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High-Power Prismatic Devices for Oblique Peripheral Prisms
Eli Peli1, Alex R Bowers, Karen Keeney
1*MS, OD, FAAO †PhD, FAAO ‡MS §PhD Schepens Eye Research Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts (EP, ARB, J-HJ); and Chadwick Optical, Inc., Souderton, Pennsylvania (KK).
Summary
New prism designs for hemianopia expand visual fields centrally, addressing limitations of conventional prisms. These innovations aim to improve visual function and safety, particularly for driving, by closing the central visual gap.
Area of Science:
- Ophthalmology
- Optics
- Visual Neuroscience
Background:
- Conventional horizontal peripheral prisms for hemianopia expand visual fields but leave a central vertical gap, crucial for activities like driving.
- Tilting prisms centrally closes this gap but reduces lateral field expansion, necessitating higher prism powers.
Purpose of the Study:
- To develop and test novel prism designs that increase prism power to eliminate the central visual gap while maintaining broad lateral field expansion.
- To overcome limitations of existing prisms, such as reduced scanning range and binocular impact.
Main Methods:
- Investigated yoked-prism carriers, bi-part Fresnel prisms (two segments angled), and reflective prisms (nonparallel periscopic mirrors).
- Focused on designs to increase prism power and address the central gap in hemianopic field expansion.
Main Results:
- Yoked-prism carriers offered a modest increase in lateral power.
- Bi-part Fresnel prisms achieved high power but with some image quality reduction.
- Reflective prisms showed potential for high power and superior optical quality, though field extent and interruptions were considerations.
- High-power bi-part and reflective prisms enabled an effective eye scanning range exceeding 15 degrees into the blind hemifield.
Conclusions:
- Developed prism designs may overcome limitations of conventional prisms, such as apical scotomas and reduced scanning range.
- These novel designs offer potential for improved visual field expansion in hemianopia and other applications.
- High-power prisms are feasible and enhance the scanning range into the blind hemifield.