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Peripheral Prisms for Visual Field Expansion

Lezing van Prof. Dr. Eli Peli, O.D. op het NAH-congres Bekijk het eens anders: visuele waarnemingsproblemen door niet-aangeboren hersenletsel (NAH) bekeken vanuit verschillende perspectieven.


Prism corrections for visual field loss have been in use for many decades and increased in popularity with the introduction of the press-on™ Fresnel prism by 3M. The main limitations of the prior prism designs for homonymous hemianopia are: a small (10º) field expansion only when looking to the blind side with central confusion, central diplopia, and pericentral apical (optical) scotoma. To eliminate the annoyance and disturbance of central confusion and diplopia, we use peripheral prism segments mounted above and below the line of sight on one lens on the side of the field loss.  The clear area between the prism segments permits continuous single undisrupted central binocular vision while the extent of the prism across the lens provides perimetrically measurable peripheral field of view expansion at most positions of gaze. The peripheral prisms were initially implemented in a “horizontal” design using 40D (providing 20° field expansion) followed by the development of a 57D high power PMMA prism, providing 30° of field expansion. A new “oblique” design was developed that enables expansion of blind side field of view through the windshield of a car while single binocular vision is maintained centrally. A series of studies including multi center community based clinical trials have confirmed that about 3/4 of participated patients with hemianopia found the peripheral prisms helpful for obstacle avoidance when walking and 1/2 of them continued to wear it for an extended period (>12 months).  A randomized control trial in Belgium has shown that the prisms improve on road driving performance and recent driving simulator study has shown
improved pedestrians detection. To address the needs of field expansion for monocular patients, we have developed a novel optical device the multiplexing prism (MxP) which overcomes the apical scotoma even in monocular condition.  We analyzed the risk of collision between pedestrian in open environments, where pedestrians walking directions are not regulated, and found that the risk for such collisions is highest from pedestrians at eccentricity of 45°. We developed a novel optical element, multi pericopic prism (MPP), a cascade of refection-based prism-like devices that provides high angle of deflection (45°).  The field of view covered is up to 60° wide, the eye scanning range is more than twice wider than that afforded by the lower power (30°) prism, and the image quality is dramatically better than that available with current Fresnel prisms.

About the speaker

Dr. Peli is the Moakley Scholar in Aging Eye Research at Schepens Eye Research Institute, MEE, and Professor of Ophthalmology at Harvard Medical School. Since 1983 he has been caring for visually impaired patients at Tufts Medical Center. Dr. Peli is a Fellow of the American Academy of Optometry, the Optical Society of America, the Society for Information Display, and the International Society of Optical Engineering.  Dr. Peli's principal research interests are image processing in relation to visual function and clinical psychophysics in low vision rehabilitation, image understanding and evaluation of display-vision interaction. He also maintains an interest in oculomotor control and binocular vision.  Dr. Peli is a consultant to many companies in the ophthalmic instrumentation area and to manufacturers of head mounted displays (HMD). He served as a consultant on many national committees, including the NIH, NASA, US Air Force, Department of Veterans Affairs, US Navy Postdoctoral Fellowships Program, US Army Research Labs, and US Department of Transportation.  Dr. Peli has published more than 220 peer reviewed scientific papers and has been awarded 11 US Patents. He edited a book entitled Visual Models for Target Detection with special emphasis on military applications and co-authored a book entitled Driving with Confidence: A Practical Guide to Driving with Low Vision. He was presented the Glenn A. Fry, the William Feinbloom, the Charles Prentice awards by the AAO, the Alfred Bressler Prize, the Pisart Vision Award, the Alcon Research Institute award, the Otto Schade Prize, and the Edwin H Land Medal.  


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