Evaluation of the Perkins handheld applanation tonometer in horses and cattle

The objective of this study was to evaluate and validate the accuracy of the Perkins handheld applanation tonometer for measuring intraocular pressure (IOP) in horses and cattle. Both eyes of 10 adult horses and cattle were evaluated in a postmortem study. The eyes from 10 clinically normal adult horses and cattle were also examined after bilateral auriculopalpebral nerve block and topical anesthesia for an in vivo study. IOP was measured postmortem using direct manometry (measured with an aneroid manometer) and tonometry (measured with a Perkins handheld applanation tonometer). The correlation coefficients (r²) for the data from the postmortem manometry and Perkins tonometer study were 0.866 for horses and 0.864 for cattle. In the in vivo study, IOP in horses was 25.1 ± 2.9 mmHg (range 19.0~30.0 mmHg) as measured by manometry and 23.4 ± 3.2 mmHg (range 18.6~28.4 mmHg) according to tonometry. In cattle, IOP was found to be 19.7 ± 1.2 mmHg (range 18.0~22.0 mmHg) by manometry and 18.8 ± 1.7 mmHg (range 15.9~20.8 mmHg) by tonometry. There was a strong correlation between the IOP values obtained by direct ocular manometry and the tonometer in both horses and cattle. Our results demonstrate that the Perkins handheld tonometer could be an additional tool for accurately measuring IOP in equine and bovine eyes.     

Intraocular pressure in normal llamas (Lama glama) and alpacas (Lama pacos)

Objective: To determine the mean intraocular pressure in llamas ( Lama glama ) and alpacas ( Lama pacos ) using applanation tonometry. Animals studied: Ten llamas and 10 alpacas. Procedures: Intraocular pressure (IOP) was measured with a Tono-Pen™ XL (Mentor Ophthalmics, Inc., Norwell, MA, USA). Three values, with 5% variance, were recorded for each eye. Least-squares means were determined for IOP for each eye of llamas and alpacas. Controlling for age, differences between left and right eye were analyzed using anova . Two age groups were established, less than 5 years and greater than 5 years. The effect of age on IOP within each group was analyzed by linear regression. Probability values of less than 0.05 were considered significant. Results: Comparison of mean IOP between right ( n  = 20) and left eyes ( n  = 20), independent of species type, showed no differences in IOPs for llamas and alpacas. Mean IOP declined with increasing age in llamas and alpacas. Mean IOPs for 20 eyes in 10 llamas was 16.96 ± 3.51 mmHg. Mean IOP for 20 eyes in 10 alpacas was 16.14 ± 3.74 mmHg. Mean IOP for all eyes ( n  = 40), independent of species, was 16.55 ± 3.55 mmHg. The range of IOP in normal llamas and alpacas within 2 SD (95% of the population) was 14.89±18.21 mmHg. Conclusions: There was no significant difference in IOP between alpacas and llamas. Mean IOP in both species decreased with increased age.     

Evaluation of a rebound tonometer (Tonovet®) in clinically normal cat eyes

Objective  To determine the accuracy of and to establish reference values for a rebound tonometer (Tonovet^®) in normal feline eyes, to compare it with an applanation tonometer (Tonopen Vet^®) and to evaluate the effect of topical anesthesia on rebound tonometry.
Procedures  Six enucleated eyes were used to compare both tonometers with direct manometry. Intraocular pressure (IOP) was measured in 100 cats to establish reference values for rebound tonometry. Of these, 22 cats were used to compare rebound tonometry with and without topical anesthesia and 33 cats to compare the rebound and applanation tonometers. All evaluated eyes were free of ocular disease.
Results  Both tonometers correlated well with direct manometry. The best agreement with the rebound tonometer was achieved between 25–50 mmHg. The applanation tonometer was accurate at pressures between 0 and 30 mmHg. The mean IOP in clinically normal cats was 20.74 mmHg with the rebound tonometer and 18.4 mmHg with the applanation tonometer. Topical anesthesia did not significantly affect rebound tonometry.
Conclusions  As the rebound tonometer correlated well with direct manometry in the clinically important pressure range and was well tolerated by cats, it appears suitable for glaucoma diagnosis. The mean IOP obtained with the rebound tonometer was 2–3 mmHg higher than that measured with the applanation tonometer. This difference is within clinically acceptable limits, but indicates that the same type of tonometer should be used in follow-up examinations in a given cat.     

Distribution of intraocular pressure in dogs

Intraocular pressure (IOP) was measured by four different applanation tonometers in normal dogs. By MacKay-Marg tonometry in 391 dogs (772 eyes) the mean ± SD IOP was 18.8 ± 5.5 mmHg (range 8–52 mmHg). Using Tono-Pen XL tonometry in 421 dogs (823 eyes) the mean IOP was 19.2 ± 5.9 mmHg, and the range was 4.42 mmHg. With MMAC-II tonometry in 80 dogs (158 eyes), the mean IOP was 15.7 ± 2.8 mmHg with a range of 10–30 mmHg. By pneumatonograph tonometry in 135 dogs (255 eyes), the mean IOP was 22.9 ± 6.1 mmHg and the range was 10–47 mmHg. In this study 53 breeds were represented. Of those breeds with six animals or more, no significant differences were detected in IOP between breeds ( P > 0.353) or sex ( P > 0.270). There was a significant decline of 2–4 mmHg ( P > 0.0001) in IOP as age increased from less than 2 years to greater than 6 years of age. This trend was present with all of the four tonometers. There were no significant differences between the MacKay-Marg and TonoPen-XL tonometers ( P > 0.198), but significant differences with the MMAC-II ( P > 0.001) and pneumatonograph ( P > 0.001) tonometers existed compared to the first two instruments. Based on this study and the literature, the mean IOP for the normal dog is 19.0 mmHg with a range of 11 (5%) and 29 (95%) mmHg.     

Comparison of the TONOVET Plus®, TonoVet®, and Tono-Pen Vet™ tonometers in normal cats and cats with glaucoma

Objectives

To determine the accuracy, precision, and clinical applicability of the ICare® TONOVET Plus (TVP) in cats.

Animals and Procedures

IOP readings obtained with the TVP were compared to values obtained concurrently with the original TONOVET (TV01) and Tono-Pen Vet™ (TP) in 12 normal cats (24 eyes) and 8 glaucomatous LTBP2-mutant cats (13 eyes) in vivo. Reproducibility of TVP readings was also assessed for three observers in the above cats. The anterior chambers of five different normal cat eyes were cannulated ex vivo. IOP was measured with the TVP, TV01, and TP at manometric IOPs ranging from 5 to 70 mmHg. Data were analyzed by linear regression, ANOVA and Bland–Altman plots. ANOVA was used to assess reproducibility of TVP readings obtained by different observers and an ANCOVA model controlled for variation of individual cats. p < .05 was considered significant.

Results

TVP values strongly correlated with TV01 values (y = 1.045x + 1.443, R² = .9667). The TP significantly underestimated IOP relative to the TVP and TV01, particularly at high IOP. IOP values obtained by 1 observer were significantly higher (~1 mmHg average) compared to the other 2 observers via ANCOVA analysis (p = .0006479 and p = .0203). Relative to manometry, the TVP and TV01 were significantly more accurate (p < .0001) and precise (p < .0070) than the TP in ex vivo eyes.

Conclusions

IOP readings obtained with the TVP and TV01 are broadly interchangeable between models and between observers, but subtle differences may be important in a research context. TP readings vastly underestimate high IOP in feline glaucoma.     

Effect of central corneal thickness on intraocular pressure with the rebound tonometer and the applanation tonometer in normal dogs

Objective To evaluate the effect of central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) with the rebound (TonoVet^®) and applanation (TonoPen XL^®) tonometers in beagle dogs. Animal studied Both eyes of 60 clinically normal dogs were used. Procedures The IOP was measured by the TonoVet^®, followed by the TonoPen XL^® in half of the dogs, while the other half was measured in the reverse order. All CCT measurements were performed 10 min after the use of the second tonometer. Results The mean IOP value measured by the TonoVet^® (16.9 ± 3.7 mmHg) was significantly higher than the TonoPen XL^® (11.6 ± 2.7 mmHg; P < 0.001). The IOP values obtained by both tonometers were correlated in the regression analysis (γ² = 0.4393, P < 0.001). Bland–Altman analysis showed that the lower and upper limits of agreement between the two devices were ?0.1 and +10.8 mmHg, respectively. The mean CCT was 549.7 ± 51.0 μm. There was a correlation between the IOP values obtained by the two tonometers and CCT readings in the regression analysis (TonoVet^® : P = 0.002, TonoPen XL^® : P = 0.035). The regression equation demonstrated that for every 100 μm increase in CCT, there was an elevation of 1 and 2 mmHg in IOP measured by the TonoPen XL^® and TonoVet^®, respectively. Conclusions The IOP obtained by the TonoVet^® and TonoPen XL^® would be affected by variations in the CCT. Therefore, the CCT should be considered when interpreting IOP values measured by tonometers in dogs.     

Intraocular pressure and Schirmer tear test results in clinically normal Long-Eared Hedgehogs (Hemiechinus auritus): reference values

Objective The present study was undertaken to establish reference values for Schirmer tear test (STT) and intraocular pressure (IOP) in the long‐eared hedgehog (Hemiechinus auritus). Animals Fourteen healthy long‐eared hedgehogs (H. auritus) of either sex were studied. Procedures The hedgehogs were individually immobilized with an intramuscular injection of combined Ketamine (20 mg/kg) and Diazepam (0.5 mg/kg), and each animal underwent ophthalmic examinations including: STT, tonometry, biomicroscopy, and indirect ophthalmoscopy. Results No significant effects of animal gender, weight, side (right vs. left eye) were found in this study. Mean (SD) STT values for all eyes (n = 28) were 1.7 ± 1.2 mm/1 min with a range of 0–4 mm/1 min. Mean STT in male animals was 2.2 ± 1.2. Mean STT in female Hedgehogs was 1.3 ± 1.1. Mean (SD) IOP values by applanation tonometry were 20.1 ± 4.0 mmHg (range 11.5–26.5 mmHg). Mean (SD) IOP values by applanation tonometry were 18.2 ± 4.0 and 22.0 ± 3.2 mmHg for males and females, respectively. Conclusions This study reports STT and IOP findings in long‐eared hedgehogs (H. auritus).     

Comparison of the rebound tonometer (TonoVet) with the applanation tonometer (TonoPen XL) in normal Eurasian Eagle owls (Bubo bubo)

OBJECTIVE: To examine the feasibility and accuracy of a handheld rebound tonometer, TonoVet, and to compare the intraocular pressure (IOP) readings of the TonoVet with those of an applanation tonometer, TonoPen XL, in normal Eurasian Eagle owls. ANIMALS STUDIED: Ten clinically normal Eurasian Eagle owls (20 eyes). PROCEDURES: Complete ocular examinations, using slit-lamp biomicroscopy and indirect ophthalmoscopy, were conducted on each raptor. The IOP was measured bilaterally using a rebound tonometer followed by a topical anesthetic agent after 1 min. The TonoPen XL tonometer was applied in both eyes 30 s following topical anesthesia. RESULTS: The mean +/- SD IOP obtained by rebound tonometer was 10.45 +/- 1.64 mmHg (range 7-14 mmHg), and by applanation tonometer was 9.35 +/- 1.81 mmHg (range 6-12 mmHg). There was a significant difference (P = 0.001) in the IOP obtained from both tonometers. The linear regression equation describing the relationship between both devices was y = 0.669x + 4.194 (x = TonoPen XL and y = TonoVet). The determination coefficient (r(2)) was r(2) = 0.550. CONCLUSIONS: The results suggest that readings from the rebound tonometer significantly overestimated those from the applanation tonometer and that the rebound tonometer was tolerated well because of the rapid and minimal stress-inducing method of tonometry in the Eurasian Eagle owls, even without topical anesthesia. Further studies comparing TonoVet with manometric measurements may be necessary to employ rebound tonometer for routine clinical use in Eurasian Eagle owls.     

Evaluation of the Perkins® handheld applanation tonometer in the measurement of intraocular pressure in dogs and cats

Objective  To evaluate and to validate the accuracy of the Perkins^® handheld applanation tonometer in the measurement of IOP in dogs and cats.
Animals  Twenty eyes from 10 dogs and 10 cats immediately after sacrifice were used for the postmortem study and 20 eyes from 10 clinically normal and anesthetized dogs and cats were used for the in vivo study. Both eyes of 20 conscious dogs and cats were also evaluated.
Procedure  Readings of IOP postmortem and in vivo were taken using manometry (measured with a mercury column manometer) and tonometry (measured with a Perkins^® handheld applanation tonometer). The IOP measurement with Perkins^® tonometer in anesthetized and conscious dogs and cats was accomplished by instillation of proxymetacaine 0.5% and of 1% fluorescein eye drops.
Results  The correlation coefficient ( r ²) between the manometry and the Perkins^® tonometer were 0.982 (dogs) and 0.988 (cats), and the corresponding linear regression equation were y  = 0.0893 x  + 0.1105 (dogs) and y  = 0.0899 x  + 0.1145 (cats) in the postmortem study. The mean IOP readings with the Perkins^® tonometer after calibration curve correction were 14.9 ± 1.6 mmHg (range 12.2–17.2 mmHg) in conscious dogs, and were 15.1 ± 1.7 mmHg (range 12.1–18.7 mmHg) in conscious cats.
Conclusion  There was an excellent correlation between the IOP values obtained from direct ocular manometry and the Perkins^® tonometer in dogs and cats. The Perkins^® handheld tonometer could be in the future a new alternative for the diagnosis of glaucoma in veterinary ophthalmology.     

Effects of Intravenous Detomidine on Intraocular Pressure Readings Obtained by Applanation Tonometry in Clinically Normal Horses

This study was conducted to determine effects of intravenous detomidine on intraocular pressure (IOP) readings obtained by applanation tonometry in clinically normal horses. Twenty horses were randomly divided into two groups of 10 each (treatment and control). All horses in the treatment group received intravenous detomidine alone (20 μg/kg). The horses in the control group received only intravenous saline (0.2 mL/100 kg). The IOP values were measured before the treatment (T₀) and then at 5 (T₅), 20 (T₂₀), 60 (T₆₀), and 120 (T₁₂₀) minutes after drug administration in both groups. A significant decrease in IOP values was observed in both right and left eyes of the horses in the treatment group at T₅, T₂₀, and T₆₀ in comparison with the baseline values (P < .001). The observed decrease was only statistically significant in the right eyes of the treatment group horses at T₁₂₀ (P = .044). Mean IOP was not significantly altered at any time point during the treatment period compared with the baseline evaluations in both eyes of the horses in the control group. This study demonstrates that the use of intravenous detomidine lowers IOP quickly.     

Comparison of three rebound tonometers in normal and glaucomatous dogs

Objective

The objectives of the study were to compare intraocular pressure (IOP) readings across a wide range and obtained via three rebound tonometers in ADAMTS10-mutant Beagle-derived dogs with different stages of open-angle glaucoma (OAG) and normal control dogs and to investigate the effect of central corneal thickness (CCT).

Animals Studied

Measurements were performed on 99 eyes from 50 Beagle-derived dogs with variable genetics—16 non-glaucomatous and 34 with ADAMTS10-OAG. Seventeen OAG eyes were measured twice—with and without the use of IOP-lowering medications.

Procedures

IOP was measured in each eye using three tonometers with their “dog” setting—ICare® Tonovet (TV), ICare® Tonovet Plus® (TVP), and the novel Reichert® Tono-Vera® Vet (TVA)—in randomized order. CCT was measured with the Accutome® PachPen. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and regression analyses of tonometer readings and pairwise IOP-CCT Pearson correlations (MiniTab®).

Results

A total of 116 IOP measurements were taken with each of the three tonometers. When comparing readings over a range of ~7–77 mmHg, mean IOPs from the TV were significantly lower compared with TVP (−4.6 mmHg, p < .001) and TVA (−3.7 mmHg, p = .001). We found no significant differences between TVA and TVP measurements (p = .695). There was a moderate positive correlation between CCT and IOP for TVA (r = 0.53, p < .001), TVP (r = 0.48, p < .001), and TV (r = 0.47, p < .001).

Conclusions

Our data demonstrate strong agreement between TVP and TVA, suggesting that the TVA may similarly reflect true IOP values in canines. CCT influenced IOP measurements of all three tonometers.     

Effects of topical 0.5% tropicamide on intraocular pressure in normal cats

The objective of the study was to determine the effect of topical 0.5% tropicamide on intraocular pressure (IOP) in normotensive feline eyes. IOP was measured bilaterally in 70 clinically healthy cats and gonioscopy (and goniophotography) was performed. Thereafter, 50 cats were treated unilaterally with one drop of 0.5% tropicamide. The contralateral, left eye served as a control. In the placebo group consisting of 20 cats, one drop of physiologic saline solution was administered to the right eye. In all cats, IOP of both eyes was measured 30, 60 and 90 min after topical administration. After unilateral tropicamide application, IOP increased significantly both in the right and in the left eye. Maximum average IOP increase was observed at the control measurement performed 90 min after treatment, with an elevation of 3.8 +/- 4.2 mmHg in the right eye and 3.5 +/- 3.6 mmHg in the left eye. Maximum IOP increase after treatment was 18.0 mmHg in the treated eye and 17.0 mmHg in the left eye. Measurements made at 60 min after treatment revealed a significantly higher increase in IOP in the right eye as compared to the left eye (P60 < 0.05), whereas the differences between right and left eye in IOP increase were not significant at 30 and 90 min after mydriatic application (P30 = 0.123; P90 = 0.305). Although tropicamide-induced mydriasis was observed in the treated eye, the contralateral eye did not show any changes in pupillary function at any time. With increasing age of the cats, IOP increase was found to be more moderate, whereas the gender of the cats did not have any significant influence on IOP changes. In the 20 cats in the placebo group, no significant changes in IOP were observed. We conclude that topical 0.5% tropicamide causes a significant elevation of IOP in the treated and untreated eye in normal cats.