Measuring Low Vision: Perception and Function

Abstract

The impact of vision impairment affects both what can be perceived as well as how effectively visual tasks can be carried out. Therefore, a complete understanding of the effects of vision impairment must account for both its functional and sensory impact. This dissertation investigates both sides, focusing on function in the context of a visual search task, and focusing on sensation in the context of remote tests of visual acuity and contrast sensitivity. Chapter 1 provides an overview of the thesis and introduces key concepts employed throughout the research. Chapter 2 evaluates how visual impairment affects functioning in the context of a visual search task, focusing on how illumination and contrast affect object visibility, a key factor determining whether a space is safe and easy to move through with impaired vision. While recommendations for improving object visibility typically center on increasing illumination, suggesting “brighter is better,” we aimed to determine whether the efficacy of such interventions depend on the degree to which they also increase contrast. Normally sighted participants wore blur goggles that severely restricted their visual acuity, artificially restricting it to 20/1250. They then walked through a room, visually searching for target objects, some of which received enhanced illumination from spotlights. Results showed that enhanced illumination improved the rate at which targets were seen only if it also improved the target’s contrast with the background behind it, and this information was used to provide guidelines for implementing focused lighting for visual accessibility. Chapter 3 focuses on evaluating the sensory impact of visual impairment by describing the development and initial validation process for novel remote tests of visual acuity and contrast sensitivity. Remote testing allows patients to undergo vision evaluation from a location outside a clinic, and typically involves the digital presentation of test stimuli over a device the patient owns. Such tests are especially valuable during times when travel is restricted (e.g. COVID-19 lockdown), or for individuals with limited mobility, as the tests can be taken without leaving home. The new tests can measure much poorer acuities than other currently available remote tests, and overcome challenges in contrast calibration not addressed by other digital contrast sensitivity tests. To validate the new tests, normally sighted participants with artificially restricted visual acuity and contrast sensitivity were tested in a laboratory environment using both the remote tests and gold-standard clinical charts for comparison. The novel tests showed good agreement with the charts, demonstrating similar scores with low variance. Chapter 4 reports on the continued validation process of the tests developed in Chapter 3, moving from a controlled laboratory testing environment to remote testing of low vision participants at their homes. We found that the tests demonstrated similar scores on average, but scores were also more variable compared to testing in a laboratory environment, potentially due to uncontrolled viewing conditions in the home environment. Altogether, the studies presented in this dissertation provide insight into how the complex functional and sensory consequences of vision impairment can be both measured and addressed. The guidelines and tools developed in this work serve as valuable resources, applicable to both the creation of visually accessible spaces and the administration of remote vision testing.