Q) My daughter is consider-ing swapping her regular soft daily-wear contact lenses for 30-day silicone hydrogel lenses, but I've heard that they increase your risk of infection. Can you tell me a bit more about these lenses and whether they are safe?-E.S., via e-mail
A) Extended-wear contact lenses can be worn over-night and for up to a month without being removed. As well as offering a hassle-free alternative to glasses and sur-gery, these lenses-made of silicone hydrogel, or 'SiHy'-can alleviate some of the common problems of conventional soft contact lenses such as dry eyes and physical discomfort.
Among 1092 current soft-contact-lens wearers, 112 were refitted with the new-generation SiHy lenses (Johnson & Johnson's Acuvue Oasys). Two weeks later, 88 per cent of these patients noted improvement in overall comfort, 76 per cent had fewer uncomfortable hours of wear and 75 per cent had less dryness(Eye Contact Lens, 2006; 32: 281-6).
Patients who switched to Acuvue Oasys SiHy lenses saw improvement in comfort in 12 out of 12 'challeng-ing environments', such as using a computer, napping or air travel. Similarly, those who tried Ciba Vision's Air Optix reported greater comfort in 9/12 environments (Optom Vision Science, 2007; 84: 302-8).
However, none of them slept in their SiHy lenses. So, the question is: is it safe to wear them overnight and for extended periods of time?
As you rightly point out, the main concern with extended-wear lenses is the risk of infection. All contact-lens wearers are at some such risk, as all types of contact lenses reduce the amount of oxygen that reaches your cornea-the clear membrane over-lying the pupil and iris-and less oxygen can promote infection. And studies show that the incidence of eye infections is higher among people who sleep in their lenses.
In the 1980s, when extended-wear lenses first came out, a four- to 15-fold increase in the risk of infection was seen when lenses were worn overnight, rather than just during the day (Br J Opthalmol, 2000; 84; 327-8). Users of extended-wear lenses who wore them overnight had a 10- to 15-times greater risk of ulcerative keratitis, inflammation and ulcera-tion of the cornea, compared with those who didn't sleep in their lenses (N Engl J Med, 1989; 321: 773-8). Ulcer-ative keratitis (inflammation and ulceration of the cornea) is consider-ed the most serious adverse effect of contact lenses as it can lead to scarring and blindness.
As a result of these findings, the US Food and Drug Administration (FDA) recommended that lenses approved for extended wear should be worn for no more than one week. And many worried eyecare physicians discouraged patients from sleeping in their lenses.
Recently, however-thanks to the highly permeable silicone hydrogel-extended-wear lenses have made a comeback. SiHy lenses allow more oxygen to reach the eye than conven-tional soft lenses, making overnight wear safer than before. In fact, they deliver so much oxygen to the cornea that some brands of SiHy lenses are approved for 30 days of continuous wear.
CIBA Vision's Night and Day are among the 30-day lenses now on the market. In more than 6000 people who wore these lenses for up to 30 nights consecutively, the incidence of bacterial or fungal infection of the eye was low, around 18/10,000 users. Also, the rate of microbial infection resulting in loss of visual acuity was only about 3.6/10,000 wearers (Oph-thalmology, 2005; 112: 2172-9).
However, these rates are still higher than with daily-wear lenses, and SiHy lenses on a daily-wear basis have fewer adverse events than when wearing them continuously (Eye Contact Lens, 2007; 33: 288-92). One study concluded that "extended wear with even these newer [SiHy lenses] is still a risk factor in the development of microbial keratitis" (Br J Ophthalmol, 2002; 86: 355-7).
In the end, your daughter needs to decide whether the increased freedom of extended-wear lenses is really worth the greater risk of infection. Also, as not everyone is suitable for 30-day lenses, make sure she consults a professional who can recommend a wearing schedule based on her individual needs.
She may also wish to consider 'flexible wear', which calls for remov-ing the extended-wear lenses each night. But when she wants to sleep in them-say, for a weekend away or an afternoon nap-it's considered safe to do so.
Finally, as with all types of contact lenses, the risk of infection can be reduced by carefully following the instructions for their wear, care and replacement.
Some lens safety tips
- Listen to your eyes: they should look well and feel comfortable, and vision should be clear
- If you have a problem, immediately remove your lenses and contact your eyecare professional
- Never wear them for longer than prescribed
- Always wash and rinse your hands thoroughly before handling them
- Wear good-fitting goggles if you go swimming with them
- Avoid wearing them overnight if you are unwell
- See your eyecare professional for regular checkups.