Contact lenses carry the risk of several complications, including visual loss, corneal edema (swelling), scar, microbial keratitis (corneal infection), and corneal ulcers. Different contact lens types and materials have different rates of infection. Many patients are very aware of the risks of LASIK and PRK laser vision correction — of course there is a degree of risk with any eye surgery — but few realize the degree to which one common alternative to laser eye surgery, contact lenses, also carries risk. In a previous blog, I looked at the overall rate of infection with contact lenses compared to LASIK and PRK. Overall, the risk of corneal infection is actually lower with laser eye surgery than with contacts and the types of infection tend to be less aggressive with laser eye surgery than with contact lenses.

In this blog, we’ll look at the fact that different types of contact lenses (rigid, soft, extended wear, daily wear) all have different rates of infection. If you choose to wear contact lenses instead of having laser refractive surgery, then it is of course best to choose the lens type with the lowest infection rates.

Contact lenses pose several risks to the cornea, including chronic oxygen deprivation, which can lead to abnormal neww vessels (corneal neovascularization) growing over the edge of the cornea, to corneal swelling (corneal edema), and to loss of corneal endothelial cells (critical cells on the back surface of the cornea that the body is not capable of replacing). Contact lenses also can cause irritation and discomfort. In some cases, contact lenses can cause scar like nodules (Salzman nodules) on the cornea. The most dreaded contact lens complication, however, is microbial keratitis (infection) of the cornea, often associated with corneal ulcers created by the microorganism actually eating into the corneal tissue. In rare cases, depending on the organism involved, these infections can be extremely aggressive and rapidly progress to blindness. Contact lens corneal infections can also cause scars in the cornea with visual loss. In other severe cases, microbial keratitis can cause the need for a corneal transplant in which the infected cornea is replaced by a donor cornea from a human cadaver.

Overall risk of contact lenses is defined by the most serious complication: the risk of corneal infection (microbial keratitis). An Australian study referenced by the FDA looked at the rates of microbial keratitis with different types of contact lens materials and different wear patterns. In this study, the overall rate of contact lens related corneal infection was 4.8 per 10,000 wearers. The annual incidence of moderate or severe culture proven keratitis was 0.9 per 10,000 in those using daily disposable contacts, 3.1 per 10,000 in daily wear soft contact lens users, 4.5 per 10,000 in daily wear silicone hydrogel contact lens users, 11.7 in extended wear soft contact lens users, and 19.3 in extended wear silicone hydrogel contact lens users.

In the study, the rate of infection was clearly higher in silicone hydrogel contact lenses than conventional soft lenses, which is surprising since these lenses transmit more oxygen to the cornea. However, visual loss occurred more frequently with extended wear soft contact lenses than with extended wear silicone hydrogel lenses. Perhaps the different oxygen permeability of the two different types of lenses resulted in different types of organisms causing the infections, with more aggressive organisms possibly being associated with the less oxygen permeable lenses. Perhaps also the poorer oxygen environment simply inhibited the eye’s natural immune response more than was seen in the case with better the oxygen permeability of the silicone hydrogel material.

Also of note, in this study, corneal infection was seen with a longer duration of use in the silicone hydrogel extended wear lens patients than in those wearing conventional extended wear soft contact lens. This means that infections tended to occur sooner in those wearing conventional extended wear soft lenses. So, while the rate of corneal infection in extended wear conventional soft lenses was lower than in extended wear silicone hydrogel lenses, the infections tended to occur sooner and were more likely to cause visual loss.

In the end, when considering alternatives to LASIK or PRK, one must carefully weigh all the risks and benefits of each option. If contact lenses are selected, then it makes sense to wear them as safely as possible. I personally prefer that patients wear daily contact lenses instead of extended wear contact lenses worn overnight. Interestingly, the lowest rate of infection was seen with daily wear disposable soft lenses, but conventional lens material causes more oxygen deprivation to the cornea than does use of daily wear silicone hydrogel lenses. Chronic oxygen deprivation to the cornea carries its own set of problems. Of course, it is always important to have your contact lenses purchased from a reputable source, with a prescription, and only after being carefully fit and examined on a regular basis by an qualified eye care professional, either an optometrist or an ophthalmologist (“Eye-M.D.”).

See Also

LASIK (FDA)
The FDA website looking at LASIK, an alternative to contact lens wear.

Contact Lenses (FDA)
FDA website for contact lenses.

Contact Lens Risk (FDA)
FDA website for contact lens risks.

Corneal Edema
A review of corneal edema from multiple causes, including contact lens oxygen deprivation.

Care of the Contact Lens Patient
The American Optometric Association guidelines for care of the contact lens patient.

I Swam With My Contact Lenses In – Now I’m Blind in One Eye
Newspaper account of tragic, real world complication of contact lens use.

Fungal Eye Infections and Contact Lenses
All About Vision review of fungal keratitis associated with contact lens use.

A 1-Year Prospective Clinical Trial of Balafilcon A (PureVision) Silicone Hydrogel Contact Lenses Used on a 30 Day Continuous Wear Schedule
A long term prospective study of a silicone hydrogel contact lens worn on an extended wear basis.

The Incidence of Contact Lens Related Microbial Keratitis in Australia
Study referenced by the FDA in its review of the rate of microbial keratitis (corneal infection) seen with wear of different types of contact lenses and contact lens materials.

Facts About the Cornea and Corneal Disease
National Institutes of Health and National Eye Institute website on the cornea.

Corneal Neovascularization
A review of corneal neovascularization, a complication of contact lens abuse.

Corneal Ulcers
U.S. National Library of Medicine and National Institutes of Health review of corneal ulcers and corneal infections.

Silicone Hydrogel Contact Lenses and the Ocular Surface
A review of silicone hydrogel contact lenses, contacts which transmit oxygen better than conventional soft contact lenses.

Extended Wear Soft Contact Lenses: Are They Safe?
All About Vision review of safety of extended wear soft contact lenses.