Validation of the TonoVet® rebound tonometer in normal and glaucomatous cats

Objective  To validate intraocular pressure (IOP) readings obtained in cats with the TonoVet^® tonometer. Animals studied  IOP readings obtained with the TonoVet^® were compared to IOP readings determined by manometry and by the Tono‐Pen XL^? in 1 normal cat and two glaucomatous cats. TonoVet^® and Tono‐Pen XL^? readings were also compared in a further six normal and nine glaucomatous cats. Procedures  The anterior chambers of both eyes of three anesthetized cats were cannulated and IOP was varied manometrically, first increasing from 5 to 70 mmHg in 5 mmHg increments, then decreasing from 70 to 10 mmHg in 10 mmHg decrements. At each point, two observers obtained three readings each from both eyes, with both the TonoVet^® and Tono‐Pen XL^?. IOP was measured weekly for 8 weeks with both tonometers in six normal and nine glaucomatous unsedated cats. Data were analyzed by linear regression. Comparisons between tonometers and observers were made by paired student t‐test. Results  The TonoVet^® was significantly more accurate than the Tono‐Pen XL^? (P = 0.001), correlating much more strongly with manometric IOP. In the clinical setting, the Tono‐Pen XL^? underestimated IOP when compared with the TonoVet^®. Conclusions  Both the TonoVet^® and Tono‐Pen XL^? provide reproducible IOP measurements in cats; however, the TonoVet^® provides readings much closer to the true IOP than the Tono‐Pen XL^?. The TonoVet^® is superior in accuracy to the Tono‐Pen XL^? for the detection of ocular hypertension and/or glaucoma in cats in a clinical setting.     

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.     

Comparison of the rebound tonometer (ICare) to the applanation tonometer (Tonopen XL) in normotensive dogs

OBJECTIVE: To compare intraocular pressure (IOP) measurements obtained by recently introduced rebound tonometer (ICare) and the well-known applanation tonometer Tonopen XL in normal canine eyes. METHODS: In a prospective, randomized, single-center study, IOP measurements by ICare and Tonopen XL tonometers were compared in 160 nonpathologic canine eyes (80 dogs). Complete slit-lamp biomicroscopy and indirect ophthalmoscopy were performed on each dog. Rebound tonometry was performed first and immediately after topical anesthetic drops were instilled in both eyes. One minute after the application of the topical anesthetic, applanation tonometry was performed in both eyes. The intraocular pressures obtained by use of both techniques were compared by statistical analysis. RESULTS: The mean IOP readings were 9.158 mmHg (SD 3.471 mmHg) for the ICare tonometer (x) and 11.053 mmHg (SD 3.451 mmHg) for the Tonopen XL readings (y). The mean difference in intraocular pressures (-1.905 mmHg) was within clinically acceptable limits. The correlation coefficient (r2) of the relationship within both tonometers was r2=0.7477. The corresponding linear regression between the tonometers readings was y=0.6662x+4.942. CONCLUSIONS: Intraocular pressures obtained with the ICare rebound tonometer were concordant with the IOP readings obtained by applanation Tonopen XL, but ICare values were significantly (P<0.0001) lower. Rebound tonometry could be an appropriate tonometry method for routine clinical use after its calibration for canine eyes.     

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 a rebound tonometer for measuring intraocular pressure in dogs and horses

OBJECTIVE: To compare intraocular pressure (IOP) measurements obtained with a rebound tonometer in dogs and horses with values obtained by means of applanation tonometry and direct manometry. DESIGN: Prospective study. ANIMALS: 100 dogs and 35 horses with clinically normal eyes, 10 enucleated eyes from 5 dogs, and 6 enucleated eyes from 3 horses. PROCEDURES: In the enucleated eyes, IOP measured by means of direct manometry was sequentially increased from 5 to 80 mm Hg, and IOP was measured with the rebound tonometer. In the dogs and horses, results of rebound tonometry were compared with results of applanation tonometry. RESULTS: For the enucleated dog and horse eyes, there was a strong (r2 = 0.99) linear relationship between pressures obtained by means of direct manometry and those obtained by means of rebound tonometry. Mean +/- SD IOPs obtained with the rebound tonometer were 10.8 +/- 3.1 mm Hg (range, 5 to 17 mm Hg) and 22.1 +/- 5.9 mm Hg (range, 10 to 34 mm Hg) for the dogs and horses, respectively. Mean IOPs obtained with the applanation tonometer were 12.9 +/- 2.7 mm Hg (range, 8 to 18 mm Hg) and 21.0 +/- 5.9 mm Hg (range, 9 to 33 mm Hg), respectively. Values obtained with the rebound tonometer were, on average, 2 mm Hg lower in the dogs and 1 mm Hg higher in the horses, compared with values obtained with the applanation tonometer. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the rebound tonometer provides accurate estimates of IOP in clinically normal eyes in dogs and horses.     

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.     

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.     

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.     

Accuracy and reproducibility of the TonoVet® rebound tonometer in birds of prey

Objective To examine the accuracy and reproducibility of intraocular pressure (IOP) measurements obtained by the TonoVet^® rebound tonometer. Animals studied Freshly enucleated healthy eyes of 44 free‐ranging birds of prey out of the species Haliaeetus albicilla, Accipiter gentilis, Accipiter nisus, Buteo buteo, Falco tinnunculus, Strix aluco, Asio otus and Tyto alba euthanized because of unrelated health problems. Procedures IOP readings from the TonoVet^® were compared with a manometric device, with IOP being set from 5 to 100 mmHg in steps of 5 mmHg by adjusting the height of a NaCl solution reservoir connected to the eye. Reproducibility of the TonoVet^® readings was determined by repeated measurements. Results TonoVet^® and manometer values showed a strong linear correlation. In the Accipitridae, the TonoVet^® tended to increasingly overestimate IOP with increasing pressure, while in the other families, it increasingly underestimated it. In the Sparrowhawk, the values almost represent the ideal line. Reproducibility of TonoVet^® values decreases with increasing pressure in the clinically important range from 5 to 60 mmHg. Conclusion IOP values measured with the TonoVet^® demonstrated species specific deviation from the manometric measurements. These differences should be considered when interpreting IOP values. Using the regression formulae presented, corrected IOP values could be calculated in a clinical setting.     

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.