Comparison of two rebound tonometers in healthy horses

Evaluation of lidocaine for auriculopalpebral nerve block in dogs: Onset, duration, and effects on intraocular pressure and eye examination

OBJECTIVES

Accurate intraocular pressure (IOP) measurement is essential for managing glaucoma, requiring tonometry. Local anesthesia is typically used, but nerve blocks may be needed for blepharospasm. This study investigated the efficacy of auriculopalpebral nerve block with lidocaine in achieving eyelid akinesia and its influence on IOP in dogs.

ANIMALS AND PROCEDURES

In a randomized, blinded trial, 12 healthy adult mixed-breed dogs (24 eyes) received either auriculopalpebral nerve block with 2% lidocaine (n = 12 eyes) or no block (n = 12 eyes). Tetracaine drops were used for topical anesthesia in half of blocked/non-blocked eyes, and the rest of the eyes got artificial tears as control. The impact of nerve block was evaluated through assessments of menace response, palpebral reflex, and IOP before the block, after drop instillation, and at 15-min intervals until block dissipation.

RESULTS

Auriculopalpebral nerve block provided effective eyelid akinesia in 58.5% (7/12 eyes) at 15 min, reaching 91.7% (11/12 eyes) at 30 min, indicating peak efficacy. Subsequently, the block gradually diminished, with 66.7% (8/12 eyes) and 33.3% (4/12 eyes) maintaining akinesia at 45 and 60 min, respectively. Importantly, neither auriculopalpebral nerve block nor tetracaine administration significantly affected IOP measurements (p > .05).

CONCLUSIONS

Auriculopalpebral nerve block using lidocaine demonstrated efficient eyelid akinesia, peaking at 30 min postinjection. This technique proved to be safe with no notable alterations in IOP, suggesting its potential utility in canine ophthalmology for procedures requiring eyelid akinesia, particularly in the management of glaucoma where maintaining accurate IOP measurements is crucial for diagnosis, treatment, and monitoring the disease.

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 first, second, and third versus the average of six probe-corneal touches for intraocular measurement of two rebound tonometers in healthy horses

The aim of this study was to evaluate the intraocular pressure (IOP) measurements obtained from first, second, and third probe-cornea touch (PCT) and compare them with the average of six PCTs using two rebound tonometers in horses. This study enrolled a total of thirty-eight stallions, comprising of 24 Arabian horses and 14 cross-breeds (with an average age of 8 ± 3 years). The IOP measurements of first, second, and third, as well as the average of six PCTs were obtained using either Tonovet (TV) or Tonovet Plus (TV+) rebound tonometers. The mean differences (95% limits of agreement) between the average of six PCTs and the first, second, and third PCTs were 0.1 (-4.8 to 5), 0.2 (-4.8 to 4.5), and 0.2 (-3.6 to 4.0) mmHg with TV, respectively. With TV+, the differences were 0.3 (-6.6 to 7.2), 1.1 (-8.6 to 10.8), and -0.2 (-3.6 to 4.0) mmHg, respectively. Compared to the average of six PCTs, only 89.5%, 92.1%, and 97.4% of IOP measurements obtained from TV and 78.9%, 73.3%, and 65.8% of IOP measurements obtained from TV+ were within 4 mmHg of the average of six PCTs for first, second, and third PCTs, respectively. In conclusion, the measurement of IOP in the first PCT achieved best agreement with the IOP measurement of six average PCTs. Therefore, the first PCT could be considered as an alternative option for measuring IOP in horses when obtaining an average of six PCTs is not feasible.

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.

Determination of intraocular pressure and Schirmer tear test and the comparison between the applanation tonometer (Tono-Pen AVIA®) and the rebound tonometer (TonoVet Plus®) in mini lionhead rabbits

OBJECTIVE

To determine intraocular pressure (IOP) and tear production, as well as to compare the IOP obtained with the TonoVet Plus® (rebound) with the Tono-Pen Avia® (applanation) tonometers.

ANIMALS

Twenty-five Mini Lionhead rabbits (n = 50 eyes).

PROCEDURE

Tear production was measured at 6:00 a.m. and 6:00 p.m. by using the STT. The IOP reading was performed with the rebound tonometer, followed by the applanation tonometer, at 6:00 a.m., 9:00 a.m., 12:00 p.m., 3:00 p.m., and 6:00 p.m. Regression analysis, analysis of variance (anova) and Bland-Altman statistics were used.

RESULTS

Daily tear production was 10.25 ± 3.75 mm/min, with no differences among the moments evaluated. Average daily IOP was 17.7 ± 3.08 mmHg with the TonoVet Plus® and 11.5 ± 4.56 mmHg with the Tono-Pen Avia®. IOP values were higher at the beginning and end of the day with both tonometers.

CONCLUSION

The IOP values are higher with the TonoVet Plus® tonometer. The reference values of IOP and tear production obtained in this work may support the diagnosis, treatment, and monitoring of ocular disorders in pet Mini Lionhead rabbits.

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

BACKGROUND

Measurement of the intraocular pressure (IOP) is a useful diagnostic tool in equine ophthalmology. Handheld tonometers, such as Tonovet and Tonovet Plus (rebound), Tono-Pen AVIA Vet (applanation), and Kowa HA-2 (applanation using the Goldmann methodology) are used to obtain IOP measurements in veterinary medicine.

OBJECTIVES

To compare and evaluate the accuracy of four handheld tonometers in measuring IOP using different methodologies in healthy horses.

STUDY DESIGN

In vivo experiment and cross-sectional survey of healthy horses.

METHODS

Intraocular pressure was measured in 72 eyes of 36 horses. An in vivo study was conducted on sedated horses to compare the real IOP values obtained using manometry versus those obtained using tonometry, and a field study was conducted on unsedated healthy horses with normal eyes to measure the IOP values using different tonometers.

RESULTS

In the in vivo study, the mean IOP values using ocular manometry was 24.9 ± 4.0 mmHg (range, 20.0-30.0 mmHg). The mean IOP values using tonometry were: Tonovet, 25.7 ± 5.8 mmHg (range 19.5-33.0 mmHg); Tonovet Plus, 24.8 ± 7.1 mmHg (range 13.2-33.2 mmHg); Tono Pen AVIA Vet, 19.2 ± 4.7 mmHg (range 13.1-26.5 mmHg); and Kowa Ha-2, 24.1 ± 1.2 mmHg (range 22.8-25.8 mmHg). In the field study, the IOP values were: Tonovet, 30.7 ± 5.6 mmHg (range 21.7-38.0 mmHg); Tonovet Plus, 29.6 ± 6.7 mmHg (range 16.2-38.6 mmHg); Tono-Pen AVIA Vet, 27.3 ± 5.8 mmHg (range 14.6-37.1 mmHg); and Kowa HA-2, 23.4 ± 2.2 mmHg (range 20.2-28.7 mmHg).

MAIN LIMITATIONS

This study included only healthy horses and a limited number of animals in the in vivo study.

CONCLUSIONS

There was a strong correlation between the IOP values and manometry for all tonometers. IOP should be estimated using the same tonometer over time, and the bias of the tonometer used, such as overestimation (rebound tonometer) and underestimation (applanation tonometer), should be acknowledged. A normal reference value for each tonometer should be established 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.

Effect of Volumes of Solutions on Intraocular Pressure During Intravitreal Injection of Low Dose Gentamicin in Horses With Recurrent Uveitis: A Randomized Controlled Study

Horses with recurrent uveitis can be treated by intravitreal injection of low dose gentamicin under sedation and after local anesthetic techniques including the retrobulbar nerve block. Since it is reported that retinal degeneration can be secondary to an acute increase of intraocular pressure (IOP), the current randomized controlled study was carried out in order to investigate the changes in IOP following retrobulbar anesthesia, with two different volumes of local anesthetic (lidocaine) solution (10 and 5 mL), and intravitreal injection of 6 mg gentamicin in two different volumes of solution (0.3 and 0.15 mL). Multivariate regression showed that IOP was significantly lower in the pathologic eye at baseline (estimated effect size -6.1 mmHg; P = .0001) and after sedation (estimated effect size -9.4 mmHg; P < .0001). The IOP was significantly higher after a 10 mL block (P .0002) but this effect was very small (+0.5 mmHg). There was no significant difference in IOP after the injection of 0.15 or 0.3 mL solution of gentamicin. There was no significant combined effect of the volume of local anesthetic used for the block and the volume of the gentamicin solution. Since the expected anesthetic effects (desensitization and akinesia) were met in all cases, the smaller volume of 5 mL of lidocaine solution would be preferable for retrobulbar block for intravitreal injections, while intravitreal injections volumes of 0.15 and 0.30 mL can be used indifferently.

Noninvasive diode laser-an effective and safe treatment of iris cysts in 46 eyes of 35 horses

BACKGROUND

Iris cysts in horses are often asymptomatic and noticed incidentally. However, cysts can cause local corneal oedema and erratic behaviour like shying, decreased performance and head-shaking.

OBJECTIVES

To describe the use of diode laser as a noninvasive treatment option for iris cysts in the horse and to document factors influencing its efficacy, associated complications, long-term outcome and rate of recurrence.

STUDY DESIGN

Retrospective case series.

METHODS

Case records of horses treated for iris cysts by diode laser at the Utrecht University Equine Clinic were reviewed between 2008 and 2020. Diagnosis was based on ophthalmic and ultrasonographic evaluation. Long-term follow-up was obtained in two phases, a telephone survey with the owner and a photographic re-evaluation of the treated eyes.

RESULTS

Thirty-five horses were included, with a total of 46 eyes treated. One day after diode laser treatment (short-term), 35/46 treated eyes had a good decrease in cyst size, 7/46 had a moderate effect, 1/46 had a minimal effect, 1/46 had no effect, and in two cases the effect was unspecified. The decrease in size after diode laser treatment in polycystic eyes (odds ratio [OR] 0.381, 95% CI 0.1530-0.724), p = 0.001), thick-walled cysts (OR = 0.139; CI = 0.023-0.726, p = 0.02) and hyperplastic corpora nigra (OR = 0.081; CI = 0.004-0.528, p = 0.03) was significantly less satisfactory, with ORs of 0.381, 0.139 and 0.081, respectively. Minor complications, such as mild reactive uveitis, were reported in 8/46 (17%) eyes. On long-term follow-up (median 19 months; IQR 25.5), clinical signs had diminished or disappeared in most cases (93%) and 83% of the owners would recommend the treatment. Based on long-term photographic re-evaluation (median 32.5 months; IQR 49.75), 2/16 cases of recurrence were seen.

MAIN LIMITATIONS

Retrospective design, follow-up by telephone questionnaire and photographic re-evaluation. Loss to follow-up in the photographic re-evaluation.

CONCLUSIONS

Both short- and long-term results indicate diode laser treatment is a useful and safe option for iris cyst size reduction, with a low risk of recurrence. Presurgical ultrasonography is recommended to assess the feasibility of treatment and to allow for better surgical planning.

Ocular abnormalities in the Icelandic horse with a focus on equine recurrent uveitis: 112 Icelandic horses living in Denmark and 26 Icelandic horses living in the United States

PURPOSE

To describe the most common ocular abnormalities in the Icelandic horse with focus on equine recurrent uveitis (ERU) and association between ocular abnormalities and summer eczema and coat colors.

METHODS

A descriptive cross-sectional study. A complete physical and ophthalmic examination as well as measurement of serum titers for Leptospira serovariants was performed on Icelandic horses from Denmark (DK) and the United States (USA).

RESULTS

One hundred and twelve Icelandic horses living in DK and 26 Icelandic horses living in the United States were included in this study (total of 138 horses, 274 eyes). The three most common ocular abnormalities were follicular conjunctivitis (55.8%, 153/274 eyes), cataracts (27.4%, 75/274 eyes), and multifocal chorioretinopathy ("bullet holes"; 19%, 52/274 eyes). The prevalence for ERU among Icelandic horses aged "eight years and older" was 8% (6/75 horses). The "insidious ERU" type was found in 83% of the ERU cohort (5/6 horses), while "classic ERU" was found in 17% (1/6 horses). A correlation between ERU and cataracts was found in the population (p < .01). Leptospiral serology results were not associated with ERU in either DK or US-Icelandic horses (p = 1.00, p = 1.00, respectively). ERU was not associated with summer eczema (p = .49), and no coat colors were associated with the ocular abnormalities found in the Icelandic horse (all p-values > .05).

CONCLUSION

Follicular conjunctivitis, cataracts, and multifocal chorioretinopathy were the three most common ocular abnormalities findings. Icelandic horses who were 8 years or older had an 8% prevalence for ERU. Summer eczema and coat color were not associated with evidence of ERU or other ocular abnormalities.

Effect of topical cyclopentolate alone or combined with phenylephrine in healthy horses

OBJECTIVE

Evaluate the effect of repeated doses of topical 1% cyclopentolate hydrochloride alone and in combination with topical 2.5% phenylephrine on pupil diameter (PD), tear production (STT-1), intraocular pressure (IOP), digestive function (gut motility and feces production), and heart rate (HR).

ANIMAL STUDIED

Six healthy mares.

PROCEDURES

In a prospective, randomized, controlled, and crossover design study, the left eye of six healthy mares was administered 0.2 mL of cyclopentolate alone and in combination with 0.2 mL of phenylephrine. The drugs were administered 3 times a day for 1 day, twice a day for 1 day, and then once a day for 2 days, as commonly used in practice. Daily and two days after the last topical drug administration, HR, digestive auscultation, feces production, STT-1, IOP, and PD were recorded.

RESULTS

The cyclopentolate alone significantly increased the horizontal and vertical PD of the treated eye from day 2 to day 6 (p < .0001) compared with the baseline value. The combination with topical phenylephrine did not have any additional effect on mydriasis compare with the cyclopentolate alone. The other ocular and digestive parameters were not affected by repeated doses of cyclopentolate alone or combined.

CONCLUSIONS

Repeated administration of cyclopentolate alone or combined with phenylephrine induce a significant mydriasis for at least 48 h after the last administration in normal horses' eyes, and do not affect STT-1, IOP, digestive function, and HR. The phenylephrine combined with the cyclopentolate did not potentiate the pupil dilation when compared with cyclopentolate alone in healthy horses.

Comparison of two rebound tonometers in healthy horses

Objective

To obtain a reference range for evaluation of intraocular pressure (IOP) in horses using Tonovet Plus^®, to compare the IOP readings obtained with Tonovet^® and Tonovet Plus^®, and to evaluate the repeatability of readings.

Animals studied and Procedures

Intraocular pressure of 30 client‐owned horses (60 eyes) with no signs of illness or ocular disease was evaluated using Tonovet^® and Tonovet Plus^® rebound tonometers. Horses’ mean age was 10.7 (range 6‐17) years. Triplicate measurements were performed without using sedatives or local anesthetics, with minimal restraint.

Results

Calculated reference intervals (the CLSI robust method) were 14.4‐27.2 mmHg for Tonovet^® and 16.0‐26.1 mmHg for Tonovet Plus^®. Mean values (± standard deviation, SD [± coefficient of variation, CV]) obtained with Tonovet Plus^® (21.6 ± 2.45 mmHg [11.3%]) were on average 0.6 mmHg higher than with Tonovet^® (21.0 ± 3.14 mmHg [15.0%]), and a negligible statistical difference between the devices was found using the paired sample t test (P = .049). The correlation coefficient for the averaged triplicate measurements was 0.73. The average CV was 4.6% and 4.4% for Tonovet^® and Tonovet Plus^®, respectively.

Conclusions

The repeatability of measurements was very good with both devices. The readings between the two devices differed statistically significantly, but the correlation was considered good and the variation was numerically small, and thus, the difference was considered clinically irrelevant. When monitoring disease process or treatment response in an individual patient, repeated readings are best performed using a similar device to avoid false interpretation of results.