfort, grittiness, blurring and burning associated with dry eye.

A measure of the tear film's overall health is tear breakup time (TBUT), which we traditionally use to monitor improvements in our dry eye patients. Recent work now shows that TBUT also has a place in contact lens practice, specifically, to measure the effectiveness of products designed to rewet and lubricate contact lenses. And we may even be able to use it to predict which patients may do well in contact lenses.

FUNCTION OF THE TEAR FILM

With a contact lens in place, the pre-lens tear film forms over the front surface of the contact lens while the post-lens tear film forms between the lens and the cornea. However, the basic functions are the same with or without a lens in place, namely, tears:

• Are bactericidal
• Bring nutrients to the eye
• Flush out foreign particles
• Provide a smooth optical surface for good image quality
• Form a physical barrier to prevent drying.

The tear film naturally begins to break up between blinks, exposing the contact lens surface to air, prompting dehydration of the lens and the cornea. Each blink of the eye renews the tear film, so if the TBUT is similar to the time between blinks, the ocular surface remains moist and healthy.

DISRUPTION OF THE TEAR FILM

Contact lenses can disrupt tears in several ways -- volume, chemical composition, rate of production, for example -- and one consequence is a shorter TBUT. Therefore, this measurement can give us an indication of tear-film function in our contact lens patients.

Tear breakup time also may be an indicator of contact lens wearing success. Glasson and coauthors (2003) found that TBUT was 7 seconds longer in patients who usually could wear contact lenses 9 or more hours a day than in patients who couldn't wear lenses this long. Although these measurements were taken without a lens in place, they suggest that a lubricating or rewetting drop that increases TBUT may help increase contact lens wear time. This difference is important because patients who are unhappy with comfort are likely to stop wearing lenses.

CLINICAL RELEVANCE

Historically, we've used TBUT as an outcome measure for dry eye treatment, and many studies report the effects of ophthalmic demulcents on TBUT. Products containing hydroxypropyl methylcellulose (HPMC), carboxy methylcellulose (CMC) and sodium hyaluronate (HA) all have been shown to increase TBUT in dry eye patients. But only HA has been shown to stabilize the tear film and increase TBUT over contact lenses.

In a recent clinical study, a hyaluronate-based solution (Blink Contacts, 0.15% HA) increased TBUT in contact lens wearers by 3.1 seconds over baseline after 30 days of use (Figure. 1). Three seconds may not seem like much, but when you consider that only 7 seconds separates patients able and unable to wear lenses for 9 hours, the significance becomes clearer.

The patients using this lubricant eye drop also reported improved comfort at the end of the day, suggesting that this 3-second improvement restored tear-film function toward normal in these contact lens wearers. It can mean the difference between a happy lens wearer and someone who's ready to discontinue use.

TOP: WHEN HYALURONATE MOLECULES ARE RANDOM AND TANGLED, THEY HELP RESIST MOISTURE EVAPORATION . BOTTOM: WHEN HYALURONATE MOLECULES ARE ALIGNED (UNTANGLED), FLUID CAN FLOW FREELY OVER THE OCULAR SURFACE.

UNCOMPLICATE LENS WEAR

Keeping patients happily wearing contact lenses can be difficult. Environmental conditions -- both outdoors and indoors -- seem to conspire to make lens wear difficult for many patients. We should consider the options carefully before we recommend a solution for these patients. Blink Contacts is one of a new generation of lubricant eye drops for contact lens wearers that really address the problem of the disrupted tear film. Blink Contacts lubricant eye drops increase TBUT to provide long-lasting moisture and comfort to counter the demanding conditions that complicate contact lens wear.

References
1. Faber E, Golding TR, Lowe R, Brennan NA. Effect of hydrogel lens wear on tear film stability. Optom Vis Sci 1991;68:380-384.
2. Glasson MJ, Stapleton F, Keay Lisa, Sweeney D, Willcox MDP. Differences in clinical parameters and tear film of tolerant and intolerant contact lens wearers. Invest Ophthalmol Vis Sci 2003;44:5116-5124.
3. Toda I, Shinozaki N, Tsubota K. Hydroxypropyl methylcellulose for the treatment of severe dry eye associated with Sj�gren's syndrome. Cornea 1996;15:120-128.
4. Lenton LM, Albietz JM. Effect of carmellose-based artificial tears on the ocular surface in eyes after laser in situ keratomileusis. J Refract Surg 1999;15(Suppl):S227-S231.
5. Hamano T, Horimoto K, Lee M, Komemushi S. Sodium hyaluronate eyedrops enhance tear film stability. Jpn J Ophthalmol 1996;40:62-65.
6. Kao E, Lasswell L, Cook J, Huth S. Clinical study of new contact lens rewetter formulated with sodium hyaluronate. Poster presentation, American Optometric Association meeting, Orlando, FL, June 23-27, 2004.

Dr. DePaolis is in private group practice in Rochester, N.Y. He's an adjunct faculty member at the Pennsylvania College of Optometry and is a Clinical Associate at the University of Rochester School of Medicine.