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Contact Lens Shift Can Compromise Vision of People with Astigmatism with the Blink of an Eye
December 17th, 2007
2007 DEC 17 -- For contact lens wearers who wonder why their vision may sometimes fluctuate during the day, the answer may lie in the design of their contact lens, a new clinical study demonstrates. The findings, say researchers, may be of particular interest to the more than 11 million wearers of soft toric contact lenses for the treatment of astigmatism, a common vision condition in which surfaces of the eye, including the cornea, have an oval shape. The findings appear in the current issue of Optometry and Vision Science, the peer-reviewed journal of the American Academy of Optometry. According to the study, which used a novel, infrared, video-based technique to evaluate the clinical performance of two of the most frequently prescribed toric soft contact lenses in the United States, lenses utilizing an Accelerated Stabilization Design were superior when compared to lenses using a Prism Ballast Design in two of four tasks designed to mimic real-world viewing conditions involving quick, simultaneous movements of both eyes in the same direction. "During wide angle eye movements, tasks such as scanning a newspaper for information, gazing to the extreme side for changing lanes while driving or parking/backing up, or trying to view a flag on a putting green while teeing off in golf, a rotated contact lens can greatly compromise vision, resulting in blur and a temporary loss of visual clarity," says study co-author George A. Zikos, O.D., M.S., Manhattan Vision Associates/Institute Vision Research. "The rotational position and stability of a contact lens on the eyes during movement are critical in ensuring consistent vision while wearers are performing eye movement tasks required for work or recreation. Although the fit of a contact lens may be acceptable while in the doctor's examination chair, it may not necessarily correlate with the wearer's sense of vision quality during daily activities." Contact lenses using a Prism-Ballast design rely primarily on the effect of gravity and to a small degree the squeezing force of the upper eyelid to align the lens on the eye. Although this design concept has been shown to be effective in orienting lenses while in the doctor's chair, it's prone to rotating with the eyelids' movements (i.e., during blinking) or when the forces of gravity are not aligned with the direction of the lid forces, such as when the head is tilted when watching TV from a reclining position or while playing sports that require large eye and head movement. This may cause wearers to experience contact lens instability and some blurriness or fluctuation in vision. In contrast, much like the on-demand four-wheel drive feature now available in many cars, contact lenses using an Accelerated Stabilization Design rotate quickly to the desired position and remain stable when properly aligned. Lenses using this design concept harness the natural pressures of a blinking eye to balance the lens in place and quickly realign the lens if it rotates out of position during all eye and head movements. Keywords: Astigmatism, Clinical Trial Research, Contact Lens, Medical Device, Vistakon. This article was prepared by Biotech Business Week editors from staff and other reports. Copyright 2007, Biotech Business Week via NewsRx.com.
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