Retrospective Analysis of Factors Predicting Functional Success in Telescopic Spectacle Use by Low Vision Patients

Abstract

Telescopic spectacles are frequently prescribed for visually impaired patients, but clinical observation reveals that low vision patients often do not achieve expected functional use of these costly visual aids. This may be a result of patients’ inability to maintain adequate stability of magnified images on the retina during unintended head movements caused by ambulation, tremor, and postural instability. Although the visual-vestibulo-ocular reflex (VVOR) produces eye movements that partially compensate for head movements, this compensation is incomplete when images are magnified by head-mounted telescopes.1 It has been demonstrated in normally sighted subjects wearing telescopic spectacles that head motion significantly decreases dynamic visual acuity (DVA), the acuity during head motion.2 We hypothesized that insufficient compensation of head instability might cause reduced DVA and motion sickness, and might thus predict failure of low vision patients to make functional use of telescopic spectacles. We have been testing this retinal image instability hypothesis to develop methods that may be useful in prediction of the successful use of telescopic spectacles.

Comparative effectiveness between two types of head-mounted magnification modes using a smartphone-based virtual display

“…Because head-stabilizing strategies improve performance with telescopic viewing systems, 7 we wanted to investigate a magnification display that would improve the overall viewing experience by minimizing symptoms of visual discomfort caused by magnified image motion. One way to get rid of the magnifying image motion is with the virtual bioptic telescope display.…”

“…Thus, the compensatory visual-vestibulo-ocular reflex gain must match the magnification factor of the viewing system. If not, retinal image slip will occur causing motion sickness 6,7 . Demer et al 7 have shown that retinal image stability increases the likelihood low-vision patients will tolerate the use of a telescopic aid in real-world environments.…”

“…If not, retinal image slip will occur causing motion sickness 6,7 . Demer et al 7 have shown that retinal image stability increases the likelihood low-vision patients will tolerate the use of a telescopic aid in real-world environments. There are two reasons for this: (1) dynamic or functional visual acuity improves with head (and retinal image) stabilization, and (2) improved retinal image stability reduces vestibular ocular mismatch responsible for motion sickness 7 .…”

“…Demer et al 7 have shown that retinal image stability increases the likelihood low-vision patients will tolerate the use of a telescopic aid in real-world environments. There are two reasons for this: (1) dynamic or functional visual acuity improves with head (and retinal image) stabilization, and (2) improved retinal image stability reduces vestibular ocular mismatch responsible for motion sickness 7 . Thus, strategies to improve retinal image stabilization through a magnified viewing system are key for minimizing adverse symptoms and for improving overall performance with the device.…”

Smooth pursuit deficits impact dynamic visual acuity in macular degeneration

“…26), most studies in macular degeneration have examined dynamic visual acuity with head movements and stationary targets, particularly in the context of the use of telescopic magnification. For example, Demer and colleagues 30 identified retinal image stability (appropriate vestibulo-ocular reflex [VOR] gain) as the key factor for participants' functional vision and ability to adapt to the use of telescopic lenses. This study examined VOR gain in response to head rotations, a task that, unlike smooth pursuit, stabilizes the full visual field, 31 regardless of fixation location.…”