Date of Award
Doctor of Philosophy
Biomedical Sciences (Pharmacology)
Jonathan P Mochel
Today’s high failure rate in ophthalmic clinical trials can be largely explained by two major shortcomings: (i) the animals routinely studied (rabbits, mice, rats) are not representative of the affected population due to apparent anatomical and physiological differences with humans; and (ii) studies conducted in healthy eyes do not account for physiological disturbances in ocular homeostasis present in diseased eyes. Unlike traditional laboratory animals, diseases in dogs better reflect the complex genetic, environmental, and physiological variation present in humans; however, the translational potential of canine research is currently limited by scarce information on normative data specific to dogs, and the limited means to mimic ocular disease in a reliable and non-invasive manner in this species.
The work conducted in the dissertation provides a deeper understanding of the canine ocular surface in health and disease states, investigating laboratory Beagle dogs and canine patients of varied breeds and cephalic conformations. Tear fluid was collected from canine eyes in successive experiments – primarily via Schirmer tear strips but also capillary glass tubes and absorbent sponges – and subsequent bioanalytical tools included fluorophotometry (tear film fluorescence), infrared spectroscopy (total protein content), immunoassays (serum albumin, cytokines, chemokines) and liquid chromatography-mass spectrometry (corticosteroids). Data analysis combined conventional statistical tests with nonlinear mixed-effects mathematical modeling to improve the robustness of the predictions.
The main research outcomes of the dissertation work are the following: (i) Normative data were established for canine tear film dynamics, including tear volume (65.3 µL), basal tear turnover rate (12.2%/min) and reflex tear turnover rate (50%/min). In both clinical and research settings, successive lacrimal tests should be spaced by ≥ 10 min in dogs to provide sufficient time for the tear film to replenish. (ii) The volumetric capacity of the canine palpebral fissure was 31.3 µL, approximating the volume of a single eyedrop. Kinetic studies confirmed that a single drop is sufficient for topical administration in dogs, any excess being lost predominantly by blinking and spillage over the periocular skin. (iii) Topical histamine solutions of 1, 10, and 375 mg/mL induced mild, moderate, and severe conjunctivitis in dogs, respectively. The resulting disruption of the blood-tear barrier promoted leakage of plasma compounds (eg., albumin) into the tear film, a finding confirmed in dogs with naturally acquired ocular diseases. This ‘large animal’ model was robust, non-invasive, and self-resolving, providing a unique opportunity to investigate the ocular surface in health and disease. (iv) Acute conjunctivitis increased tear quantity and decreases tear stability, although ocular surface homeostasis was rapidly restored. (v) Corticosteroid levels in the tear film did not change significantly between healthy vs. diseased eyes following oral prednisone administration, although findings may differ for drugs with other physicochemical properties. (vi) Albumin in tears lowered the ocular bioavailability of topically administered drugs, as shown for tropicamide and (to a lesser extent) latanoprost in dogs.
The thesis concludes with a comprehensive review of key ocular parameters in humans, dogs, and traditional laboratory species (rabbits, mice, rats), detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition, and highlighting the benefits of integrating dogs into preclinical studies given striking resemblances between the canine and human eyes (One Health approach).
Sebbag, Lionel, "An eye on the dog as a translational model for ocular pharmacology" (2020). Graduate Theses and Dissertations. 18223.