Peli Eli, Jung Jae-Hyun
Schepens Eye Research Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts.
Optom Vis Sci. 2017 Aug;94(8):817-829. doi: 10.1097/OPX.0000000000001102.
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.
用于视野扩展的棱镜受棱镜顶点处的光学暗点（顶点暗点）限制。对于双眼功能正常的患者，单侧佩戴棱镜可使另一只眼睛补偿顶点暗点。由于存在顶点暗点，单眼患者的视野缺损无法通过传统棱镜或菲涅耳棱镜进行扩展。为克服单眼视野扩展中顶点暗点的限制，研发了一种新发明的光学装置——复用棱镜（MxP）。
一种类似菲涅耳棱镜的装置，其棱镜和平板元件交替排列，叠加了偏移和透视视图，从而产生视野扩展所需的（单眼）视觉混淆并消除顶点暗点。针对不同单眼视野缺损情况展示并初步评估了几种实施方案。使用计算和测量的视野检查法将MxP的视野扩展效果与传统棱镜的效果进行比较。
对于患有偏盲或周边视野受限的单眼患者，无顶点暗点的视野扩展显示有效。对于仅有一只眼睛的患者以及患有双颞侧偏盲的患者，MxP可增加鼻侧视野。置于颞侧远视野处的MxP可扩展正常视野。验证了控制两个图像之间对比度的能力。
一种新型光学装置在多种情况下被证明具有视野扩展技术的潜力。这些装置可能价格低廉，并且可以制造成外观上可接受的形式。
