Self-Adjusting Glasses

September 13, 2006 The Aging Eye: Presbyopia When we view an object, the image coming into the eye is bent (refracted) by the cornea and focused by the lens onto the retina. The retina acts like film in a camera, transforming the information into nerve signals that are sent to the brain for processing. Normally, the lens of the eye adapts for near and distance vision, changing focus as necessary to give the image clarity. But as we age, the lens gradually loses its ability to quickly change focus. This is a condition, called presbyopia. Over time, people have more difficulty seeing close objects. A common sign of the condition is the need to hold reading material at arms length to bring the print into focus. Other potential signs of presbyopia are eyestrain or fatigue and headache associated with close-up work. Presbyopia is a condition that progresses gradually. Most people begin to show signs between 40 and 50. The American Optometric Association (AOA) says the most common ages at which patients begin to notice the effects are between 42 and 44. Based on 1995 population estimates, the AOA believes roughly 106 million Americans have presbyopia. Correcting Presbyopia Presbyopia is a natural occurrence that cant be prevented or halted. However, there are ways to compensate for the problem. People who otherwise have good vision may use a pair of reading glasses. Those who dont want to wear glasses may opt for a single contact lens for near-viewing. Those who need corrective lenses for other vision problems (like, nearsightedness, farsightedness or astigmatism) may have two pairs of glasses - one for near vision and one for distant vision. More commonly, patients opt for bifocal lenses. These are glasses with two different lenses that are combined into a single lens for each eye. The top of the bifocal lens is used for distance vision. A smaller portion of the lower lens aids near vision. For people who prefer contacts, one lens can be tailored for distant vision and the other for near vision. However, in some people, wearing two different contact lenses can cause problems with depth perception and spatial perception. Another option for those who want to avoid glasses is bifocal contact lenses. Bifocals of the Future The National Eye Institute estimates more than 150 million Americans wear corrective eyewear (that includes people who wear lenses for nearsightedness, farsightedness and some other vision problems), spending over $15 billion dollars each year on lenses, frames and contacts. Some people have a hard time adjusting to bifocal lenses. Others dislike the "aging" look associated with bifocals. Now, researchers are working on a high-tech pair of glasses that may eventually reduce or eliminate the need for bifocal lenses. The project started about five years ago, when a company called the "Egg Factory" asked for design help from researchers at the University of Arizona. The lenses are made of liquid crystal sandwiched between two pieces of glass. When a small electrical current is applied to the lenses, the liquid crystal molecules in the lenses change their orientation, modifying the focusing power of the lens. In the prototype model, a simple switch transforms the lenses into near or distant vision. There is still much research and testing that needs to be done. In the future, researchers would like to incorporate a view finder into the glasses. The view finder would measure the distance to an image and automatically adjust the focus. Experts will also need to develop designs that will be acceptable for wear by the public. Investigators at the University of Arizona estimate it will be at least five more years before the glasses hit the market. AUDIENCE INQUIRY If you have a specific question about presbyopia or other vision problems, speak with your eye care professional. For general information: American Academy of Ophthalmology, public website, http://www.medem.com BIBLIOGRAPHY Callina, T., and T. Reynolds, "Traditional Methods for the Treatment of Presbyopia," Ophthalmology Clinics of North America, March 2006, Vol. 19, No. 1, pp. 25-33. "Care of the Patient with Presbyopia," St. Louis: American Optometric Association, downloaded from website (http://www.aoa.org), August 14, 2006. Li, G., et al., "Switchable Electro-optic Diffractive Lens with High Efficiency for Ophthalmic Application," Proceedings of the National Academy of the Sciences, USA, April 18, 2006, Vol. 103, No. 16, pp. 6100-6104. Olson, Randall, M.D., "New Intraocular Lens Technology," American Journal of Ophthalmology, October 2005, Vol. 104, No. 4, pp. 709-716. "Presbyopia," St. Louis: American Optometric Association, downloaded from website (http://www.aoa.org), August 14, 2006. "Refractive Errors and Refractive Surgery," San Francisco: American Academy of Ophthalmology, downloaded from public website (http://www.medem.com), August 14, 2006. Sakimoto, Tohru, et al., "Laser Eye Surgery for Refractive Errors," The Lancet, April 29, 2006, Vol. 367, No. 9520, pp. 1432-1447. Schachar, Ronald, M.D., Ph.D., "Presbyopia: Cause and Treatment," eMedicine, updated July 14, 2006, downloaded from website (http://www.emedicine.com), August 14, 2006. Stahl, J., "Conductive Keratoplasty for Presbyopia," Journal of Refractive Surgery, February 2006, Vol. 22, No. 2, pp. 137-144. "Vision Problems in the U.S.," Bethesda: National Eye Institute, downloaded from website (http://www.nei.nih.gov), August 22, 2006. Research compiled and edited by Barbara J. Fister