Overall, the safety of wearing contact lenses is stellar. Fortunately, sight-threatening corneal infections are exceedingly rare. But when microbial keratitis does occur, any loss in vision is catastrophic. Microbial keratitis has remained a somewhat unsolved problem for many years. The incidence of corneal infection in contact lens wearers has not changed significantly since first reported in 1989 (one out of 500 extended wear users and one out of 2,500 daily wear users).1 Despite large advances in lens materials, care products and attention drawn to modifiable risk factors, the number of infections reported has remained static.
Still, there is some good news. Daily disposable lenses, when worn as intended as single-use devices, are now considered safer than wearing gas permeable lenses.2 When infections do happen in daily disposable lens users, they tend to have a lower rate of environmental causes (i.e., Pseudomonas aeruginosa), are more likely to have an endogenous cause and are less likely to have culture-positive results. Infections related to endogenous (or lid pathogen) sources tend to generally be less severe and resolve faster than those from environmental sources.
A Frontier with Promise
Beyond manufacturers providing new materials and accoutrement, identifying modifiable risks and screening appropriately, the next frontier will likely be identifying genes and looking for any genetic predisposition that contributes to the pathophysiology of corneal disease. Identifying those most susceptible and knowing who might experience a more severe response might be a new realistic approach to reducing infection rates. Researchers at Case Western Reserve University and University Hospitals of Cleveland have recently been funded to study exactly that.
Published works have associated genetic variants in different cytokine genes and one beta-defensin gene, DEFB1, with susceptibility and severity to microbial keratitis in contact lens users.3 Cytokines are small proteins released by cells that have a specific effect on the interactions and communications between cells.4 This remains a focused area of investigation when it comes to identifying important steps in any pathophysiology process.
Researchers have looked closely at single nucleotide polymorphisms and recruitment strategies associated with contact lens related keratitis. Pro-inflammatory IL-6 cytokine deficiencies are associated with more severe disease states with a three to six times worse outcome; so, IL-6 may play a protective role against microbial keratitis.3 Variants in cytokine genes, in addition to IL-6, define one’s inherent inflammatory profile, which may help determine susceptibility and severity of response to corneal infection. An altered immune system surely plays a significant role in the pathophysiology of any disease process.
The cornea does have inherent protection; however, when things go wrong, a cascade of catastrophic events occur that can lead to bacterial adherence and infection. The eye has a normal community of flora expected to confer some resistance to infection. Yet, the bacterial flora in contact lens wearers has been shown to differ significantly from those who don’t wear lenses. This may provide insight into the microbiome’s possible role in increasing the risk for infection.5
How do we go about managing or mitigating this conspiracy between the epithelium when injured and microbial contamination that results in a devastating event in contact lens wearers? Genetic susceptibility testing and proper patient communication may just provide the answer.
Innovations in lens material, lens designs, care products and strategies to minimize infection and reduce overnight wear have not reduced the rate of corneal infection to a desirable level. Knowing ahead of time a patient’s genetic predisposition may add immensely to our ability to alter the course of this dreaded complication. Contact lens safety is satisfactory, but there are areas that need improvement. Perhaps this new area of investigation may someday help us pick who might be most susceptible to infection and drive the rate of corneal infection to a desirable level.
1. Poggio EC, Glynn RJ, Schein OD, et al. The incidence of ulcerative keratitis among users of daily-wear and extended wear soft contact lenses. N Engl J Med. 1989;321:779-83.
2. Stapleton F: Glenn Fry Award Lecture, American Academy of Optometry; San Antonio, November 9, 2018.
3. Shin H, Price K, Albert L, et al. Changes in the eye microbiota associated with contact lens wearing. mBio. 2016;7(3):198.
4. Carnt NA, Willcox MD, Hau S, et al. Immune defense single nucleotide polymorphisms and recruitment associated with contact lens keratitis. Ophthalmol. 2012;119:1997-2002.
5. Zhang JM, An J. Cytokines, inflammation and pain. Int Anesthesiol Clin. 2007;45(2):27-37.