dry eye dx and tx
A Contact Lens on a Dry Eye
BY WILLIAM TOWNSEND, OD, FAAO
We all have contact lens patients who seem to do well as long as they are not wearing their lenses. But once they place a lens on the eye, things change. Here we'll look at the impact a contact lens may have on the ocular surface and what we can do to help compensate for those changes.
A contact lens is a foreign object resting on the surface of one of the body's most delicate and sensitive tissues. It floats on the tear film, which we now understand is composed of phases, each of which interacts with the other phases. Mucin extends up into the aqueous phase, and lipids interact with mucins in the aqueous phase. Tears protect the ocular surface from friction, bring oxygen and nutrients to the epithelium, and transport waste products and sloughed surface cells away.
Evidence exists that the impact of a lens is more evident in individuals who already have dry eyes.
A contact lens placed on the eye immediately changes several things. It divides the tear layer into pre-lens and pre-corneal layers. Nichols and Sinnot (2006) showed that the pre-lens tear film thins approximately 25 percent faster in contact lens wearers with dry eye compared to normal lens wearers. They concluded that the two factors most likely responsible for this finding were evaporation and lens surface dewetting.
One of their findings may explain accelerated contact lens-related evaporative changes: lipid layer thickness was substantially lower in dry eye subjects compared to non-dry eye patients. Craig and Tomlinson (1997) reported that stenosed meibomian glands result in a fourfold increase in evaporation and a severely compromised lipid layer.
Increased tear film osmolarity is a significant and repeatable finding in dry eye. In Nichols' and Sinnot's study, osmolarity was elevated by a clinically significant amount in the dry eye group. Gilbard et al (1989) suggested that elevated tear film osmolarity is a consistent finding in dry eye and may cause some of the surface alterations of that condition.
Increased rates of infection including infectious keratitis are associated with contact lens wear. Lemp (2003) described factors that may increase the risk for dry eye-associated infection. Those include contact lens-induced changes in tear flow; evaporative tear loss; lens deposits, predisposing to bacterial attachment; and the loss of antimicrobial ocular defense mechanisms.
Managing Lens Wearers Who Have Dry Eye
A review of salient studies reveals a multitude of complications that may occur from placing contact lenses on the eyes of a patient who has dry eyes. While this condition does not contraindicate contact lens wear, it should alert you to be especially vigilant in managing these individuals. Patients with these conditions must be educated and monitored carefully for potential complications. Also make sure you select materials that are formulated to be "dry eye friendly."
In my experience, some of the newer silicone hydrogel materials such as senofilcon A (Acuvue Oasys, Vistakon), lotrafilcon B (Air Optix Aqua, CIBA Vision), and comfilcon A (Biofinity, CooperVision) that are specifically formulated to reduce drying effects of contact lenses on the ocular surface are beneficial to patients who have dry eye. Their surfaces are designed to increase their wettability and to decrease their susceptibility to protein and lipid deposition.
Lens solutions are formulated to be compatible with existing lens materials and to extend comfortable lens wearing time. To do this, chemists have designed molecules that enhance and extend the wettability of the contact lens surface.
Staying abreast of the latest developments in lens materials and solutions will benefit lens wearers who have dry eye. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #160.
Dr. Townsend practices in Canyon, Texas and is an adjunct faculty member at UHCO. E-mail him at email@example.com.