By Kristin Birks
Silicone hydrogel lenses were commercially introduced in 2001, but they have not proven to be the Holy Grail eye care professionals had hoped.
“When silicone hydrogel lenses were first introduced for overnight wear, I think the entire industry was very hopeful they would significantly reduce the risk of infection,” said Nancy Keir, OD, practicing optometrist and Senior Clinical Scientist at the University of Waterloo’s Centre for Contact Lens Research.
Microbial infections can be associated with contact lens wear and it was once thought that increasing levels of lens-oxygen transmissibility would lower the incidence of microbial keratitis.
On the one hand, “they have successfully reduced the level of hypoxia with soft contact lens wear due to their increased oxygen transmissibility,” she said. “Generally, silicone hydrogels are considered a breakthrough in material development.”
However, microbial keratitis is not solely the result of oxygen transmissibility with contact lenses and the reasons can be multifactorial, said Keir Danielle Robertson, OD, PhD is an Assistant Professor at the University of Texas Southwestern
Medical Center concurs.
She wrote a review article on the effects of silicone hydrogel lens wear on the corneal epithelium and risk of microbial keratitis. It was published in the January 2013 issue of Eye & Contact Lens.
In her article, Robertson reports that the risk for patients developing microbial keratitis was greatest during the first six months of wearing silicone hydrogel lenses, suggesting that some type of adaptation takes place.
In addition, Robertson says there are no differences between patients who wear their lenses for six days and nights and those patients who wear their lenses for 30 days and nights.
“Sleeping in lenses, regardless of duration, puts the patient at risk for problems,” she said.
Finally, Robertson says that despite initial high hopes when the lenses were first developed, wearing silicone hydrogel lenses has not altered the overall incidence of microbial keratitis.
Eye care professionals should feel reassured because microbial keratitis occurs relatively rarely.
“Contact-lens related microbial keratitis occurs in four patients per 10,000 people per year and about one patient in 500 people per year in people who sleep in their lenses,” said Robertson. “But, whenyou have about 140 million patients
worldwide we start to see these numbers pop up a little more than we want.”
To reduce the risk of microbial keratitis during lens wear, Robertson advocates reducing the bacterial bioburden on the lens and in the lens case.
“This comes down to compliance,” said Robertson.
Keir agrees. She advises making sure that lenses and lens cases are clean, disinfected and replaced at appropriate intervals. Patients should be instructed to wash their hands before handling their lenses and not to use tap water or swim with their
lenses. These “are all important ways of reducing bacterial bio-burden,” said Keir. “In addition, patients who are sick or unwell should not wear their lenses.”
“Infections with silicone hydrogel lenses don’t always initially present with severe signs and/or symptoms,” said Keir. “It remains important to reinforce compliance with patients and to advise them to always be aware of how they see and how their eyes look and feel.”
“If they notice a problem the first thing they should do is remove their lens. If their eye doesn’t feel better, or starts to feel worse, they should seek medical attention immediately. Although rare, microbial infections are serious.”
The key role eye care professionals play in post-market surveillance Keir notes it’s important for eye care professionals to report problems so post-marketing data can uncover unexpected problems.
Keir advocates that eye care professionals keep abreast of current research and general risk factors, such as poor patient compliance and lens case hygiene.
“The bottom line is that optometrists play an important role in helping the industry monitor problems with lenses,” said Keir.
“They can do this by reporting adverse reactions through the appropriate channels these products have once they’ve been released for commercial use.”
The good news is that silicone hydrogels, like their hydrogel counterparts, are generally safe when used correctly.