This article is more than 5 years old. Information may no longer be current.
Long-term contact lens wear negatively impacts corneal thickness and curvature
Study shows refractive surgery candidates could be at risk for developing keratoconus.
Click Here to Manage Email Alerts
MIAMI — A decrease in entire corneal thickness and an increase in corneal curvature and surface irregularity are the effects of long-term contact lens wear, according to a prospective, case-control study. Results of the study, which compared 40 eyes of 20 normal subjects with 64 eyes of 35 subjects wearing contact lenses for more than 5 years, appeared in the journal Ophthalmology.
The authors were inspired to undertake the clinic-based study because of their refractive surgery candidates. “With laser in situ keratomileusis [LASIK], we routinely check the corneal thickness. You can’t perform LASIK if the cornea is too thin,” said co-author Stephen C. Pflugfelder, MD, a professor of ophthalmology here at the Bascom Palmer Eye Institute at the University of Miami School of Medicine. “We started to notice that some people had corneas that were really abnormally thin. This seemed to correlate with long-term contact lens wear. So we prospectively looked at this group and found the association to be highly significant,” he said in an interview with Ocular Surgery News.
Dr. Pflugfelder, along with first author Zuguo Liu, PhD, MD, used the Orbscan Corneal Topography system (Bausch & Lomb Surgical, Claremont, U.S.A.) to evaluate the entire corneal thickness and curvature, anterior curvature and the anterior and posterior elevation topographic patterns. The average duration of contact lens wear was 13.45 years (range of 5 to 35 years). In addition, the majority of these eyes wore soft contact lenses (84.38%), compared with hard contact lenses (15.62%). Furthermore, 21 of the 35 subjects had worn hard contact lenses for at least 10 years before switching to soft contact lenses.
Reduction of 30 µm to 50 µm
---Stephen C. Pflugfelder,
MD
Among contact lens wearers, the mean corneal
thickness in the center and in eight peripheral areas was significantly reduced
by about 30 µm to 50 µm compared with normal subjects (P < .001
for central and peripheral sites). But no correlation was found between central
corneal thickness and degree of myopia in diopters. Still, the corneal
curvature and maximum keratometry and minimum keratometry readings were
significantly steeper in eyes wearing contact lenses (P < .01 for maximum
and minimum keratometry measured by both the Orbscan and the TMS-1 Corneal
Topography system [Tomey Corp., Waltham, U.S.A.]).
The investigators found no difference in the mean corneal astigmatism between the two groups. However, the surface regularity index (SRI) and surface asymmetry index (SAI) — but not the potential visual acuity (PVA) index — of the TMS-1 were significantly greater in contact lens wearers (P < .01 for both SRI and SAI; P = .15 for PVA). Finally, the color-coded patterns of all curvature and elevation maps generated by both instruments showed no significant difference between the two groups.
Possible reasons for thinning
Although significant thinning of both the corneal epithelium and stroma has been observed previously in contact lens wearers, the specific reason for this corneal thinning has yet to be established. “It could be the result of mechanical trauma, particularly from hard lenses,” Dr. Pflugfelder said. “Hypoxia is another possible reason. It also could be biochemical changes as a result of hypoxia; for instance, increased production of enzymes that degrade the cornea.” Increased tear osmolarity and increased apoptosis of keratocytes and epithelial cells in the corneas of contact lens wearers are two other factors that may contribute to this corneal thinning, he said.
In addition, corneal curvature becoming significantly steeper in contact lens wearers “may be related to thinning,” Dr. Pflugfelder said. “If the cornea thins, it may protrude a little bit. But again, we don’t know the mechanism.” Nonetheless, one of the implications of the study is that contact lens wearers may eventually develop keratoconus.
“Doctors should be aware that if their patients are wearing contact lenses, they may have an irregular cornea and may need to stay out of their contacts for a long period — months to a year — before refractive surgery so that their corneas can return to normal. Otherwise, there may be a problem after LASIK,” Dr. Pflugfelder said. He added, though, that with today’s contact lens technology, corneal problems may not be as apparent. “There is a whole new generation of soft contact lenses that is highly oxygen permeable. Plus, lenses are now generally a better fit,” he said.
For Your Information:Reference:
- Stephen C. Pflugfelder, MD, can be reached at Bascom Palmer Eye Institute, 900 N.W. 17th St., Miami, FL 33136 U.S.A.; +(1) 305-326-6368; fax: +(1) 305-326-6337; e-mail: spflugfelder@bpei.med.miami.edu. Dr. Pflugfelder has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Liu Z, Pflugfelder SC. The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity. Ophthalmology. 2000;107:105-111.