Corneal sensitivity and aqueous tear production in dogs undergoing evisceration with intraocular prosthesis placement

Chemical ciliary body ablation in dogs with chronic glaucoma and anterior lens luxation: A retrospective review from 2017 to 2022

OBJECTIVES

To evaluate the clinical outcomes of chemical ciliary body ablation (CBA) in dogs with chronic glaucoma and concurrent anterior lens luxation and to investigate adverse ocular effects of this procedure.

PROCEDURES

Retrospective review of 17 dogs (18 eyes) with chronic glaucoma and concurrent anterior lens luxation treated with intravitreal gentamicin with or without dexamethasone sodium phosphate or triamcinolone acetonide. Data collected included signalment, concurrent ocular disease, topical medications prescribed, follow-up duration, and intraocular pressure (IOP) pretreatment, posttreatment, and at the last follow-up visit. Success was defined as an IOP <25 mmHg with no additional procedures or ocular hypotensive medications at the last examination to date.

RESULTS

The success rate for CBA in dogs with chronic glaucoma and concurrent anterior lens luxation was 88.9% without the need of additional surgical or ocular hypotensive therapies. Glaucoma was suspected to be secondary to lens luxation in 72.2% of cases. The most common postoperative complications were phthisis bulbi (50.0%), keratoconjunctivitis sicca (27.8%), and uveitis (27.8%). Long-term management with topical nonsteroidal anti-inflammatories, corticosteroids, and/or immunomodulators was needed in 70.6% of cases.

CONCLUSIONS

CBA with intravitreal injection of gentamicin is effective at maintaining an IOP <25 mmHg in dogs with chronic glaucoma and concurrent anterior lens luxation. Management of postoperative sequelae commonly requires continued use of topical medications.

Evisceration with implantation of an intrascleral silicone prosthesis in dogs: A retrospective study of 107 cases (2010-2019)

OBJECTIVE

To retrospectively analyze the preoperative clinical characteristics and surgical outcomes of evisceration with implantation of an intrascleral silicone prosthesis (EIISP) procedures in dogs and evaluate whether brachycephalic dogs are more prone than non-brachycephalic dogs to develop postoperative complications after EIISP.

ANIMAL STUDIED

Ninety-One dogs (19 of which were brachycephalic) were included.

PROCEDURES

Medical records from 2010 to 2019 were reviewed. Signalment, reason for EIISP, postoperative complications, follow-up time, and postoperative eye appearance were analyzed.

RESULTS

The most frequently represented breeds were French Bulldog [11/91 (12%) dogs], Jack Russell Terrier [6/91 (7%)], and Shih Tzu [6/91 (7%)]. Brachycephalic dogs were statistically younger than non-brachycephalic dogs at the time of EIISP (p = 1.61 × 10-5 ). Uncontrolled glaucoma was the most common reason for EIISP in both groups. Short-term complications (from D0 to D15) seen in 7/91 (8%) dogs included epithelial corneal ulcers (n = 3), keratoconjunctivitis sicca (KCS) (n = 2), and prosthesis extrusion (n = 2). Long-term complications seen in 26/91 (29%) dogs included KCS (n = 11), epithelial corneal ulcers (n = 7), stromal ulcers (n = 3), entropion (n = 4), and prosthesis extrusion (n = 1). Extrusion of the prosthesis occurred twice in eyes that had undergone diode laser transscleral cyclophotocoagulation. The risk of postoperative complications was not significantly different between brachycephalic and non-brachycephalic dogs (p = .3).

CONCLUSIONS

Brachycephalic status in dogs does not appear to influence the risk of complications from EIISP. Nevertheless, the present study is a reminder that EIISP focuses on esthetics, and considering the possible complications associated with it, it does not provide a benefit to the patient compared to enucleation.

Diagnostic Tests Used During the Ocular Examination

This article provides a review of the required ocular tests during the ophthalmologic examinations of canine and feline patients. Knowledge of medications affecting ocular parameters and awareness of available instrumentation and test materials is essential for accurate diagnoses.

The Clinical Approach to Canine Glaucoma

This article provides a simplified approach to diagnosis and clinical decision making in cases of canine glaucoma for the general practitioner. An overview of the anatomy, physiology, and pathophysiology related to canine glaucoma is provided as a foundation. Classifications of glaucoma based on cause are described as congenital, primary, and secondary, and a discussion of key clinical examination findings is provided to guide appropriate therapy and prognostication. Finally, a discussion of emergency and maintenance therapy is provided.

A review of diagnostic tests for qualitative and quantitative tear film deficiency in dogs

Dry eye disease (DED) is a complex multifactorial condition caused by loss of ocular surface homeostasis from quantitative and/or qualitative tear film deficiency. Schirmer tear test (STT) is often the only diagnostic test used to assess for DED in veterinary practice. STT is invaluable in the diagnosis and monitoring of quantitative tear film deficiency (i.e., keratoconjunctivitis sicca); however, it is not sufficient to optimize therapy and fully recognize other contributing factors for the disturbance in ocular surface homeostasis. The present work reviews diagnostic tests for assessing aqueous tear production in veterinary medicine, as well as the quality of tears, corneal epithelial barrier integrity, and the lacrimal functional unit.

Effects of orally administered gabapentin, tramadol, and meloxicam on ocular variables in healthy dogs

OBJECTIVE

To determine the effects of gabapentin, tramadol, and meloxicam on tear production, intraocular pressure (IOP), pupillary diameter, tear break-up time, and corneal touch threshold in healthy dogs when given orally for 3 days.

ANIMALS

9 healthy research Beagles.

PROCEDURES

A randomized, blinded, case-crossover study with a 6-sequence, 3-treatment, and 3-period design was performed. A 7-day acclimation period was followed by 3 treatment phases, each with a 3-day treatment period followed by a 7-day washout period for 3 different drugs. Block randomization was used to group dogs for treatments with drug A (gabapentin), B (tramadol), or C (meloxicam). Measurements of tear production, IOP, pupillary diameter, tear break-up time, and corneal touch threshold were performed on a schedule. A generalized mixed-effects linear regression model was created for each ocular variable, accounting for repeated measures within individuals.

RESULTS

Intraocular pressure was the only variable to have differed substantially between the first 5 and last 2 days of the acclimation period. When treatment phase, day, time of day, dog identification, baseline value, and eye were accounted for, the mean IOP was lower for dogs during treatment phases with gabapentin or tramadol, compared with meloxicam, but this difference was not considered clinically meaningful.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a minimum 5-day acclimation period is necessary for IOP measurements to return to baseline in dogs. The statistically identified effect of gabapentin and tramadol on IOP in dogs of the present study warrants further investigation. It is possible that at higher dosages, or in dogs with glaucoma, this effect may become clinically significant.

Glaucoma-associated pain results in mechanical sensitivity changes in dogs: A pilot study

PURPOSE

To explore the effects of chronic, uncontrolled glaucoma on pressure sensitivity in dogs before and after enucleation of the painful globe.

METHODS

Client-owned dogs undergoing enucleation for chronic glaucoma with no other sources of pain were enrolled. Normal dogs of similar breeds and skull morphology were enrolled as controls. Craniofacial ratio (CFR) and relative palpebral fissure width (RPFW) were assessed in all patients. Serial mechanical quantitative sensory testing (QST) was performed the day before surgery, and 14, 30, 60, and 120 days after surgery. QST consisted of electronic Von Frey (eVF), and blunt algometry (BA) performed above and below the nonglaucomatous eye, the metacarpus, and metatarsus. Cochet-Bonnet esthesiometry (CB) was also performed on the remaining eye.

RESULTS

Twelve dogs (6 per group) were included. Compared to baseline values, sensitivity tended to decrease over time (increased thresholds) in treatment dogs while it stayed constant or increased slightly in control dogs. The difference in change from baseline sensitivity between control and treatment groups was significant at day 120 using BA at supraorbital (P = .0153), infraorbital (P = .0209), and metacarpal sites (P = .007) and overall (P = .0470). This divergence was also significant using CB (P = .0470) on the opposite cornea. As patient CFR and RPFWV increased, both eVF (P = .005-.023) and BA (P = .004-.041) increased.

CONCLUSIONS

Sensitivity to mechanical stimuli decreased both locally and at remote sites in dogs following enucleation for painful chronic glaucoma. Cranial conformation is associated with differences in sensitivity.

Nerve growth factor in dogs: Assessment of two immunoassays and selected ocular parameters following a nicergoline challenge per os

Impairment of corneal nerves can result in the development of ocular surface diseases such as aqueous tear deficiency and neurotrophic keratopathy. This study investigates oral nicergoline, an α-adrenoceptor antagonist shown to enhance endogenous secretion of nerve growth factor (NGF) by the lacrimal gland, as a potential therapy for these conditions. Five female spayed Beagle dogs received a 2-week course of oral nicergoline (10 mg twice daily). Drug safety was evaluated with ophthalmic and physical examinations, blood pressure monitoring, bloodwork, and urinalysis. The effect of nicergoline on the ocular surface was assessed with corneal esthesiometry, Schirmer tear test-1, and tear film breakup time. Drug effect on NGF levels was assessed by collecting tears and blood at baseline and completion of therapy using a bead-based immunoassay and an enzyme-linked immunosorbent assay. Although nicergoline was well tolerated in all dogs, it did not have a significant impact on corneal sensitivity, tear production, or tear stability. Of note, NGF was below the limit of quantification in all tear samples and was only detected in 8/20 serum samples with no significant difference between levels at baseline (189.4 ± 145.1 pg/mL) and completion of therapy (149.4 ± 79.4 pg/mL). Further validation of NGF analytical assays is warranted before nicergoline is investigated in clinical patients.

Corneal hypoesthesia, aqueous tear deficiency, and neurotrophic keratopathy following micropulse transscleral cyclophotocoagulation in dogs

OBJECTIVE

To describe ocular surface complications following micropulse transscleral cyclophotocoagulation (MP-TSCPC) in dogs.

ANIMALS STUDIED

Eighteen dogs treated with MP-TSCPC at two institutions for glaucoma management.

PROCEDURES

MP-TSCPC was applied to each eye (avoiding 3 and 9 o'clock positions) with 31.3% duty cycle, 2000-3000 mW energy, and 90-180 seconds duration per hemisphere. Central corneal tactile sensation (CTS) and Schirmer tear test-1 (STT-1) were measured at baseline and ≥2 post-operative visits in each dog.

RESULTS

Corneal sensitivity decreased in 16/18 dogs (89%) by an average of 10%-42% (up to 100% in 4 dogs). CTS decline was rapid (≤1 week) and only fully recovered in 50% of dogs within 8-180 days. Patients' age, glaucoma duration, laser energy, and total energy delivered did not affect CTS at any visit. However, brachycephalic dogs had significantly lower CTS and likelihood to recover full sensation compared with nonbrachycephalic dogs. Aqueous tear deficiency (STT-1 < 15 mm/min) occurred in 8/18 dogs (44%) within 7-270 days, and concurrent signs of keratoconjunctivitis sicca were noted in 2/18 dogs (11%). Neurotrophic corneal ulcers developed in 6/18 dogs (33.3%) and required 16-53 days to heal.

CONCLUSIONS

Corneal hypoesthesia is a common complication of MP-TSCPC in dogs, and can lead to serious adverse effects such as aqueous tear deficiency and neurotrophic corneal ulcers. Brachycephalic dogs represent a population at higher risk. Close monitoring of ocular surface health is recommended for months following MP-TSCPC in dogs.

Relationship between corneal sensitivity, corneal thickness, corneal diameter, and intraocular pressure in normal cats and cats with congenital glaucoma

OBJECTIVE

To determine the effect of feline congenital glaucoma (FCG) on corneal sensitivity, and relationships between corneal sensitivity, central corneal thickness (CT), and corneal diameter (CD).

ANIMALS AND PROCEDURES

Corneal sensitivity (estimated by corneal touch threshold [CTT] using Cochet-Bonnet esthesiometry); CT using ultrasonic pachymetry; intraocular pressure (IOP) using rebound tonometry; and maximal horizontal CD were measured in 16 normal and 14 FCG cats, both males and females, aged 7 months-3.5 years. All procedures complied with an Institutional Animal Care and Use Committee-approved protocol. Data were analyzed by linear regression: paired Student's t tests for between-eye comparisons, and unpaired Student's t tests for comparisons between groups. Relationships between parameters were evaluated by Pearson correlation coefficients and linear mixed effects modeling. For statistical tests, with the exception of values that were Benjamini-Hochberg adjusted for multiple comparisons, P-values < 0.05 were considered significant.

RESULTS

Mean CTT and CT values were lower in FCG eyes relative to normal eyes, but differences were not statistically significant. Mean CD was significantly larger in FCG eyes relative to normal eyes, and there was a significant negative correlation between CD and CTT in FCG (r = -0.8564, corrected P = 0.005). These associations were confirmed in linear mixed effects models.

CONCLUSIONS

Eyes with FCG have significantly larger CDs when compared with normal eyes, and larger CDs correlated with decreased corneal sensitivity in this group. Further studies are warranted to explore the effect of buphthalmos and corneal enlargement on corneal sensitivity and innervation in feline subjects with chronic glaucoma.

Effects of topical flurbiprofen sodium, diclofenac sodium, ketorolac tromethamine and benzalkonium chloride on corneal sensitivity in normal dogs

To evaluate corneal sensitivity by using the Cochet-Bonnet® esthesiometer in normal canine eyes at different time points following instillation of three different topical non-steroidal anti-inflammatory drugs (flurbiprofen sodium 0.03%, diclofenac sodium 0.1% and ketorolac tromethamine 0.5%) and benzalkonium chloride 0.01%. Six healthy mixed breed dogs from the same litter were used in two different stages. First, one drop of flurbiprofen sodium 0.03% and diclofenac sodium 0.1% in each eye; second, one drop of ketorolac tromethamine 0.5% and benzalkonium chloride 0.01% in each eye. Baseline esthesiometry was obtained before eye drop application and every 15 minutes thereafter until a total of 105 minutes of evaluation time. A one-week interval was allowed between the two treatment phases. Statistical analysis was used to compare means according to time of evaluation and drug used. Diclofenac sodium 0.1% decreased corneal sensitivity at 75 and 90 minutes (P > 0.015) with possible interference on neuronal nociceptive activity and analgesic effect while ketorolac tromethamine 0.5% did not show any variation for esthesiometry means along the evaluation. Flurbiprofen sodium 0.03% resulted in increased esthesiometry values 30 minutes after instillation (P > 0.013), increasing corneal sensitivity and possibly producing a greater irritant corneal effect over its analgesic properties. Benzalkonium chloride 0.01% significantly increased corneal sensitivity at 15 minutes of evaluation (P > 0.001), most likely resulting from its irritating effect. Esthesiometry did not allow a definite conclusion over the analgesic effect of the NSAIDs tested; however it was effective in detecting fluctuations in corneal sensitivity.

Corneal sensitivity in healthy bovine calves

OBJECTIVE

To evaluate corneal sensitivity as measured by the corneal touch threshold in healthy bovine calves.

ANIMALS STUDIED

Twelve clinically normal male calves with predominantly Holstein genetics and a median age of 76.5 days (range, 67-92 days).

PROCEDURES

Corneal touch threshold (CTT) of the central cornea was measured in both eyes of each calf using a Cochet-Bonnet aesthesiometer.

RESULTS

The mean ± standard deviation corneal touch threshold of all eyes was 1.33 ± 1.1 g/mm(2) (range, 0.62-66.15 g/mm(2) ), corresponding to a filament length of 34.56 ± 8.02 mm (range, 14-47.5 mm). There was no significant difference between fellow eyes.

CONCLUSIONS

Cochet-Bonnet aesthesiometry was well tolerated in all 12 calves using a modified head restraint. Calves in this study may have a relatively sensitive central cornea compared to adult cattle and some other species; however, wide variation among individuals and eyes may be possible. Studies utilizing larger calf populations are necessary to establish reference ranges.

Followup of a Dog with an Intraocular Silicone Prosthesis Combined with an Extraocular Glass Prosthesis

Because of unpredictable corneal changes, evisceration and implantation of a silicone prosthesis does not always lead to a satisfying cosmetic result. This paper describes the use of an intraocular silicone prosthesis in combination with an extraocular glass prosthesis and shows a followup of two and a half years in a nonexperimental study. An intraocular silicone prosthesis was implanted after evisceration of the left eye in a five-month-old Bernese mountain dog. A glass prosthesis was fitted four weeks after evisceration. Two and a half years after the operation, the dog is in good health and free of medication. No short-term or long-term complications were seen. The owners do not have trouble with handling the glass prosthesis. The combination of both prostheses shows a perfect solution to retrieve a normal looking and moving eye after evisceration.