Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Biomedical Engineering

Major Professor

Christopher L. Passaglia, Ph.D.

Committee Member

Robert D. Frisina, Ph.D.

Committee Member

Mark J. Jaroszeski, Ph.D.

Committee Member

Ismail Uysal, Ph.D.

Committee Member

Manas R. Biswal, Ph.D.

Keywords

Anesthetics, Body Temperature, Glaucoma, Locomotor Activity, Stress, Tonometry

Abstract

Eye health depends partially on intraocular pressure (IOP) as abnormal levels can lead to ocular tissue damage. Glaucoma is a neurodegenerative disease that affects nearly 80 million people worldwide [1]. It is associated with elevated IOP, which can lead to irreversible blindness. Relatively little is known about IOP dynamics and the physiological factors that affect it as IOP is typically monitored using tonometry. Tonometry is a common tool used by clinicians and researchers to measure IOP noninvasively. It provides a good estimate of IOP mean but not variance because data collection takes time. Readings can also be influenced by subject stress and tonometer operation. To resolve this issue, our lab has developed a novel telemetry system to monitor IOP continuously in conscious freely moving rats. The device works by conducting pressure from a microcannula implanted in the anterior chamber to a transducer worn as a backpack. To improve our understanding of IOP as a risk factor for glaucoma, we used this system to test the effects of various internal and external factors including stress, anesthetics, temperature, tonometry, light cycle, and locomotor activity. Our results indicate that IOP varies continuously over fast and slow time scales. IOP fluctuations can naturally range over 5 - 10 mmHg, which is quite large considering the resting level is 10 - 15 mmHg and chronic elevation by this amount can cause glaucomatous nerve damage. Physiological mechanisms must therefore exist to slowly and rapidly modulate IOP. Autoregulatory processes that control ocular hemodynamics are one known mechanism, and efferent nerve signals from the brain are another. We conclude that IOP in rats, much like in higher mammals, is a complex time-dependent variable due to internal and external perturbing forces and homeostatic feedback mechanisms.

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