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According to research presented at the American Academy of Optometry, contact lenses prescribed for longer replacement intervals can lead to more extreme over-wear, causing undesirable clinical effects. An article from opticianonline revealed some of the concerning figures about this situation. According to results of the research, more than half of wearers of frequent replacement contact lenses did not comply with their prescribed replacement schedule.

Participants in the survey contained two groups: one of them wore two-week contact lenses and the other group wore monthly lenses. Their responses were both disappointing. The research conducted an online sponsor-masked survey which took a random sample of 645 frequent replacement contact lens wearers. The results were quite bad and similar.

In the group containing two-week lens wearers, only 43% of them replaced their lenses as prescribed. There were 65% of them replaced lenses every three weeks, 85% at eight weeks or more and 2% at ten weeks or more. When researchers came to assess the group who wore monthly lenses, only 36% of them maintained lens replacement as required. About 55% only replaced their lenses at five weeks, 23% at eight weeks or more and 14% at 10 weeks or more.

Among all of these unexpected numbers, the most surprising one was the percentage of patients who extended lens replacement to eight weeks or more. Such an interval was significantly longer than a normal requirement. This result considerably surprised the study author Sheila Hickson-Curran who was also director of medical affairs at Vistakon.

The survey of the research is just an example of the popular practice among contact lens wearers. Most wearers will ask their doctors to extend the Rx “this one time” but will not schedule an appointment when they run out of their lenses. Encountering such kind of patients, eye doctors would wish them go to a retail chain for Rx and materials instead.

Transition lenses have long been on the market for nearly 40 years. But only eyeglass lenses are available. These eyeglass lenses would automatically darken in response to bright sunlight and restore their normal brightness once sunlight is removed. The basic principle of these transition sunglasses is to use millions of molecules of photochromic dyes. These dyes can absorb UV light, which leads to a shape change. As a result, the lenses will darken. Once UV light disappears, the molecules will restore their normal shape and maintain transparent. 

This flexibility has never been successfully adapted to contact lenses. But now, researchers in Singapore are addressing this challenge. They have partially succeeded in developing UV-responsive contact lenses that offer similar functions as photochromic sunglass lenses. Under the Institute for Bioengineering and Nanotechnology (IBN), researches led by Jackie Ying have successfully developed their photochromic contact lenses and plan to test them in animals. 

The most important factor that assesses the success of their UV-responsive contact lenses is to see whether the dyes are contained within the lenses stably. In fact, the most difficult task is to fill the dyes that are responsible for brightness change in the lenses. Jackie Ying and his colleagues use a novel polymer laced with an intricate network of nano-sized tunnels to “store” the dyes. This most challenging task of applying dye coatings to the lens surface has been solved. In other words, photochromic contact lenses developed by these researchers embed dyes uniformly throughout the lens material. In this way, more dye molecules can be packed into the lens material. 

Speed of transition is the most critical factor for both photochromic eyeglass lenses and UV-responsive contact lenses. For instance, a car suddenly going into a tunnel requires immediate brightness change in the driver’s lenses. Thanks to the special design from IBN, their photochromic contact lenses have greater sensitivity to light and offer a faster response. According to Ying, their UV-responsive contact lenses take only 10 to 20 seconds to darken or brighten.