Clinical study compares rotational stability of two differently designed toric soft contact lenses over a range of every day viewing conditions
JACKSONVILLE, Fla., Dec. 5 /PRNewswire/ -- 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.
About the Study
The purpose of the study was to compare objectively the rotational stability of two differently-designed toric soft contact lenses over a range of natural viewing conditions using a novel, infrared, video-based technique.
Twenty contact lens wearers (10 men, 10 women), ranging in age from 23-55, participated in this double-blind, randomized, crossover study. Following a baseline evaluation, participants were randomly fit with one of the top two selling toric lenses -- ACUVUE(R) ADVANCE(R) Brand Contact Lenses for ASTIGMATISM (Vistakon(R), Division of Johnson & Johnson Vision Care, Inc.), which employs an Accelerated Stabilization Design, and SoftLens(R) Toric (Bausch & Lomb), which features the Prism-Ballast Design. After performing a series of tasks, the first lens was removed. Following a 10-minute rest period, the second lens was inserted and immediately tested.
Researchers used the Eyetrack Monitoring System (ETMS), an infrared, video-based system that has been used previously to compare head and eye movements during reading for different spectacle progressive addition lens designs (corrective lenses used in eyeglasses to correct presbyopia). The custom-designed, head-mounted video camera was used to capture the image of the left eye with the contact lenses in place on both eyes during binocular viewing. Lenses were marked with small, black dots to assess lens position. The ETMS captured lens rotational images immediately upon lens insertion, and it continuously collected them at 30 frames per second, until all testing was completed.
Four tasks involving saccades (quick, simultaneous movements of both
eyes in the same direction), chosen to mimic real-world situations, were
then assessed in the following order:
-- Settling Time - Participants were allowed to view the examination room
freely for 15 minutes, while the lens was settling on the eye.
-- Reading - Participants read a newspaper with wide text for 2 minutes.
-- Visual Search - Participants gazed centrally, and then were instructed
to identify a number embedded within the text of a newspaper, read the
specified paragraph, and then return to primary position. The
paragraphs were positioned randomly from the center of the field in
-- Large versional tasks - Participants were instructed to blink to the
sound of a metronome set at 40 beats per minute. At approximately 20-
second intervals, they were instructed to gaze at targets located on a
large board positioned approximately two-feet away.
Following each task, participants gazed into primary position for recording of lens position.
The results showed that lenses using the Accelerated Stabilization Design were significantly more stable than the Prism-Ballast Design during settling time and during the large versional tasks that required the eyes to move synchronously and symmetrically in the same direction. For the other two tasks, performance was similar.
"The findings suggest that lenses featuring the Accelerated Stabilization Design may provide better performance under certain 'real world' eye movement situations by offering a more consistent visual experience and less variability in vision," says Dr. Zikos. "For some patients, it may be necessary to find the most stable lens required for their lifestyle."
The study was supported by Vistakon(R), Division of Johnson & Johnson Vision Care. Prior to publication, data was presented in part at the Association for Research in Vision and Ophthalmology meeting in Fort Lauderdale, Florida, 2006.
ACUVUE(R), Brand Contact Lenses are indicated for vision correction. As with all contact lenses, eye problems, including corneal ulcers, can develop. Some wearers may experience mild irritation, itching or discomfort. Lenses should not be prescribed if patients have any eye discomfort, excessive tearing, vision changes, redness or other eye problems. Consult the package insert for complete information. Complete information is also available from VISTAKON(R), Division of Johnson & Johnson Vision Care, Inc., by calling 1- 800-843-2020 or by visiting http://www.ecp.acuvue.com (for eye care professionals) or http://www.acuvue.com (for consumers).
ACUVUE(R), ACUVUE(R) ADVANCE(R), and VISTAKON(R) are trademarks of Johnson & Johnson Vision Care, Inc. SoftLens(R) is a registered trademark of Bausch & Lomb
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