Evaluating inherent risks

A small corneal abscess with intense infiltration in the surrounding cornea, resulting from contact lens use
Source: Daljit Singh, M.D.

Although LASIK involves inherent risks—as does any surgical procedure—a new study suggests that contact lens wear could be more dangerous in certain scenarios. The study, published in the November 2009 issue of the Journal of Cataract & Refractive Surgery, compared the risk for vision loss after LASIK and contact lens wear using decision analysis.
“Indeed, contrary to intuition, this decision analysis shows that in some commonly occurring situations, contact lenses may be riskier than LASIK,” according to study co-author William D. Mathers, M.D., Casey Eye Institute, Oregon Health & Science University, Portland, Ore. “It is a significant departure from conventional wisdom to think that the safety of LASIK could even approach that of contact lenses.”
That being said, there were other scenarios in which the study found contact lens wear to be safer than LASIK. The study was not based on randomized, controlled testing. It used a decision tree created using Markov modeling. “An outcome variable, visual acuity-adjusted life-year (VALY), was defined to account for timing and severity of vision loss,” Dr. Mathers noted. “The VALYs were tallied over a 30-year simulation to determine whether the risk for vision loss with contacts exceeded that with LASIK.”
The researchers conceded that “conclusions of this model were very sensitive to changes in some parameters,” while conclusions were relatively unaffected by changes in other parameters.

Major conclusions

Although the study used complex modeling too detailed to be properly covered by this article, it is worthwhile to highlight some of the conclusions, which favor contact lenses in some instances and LASIK in others.
Variables tested included probability of contact lens-related keratitis, probability of ectasia after LASIK, and probability of early post-LASIK vision loss. Vision loss rates were based on published literature reports.
“For contact lenses, the mechanism of vision loss is via infectious keratitis and this correlates closely with the type of lens used,” Dr. Mathers noted. “For LASIK, vision loss can occur for many reasons in the early postoperative period, or from post-LASIK ectasia as a late complication.”
Rigid gas permeable lenses essentially provided minimal visual risk. “In no scenario tested was the risk for vision loss with RGP lenses higher than that with LASIK over the 30 years of simulation,” Dr. Mathers reported.
Daily soft contact lens wear, meanwhile, carried more moderate risk. “The risk with daily-wear soft contact lenses exceeded that with LASIK after approximately 15 years if the risk for ectasia was low (1 case per 10,000 patients) but never exceeded that with LASIK if the ectasia risk was higher (1 case per 1,000 patients),” Dr. Mathers reported.
Risks associated with extended wear contact lenses depended on the true risk of ectasia after LASIK. “If the true risk for ectasia were 1 case per 500 (0.20%), even extended-wear soft contact lenses would have lower risk for vision loss than LASIK,” Dr. Mathers noted. “If the true risk for ectasia were low, however, the risk for vision loss with LASIK would be exceeded by extended-wear soft contact lenses, even with an early postoperative risk of 0.48% (almost 1 case in 200).”
It’s also possible that daily soft contact lens wear could be riskier than LASIK. “The risk with daily-wear soft contact lenses would exceed that with LASIK only under conditions most favorable to LASIK,” Dr. Mathers concluded.
Other factors are important to consider in the case for contacts versus LASIK and vice versa. “First, there may be more events of vision loss with long-term soft contact lens wear than with LASIK,” Dr. Mathers reported. “Second, the events associated with LASIK occur earlier; thus, patients accumulate more time with vision loss. Third, the vision loss from contact lens-associated keratitis can be more severe than vision loss with LASIK; therefore, the years of relatively worse disability must be weighted more heavily.”
Interestingly, even if some contact lens wear situations do carry more risk than LASIK, patients may be more willing to accept vision loss after contact lens wear than after LASIK “because of a sense of their own responsibility for the outcome,” Dr. Mathers suggested, although this was not studied here.
John D. Sheppard, M.D., professor of ophthalmology, microbiology, and immunology, Eastern Virginia Medical School, Norfolk, Va., suggested that modern refractive procedures are very safe. “The bottom line is that all procedures carry extremely low risk,” he said. “Cataract procedures are safer with smaller incisions. LASIK is safer with femtosecond flaps.”
He did acknowledge both short- and long-term potential problems with LASIK. Immediate risks include flap complications and infection, he said. Problems with corneal nerve regeneration could lead to dry eye.
Contact lens risks, meanwhile, are “very definitely limited with a few simple gestures,” he said, including proper hygiene and eliminating overnight wear.

Editors’ note: Dr. Mathers has no financial interests related to this study. Dr. Sheppard has no financial interests related to his comments.

Contact information

Mathers: mathersw@ohsu.edu
Sheppard: 757-622-2203, jsheppard@vec2020.com