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.     

Ophthalmic examination findings in adult pygmy goats (Capra hicus)

Objective To document normal ophthalmic findings and ocular abnormalities in captive adult pygmy goats. Animals studied Ten healthy adult pygmy goats (five male, five female; 5–11 years of age; 26–45 kg body mass) underwent complete ophthalmic examinations. Procedure Direct illumination, diffuse and slit‐beam biomicroscopy, indirect ophthalmoscopy, IOP measurements and Schirmer tear tests were performed. TonoVet^® rebound tonometry, followed by topical application of 0.5% ophthalmic proparacaine, and Tono‐Pen XL^® applanation tonometry were performed in each eye to obtain estimates of IOP. Results Ophthalmic abnormalities included corneal scars and pigmentation, incipient cataracts, lenticular sclerosis, and vitreal veiling. Mean STT values were 15.8 mm/min, with a range of 10–30 mm/min. Mean IOP values were 11.8 mmHg for TonoVet^®‐D, with a range of 9–14 mmHg; 7.9 mmHg for TonoVet^®‐P, with a range of 6–12 mmHg; and 10.8 mmHg for Tono‐Pen XL^®, with a range of 8–14 mmHg. Conclusions Ophthalmic examination findings in adult pygmy goats, including normal means and ranges for STT and IOP measurements, using applanation and rebound tonometry, are provided.     

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.     

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.     

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.     

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.     

Comparison of the use of new handheld tonometers and established applanation tonometers in dogs

OBJECTIVE: To examine the practical aspects, accuracy, and reproducibility of 2 new automatic handheld tonometers in dogs and compare them with results for 2 established applanation tonometers. ANIMALS: 15 freshly enucleated canine eyes for manometric evaluation and 20 conscious research dogs, 20 client-owned dogs, and 12 dogs with acute glaucoma for clinical tonometry. PROCEDURE: Calibration curves were determined for all 4 tonometers on 15 enucleated canine eyes. Intraocular pressure (IOP) was measured with each tonometer consecutively in conscious dogs, with the MacKay-Marg applanation tonometer as the reference device. Measurements were repeated in 20 sedated dogs. An induction-impact tonometer was evaluated clinically on dogs with acute glaucoma. Additionally, measurements obtained by an experienced and an inexperienced examiner and with or without use of topical anesthesia were compared. RESULTS: The portable pneumatonometer was cumbersome and time-consuming. Compared with results for the reference applanation tonometer, and confirmed by manometry, the portable pneumatonometer increasingly underestimated actual IOP values with increasing IOP. The induction-impact tonometer provided accurate and reproducible measurement values. There was a significant strong correlation between the IOP values obtained by the 2 examiners (r2, 0.82) and also with or without topical anesthesia (r2, 0.86). In dogs with glaucoma, the fitted line comparing values for the reference applanation tonometer and induction-impact tonometer closely resembled an ideal 1:1 relationship. CONCLUSIONS AND CLINICAL RELEVANCE: Use of the portable pneumatonometer in dogs appears to have disadvantages. The induction-impact tonometer appears to provide a promising alternative to the use of applanation tonometers in dogs.     

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.     

Tonometry in adult yellow-footed tortoises (Geochelone denticulata)

Objective To determine intraocular pressure (IOP) in adult yellow‐footed tortoises using applanation tonometry. Animals Fifteen healthy adult captive yellow‐footed tortoises (eight males and seven females). Procedures Intraocular pressures were estimated for tortoises by using an applanation tonometer after topical anesthesia. Body length, measured from nuchal to anal scutes, ranged from 27.5 to 57.2 cm. Five measurements from each eye were obtained by a single observer in an ambient temperature of approximately 30 °C. Results Mean ± SEM IOP of 30 eyes of 15 yellow‐footed tortoises was 14.2 ± 1.2 mmHg. Range of IOP was 6–30 mmHg for tortoises. Significant differences were detected neither between right and left eyes (P = 0.357) of individual tortoises, nor between males and females (P = 0.524). Observer's readability was good (intraclass coefficient = 0.65), and IOP did not change over the ordered five measurements. Conclusions There was no significant difference in IOP between males and females in this specie. Tonometry values for normal eyes may represent a useful diagnostic methodology for recognition and treatment of ocular diseases in reptiles.     

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.     

Intraocular pressure in normal dairy cattle

Intraocular pressure (IOP) was measured in normal dairy cows by applanation tonometry. In the first study of 15 Holstein and 17 Jersey cows the mean IOP by Mackay-Marg tonometry was 27.5 ± 4.8 mmHg (range 16–39 mmHg); no significant differences ( P < 0.92) were observed between the Holstein and Jersey breeds. In the second study of 15 Holstein and 12 Jersey cows, the mean IOPs by Mackay-Marg and TonoPen-XL tonometry were 28.2 ± 4.6 mmHg (range 19–39 mmHg) and 26.9 ± 6.7 mmHg (range 16–42 mmHg), respectively. Comparisons of the Mackay-Marg and TonoPen tonometers indicated no significant differences ( P < 0.16). The mean and range of IOP in normal dairy cows within 2 SD (95% of the population) is 27 mmHg with a range of 16–36 mmHg.     

Suitability and calibration of a rebound tonometer to measure IOP in rabbit and pig eyes

Objective To utilize the Icare tonometer TAO1 for intraocular pressure (IOP) determination in experimental animals. To calculate true IOP calibration functions for rabbit and porcine eyes. Animals Enucleated eyes of 3‐year‐old healthy experimental rabbits (New Zealand white), and healthy 1 year old experimental pigs (Deutsche Landrasse) were used for the determination of IOP. Procedures Manometric (Geuder GmbH, Heidelberg/Germany) and rebound tonometry (Icare tonometer TAO1, Icare, Helsinki/Finland) were used to record IOP in enucleated animal eyes (rabbit n = 2, pig n = 3). Results The Icare tonometer TAO1 measurements underestimated true IOP by 37–60% in rabbit eyes and 17–63% in porcine eyes. IOP values obtained by both rebound and manometric tonometry for rabbit and porcine eyes followed a linear regression curve. Linear functions were calculated to correct the Icare tonometer TAO1 measurements to true IOP for both rabbit (p = 1.4244p_ic + 4.2421) and porcine eyes (p = 1.0799p_ic + 5.8557). Conclusions The Icare tonometer TAO1 can be utilized for IOP determination in rabbit and porcine eyes when measured values are corrected with the appropriate linear function.     

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.     

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).     

Ophthalmic examination findings in a colony of Screech owls (Megascops asio)

Objective To report ophthalmic findings in the Screech owl (Megascops asio). Sample population Twenty‐three, apparently healthy adult captive Screech owls in Maryland. Procedures OU of all owls underwent complete ophthalmic examination. One randomly assigned eye of each bird was measured by phenol red thread tear test (PRT), and the other eye by Schirmer tear test (STT). TonoVet^® rebound tonometry and TonoPen‐XL^® applanation tonometry were performed in each eye to measure IOP. Conjunctival swabs were cultured from one eye of 10 birds, corneal diameter was measured in OU of eight birds, and streak retinoscopy was performed on OU of seven birds. Ten birds were anesthetized, and A‐scan ultrasonography using a 15‐MHz probe was performed to obtain axial intraocular measurements. Results Ophthalmic abnormalities were noted in 24/46 (52%) of eyes. Median STT result was ≤ 2 mm/min, ranging ≤ 2–6 mm/min, and mean ± SD PRT was 15 ± 4.3 mm/15 s. Mean ± SD IOP were 9 ± 1.8 mmHg TonoVet^®‐P, 14 ± 2.4 mmHg TonoVet^®‐D, and 11 ± 1.9 mmHg TonoPen‐XL^®. Coagulase negative staphylococcal organisms were cultured from all conjunctival swabs. Mean ± SD corneal dimensions were 14.5 ± 0.5 mm vertically and 15.25 ± 0.5 mm horizontally. All refracted birds were within one diopter of emmetropia. Mean ± SD axial distance from the cornea to the anterior lens capsule was 4.03 ± 0.3 mm, from cornea to the posterior lens capsule was 10.8 ± 0.5 mm, and from cornea to sclera was 20.33 ± 0.6 mm. Conclusions This study reports ophthalmic examination findings in Screech owls, and provide means and ranges for various ocular measurements. This is the first report of rebound tonometry and PRT in owls.     

Reference values for selected ophthalmic diagnostic tests of the capuchin monkey (Cebus apella)

Purpose To perform selected ophthalmic diagnostic tests in healthy capuchin monkeys (Cebus apella) with the aim of establishing normal physiological reference values for this species. Methods A total of 15 healthy, capuchin monkeys were used to test most of the parameters in this investigation. Five of the 15 monkeys were used for the evaluation of normal conjunctival flora. Ages varied from 6 to 20 years of age. Selected diagnostic ocular tests were performed including Schirmer tear test (STT), tonometry using an applanation tonometer (Tonopen^®), central corneal thickness (CCT) using an ultrasonic pachymeter (Sonomed, Micropach^®, Model 200P+) and culture of the normal conjunctival bacterial flora. Results and discussion Results for selected ocular diagnostic tests investigated here for the capuchin monkey eye were as follows: IOP: 18.4 ± 3.8 mmHg; STT: 14.9 ± 5.1 mm/min; CCT: 0.46 ± 0.03 mm. No statistically significant differences between ages or genders were found for any of the results. Streptococcus sp. and Corynebacterium sp. were isolated from healthy conjunctival and eyelid margins, suggesting they are normal constituents of the conjunctival flora of the capuchin monkey. The data obtained in this investigation will help veterinary ophthalmologists and laboratory animal medicine specialists to more accurately diagnose ocular diseases in the capuchin monkey. These ophthalmic reference values will be particularly useful to diagnose discrete or unusual pathological changes of the capuchin monkey eye.     

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 the human and canine Schiotz tonometry conversion tables in clinically normal dogs.

Intraocular pressure (IOP) was measured in 114 eyes of 57 clinically normal dogs with 2 applanation tonometers (Tono-Pen and Mackay-Marg) and the Schiotz indentation tonometer, using the 5.5- and 7.5-g weights. Significant differences were not detected between measurements obtained with the Tono-Pen and Mackay-Marg tonometers the Mackay-Marg and Schiotz tonometers using either weight and conversion with the human calibration table, or the Tono-Pen and Schiotz tonometers using the 7.5-g weight and the human calibration table. Values obtained by use of the Tono-Pen tonometer were significantly less (P less than 0.005) than values obtained with the Schiotz tonometer when a 5.5-g weight and the human calibration table were used, but the amount was clinically unimportant. Estimates of IOP using the Schiotz tonometer and the canine calibration table, and either the 5.5- or 7.5-g weight were clinically and significantly much higher (P less than 0.0001) than estimates obtained with the Tono-Pen, Mackay-Marg, or Schiotz tonometers, using the human calibration table and either weight. Sixty to 70% of clinically normal dogs had an IOP greater than or equal to 30 mm of Hg when Schiotz scale measurements were converted with the canine conversion table. For clinically normal dogs, the human calibration table was the most clinically useful table for converting Schiotz tonometer measurements to mm of Hg. Normal mean (+/- SD) canine readings with the Schiotz tonometer and the 5.5-g weight was 4.9 +/- 1.5 tonometer scale units (range, 2 to 11; 95% confidence interval, 1.9 to 7.9).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of two applanation tonometers in horses

Comparisons were made of measurements obtained in horses, using 2 applanation tonometers in vivo and in vitro. In vitro comparisons indicated that although neither instrument accurately recorded intraocular pressure (IOP), compared with manometric measurements, results of both instruments indicated linear digression from manometric IOP values that could readily be corrected, thereby accurately estimating IOP in horses. For tonometer 1 (MacKay-Marg), calculated actual IOP = 1.48 - 0.9 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual IOP = 1.38 + 2.3 mm of Hg. The coefficients of determination (r2) values were markedly high (0.99 for both equations). In vivo comparisons in clinically normal horses did not reveal significant differences in measured IOP between the 2 instruments, and IOP was not altered from baseline after auriculopalpebral nerve block. Mean (+/- SD) IOP in clinically normal horses was 23.5 +/- 6.10 mm of Hg and 23.3 +/- 6.89 mm of Hg, for tonometers 1 and 2, respectively.     

Evaluation of three applanation tonometers in dogs

The Mackay-Marg, Tono-Pen, and Challenger applanation tonometers were evaluated in vivo in 12 clinically normal eyes of 6 dogs. Tonometric measures of intraocular pressure (IOP) were compared with closed manometric IOP measurements from the anterior chamber of anesthetized dogs. The tonometers were evaluated at IOP that ranged from 5 to 100 mm of Hg. The Mackay-Marg tonometer was the most reliable instrument when evaluated at IOP from 5 to 100 mm of Hg (r2 = 0.996) and from 10 to 30 mm of Hg (r2 = 0.962). The Tono-Pen tonometer was also reliable (r2 = 0.967) over the range of IOP, but consistently overestimated IOP at lower pressures and underestimated IOP at higher pressures. The Mackay-Marg and Tono-Pen measurements were essentially linear. When evaluated from 10 to 30 mm of Hg, r2 was 0.828 for the Tono-Pen tonometer. The Challenger tonometer, although reliable over the full range of IOP (r2 = 0.965), proved to be less accurate, as indicated by lack of a good linear equation.