Date of Degree

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Vision Science

Advisor

Jeff C. Rabin

Advisor

Charles G. Connor

Advisor

Lydsey M. Ferris

Advisor

Brian K. Foutch

Advisor

Srihari Narayanan

Abstract

Visual acuity (VA) is universally accepted as the gold standard metric for ocular vision and function. Contrast sensitivity (CS), color vision, and electrophysiological testing for clinical and occupational settings are warranted despite being deemed ancillary and minimally utilized by clinicians. These assessments provide essential information to subjectively and objectively quantify and obtain optimal functional vision. They are useful for baseline data and monitoring hereditary and progressive ocular conditions and cognitive function. The studies in this dissertation highlight the value of contrast sensitivity, color vision, and cone specific electrophysiological testing, as well as the novel metrics obtained with potential practical clinical applications for visual function and perception evaluation in patients in various settings.

The first study aimed to design a clinically expedient method to combine color CS and color naming (CN) into a single, multi-metric test of color vision, the Color Contrast Naming Test (CCNT). This was accomplished by comparing and validating it with the standardized computerized Cone Contrast Test (CCT; Innova Systems, Inc.). Color vision deficient (CVD) and color vision normal (CVN) findings showed a strong correlation between the CCNT CS and the standard CCT. Furthermore, CCT CS showed distinct scores in 50% of CVDs, while the CCNT composite score (mean of CS and CN) showed distinct scores in 70% of CVDs, showing better potential discrimination of CVD color abilities. This novel metric has potential applications for identifying hereditary or progressive CVD severity and capabilities.

The second study focused on electrophysiological diagnostics, specifically cone specific visual evoked potentials (VEPs), to objectively measure long-term neural adaptive responses to color-correcting lenses (CCLs). Dr. Werner and colleagues determined that extended wear (for 12 days) of color-correcting lenses improved red-green color perception in hereditary CVD even without wearing CCLs. Furthermore, Dr. Rabin and colleagues were able to objectively measure both immediate short-term (baseline, 4, 8, 12 days) and long-term (3, 6, 12 months) improvements of color perception status post-CCL removal with cone specific VEPs – something that has never been done before. The novel findings from both studies support the notion that neural adaptive changes can occur over short- and longer-term periods despite minimal daily wear time. More importantly, this further supports the value of suprathreshold cone VEPs to objectively assess color vision function in both clinical and occupational settings.

Most dry eye studies use measures of tear quality and volume coupled with standard clinical tests such as high contrast visual acuity (VA), while fewer studies have investigated the effects of dry eyes on low contrast vision. The final study was designed to determine the impact of Meibomian Gland Dysfunction (MGD) dry eye on high and low-contrast vision, including both black/white (luminance) and cone specific color vision. A primary intent was to determine if these novel metrics improved following minimal meibomian gland (MG) expression. The computerized CCNT and CCT (cone and black/white) tests used in this study confirmed that minimal MG expression improved low contrast performance for long (L cone) and short (S cone) wavelength-sensitive cones. These improvements were most significant using throughput (CS/response time) and CCNT composite scores, both novel metrics for potential use in dry eye diagnosis, treatment, and management. Physical optics, including decreased destructive interference in the stroma, most detrimental with red light, and increased scattering by subtle epithelial, endothelial, and/or tear film defects, most detrimental for blue light, could each decrease retinal image contrast most evident with L and S cone CS.

Contrast sensitivity, color vision, and cone specific electrophysiological testing are non-optimally and infrequently utilized in basic, clinical, applied, and translational research or occupational settings. These studies showed provocative results within their respective categories and confirmed their validity and importance for identifying and monitoring ocular conditions and neural adaptive or cognitive functions. Furthermore, novel metrics such as throughput and CCNT composite scores serve as potential tangible and practical visual function and perception assessment standards.

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