All ETDs from UAB

Advisory Committee Chair

J Crawford Downs

Advisory Committee Members

Lawrence C Sincich

Christopher A Girkin

Jeffrey W Kiel

Brian C Samuels

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) School of Optometry

Abstract

While cataracts (the leading cause of blindness worldwide) can be reversed surgical-ly, glaucoma is the leading cause of irreversible blindness, affecting over 70 million people worldwide [1]. Elevated intraocular pressure (IOP) and age are the primary risk factors for glaucoma [2] and lowering IOP is the only proven treatment for the disease [3]. IOP and its fluctuations affect nearly every aspect of ocular physiology and homeo-stasis, as well as playing a dominant role in glaucoma pathophysiology, yet very little is known about IOP due to the current clinical standard of measuring mean IOP during infre-quent clinic visits. We use a novel IOP telemetry system to show that transient IOP fluctua-tions (< 3-5 s duration) account for up to 17% of the total IOP-related mechanical energy the eye must absorb, and the eye is subjected to 2000-5000 transient IOP fluctuations ~40% above baseline IOP every hour during waking hours. Furthermore, we show that IOP changes with body position changes, eye rubbing, and acute stress and quantify these changes. This dissertation shows that IOP is incredibly dynamic at multiple timescales; IOP changes second-to-second, minute-to-minute, hour-to-hour, and day-to-day. IOP changes up to 58% with body position change, up to 310 mmHg above baseline due to eye rubbing, and increases an average of 27% above baseline when the animals experience acute stress. While previous studies have shown IOP fluctuations occur [4-6], transient IOP fluctuations have rarely been studied or quantified due to technological barriers, and have therefore never been correlated with either ocular homeostasis or disease. If transient IOP fluctuations prove important in glaucoma pathophysiology, it would open entirely new avenues for glaucoma treatments that damp transient IOP fluctuations. Also, IOP-related clinical and basic studies have primarily focused on quantifying results associated with mean IOP elevations [7-9], or single steps of pressure or stretch [10], none of which reflect the true dynamic nature of IOP. For these reasons, the reported results have profound implications for understanding ocular physiology and disease, as well as clinical, animal, and cellular mechanotransduction studies in which IOP dynamics could affect ocular tissue and/or cellular function.

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Optometry Commons

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