An eye on the dog as a translational model for ocular pharmacology

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)

Diagnosis and Treatment of Ocular Proptosis

Proptosis, or traumatic forward displacement of the globe out of the orbit, is a serious ocular emergency that requires immediate attention to minimize discomfort and damage to the eye (Figure 1). With proptosis, the eyelid margins are trapped behind the equator of the globe and, together with profound tissue swelling in the orbit, prevent the eyeball from returning to a normal position

An eye on the dog as the scientist\u27s best friend for translational research in ophthalmology: Focus on the ocular surface

Preclinical animal studies provide valuable opportunities to better understand human diseases and contribute to major advances in medicine. This review provides a comprehensive overview of ocular parameters in humans and selected animals, with a focus on the ocular surface, detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition. We describe major pitfalls that tremendously limit the translational potential of traditional laboratory animals (i.e., rabbits, mice, and rats) in ophthalmic research, and highlight the benefits of integrating companion dogs with clinical analogues to human diseases into preclinical pharmacology studies. This One Health approach can help accelerate and improve the framework in which ophthalmic research is translated to the human clinic. Studies can be conducted in canine subjects with naturally occurring or noninvasively induced ocular surface disorders (e.g., dry eye disease, conjunctivitis), reviewed herein, and tear fluid can be easily retrieved from canine eyes for various bioanalytical purposes. In this review, we discuss common tear collection methods, including capillary tubes and Schirmer tear strips, and provide guidelines for tear sampling and extraction to improve the reliability of analyte quantification (drugs, proteins, others)

Tear fluid collection in dogs and cats using ophthalmic sponges

Objective - To compare the use of two ophthalmic sponges for tear collection in dogs and cats. Animals studied - Ten healthy dogs and 10 healthy cats. Procedures - A strip (4x10 mm) of either cellulose or polyvinyl acetal (PVA) sponge was inserted into the ventral fornix of each eye for either 15, 30 or 60 seconds. The wetted strip was placed into a 0.2-mL tube that was first punctured at its bottom. Tears were eluted through the drainage hole into a 1.5-mL tube via centrifugation. Tear volume absorbed (VA) and tear volume recovered (VR) were calculated as the difference of the post- and pre- collection weight of the 0.2-mL tube and 1.5-mL tube, respectively. Recovery ratio (RR) was determined as the ratio between VR and VA. Results - Ophthalmic sponges were well tolerated by all subjects. In dogs and cats, median (95% range) VA, VR and RR were: 44 μL (11-106 μL) and 16 μL (2-43 μL); 27 μL (1-84 μL) and 6 μL (0-29 μL); 64 % (7-91%) and 35% (0-86%), respectively. PVA sponges achieved significantly greater VR in cats and RR in both species. All parameters were significantly greater with a collection time of 60 vs. 30 and 15 seconds. Body weight was associated with VA and VR in dogs but not cats. Conclusions – PVA is better than cellulose for tear collection given its superior recovery. Ophthalmic sponges could facilitate routine analysis of tear fluid in dogs and cats, although further studies are needed to evaluate the quality of tears obtained with this method

Albumin Levels in Tear Film Modulate the Bioavailability of Medically-Relevant Topical Drugs

The breakdown of blood-tear barrier that occurs with ocular pathology allows for large amounts of albumin to leak into the tear fluid. This process likely represents an important restriction to drug absorption in ophthalmology, as only the unbound drug is transported across the ocular tissue barriers to exert its pharmacologic effect. We aimed to investigate the effects of albumin levels in tears on the bioavailability of two commonly used ophthalmic drugs: tropicamide, an antimuscarinic that produces mydriasis and cycloplegia, and latanoprost, a PGF2α analog used for the treatment of glaucoma. Eight female beagle dogs underwent a randomized, vehicle-controlled crossover trial. For each dog, one eye received 30 µl of artificial tears (control) or canine albumin (0.4 or 1.5%) at random, immediately followed by 30 µl of 1% tropicamide (2 days, 24 h washout) or 0.005% latanoprost (2 days, 72 h washout) in both eyes. Pupil diameter (digital caliper) and intraocular pressure (IOP; rebound tonometry) were recorded at various times following drug administration (0 to 480 min) and compared between both groups with a mixed model for repeated measures. Albumin in tears had a significant impact on pupillary diameter for both tropicamide (P ≤ 0.001) and latanoprost (P ≤ 0.047), with no differences noted between 0.4% and 1.5% concentrations. Reduction in the maximal effect (pupil size) and overall drug exposure (area under the effect time-curve of pupil size over time) were significant for tropicamide (6.2–8.5% on average, P ≤ 0.006) but not for latanoprost (P ≥ 0.663). The IOP, only measured in eyes receiving latanoprost, was not significantly impacted by the addition of either 0.4% (P = 0.242) or 1.5% albumin (P = 0.879). Albumin in tear film, previously shown to leak from the conjunctival vasculature in diseased eyes, may bind to topically administered drugs and reduces their intraocular penetration and bioavailability. Further investigations in clinical patients and other commonly used ophthalmic medications are warranted

Feline dry eye syndrome of presumed neurogenic origin: a case report

Case summary A 14-year-old female spayed Abyssinian cat, which about 1 year previously underwent thoracic limb amputation, radiotherapy and chemotherapy for an incompletely excised vaccine-related fibrosarcoma, was presented for evaluation of corneal opacity in the left eye (OS). The ocular surface of both eyes (OU) had a lackluster appearance and there was a stromal corneal ulcer OS. Results of corneal aesthesiometry, Schirmer tear test-1 (STT-1) and tear film breakup time revealed corneal hypoesthesia, and quantitative and qualitative tear film deficiency OU. Noxious olfactory stimulation caused increased lacrimation relative to standard STT-1 values suggesting an intact nasolacrimal reflex. Various lacrimostimulants were administered in succession; namely, 1% pilocarpine administered topically (15 days) or orally (19 days), and topically applied 0.03% tacrolimus (47 days). Pilocarpine, especially when given orally, was associated with notable increases in STT-1 values, but corneal ulceration remained/recurred regardless of administration route, and oral pilocarpine resulted in gastrointestinal upset. Tacrolimus was not effective. After 93 days, the cat became weak and lame and a low thyroxine concentration was detected in serum. The cat was euthanized and a necropsy performed. Both lacrimal glands were histologically normal, but chronic neutrophilic keratitis and reduced conjunctival goblet cell density were noted OU. Relevance and novel information The final diagnosis was dry eye syndrome (DES) of presumed neurogenic origin, associated with corneal hypoesthesia. This report reinforces the importance of conducting tearfilm testing in cats with ocular surface disease, as clinical signs of DES were different from those described in dogs

Impact of Flow Rate, Collection Devices, and Extraction Methods on Tear Concentrations Following Oral Administration of Doxycycline in Dogs and Cats

Purpose: Compare the precision of doxycycline quantification in tear fluid collected with either Schirmer strips or polyvinyl acetal (PVA) sponges following oral drug administration. Methods: Three dogs and 3 cats were administered doxycycline orally at a dose of 4.2–5 mg/kg every 12 h for 6 consecutive days. At day 5 and 6, blood and tear fluid were sampled to capture doxycycline trough and maximal concentrations. Tear fluid was collected 3 times (spaced 10 min apart) at each session with the absorbent material placed in the lower conjunctival fornix until the 20-mm mark was reached (Schirmer strip, one eye) or for 1 min (PVA sponge, other eye). Tear extraction was performed with either centrifugation or elution in methanol. Doxycycline concentrations were measured with liquid chromatography–mass spectrometry. Low (100 ng/mL) and high (1,000 ng/mL) tear concentrations measured in vivo were spiked into each absorbent material in vitro to evaluate percentage drug recovery. Results: After oral administration of doxycycline, the drug reached the tear compartment at concentrations of 45.1–900.7 ng/mL in cats and 45.4–632.0 ng/mL in dogs, representing a tear-to-serum ratio of 12% and 16%, respectively. Doxycycline tear concentrations were significantly more precise when tear collection was performed with Schirmer strips rather than PVA sponges (P = 0.007), but were not correlated with tear flow rate. In vitro doxycycline recovery was poor to moderate (\u3c75%). Conclusions: Schirmer strips represent a good option for lacrimal doxycycline quantification, although the collection and subsequent extraction have to be optimized to improve drug recovery

Efficacité des avermectines contre les acarioses du chien : revue systématique

Les formulations à base d’avermectine sont couramment utilisées en médecine vétérinaire. Cependant, dans la lutte contre les acarioses du chien, beaucoup de ces produits sont utilisés hors AMM. A travers une analyse critique de la littérature scientifique vétérinaire, le but de cette thèse est d'accompagner le praticien dans une démarche scientifique fondée sur la preuve, et de fournir ainsi une synthèse raisonnée sur l’utilisation des avermectines contre les acariens du chien. Les acariens concernés par cette étude sont : Demodex spp., Sarcoptes scabiei, Cheyletiella spp., Otodectes cynotis, Notoedres spp., Straelensia cynotis et Pneumonyssoides caninum

Clinical features of cats with aqueous tear deficiency: a retrospective case series of 10 patients (17 eyes)

Objectives The aim of this study was to describe the clinical findings, diagnostic test results and response to therapy of cats with Schirmer tear test 1 (STT-1) values below the reference interval. Methods The medical records of three institutions were searched for cats with ocular surface disease and STT-1 values/min, confirmed at two or more separate visits. Results Ten cats (17 eyes) were included. The mean ± SD (range) age and STT-1 values in affected eye(s) were 6.1 ± 5.7 (0.2–16) years and 2.4 ± 3.1 (0–8) mm/min, respectively. Concurrent ocular surface disease was bilateral in 5/10 cats. Clinical signs included conjunctivitis (14/17 eyes), corneal ulceration (6/17 eyes), non-ulcerative keratitis (4/17 eyes), symblepharon (4/17 eyes), eosinophilic keratitis (3/17 eyes), corneal sequestrum (3/17 eyes), corneal fibrosis (2/17 eyes) and meibomitis (2/17 eyes). Management included topically applied lacrimomimetics, antiviral drugs, corticosteroids or immunomodulatory drugs; orally administered famciclovir; or surgical procedures, in various combinations. Response to therapy (defined as an increase in STT-1 value of ⩾5 mm/min) was transient (seen at a single reassessment) in 65% of eyes and sustained (seen at ⩾2 consecutive reassessments) in 18% of eyes. Conclusions and relevance Clinical features seen in cats with low STT-1 values are described, although the association between aqueous deficiency and the reported ocular changes is unknown at this time. We encourage clinicians to assess the tear film in cats with ocular surface disease, and initiate therapy with lacrimomimetics if STT-1 values are repeatedly below normal. Such information will further define aqueous tear deficiency in cats, providing a better understanding of disease prevalence, pathogenesis and treatment

Histamine-Induced Conjunctivitis and Breakdown of Blood–Tear Barrier in Dogs: A Model for Ocular Pharmacology and Therapeutics

Conjunctival inflammation disturbs the blood–tear barrier and thus affects the tear film stability and composition. We aimed to develop a non-invasive and reliable method to induce conjunctivitis in dogs, a large animal model for translational work on ocular surface disease in humans. Six beagle dogs underwent a randomized, vehicle-controlled, balanced crossover trial—on six separate days, one eye received topical artificial tears (vehicle), while the other eye received one of six concentrations of histamine solution (0.005–500 mg/ml). At sequential times after eyedrop administration, a conjunctivitis score was given to each eye based on the degree of palpebral and bulbar conjunctival hyperemia and chemosis, ocular pruritus, and discharge. Total protein content (TPC) and serum albumin were quantified in tear fluid at baseline and 20 min. Additionally, 13 dogs presenting for various ophthalmic diseases with associated conjunctivitis were examined. Experimentally induced conjunctivitis developed rapidly (\u3c1 min) following topical histamine administration and lasted for 1–3 h (four lowest doses) to 6–8 h (two highest doses). The severity of conjunctivitis was dose-dependent. Histamine was overall well tolerated, although transient blepharitis, aqueous flare, and ocular hypertension occurred in a few dogs receiving histamine ≥375 mg/ml. TPC and serum albumin levels increased in tears of eyes receiving histamine ≥1.0 mg/ml, being significantly higher than vehicle and baseline in eyes receiving histamine ≥375 mg/ml. Lacrimal albumin levels were also increased in 13 dogs with naturally acquired conjunctivitis, up 2.7–14.9 fold compared to contralateral healthy eyes. Histamine-induced conjunctivitis represents a robust model for translational work on the ocular surface given the low cost, non-invasiveness, self-resolving nature, ability to adjust the duration and severity of the disease, and shared features with naturally occurring ocular diseases. Histamine solutions of 1, 10, and 375 mg/ml induce mild, moderate, and severe conjunctivitis in dogs, respectively. Leakage of serum albumin in tear fluid of eyes with conjunctivitis suggests a breakdown of the blood–tear barrier