contact lens Q&A
Managing Microcysts and More
BY JAMES V. AQUAVELLA, MD
JUNE 1998
While most contact lens-wearing eyes are free of signs and symptoms at each check-up, there are a variety of clinical presentations that can reveal valuable information about a patient's ocular well-being. Here's what you should know when you're confronted with microcysts, corneal warpage and abnormal tear film break up time.
What is the significance of the presence of microcysts in contact lens wearers?
ANSWER: While microcysts have been observed in non-contact lens wearers, these small intraepithelial lesions are thought to be an indicator of reduced oxygen transmission during contact lens wear. Most patients with microcysts exhibit no apparent visual or other adverse sequelae.
Factors other than hypoxia that may contribute to microcyst formation include contact lens induced trauma in the midperipheral area, the accumulation of debris in the contact lens-corneal epithelium interface and inadequate movement of the contact lens. While the presence of microcysts may indicate marginal oxygen transmission to the epithelial surface in a particular patient, if the patient is comfortable and there are no other adverse symptoms, it is not necessary to modify the contact lens or the wearing schedule.
What is the best method to differentiate contact lens induced corneal warpage from keratoconus?
ANSWER: Contact lens induced corneal warpage can occur in both soft and rigid gas permeable contact lens wearers. In cases of warpage, corneal topography maps often reveal a reversal of the normal progressive peripheral flattening and a loss of radial symmetry.
Topographic changes that occur in rigid contact lens wearers are often the result of a superior resting position of the lens with associated inferior peripheral corneal steepening. This type of pattern has been termed "pseudokeratoconus." By removing the contact lens and monitoring keratometric and topographic changes until the topography and refraction have stabilized, the patterns will usually shift to that of a typical bow tie.
If the pseudokeratoconus pattern persists, advise the patient to remove the contact lenses for several months, after which time you should repeat the topography. On the other hand, incipient keratoconus will often become aggravated following removal of a rigid contact lens. Another technique for making this difficult diagnosis is to examine both eyes serially. In true keratoconus, one eye is usually much more advanced than the other; in pseudokeratoconus, the topographic patterns of the two eyes may be similar.
What is the value of tear film break up time in selecting appropriate contact lens candidates?
ANSWER: In individuals with normal tear film and blink response, the tear film will remain stable for upwards of 20 seconds with little break up. If the patient continues to stare without blinking, a gradual thinning and ultimate rupture of the surface of the tear film with drying of the underlying epithelium will occur. If the tear film is significantly compromised quantitatively or qualitatively, you'll see breaks in the integrity of the tear film almost immediately following the blink cycle. Obviously, patients with poor tear film quality are not ideal contact lens candidates. Break up time observations should be utilized in conjunction with assessment of the blink mechanism and of the thickness of the tear film at the lower lid margin. Keep in mind that while fluorescein can be helpful in identifying surface breaks, it can mask the development of incipient dry spots. CLS
Dr. Aquavella is chairman of the Genesee Valley Eye Institute and director of the corneal research lab at the University of Rochester.