Comparison of four tonometers in the measurement of intraocular pressure in healthy horses

Clinical features and outcomes of horses presenting with presumed equine immune mediated keratitis to two veterinary hospitals in the United Kingdom and Finland: 94 cases (2009-2021)

BACKGROUND

There is limited literature regarding equine immune mediated keratitis (IMMK) in Europe. North America-based publications describe minimal blepharospasm, rare corneal ulceration and no uveitis; clinical impression suggests these are seen in Europe.

OBJECTIVES

Assess the prevalence of blepharospasm, corneal ulceration and uveitis and their impact on outcome in horses diagnosed with IMMK in Europe (UK and Finland).

STUDY DESIGN

Retrospective case series.

METHODS

Clinical records of 94 horses with IMMK were evaluated. The UK and Finland populations were comparable; therefore, descriptive statistics were performed on combined data on subtypes of IMMK and clinical features. Odds ratios (OR) and confidence intervals (CI) were calculated for impact of blepharospasm, ulceration or presence of uveitis on the outcome of enucleation and treatment duration.

RESULTS

IMMK subtype was classified as 10/94 (10.6%) epithelial, 50/94 (53.2%) anterior stromal, 14/94 (14.9%) mid-stromal, 4/94 (4.25%) endothelial and 16/94 (17.0%) unrecorded. After excluding three horses with incidental corneal ulceration, blepharospasm was documented in 34/91 (37.4%), corneal ulceration in 26/91 (28.6%), and signs of uveitis in 23/91 (25.3%) horses. Increased odds of enucleation were significantly associated with the presence of blepharospasm (OR 5.5, 95% CI 1.6-19.4, p = 0.008) and signs of uveitis (OR 8.9, 95% CI 2.6-30.8, p < 0.001), but not corneal ulceration. The presence of blepharospasm, corneal ulceration or uveitis did not significantly alter the odds of ongoing medication.

MAIN LIMITATIONS

Data were collected over a wide timeframe; the diagnosis was mainly made without histopathology; a broad definition of uveitis was used and there was a bias towards complicated cases being retained for follow-up.

CONCLUSIONS

The clinical features of IMMK were similar between two European countries but differed to USA descriptions. Blepharospasm, corneal ulceration and signs of uveitis can occur with IMMK; presence of blepharospasm and uveitis increase the odds of enucleation.

Comparison of three methodologies for measuring intraocular pressure in healthy cats

Background and Aim

Measuring intraocular pressure (IOP) is crucial for identifying potentially damaging changes in the eyes, including diseases as glaucoma and uveitis. This study compared intraocular pressure (IOP) measurements in cats using the Tonovet and Tonovet Plus (rebound), Tono-Pen Avia Vet (applanation), and Kowa HA-2 (Goldman's methodology applanation) tonometers.

Materials and Methods

55 healthy cats (108 eyes) were assessed through three distinct studies: An ex vivo experiment (10 eyes of five cats) to correlate IOP manometry and tonometry values and ascertain the correlation coefficient (r2); an in vivo study (10 eyes of five sedated cats) to contrast manometer and tonometer readings; and an outpatient clinical trial (80 eyes of 45 cats) to analyze only tonometer measurements.

Results

The r 2 values observed in the ex vivo study were Tonovet (0.923), Tonovet Plus (0.925), Tono-Pen Avia Vet (0.877), and Kowa HA-2 (0.901). The IOP values in mmHg in the in vivo study were as follows: Manometer (16.1 ± 2.7), Tonovet (21.1 ± 3.6), Tonovet Plus (19.7 ± 7.2), Tono-Pen Avia Vet (17.6 ± 7.9), and Kowa HA-2 (16.8 ± 2.0). In the outpatient clinical study, the IOP values in mmHg were as follows: Tonovet (19.7 ± 6.6), Tonovet Plus (17.1 ± 5.4), Tono-Pen Avia Vet (16.3 ± 4.3), and Kowa HA-2 (14.5 ± 2.2).

Conclusion

IOP and manometry readings were strongly correlated by all tonometers. In the clinical setting, the most and least IOP measurements were recorded using Tonovet and Kowa HA-2, respectively, stressing the importance of an IOP reference table for each tonometer in feline practice.

Comparison of Tonovet® and Tonovet plus® tonometers for measuring intraocular pressure in dogs, cats, horses, cattle, and sheep

Background and Aim

Reference ranges for intraocular pressure (IOP) in healthy animals are device-specific; therefore, it is strongly recommended to use appropriate reference values according to the device. Therefore, our aim was to compare IOP readings made by TonoVet® and TonoVet Plus® in healthy dogs, cats, sheep, cattle, and horses. We compared IOP values measured by TonoVet® and TonoVet Plus® tonometers in clinically normal eyes of dogs, cats, horses, cattle, and sheep.

Materials and Methods

Five groups comprising 20 animals each of dogs (various breeds, 9 months-10 years old, 14 females, 6 males), cats (various breeds, 6 months-12 years old, 8 females, 12 males), horses (various breeds, 5-12 years old, 12 females, 8 males), cattle (Holstein, 1-7 lactation, female), and sheep (Latvian Darkhead ewes, 1-8 years old) were included in the study. Both eyes of all animals were subjected to ophthalmic examination, including evaluation of IOP by rebound tonometry using TonoVet® and TonoVet Plus® devices. Normality was determined using the Shapiro-Wilk test. The independent t-test was used to determine differences between IOP values in the right and left eyes and between both tonometers. This study was approved by the Ethical Commission of the Latvia University of Life Sciences and Technologies (Nr. LLU_Dzaep_2022-2-4).

Results

No differences in IOP between the right and left eyes were found in all cases (p > 0.05). The mean IOP ± standard deviation values in both eyes for TonoVet® and TonoVet Plus® tonometers were as follows: for dogs, 15.25 ± 2.73 mmHg and 19.65 ± 3.46 mmHg; and in cats, 18.88 ± 3.98 mmHg and 18.78 ± 4.26 mmHg, respectively. In horses, mean IOP was 22.15 ± 3.74 mmHg and 24.28 ± 3.00 mmHg; in cattle, 24.73 ± 2.89 mmHg and 23.28 ± 2.97 mmHg; and in sheep, 18.05 ± 3.54 mmHg and 22.49 ± 4.66 mmHg, respectively. Significant differences in IOP values were observed between the tonometers in sheep, dog, and horse groups (mean difference -4.40, -4.48, and 2.13, respectively).

Conclusion

This study showed significantly higher IOP values measured by the TonoVet Plus® tonometer in dogs and sheep.

Comparing the effects of intraocular pressure and tear production measurements in horses in two different environments: Horse stable and medical barn

BACKGROUND

To date, there are no studies on the impact of two distinct environments-one familiar to the horse and another unfamiliar-on intraocular pressure (IOP) and tear production.

OBJECTIVES

To compare the measured IOP and tear production values in horses between a horse stable and a medical barn.

STUDY DESIGN

Cross-over.

METHODS

Thirty healthy male Arabian horses, aged 6.88 ± 3.34 years were used. IOP and tear production measurements were assessed in both the horse stable and the medical barn, with a paired Student's t-test and Bland-Altman analysis conducted for comparison and agreement, respectively.

RESULTS

A significant increase in IOP was observed in the medical barn (34.2 ± 6.8 mmHg) compared with the horse stable (29.5 ± 7.2 mmHg, p = 0.02). However, no statistically significant difference in tear production was found between horse stable (22.1 ± 2.8 mm/min) and medical barn (23.6 ± 3.4 mm/min) (p = 0.09). The standard error of the slope was 0.36 for the IOP measured in the medical barn, indicating a difference of -4.7 mmHg compared with the IOP measured in the horse stable (p = 0.02). The bias was fitted to y = -7.9350 + 0.1003x. The standard error of the slope was 0.39 for the tear production measured in the medical barn, indicating a difference of -1.5 mm/min compared with the tear production measured in the horse stable (p = 0.09). The bias was fitted to y = 6.1530 + -0.3367x.

MAIN LIMITATIONS

The absence of horses with ocular disorders and an assessment of the potential impact of transportation.

CONCLUSIONS

A notable increase in IOP was observed in the medical barn compared with the horse stable, while tear production exhibited no significant variance between the two environments. The Bland-Altman analysis highlighted a discrepancy in IOP measurements in the horse stable, emphasising the potential influence of the environment on ocular parameters in horses.

Preliminary evaluation of safety and migration of immune activated mesenchymal stromal cells administered by subconjunctival injection for equine recurrent uveitis

Introduction

Equine recurrent uveitis (ERU), an immune mediated disease characterized by repeated episodes of intra-ocular inflammation, affects 25% of horses in the USA and is the most common cause of glaucoma, cataracts, and blindness. Mesenchymal stromal cells (MSCs) have immunomodulatory properties, which are upregulated by preconditioning with toll-like receptor agonists. The objective was to evaluate safety and migration of TLR-3 agonist polyinosinic, polycytidylic acid (pIC)-activated MSCs injected subconjunctivally in healthy horses prior to clinical application in horses with ERU. We hypothesized that activated allogeneic MSCs injected subconjunctivally would not induce ocular or systemic inflammation and would remain in the conjunctiva for >14 days.

Methods

Bulbar subconjunctiva of two horses was injected with 10 × 106 pIC-activated (10 μg/mL, 2 h) GFP-labeled MSCs from one donor three times at two-week intervals. Vehicle (saline) control was injected in the contralateral conjunctiva. Horses received physical and ophthalmic exams [slit lamp biomicroscopy, rebound tonometry, fundic examination, and semiquantitative preclinical ocular toxicology scoring (SPOTS)] every 1-3 days. Systemic inflammation was assessed via CBC, fibrinogen, and serum amyloid A (SAA). Horses were euthanized 14 days following final injection. Full necropsy and histopathology were performed to examine ocular tissues and 36 systemic organs for MSC presence via IVIS Spectrum. Anti-GFP immunohistochemistry was performed on ocular tissues.

Results

No change in physical examinations was noted. Bloodwork revealed fibrinogen 100-300 mg/dL (ref 100-400) and SAA 0-25 μg/mL (ref 0-20). Ocular effects of the subjconjucntival injection were similar between MSC and control eyes on SPOTS grading system, with conjunctival hypermia, chemosis and ocular discharge noted bilaterally, which improved without intervention within 14 days. All other ocular parameters were unaffected throughout the study. Necropsy and histopathology revealed no evidence of systemic inflammation. Ocular histopathology was similar between MSC and control eyes. Fluorescent imaging analysis did not locate MSCs. Immunohistochemistry did not identify intact MSCs in the conjunctiva, but GFP-labeled cellular components were present in conjunctival phagocytic cells.

Discussion

Allogeneic pIC-activated conjunctival MSC injections were well tolerated. GFP-labeled tracking identified MSC components phagocytosed by immune cells subconjunctivally. This preliminary safety and tracking information is critical towards advancing immune conditioned cellular therapies to clinical trials in horses.

Comparison of three methods of tonometry in horses presented for ophthalmic disease

OBJECTIVE

To compare the measurement of intraocular pressure in horses with clinical ocular disease using three tonometry devices.

ANIMALS STUDIED

A total of fifty horses were presented to the New Bolton Center Ophthalmology Service.

PROCEDURE

Intraocular pressure was taken on 50 client-owned horses (100 eyes) using the TonoVet, TonoVet Plus and Tono-Pen Avia tonometers. Clinical equine patients included were presented to New Bolton Center for ophthalmic examination. Auriculopalpebral blocks were performed but horses were unsedated.

RESULTS

All three tonometers were found to have strong agreement among them. The strongest agreement was between the TonoVet and the TonoVet Plus with the TonoVet on average 1.330 mmHg less than the TonoVet Plus (standard deviation 4.388 mmHg). This was followed by the TonoVet and the Tono-Pen Avia Vet with the TonoVet on average 2.531 mmHg greater than the Tono-Pen Avia Vet (standard deviation 4.124 mmHg). The weakest agreement was between the TonoVet Plus and the Tono-Pen Avia with the TonoVet Plus on average 3.854 mmHg greater than the Tono-Pen Avia (standard deviation 4.724 mmHg).

CONCLUSIONS

All three tonometers showed strong agreement, however, the TonoVet and the TonoVet Plus carried the strongest agreement with the TonoVet Plus having slightly higher measurements overall compared with the TonoVet. Due to small variations between devices, it is recommended that the same device be used for serial measurements of intraocular pressure. However, all three devices are appropriate to use in horses presented for ophthalmic evaluation.