Prisms used for field expansion are limited by the optical scotoma at a prism apex (apical scotoma). For a patient with two functioning eyes, fitting prisms unilaterally allows the other eye to compensate for the apical scotoma. A monocular patient’s field loss cannot be expanded with a conventional or Fresnel prism because of the apical scotoma. A newly invented optical device, the multiplexing prism (MxP), was developed to overcome the apical scotoma limitation in monocular field expansion.
A Fresnel–prism–like device with alternating prism and flat elements superimposes shifted and see-through views, thus creating the (monocular) visual confusion required for field expansion and eliminating the apical scotoma. Several implementations are demonstrated and preliminarily evaluated for different monocular conditions with visual field loss. The field expansion of the MxP is compared with the effect of conventional prisms using calculated and measured perimetry.
Field expansion without apical scotomas is shown to be effective for monocular patients with hemianopia or constricted peripheral field. The MxPs are shown to increase the nasal field for a patient with only one eye and for patients with bitemporal hemianopia. The MxPs placed at the far temporal field are shown to expand the normal visual field. The ability to control the contrast ratio between the two images is verified.
A novel optical device is demonstrated to have the potential for field expansion technology in a variety of conditions. The devices may be inexpensive and can be constructed in a cosmetically acceptable format.
Schepens Eye Research Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
Corresponding Author: Eli Peli Schepens Eye Research Institute 20 Staniford St Boston, MA 02114 e-mail: firstname.lastname@example.org
Supplemental Digital Content: Contrast reduction of the see-through and shifted views in multiplexing prism is analyzed for different aperture ratios and angles of incidence in the Appendix, available at http://links.lww.com/OPX/A301. This contrast reduction is the main adverse effect of the multiplexing prism and is affected by the two variables analyzed.
Submitted: July 12, 2016
Accepted: May 3, 2017
Published Online: July 19, 2017
Funding/Support: Supported in part by National Institutes of Health grant R01EY023385.
Conflict of Interest Disclosure: Dr. Peli has a patent application pending for the multiplexing prism and its applications, assigned to the Schepens Eye Research Institute.
Author Contributions and Acknowledgments: Conceptualization:EP, JHJ; Data curation: EP, JHJ; Formal analysis: EP, JHJ; Funding acquisition: EP; Investigation: EP, JHJ; Methodology: EP, JHJ; Project administration: EP; Resources: EP; Supervision: EP; Validation: EP, JHJ; Writing – original draft: EP, JHJ; Writing – review & editing: EP, JHJ; Software: JHJ; Visualization: JHJ. The authors thank Henry Apfelbaum for help with the manuscript and figures generation and Amy Doherty and Kassandra Lee for help with subject tests.