Lens Materials and Limbal Stem Cell Health
BY LORETTA B. SZCZOTKA-FLYNN, OD, MS, FAAO
Can contact lenses destroy the precious limbal stem cells of the ocular surface? If so, what are the mechanisms? Could it be related to hypoxia? These are questions posed by many researchers andand clinicians, especially when considering switching patients to high- or hyper-Dk contact lens materials.
Limbal Cell Deficiency
Figure 1. Patient with possible contact-lens related LSCD.
The integrity of the cornea's self-renewing epithelium relies on the existence of normal limbal stem cells. Limbal stem cell deficiency (LSCD) is an irreversible condition that can result in reduced vision and chronic ocular irritation. Normal limbal stem cells prevent conjunctival epithelial cells from migrating onto the corneal surface, and when these cells are depleted, conjunctivalization occurs.
Examples of known ocular surface injuries that might cause LSCD are alkali burn, thermal injury, Stevens-Johnson syndrome and ocular cicatricial pemphigoid. However, researchers also postulate that contact lens-related epitheliopathy may be a cause of LSCD. In fact, a study by Donisi et al (2003) showed that of a sample of 13 patients who had complications from wearing contact lenses, 72 percent had mild diffuse or sectoral LSCD measured by impression cytology.
Dr. Eric Papas at the Cornea and Contact Lens Research Unit (CCLRU), who has extensively studied contact lens effects at the limbus, has speculated that hypoxia from thick, soft lens peripheries that overlie the limbal region may change epithelial cell function in that region. In fact, his colleague, Dr. Isabelle Jalbert, has shown differences in basal cell regularity between high-Dk and low-Dk lens wearers, which could point to the role of oxygen in cellular growth and epithelial turnover.
A Memorable Patient
Several years ago I encountered a patient who appeared to have contact lens-related LSCD with sectoral neovascularization and conjunctivalization (Figure 1). He wore –6.00D low-Dk hydrogels on a daily wear basis for eight years.
Voicing concern over the possible effect of hypoxia on the limbal stem cells, I recommended a refit to hyper-Dk GP lenses, which was unsuccessful because of occupational discomfort from his dusty work environment. However, we successfully refit the patient into a silicone hydrogel lens (PureVision, Bausch & Lomb) with no progression of damage until he was lost to follow up. However, I will never forget this case, and when I share this photo with other practitioners at CE meetings, at least half of the audience recalls similar cases in their practices.
Providing More Oxygen
Isolated cases like these are by no means scientific. Similar effects could have resulted from solution toxicity or non-lens-related causes. Because very little has been written about limbal stem cell health and contact lenses, I can only postulate that hypoxia plays a role.
One step forward I can make in possibly preventing such future irreversible complications is to provide the cornea with as much oxygen as I can deliver with silicone hydrogel lenses and hyper-Dk GPs. CLS
Dr. Szczotka-Flynn is an associate professor at Case Western Reserve University Dept. of Ophthalmology and is director of the Contact Lens Service at University Hospitals of Cleveland.