Measurements of Iris Structure using Handheld Optical Coherence Tomography and its Relation to Pigmentation

Abstract

The iris is a pigmented structure at the front of the eye responsible for controlling the amount of light entering the eye and, hence, controlling glare. Non-invasive iris imaging in awake children under the age of 3 years has been difficult previously; however, handheld anterior segment optical coherence tomography (HH-ASOCT) now makes this feasible. The aim of the first part of this thesis (chapters 3 and 4) was to characterise iris development using HH-ASOCT imaging, including nasal and temporal full iris profiles, from the eyes of 187 healthy participants aged from birth to 30 years. We also investigated the effect of iris pigmentation on iris development. This data also serves as important reference data for future studies. We observe that iris development is a complex, non-linear process, with temporal and nasal asymmetries affected by pigmentation. In the second part of this thesis (chapters 5 and 6) we have investigated the effect of iris pigmentation in adults on: (i) dynamic physiological changes in iris shape in response to light conditions; and (ii) glare measurements. We also aimed to develop a new, simple, and cost-effective method of assessing glare that could be used clinically. We find differences in iris thickness due to pigmentation, which are more obvious in bright light conditions. However, subtle changes in mean iris thickness with light conditions mask more dramatic changes in iris structure at the ciliary and apical ends, which are apparent when comparing changes in iris quadrants. Our new method of assessing glare was not sensitive to pigmentation-related glare but was highly sensitive to age-related glare changes. In contrast, intraocular straylight assessment was sensitive to both pigmentation-related and age-related glare changes. In conclusion, iris pigmentation is important in the development of the iris, the overall iris thickness in adulthood, and the perception of glare.