Low Vision Enhancement with Head-mounted Video Display Systems: Are We There Yet?

Abstract

Head-mounted video display systems and image processing as a means of enhancing low vision are ideas that have been around for more than 20 years. Recent developments in virtual and augmented reality technology and software have opened up new research opportunities that will lead to benefits for low vision patients. Since the Visionics low vision enhancement system (LVES), the first head-mounted video display LVES, was engineered 20 years ago, various other devices have come and gone with a recent resurgence of the technology over the past few years. In this article, we discuss the history of the development of LVESs, describe the current state of available technology by outlining existing systems, and explore future innovation and research in this area. Although LVESs have now been around for more than two decades, there is still much that remains to be explored. With the growing popularity and availability of virtual reality and augmented reality technologies, we can now integrate these methods within low vision rehabilitation to conduct more research on customized contrast-enhancement strategies, image motion compensation, image-remapping strategies, and binocular disparity, all while incorporating eye-tracking capabilities. Future research should use this available technology and knowledge to learn more about the visual system in the low vision patient and extract this new information to create prescribable vision enhancement solutions for the visually impaired individual.

Figures

Figure 1

The top figure compares log contrast sensitivity as a function of log spatial frequency for the average of 5 normally sighted subjects (black points) and two low vision patients (green points and red points) from Chung and Legge. Y-intercept values out the log contrast sensitivity at the peak of the CSF for normal (black) and low vision patients (green and red) and x-intercept values are the respective cut-off frequencies. The middle figure is log contrast sensitivity at the peak of the contrast sensitivity vs spatial frequency function (CSF) vs log contrast sensitivity measured with the Pelli-Robson chart. The bottom figure illustrates log cut-off frequency for the CSF vs log visual acuity measured with the ETDRS chart expressed in units of log spatial frequency (unpublished data from 80 low vision patients obtained in 1994). The solid line in the middle and bottom figures is the identity line (slope=1 and intercept=0).]

Figure 2

Log contrast threshold vs log spatial frequency for a normally sighted person (black curve) and a low vision patient (red curve). The area within the red curve represents contrasts that are visible to the patient. The area within the black curve are contrasts visible to a normally sighted person.

Figure 3

Normal log contrast sensitivity for different average luminance levels (see legend). Cut-off frequency (corresponds to visual acuity) increases with luminance. Contrast sensitivity at the peak also increases with luminance.

Figure 4

Left picture: original unprocessed image. Middle picture: contrast stretched in the luminance (L) channel of the original image and combined with unaltered color channel images (a,b). Right picture: unsharp mask applied to luminance (L) channel of original picture and combined with unaltered color channel images (a,b).

Figure 5

Image remapped around scotoma (black area) with a tear in the image and distortions to prevent any information from being lost.

Figure 6

Two magnification bubbles of different shape. 6A depicts a rectangular bubble potentially more helpful for reading tasks, while 6B depicts a circular bubble that may be used for object and facial recognition. Note the distortion around margins of the bubble to prevent information from being lost due to image overlap.