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Abstract

Glaucoma is a progressive optic neuropathy, with early diagnosis being crucial for preventing irreversible vision loss. The research presented in this thesis aimed firstly to characterise the distribution and variability of novel functional tests in healthy controls. This enabled the subsequent evaluation of the effect of glaucoma on visual function, examined by a combination of flicker, colour, and contrast sensitivity tests, and the association between retinal function and structure, evaluated by optical coherence tomography (OCT).

In the first study, a systematic literature review was conducted to evaluate existing literature on the effects of early glaucoma and ocular hypertension (OHT) on contrast, colour, and flicker sensitivity, specifically to determine which testing modalities are diagnostic for early glaucoma. The review suggests that new psychophysical approaches that are intended to isolate specific subpopulations of RGCs (and their respective retino-geniculate pathways) may contribute to improved diagnostic performance. Flicker modulation sensitivity (FMS) was the least studied visual function impacted by glaucoma, with only 16% of studies assessing temporal contrast sensitivity (TCS) in glaucoma.

The second study reports the test-retest and intrasubject variability of the Flicker-Plus test measuring rod and cone-enhanced flicker modulation thresholds (FMTs) in healthy individuals (n=30). The findings demonstrated good (0.75-0.9) to excellent (>0.9) test-retest repeatability at all peripheral locations, under both cone and rod-enhanced conditions, with no evidence of significant learning effects, suggesting that this test would be valuable in assessing visual function loss.

The third study established the upper and lower normal age-related threshold limits and inter-subject variability of monocular cone and rod-enhanced FMT, providing an enhanced age-related reference range for future diagnostic studies. Results showed that below 45-years of age, cone- and rod-mediated FMTs remained relatively stable, both centrally and in the periphery. Above 45-years, cone and rod thresholds increased exponentially with increasing age. The rate of increase in threshold with increasing age was ~1.4 times greater for rods than for cones. Peripheral thresholds exhibited much reduced inter-subject variability as compared to central thresholds, for both rods and cones. Elevated FMTs beyond predicted age-related limits might suggest early retinal dysfunction.

In the fourth study, the correlation between retinal structure and different visual function attributes in OHT and glaucoma was explored. Results provide convincing evidence for the relationship between neural tissue integrity and chromatic processing in glaucoma. Results suggest that Y/B colour vision abnormalities appear early in glaucoma and progress to involve R/G channels. FMTs also revealed extensive sensitivity loss in both rod- and cone-mediated pathways that correlated with retinal thinning even in early disease and detected functional deterioration in OHT eyes. Contrast sensitivity was linked with superior and nasal pRNFL thickness in the early glaucoma participants, demonstrating the vulnerability of the inner retina before significant field loss.

In conclusion, the results of these studies provide novel evidence that staged, multimodal functional testing, which includes contrast, colour, and flicker sensitivity, provides a more complete picture of glaucomatous neurodegeneration.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QM Human anatomy R Medicine > R Medicine (General) R Medicine > RE Ophthalmology
Departments:	School of Health & Medical Sciences > Department of Optometry & Visual Science School of Health & Medical Sciences > School of Health & Medical Sciences Doctoral Theses Doctoral Theses

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