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

Longitudinal intraocular pressure measurements in Whooping cranes (Grus americana) and Mississippi-Sandhill cranes (Grus canadensis pulla)

OBJECTIVE

To assess intraocular pressure (IOP) development in cranes and determine the impact of age, weight, species, head position, and sex.

ANIMALS STUDIED

Whooping cranes (WC) (Grus americana), and Mississippi-sandhill cranes (MSC) (Grus canadensis pulla).

PROCEDURES

Chicks were manually restrained on days 1-3, 7, 21, 35, 60, 75, and 120 for routine examinations. IOP was opportunistically measured utilizing the Tonovet Plus® in D setting with the head above the heart (AH) and below the heart (BH). Values were also obtained longitudinally in adults (>120 days old) upon presentation in 1 year.

RESULTS

Intraocular pressure was highly correlated with age and weight in chicks. For every kilogram gained, IOP increased 2.46 ± 0.08 mmHg in WC and 2.66 ± 0.11 mmHg in MSC. Once hatched, IOP increased 1.13 ± 0.04 mmHg in WC and 0.87 ± 0.04 mmHg in MSC every 10 days. IOP was similar to adults at 120 days of age. In adult WC, mean IOP AH was 24.0 ± 0.4 mmHg, and BH was 27.9 ± 0.4 mmHg, there was a significant difference regarding head positioning and sex, females (25.3 ± 0.4 mm Hg) had lower IOP than males (26.5 ± 0.4 mmHg). In adult MSC, mean IOP AH was 20.7 ± 0.4 mmHg, and BH was 24.6 ± 0.4 mmHg. The difference between head positioning was significant.

CONCLUSIONS

This study documents the correlation between IOP and weight or age during early development in cranes, as well as the importance of head positioning.

Determination of reference values for tear production and intraocular pressure in Pygoscelis penguins of the Antarctic Peninsula

BACKGROUND

According to the literature review, this is the first study investigating tear production (TP) and intraocular pressure (IOP) in the Pygoscelis penguins living in their natural habitat. The study aimed to establish normal values for standard ocular tests in the genus Pygoscelis, namely, the Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins, in four different islands of Antarctica. Sampling was made by specifically using the left eye of the penguins. The Schirmer's tear test type I (STT-I) and the Tonovet® (rebound tonometer) were used to measure the TP and the IOP, respectively.

RESULTS

The mean TP and IOP values of 129 Adélie, chinstrap, gentoo, and 120 adult Adélie, gentoo penguins were determined as 10.2 ± 4.0 mm/min and 38.9 ± 13.2 mmHg, respectively. No statistical difference was detected between the penguin species for the mean IOP values, while the difference was determined in all the locations. However, statistical differences in the mean TP values were determined between all locations.

CONCLUSION

The results of this study provide a reference range of Schirmer's tear test (STT) and IOP values in Pygoscelis penguins and show that the IOP is significantly affected by locations. This result can be attributed to the harsh climatic conditions of the Antarctic Peninsula that change very quickly. The described data may help diagnose clinical pathological findings in Pygoscelis penguins. The STT and rebound tonometry appears to be safe and reproducible methods in Pygoscelis penguins, as the results were obtained quickly and were well tolerated by the birds. Based on our results, we propose that similar studies can be initiated in crowded colonies of three penguin species of this genus on the Antarctic Peninsula, the southern Shetland Islands, and other frequently visited islands in Antarctica.

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.

Clinical ophthalmic parameters of the Quaker parrot (Myiopsitta monachus)

PURPOSE

Ophthalmic diagnosis in many avian species remains hindered by a lack of normative values. This study aimed to establish normal ophthalmic parameters for select diagnostic tests in clinically normal Quaker parrots.

METHODS

Ninety-six captive Quaker parrots aged 8-18 years underwent ophthalmic examination to include assessment of neuro-ophthalmic reflexes, phenol red thread test, rebound tonometry, fluorescein staining, palpebral fissure length measurements, slit lamp biomicroscopy, indirect ophthalmoscopy, and ocular ultrasound biometry.

RESULTS

Menace response, dazzle reflex, and direct pupillary light reflex were present for all Quaker parrots. Tear production (mean ± SD) was 13.3 ± 4.0 mm/15 s and intraocular pressure (IOP, mean ± SD) was 10.6 ± 1.4 and 6.0 ± 1.3 mmHg in the D and P rebound tonometer calibration settings, respectively. For IOP measurement, D and P calibration settings were not interchangeable, with the lesser variation of the D setting preferred in the absence of a gold standard. Ultrasound measurement of the anterior chamber depth increased with age and males had longer axial globe and vitreous lengths. Incidental adnexal and ocular lesions, identified in 36/96 (37.5%) of Quaker parrots, did not statistically affect the created reference data.

CONCLUSIONS

This work provides reference values and clinical findings to assist with monitoring the health of wild populations and maintaining the health of captive Quaker parrots.

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.

TonoVet Plus®: Higher reliability and repeatability compared with Tono-Pen XL™ and TonoVet® in rabbits

OBJECTIVE

To evaluate the accuracy and repeatability of the Tono-Pen XL™, TonoVet® and TonoVet Plus® tonometers by manometric evaluation, and to establish adjustment equations for intraocular pressure (IOP) estimates in rabbits.

ANIMAL STUDIED

Rabbits.

PROCEDURES

A postmortem study was conducted on seven rabbit eyes to verify the correlation between manometry and tonometry with an artificial incremental increase in IOP from 5 and 60 mmHg. A clinical study was conducted to evaluate accuracy and to establish reference values for the species, with measurement of IOP in 17 animals, for 2 consecutive days, with the same tonometers and calibrations used in the postmortem evaluations.

RESULTS

There were strong linear trends for all evaluated tonometers. In the in-vivo evaluation, the mean IOP values were: 14.23 ± 1.75 (Tono-Pen XL™); 13.89 ± 2.07 (TonoVet® calibration mode 'd'); 8.88 ± 1.24 (TonoVet calibration mode 'p'); 18.59 ± 1.94 (Tonovet Plus®). There was a significant difference in the two evaluation times for the two TonoVet® calibration modes. The adjustment equations generated from the manometry for the evaluated tonometers were: Y = 0.2570X + 2.219 (Tono-Pen XL™), Y = 0.2289X + 2.389 (TonoVet® 'd'), Y = 0.4043X + 4.062 (TonoVet® 'p'), Y = 0.1233X + 0.3644 (TonoVet Plus®) (X is device-estimated IOP).

CONCLUSIONS

All evaluated tonometers were well correlated with the manometry, with an underestimation of IOP by all devices. Applying adjustment formulas may compensate for systematic errors. TonoVet Plus® was well tolerated, and showed better repeatability and reliability in successive evaluations.

Repeatability, reproducibility, and agreement of three tonometers for measuring intraocular pressure in rabbits

The aim of this study was to evaluate repeatability, reproducibility, and agreement of three commonly used tonometers in animal research (TonoLab, TonoVet, and TonoPEN AVIA) in a cohort of 24 rabbits. Additionally, the impact of sedation on IOP was investigated in 21 New Zealand White rabbits with the TonoVet tonometer. Repeatability was determined using the coefficient of variation (CoV) for two observers. For the TonoLab (6.55%) and TonoVet (6.38%) the CoV was lower than for the TonoPEN AVIA (10.88%). The reproducibility was highest for the TonoVet (0.2 ± 3.3 mmHg), followed by the TonoLab (0 ± 12.89 mmHg) and lowest for the TonoPEN AVIA (− 1.48 ± 10.3 mmHg). The TonoLab and TonoVet showed the highest agreement (r = 0.85, R² = 0.73). After sedation, a significant IOP reduction (often > 25%) was observed. Our results show that among the three tonometers tested, the TonoVet tonometer is best for use in rabbits while the TonoLab should be avoided. The impact of sedation on IOP was substantial and should be taken into account during experimentation.

Ophthalmic Evaluation of Raptors Suffering From Ocular Trauma

Ocular problems are often associated with traumatic injury in raptors. A comprehensive evaluation, including a complete ophthalmic examination, is vital in determining the patient's overall health and suitability for release. Steps for conducting ocular examination and diagnostic testing in raptors is discussed. Additionally, common clinical findings after trauma, as well as the mechanisms by which ocular injury occurs, are outlined. An overview of medical treatments recommended for commonly diagnosed ocular diseases and the utility of ancillary diagnostic procedures is also presented.

Intraocular pressure measurements using the TONOVET® rebound tonometer: Influence of the probe-cornea distance

PURPOSE

To demonstrate the effect of different probe-cornea distances during intraocular pressure (IOP) data acquisition in dogs and rats.

ANIMALS STUDIED

Twenty-four conscious dogs and 15 anesthetized Wistar rats.

METHODS

Three interchangeable three-dimensional printed polylactide plastic spacer collars were used in place of the original Icare TonoVet® collar piece, which provided different distances (4, 6, and 8 mm) between the instrument's probe and the corneal surface. IOP values were obtained in sequence by a single observer, with the tonometer probe at a 4-, 6-, and 8-mm distance from the corneal surface. The dogs were gently restrained, and the rats were anesthetized with isoflurane.

RESULTS

Intraocular pressure values obtained at 4, 6, and 8 mm from the TonoVet® probe to corneal surface distance in both dogs and rats were significantly different (P < .01). There was a small positive correlation between IOP (mm Hg) and probe-cornea distance (mm) (r_s  = 0.39 for dogs and r_s  = 0.51 for rats). In dogs, the mean IOP (± SD mm Hg) obtained at different distances were 16.2 ± 3.0 at 4 mm; 17.6 ± 3.4 at 6 mm; and 19.8 ± 3.8 at 8 mm. In rats, IOP values were 8.2 ± 1.5 at 4-mm; 9.4 ± 1.8 at 6-mm; and 10.5 ± 1.5 mm Hg at 8-mm distance.

CONCLUSIONS

Probe-cornea distance of the Icare TonoVet® significantly affects IOP readings, even within the 4- to 8-mm range recommended by the manufacturer.

Comparative intraocular pressure measurements using three different rebound tonometers through in an ex vivo analysis and clinical trials in canine eyes

Objective

To evaluate the clinical relevance of intraocular pressure (IOP) measured with three different rebound tonometers in an ex vivo analysis and clinical trials in dogs.

Animals and procedures

Ex vivo analysis and clinical trials were performed separately. For the ex vivo analysis, eight enucleated eyes were obtained from four Beagle dogs. IOP values measured with TONOVET^® (TV‐IOP), TONOVET‐Plus^® (TVP‐IOP), and SW‐500^® (SW‐IOP) were compared with manometric IOPs. For clinical trials, each tonometer was evaluated separately, depending on whether TVP‐IOP was higher or lower than 14 mm Hg. One‐way repeatedmeasures analysis of variance, simple linear regression analysis, and Bland‐Altman plots were used for statistical analyses.

Results

In ex vivo analysis, TV‐IOP and TVP‐IOP were not significantly different from manometric IOP. However, SW‐IOP underestimated IOP compared to manometry. Higher discrepancy was observed in TV‐IOP and SW‐IOP with an increase in manometric IOP. In clinical trials, no significant difference was observed between TV‐IOP (9.73 ± 2.92) and TVP‐IOP (11.36 ± 2.23) when TVP‐IOP was lower than 14 mm Hg, but SW‐IOP (8.70 ± 3.03) was significantly lower than TVP‐IOP. TV‐IOP (15.96 ± 6.47) and SW‐IOP (13.09 ± 3.72) were significantly lower than TVP‐IOP (20.08 ± 6.60) when the IOP was higher than 14 mm Hg of TVP‐IOP.

Conclusions

This study demonstrates that the TONOVET^® and TONOVET‐Plus^® provide a useful approach for ex vivo analysis. In clinical trials, results of TV‐IOP and SW‐IOP were significantly lower than of TVP‐IOP when IOP was higher than 14 mm Hg of TVP‐IOP. The characteristics of rebound tonometers should be considered in clinical settings.

Validation and comparison of four handheld tonometers in normal ex vivo canine eyes

OBJECTIVES

To determine the accuracy and precision of the Icare^® TONOVET Plus rebound tonometer and the Tono-Pen AVIA Vet™ applanation tonometer for intraocular pressure (IOP) measurement in normal ex vivo canine eyes and comparison to earlier models of these tonometers.

ANIMALS & PROCEDURES

The anterior chambers of six normal dog eyes were cannulated ex vivo. IOP was measured with the TONOVET (TV01), TONOVET Plus, Tono-Pen Vet™, and Tono-Pen AVIA Vet™ at manometric IOPs ranging from 5 to 70 mm Hg. Data were analyzed by linear regression, ANOVA and Bland-Altman plots. A P value ≤ .05 was considered significant.

RESULTS

Intraocular pressure values obtained using the TONOVET Plus and TV01 were significantly more accurate than with the Tono-Pen VET and Tono-Pen AVIA Vet, particularly at higher IOPs (30-70 mm Hg). Accuracy was not significantly different between any of the devices in the low to normal physiologic IOP range (5-25 mm Hg). Level of precision was high for all devices, though the TONOVET Plus was more precise than the Tono-Pen Vet in the 5-25 mmHg range and the TV01 was more precise than the Tono-Pen AVIA Vet over the whole IOP range.

CONCLUSIONS

All devices underestimated IOP, particularly at higher pressures. Rebound tonometers were more accurate over the full range of IOP tested and in the high IOP range; however, there were no significant differences in accuracy among devices in the physiologic IOP range. All tonometers can provide clinically useful IOP readings in dogs, but rebound and applanation tonometers should not be used interchangeably.

Normative ocular data for juvenile and adult Japanese quail (Coturnix japonica)

OBJECTIVE

To obtain normative ocular data for Japanese quail as they mature from juveniles to adults.

ANIMALS STUDIED

Twenty-six captive Japanese quail comprising thirteen males and thirteen females, free of ocular disease, were included in the study.

PROCEDURES

Ophthalmic reference values were measured in both eyes at 1 and 5 months of age. A complete ophthalmic examination was performed, including neuro-ophthalmic reflexes, slit lamp biomicroscopy, phenol red thread test (PRTT), rebound tonometry, fluorescein staining, horizontal corneal diameter measurement, indirect ophthalmoscopy, and ocular ultrasound biometry. Ultrasound biomicroscopy measurements of axial globe length, lens thickness, vitreal chamber length, and pecten length were recorded. The depth of the anterior chamber was calculated by subtracting the lens thickness and vitreous length from the axial globe length. Measures of association and descriptive statistics were analyzed using STATA-14 and STATA-15.

RESULTS

Juvenile and adult females were heavier than age-matched males. Weight, intraocular pressure, horizontal corneal diameter, axial globe length, and lens thickness measurements increased with age. No statistically significant differences were found in the remainder of measurements among individuals in different sex or age-groups.

CONCLUSIONS

This work provides reference values and clinical findings that can be used in future research on quail and ocular disease.

Intraocular Pressure Measurement by Rebound Tonometry (TonoVet) in Normal Pigeons (Columba livia)

We evaluated the applicability of a rebound tonometer (TonoVet) in pigeon eyes and established normal reference intraocular pressure (IOP) values in healthy pigeons; 20 eyes of euthanized pigeons were used for calibration of the TonoVet and 48 eyes of 24 adult pigeons were used for measurement of reference IOP. First, IOP of pigeon eyes ex vivo were measured using the 'd' and the 'p' modes of the TonoVet and compared to manometric IOP values from 5 to 80 mm Hg. Then, to establish normal reference values, IOP was measured from clinically normal pigeons in vivo. The 'd' and the 'p' modes of the TonoVet showed a strong linear correlation with the manometric IOP (R² = .996 and .991, respectively). The obtained regression formulas were: y₁ = 0.439x + 2.059 and y₂ = 0.330x - 0.673, respectively (y₁, 'd' mode of TonoVet; y₂, 'p' mode of TonoVet; x, manometric IOP). The 'd' and the 'p' modes consistently measured one-half and one-third of the actual IOP, respectively. Therefore, the formula obtained through the 'd' mode was applied to obtain reference values. The calibrated IOP of normal pigeon eyes was 19.5 ± 4.4 mm Hg. The actual IOP could be calculated using the presented formula. Considering the limitations of the 'p' mode, use of the 'd' mode is more appropriate. Therefore, the TonoVet rebound tonometry under the 'd' mode is a reliable method for measuring IOP in pigeons.

Ophthalmic findings in cinereous vultures (Aegypius monachus)

OBJECTIVE

The aim of the present study was to provide ophthalmic reference values under normal physiological conditions for Aegypius monachus (cinereous vulture).

PROCEDURES

Thirty-two eyes of sixteen adult captive cinereous vultures were used for this study. Tear tests and tonometry in conscious and anesthetized states, neuro-ophthalmic tests, measurement of corneal diameter, slit-lamp biomicroscopy, ophthalmoscopy, and funduscopy were performed.

RESULTS

Schirmer tear test (STT) value was 11.4 ± 2.6 and 11.5 ± 2.8 mm/min in the right (OD) and left eye (OS), respectively. Phenol red thread test (PRT) values were 22.3 ± 2.1 mm/15 s OD and 22.8 ± 3.0 mm/15 s OS. The results showed a strong correlation between STT and PRT in both eyes. Intraocular pressure (IOP) values were 32.8 ± 6.9 mm Hg OD and 31.9 ± 7.1 mm Hg OS with TonoVet and 20.7 ± 4.5 mm Hg OD and 19.5 ± 4.1 mm Hg OS with Tono-Pen. There were significant differences in IOPs between rebound and applanation tonometry in both OD and OS. Tear production and IOP values showed significant reductions with general anesthesia in both tear tests and both tonometry (P < .001). Horizontal corneal diameter (mm) was 15.56 ± 0.96 OD and 15.56 ± 0.96 OS. Vertical diameter (mm) was 14.13 ± 0.96 OD and 14.06 ± 1.06 OS. The horizontal diameter was significantly longer than vertical diameter (P < .001).

CONCLUSIONS

Ocular morphologic information and normal reference range values for various ophthalmic measurements were obtained in clinically healthy cinereous vultures, which can facilitate accurate diagnosis and better management of ophthalmic diseases in cinereous vultures.

Tear production and intraocular pressure values in clinically normal eyes of whooper swans (Cygnus cygnus)

The objective of this study was to determine the normal range of tear production and values of intraocular pressure (IOP) in clinically normal eyes of whooper swans (Cygnus cygnus). A total of 86 birds: 81 cygnets (6-10 weeks old) and 5 moulting - adult swans (3-6 years old) were examined in this study. Both eyes of all birds underwent a complete ophthalmic examination, including evaluation of tear production with the phenol red thread test (PRTT) and the assessment of the IOP by rebound tonometry, employing the TonoVet^® device. The mean ± standard deviation of PRTT values were as follows: all cygnets (81) 22.59±3.48 mm/15s, male cygnets (45) 22.64±3.54 mm/15s, female cygnets (36) 22.53±3.44 mm/15s. IOP was as follows: all cygnets 11.30±3.55 mmHg, male cygnets 10.93±3.56 mmHg, female cygnets 11.74±3.50 mmHg. No statistically significant differences between right and left eye and between female and male cygnets were found for IOP and PRTT values. This study provides the reference values for the PRTT and IOP in healthy whooper swan cygnets, showing that PRTT determination of the tear production and rebound tonometry to evaluate the IOP methods are practical methods for ophthalmic examination in swans.

The influence of the tonometer position on canine intraocular pressure measurements using the Tonovet® rebound tonometer

The objective of this study was to assess the variability of readings made using the Tonovet^® rebound tonometer for measurement of intraocular pressure (IOP) in the peripheral cornea and in angulated positions on the canine corneal surface. Forty-six client-owned dogs admitted for ophthalmic evaluation at the Queen's Veterinary School Hospital, University of Cambridge were included in the study. IOP readings were taken at a variety of locations and using the tonometer at a number of different angles to the cornea: 1) Perpendicularly at center of the cornea (CC); 2) At the center of the cornea but with the tonometer positioned at four angles, and 3) At four different points on the peripheral cornea. All values were compared with the values recorded at the recommended CC position. IOP values were significantly underestimated in seven positions, with median and interquartile range from 12.1 ± 4 mmHg (nasal on periphery) to 15 ± 5 mmHg (laterally angled at center), varying between 0 mmHg to 2.9 mmHg from the CC value. While dorsally angled in the central cornea were not significantly different from those at CC (p = 0.09). Median values were lower for measurements in peripheral positions when compared to angled central positions. These results demonstrate that angling the tonometer or measuring in peripheral regions can result in small but statistically significant underestimation of IOP values.

Modified Schirmer tear test and rebound tonometry in blue-fronted Amazon parrot (Amazona aestiva)

ABSTRACT: The aim of this study was to describe the modified Schirmer tear test (mSTT), intraocular pressure (IOP) by rebound tonometry and palpebral fissure length (PFL) in blue-fronted Amazon parrots (Amazona aestiva). Thirty-five healthy adult animals from a conservation breeding center in Brazil were used in this study. Modified Schirmer tear test, rebound tonometry and PFL measurements were performed in both eyes, with birds under physical restraint. Mean mSTT was 6.2±0.1mm/min and mean IOP was 6.4±0.1mmHg, while PFL was 10.1±0.1mm. A moderate correlation was seen between mSTT and PFL for OD (ρ=0.14) and OS (ρ=0.20). The results provide ophthalmic tests reference values for A. aestiva.

Determination of Tear Production and Intraocular Pressure With Rebound Tonometry in Wild Humboldt Penguins ( Spheniscus humboldti )

Tear production and intraocular pressures (IOPs) were determined in 38 and 102 wild Humboldt penguins (Spheniscus humboldti), respectively, from the Punta San Juan Marine Protected Area in Ica, Peru. Tear production was measured by Schirmer tear test, and IOP was measured with a TonoVet rebound tonometer. Adult (n = 90) and chick (n = 12) penguins were sampled from 2 different beaches (north and south facing) during 2 sampling years (2010 and 2011). Results showed a mean ± SD (range) of 9 ± 4 (2-20) mm/min for tear production and 28 ± 9 (3-49) mm Hg for IOP. Tear production in penguins differed between beach and sex, whereas IOP differed between age, year, and beach. The IOPs were negatively correlated with packed cell volume. Tear production and IOP values had greater variation in this population than it has in other avian species. Previous investigations of IOP and tear production in Spheniscus species were conducted with birds housed under professional care in artificial marine and freshwater environments. This is the first study, to our knowledge, investigating tear production and IOP in wild penguins and establishes valuable reference intervals for this species.

Reference values for selected ophthalmic tests of the blue-and-yellow macaw (Ara ararauna)

ABSTRACT: The aim of this study was to establish reference values for selected ophthalmic diagnostic tests in healthy blue-and-yellow macaws. We investigated a total of 35 adult macaws (70 eyes) of undetermined sex and with an average weight of 1 kg, who were living in captivity in the Federal District, Brazil. Tear production using the Schirmer tear test (STT), normal conjunctival flora, intraocular pressure (IOP) using a rebound tonometer and horizontal palpebral fissure length (HPFL) were evaluated. In this study, 84.1% of samples were positive for microbial growth. Bacteria, fungi and yeasts were isolated, and Staphylococcus spp. (21.9%) and Bacillus spp. (26.8%) were the most frequently isolated microorganisms. The mean value for STT was 7.6±4.6mm/min in the right eye (OD) and 6.6±4.4mm/min in the left eye (OS) (median = 7,11±0,76mm/min). Mean IOP was 11.4±2.5mm Hg OD and 11.6±1.8mm Hg OS (median = 11.49±0.22mm Hg), prior to anesthesia, and 7.6±2.4mm Hg OD and 7.8±1.8mm Hg OS (median 7.71±0.08mmHg) after anesthesia. The IOP was significantly lower when the animals were under anesthesia as compared to when they were conscious (p≤0.05). Horizontal palpebral fissure length was 11.7±0.1mm OD and 11.8±0.1mm OS (median = 11.72±0.07mm). The STT showed a positive correlation with palpebral fissure measurement for this species. These selected ophthalmic reference values will be particularly useful in diagnosing pathological changes in the eyes of blue-and-yellow macaws.

Tonometer validation and intraocular pressure reference values in the normal chinchilla (Chinchilla lanigera)

OBJECTIVES

To determine accuracy and precision of three commonly used tonometers (TonoVet^® and TonoLab^® (ICare Oy, Finland)-rebound tonometers, and Tono-Pen VET™ (Reichert, NY)-applanation tonometer) in normal chinchillas, and to establish a normal intraocular pressure (IOP) reference range in this species.

METHODS

The anterior chambers of three chinchilla eyes were cannulated ex vivo and readings obtained at manometric IOPs from 5 to 80 mmHg, using each of the three tonometers in random order. Data were analyzed by linear regression, ANOVA, and Bland-Altman plots. Tonometry was performed in both eyes of 60 chinchillas (age 8 weeks-16.2 years) using the TonoVet^® and relationship between age and IOP analyzed using linear regression. For all statistical tests, P < 0.05 was significant.

RESULTS

Intraocular pressure values obtained using the Tono-Pen VET™ and TonoVet^® (in dog calibration mode;'d') showed strong linear correlation with manometry within the physiologic and clinically relevant range of IOP (0-50 mmHg). The TonoVet^® 'd' setting displayed significantly greater precision over the full range of IOP evaluated than the Tono-Pen VET™, and both TonoVet and Tono-Pen VET™ were significantly more accurate than the TonoLab^® tonometer. Mean ± SD IOP (TonoVet^® 'd') in chinchillas was 9.7 ± 2.5 mmHg, and the 95% reference interval was 4.7-14.7 mmHg.

CONCLUSIONS

Both the Tono-Pen VET™ and TonoVet^® provided clinically acceptable estimates of IOP in chinchillas. The TonoVet^® provides accurate and precise IOP values, while Tono-Pen VET™ derived measurements showed greater variability. Values obtained either with the TonoLab^® or TonoVet^® used in the 'unspecified' calibration setting were inaccurate in this species.

Ophthalmic Diagnostic Tests and Ocular Findings in a Flock of Captive American Flamingos ( Phoenicopterus ruber ruber)

Seventeen adult captive American flamingos ( Phoenicopterus ruber ruber) (34 eyes) underwent a complete ocular examination, including assessment of menace response, pupillary light reflexes, dazzle reflex, palpebral and corneal reflexes, fluorescein staining, slit-lamp biomicroscopy, and direct ophthalmoscopy. Birds were randomly assigned to one of 2 groups for tear production and intraocular pressure measurements. Tear production was measured by modified Schirmer tear test I (n = 9 birds) or phenol red thread test (n = 8 birds), and intraocular pressure was measured indirectly by applanation (Tonopen-XL) (n = 9 birds) or rebound (TonoVet) (n = 8 birds) tonometry. Conjunctival swab samples were taken from one randomly selected eye of all 17 birds to identify surface ocular microbial flora via aerobic bacterial culture. Additionally, 3 of the 17 birds were anesthetized for bilateral B-mode ocular ultrasonography examination to obtain axial globe measurements. Results showed that the menace response and dazzle reflex were absent in all birds. Sixteen of the 17 birds were free of significant ocular disease; a small cataract and pigment on the anterior lens capsule were noted in one eye of one bird. Mean ± SD tear production was 12.3 ± 4.5 mm/min (range, 4-20 mm/min) for modified Schirmer tear test I and 24.2 ± 4.4 mm/15 s (range, 14-30 mm/15 s) for phenol red thread test. Modified Schirmer tear test I measurements were significantly lower than phenol red thread measurements (P < .001). Mean intraocular pressure was 16.1 ± 4.2 mm Hg (range, 7-22 mm Hg) for Tonopen and 9.5 ± 1.7 mm Hg (range, 7-13 mm Hg) for TonoVet. Tonopen measurements were significantly higher than TonoVet measurements (P < .001). An Enterococcus species (9/17 eyes; 53%) and a gram-positive coccus (7/17 eyes; 41%) were the bacteria most commonly isolated from conjunctival swab samples. Mean B-mode ultrasonographic globe measurements of 6 eyes (3 birds) were axial globe length, 13.8 ± 0.16 mm; anterior chamber depth, 1.75 ± 0.05 mm; lens thickness, 4.6 ± 0.06 mm; vitreous body depth, 6.95 ± 0.10 mm; and pecten dimensions, 5.1 ± 0.38 mm length, 2.2 ± 0.14 mm width. In summary, the prevalence of ocular lesions was low in this population of captive American flamingos. Results obtained from 2 types of tear and intraocular pressure measurement tests were significantly different, indicating that a single type of each diagnostic test should be consistently used. A modification of the standard Schirmer tear test or use of phenol red thread test is recommended due to the small flamingo eye.

Validation of rebound tonometry for intraocular pressure measurement in the rabbit

Rabbits play a growing role in research into glaucoma surgical models and ocular drug delivery models. However, the lack of an accurate method for measuring intraocular pressure (IOP) in this animal has been a significant deficit. In this study we validated the use of the TonoVet rebound tonometer and provide conversion tables for its use in rabbits. Experiments were performed on 18 adult New Zealand White rabbits. The TonoVet measurements were obtained and compared to manometric readings by anterior chamber (AC) cannulation. The TonoVet position and 'd' (dog or cat) and 'p' (other species) modes were compared. The sensitivity of the TonoVet tonometer in assessing IOP changes was also tested. There was a strong linear correlation for both the 'd' mode (mean slope = 0.84 ± 0.03, r(2) = 0.99 ± 0.03) and the 'p' mode (mean slope = 0.64 ± 0.02, r2 = 0.97 ± 0.01) of the TonoVet with manometric IOP. However, the TonoVet had a tendency to underestimate IOP compared to manometry and conversion formulae were possible to calculate for both modes. The orientation of the TonoVet handle had no effect on IOP reading, as long as the groove was horizontal. No significant differences were observed when comparing right and left eyes (P > 0.05). IOP recovered four days after cannulation. Younger rabbits had lower IOP compared with older rabbits (P < 0.01). Timolol produced a 2.5 mmHg reduction in IOP 2 h later as detected by the TonoVet. Using the conversion table presented, the TonoVet is a reliable and precise tool for the measurement of IOP in rabbits.

Differences in ocular parameters between diurnal and nocturnal raptors

OBJECTIVE

To establish and compare normal ocular parameters between and within diurnal and nocturnal raptor groups.

ANIMALS STUDIED

Eighty-eight ophthalmically normal raptors of six nocturnal and 11 diurnal species were studied.

PROCEDURE

Tear production was measured using Schirmer tear test (STT) and phenol red thread test (PRTT), and applanation tonometry was conducted. Ultrasonographic measurements of axial length (AL), mediolateral axis (ML), vitreous body (VB), and pecten length (PL) were recorded, and conjunctival cultures were obtained.

RESULTS

A weak correlation (R = 0.312, P = 0.006) was found between PRTT and STT. Tear production was significantly lower in nocturnal species (P < 0.001), but no difference was observed in intraocular pressure (IOP). VB and PL were significantly longer in diurnals (P < 0.001 and P = 0.021, respectively), and no significant difference was observed in AL and ML. When comparing results within these groups, there was a significant difference between most species for all parameters except IOP. Fifty-one percent of the examined raptors were positive for mycology or bacteriology, either on culture or PCR. The most common infectious agent isolated was Staphylococcus spp.

CONCLUSIONS

Phenol red thread test and STT are both valid methods to measure tear production; however, a separate baseline must be determined for each species using these methods, as the results of one method cannot be extrapolated to the other. Due to significant differences observed within diurnal and nocturnal species, it appears that a more intricate division should be used when comparing these parameters for raptors, and the classification of diurnal or nocturnal holds little significance in the baseline of these data.

Evaluation of intraocular pressure in conscious Hermann's tortoises (Testudo hermanni) by means of rebound tonometry

OBJECTIVE

To determine intraocular pressure (IOP) in healthy Hermann's tortoises (Testudo hermanni).

ANIMALS

26 outdoor-housed Hermann's tortoises (13 males and 13 females); body weight ranged from 255 to 2,310 g, and age ranged from 4 to > 50 years.

PROCEDURES

After a preliminary ophthalmic evaluation was performed, IOP was measured by means of a rebound tonometer in both eyes of each tortoise. Three measurements were obtained for each eye; successive measurements were obtained from alternate eyes. Each measurement was based on the mean of 6 values automatically provided by the rebound tonometer. Statistical analysis was used to evaluate correlations between variables and to identify sex- or size-related IOP variations, and changes in IOP over multiple measurements.

RESULTS

Mean ± SEM IOP of the 52 eyes was 15.74 ± 0.20 mm Hg (range, 9 to 22 mm Hg). Results for t tests did not reveal significant differences in IOP between the right and left eyes or between males and females. A significant moderate negative correlation (r = -0.41; r(2) = 0.169) between IOP and body weight was detected. Results of repeated-measures ANOVA revealed a significant increase in IOP over multiple measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

Rebound tonometry was a practical and rapid means of determining IOP in small- to medium-sized tortoises that required minimal manual restraint of the animals. Establishing IOP values in healthy Hermann's tortoises will provide a reference frame for use during complete ophthalmic examinations, thus allowing clinicians to diagnose a broader spectrum of ocular pathological conditions in tortoises.

Schirmer tear test type I readings and intraocular pressure values assessed by applanation tonometry (Tonopen® XL) in normal eyes of four European species of birds of prey

OBJECTIVE

To determine normal values for Schirmer tear test I and intraocular pressure in four European species of birds of prey.

ANIMALS STUDIED

Twenty birds from each of the following species: Eurasian Tawny owl (Strix aluco), Little owl (Athene noctua), Common buzzard (Buteo buteo), and European kestrel (Falco tinnunculus).

PROCEDURES

Both eyes of all birds (80 eyes) underwent a complete ophthalmic examination, which included a Schirmer tear test type I (STT-I) performed with commercially available strips and the assessment of the intraocular pressure (IOP) by applanation tonometry, employing the Tonopen-XL(®) device. The animals, which had been taken to a rescue center, were examined for ocular lesions prior to their eventual release into the wild. STT-I readings and IOP values were expressed as means ± standard deviation.

RESULTS

Schirmer tear test type I readings were as follows: Eurasian Tawny owls: 3.12 ± 1.92 mm/min; Little owls: 3.5 ± 1.96 mm/min; Common buzzards: 12.47 ± 2.66 mm/min; European kestrels: 6.20 ± 3.67 mm/min. IOP values were as follows: Eurasian Tawny owls: 11.21 ± 3.12 mmHg; Little owls: 9.83 ± 3.41 mmHg; Common buzzards: 17.2 ± 3.53 mmHg; European kestrels: 8.53 ± 1.59 mmHg.

CONCLUSIONS

The results of this study give representative values for STT-I and IOP in four of the most common species of birds of prey in Europe.

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.

Presumptive electric cataracts in a Great Horned owl (Bubo virginianus)

This case report describes suspected electrocution in a juvenile female Great Horned owl (Bubo virginianus) with subsequent bilateral cataract formation. The bird flew into a high-voltage power line and was immediately rescued. Burn wounds of the head and ataxia with apparent blindness were noted. Initial ophthalmic examination 5 days after the incident revealed bilaterally symmetrical anterior subcapsular vacuolar cataracts with absence of intraocular inflammation and a predominantly clear view to the normal appearing fundus. The bird appeared to be nonvisual. No ophthalmic medications were prescribed at initial examination. Subsequent recheck examination at 8 weeks revealed moderate resolution of the cataracts and improved vision. To the authors' knowledge, this is the first published report of suspected electric cataracts in an avian species.

Reference intervals for intraocular pressure measured by rebound tonometry in ten raptor species and factors affecting the intraocular pressure

Intraocular pressure (IOP) was measured with the TonoVet rebound tonometer in 10 raptor species, and possible factors affecting IOP were investigated. A complete ophthalmic examination was performed, and IOP was assessed in 2 positions, upright and dorsal recumbency, in 237 birds belonging to the families Accipitridae, Falconidae, Strigidae, and Tytonidae. Mean IOP values of healthy eyes were calculated for each species, and differences between families, species, age, sex, left and right eye, as well as the 2 body positions were evaluated. Physiologic fluctuations of IOP were assessed by measuring IOP serially for 5 days at the same time of day in 15 birds of 3 species. Results showed IOP values varied by family and species, with the following mean IOP values (mm Hg +/- SD) determined: white-tailed sea eagle (Haliaeetus albicilla), 26.9 +/- 5.8; red kite (Milvus milvus), 13.0 +/- 5.5; northern goshawk (Accipiter gentilis), 18.3 +/- 3.8; Eurasian sparrowhawk (Accipiter nisus), 15.5 +/- 2.5; common buzzard (Buteo buteo), 26.9 +/- 7.0; common kestrel (Falco tinnunculus), 9.8 +/- 2.5; peregrine falcon, (Falco peregrinus), 12.7 +/- 5.8; tawny owl (Strix aluco), 9.4 +/- 4.1; long-eared owl (Asio otus), 7.8 +/- 3.2; and barn owl (Tyto alba), 10.8 +/- 3.8. No significant differences were found between sexes or between left and right eyes. In goshawks, common buzzards, and common kestrels, mean IOP was significantly lower in juvenile birds than it was in adult birds. Mean IOP differed significantly by body position in tawny owls (P = .01) and common buzzards (P = .04). By measuring IOP over several days, mean physiologic variations of +/- 2 mm Hg were detected. Differences in IOP between species and age groups should be considered when interpreting tonometric results. Physiologic fluctuations of IOP may occur and should not be misinterpreted. These results show that rebound tonometry is a useful diagnostic tool in measuring IOP in birds of prey because it provides rapid results and is well tolerated by birds.

Clinical utility of a complete diagnostic protocol for the ocular evaluation of free-living raptors

OBJECTIVE

  To describe a protocol for the examination of free-living raptors and report the ophthalmic examination findings of seven raptor species native to central Illinois, namely the barred owl, Cooper's hawk, eastern screech owl, great horned owl, American kestrel, red-tailed hawk, and turkey vulture and to determine if the findings relative to visual prognosis affected eligibility for future release.

ANIMALS STUDIED

  Seventy-nine free-living raptors.

PROCEDURES

  Under manual restraint, complete ophthalmic examination including slit-lamp biomicroscopy and indirect funduscopy, applanation tonometry, rebound tonometry, ocular morphometrics, B-mode ultrasound, and electroretinography (ERG) were performed on each bird. Histopathology of enucleated globes was performed after euthanasia or death in selected cases.

RESULTS

  The examination protocol was easily performed using manual restraint alone on all birds. Ocular lesions were detected in 48.1% of birds, with 47.3% affected unilaterally and 52.6% affected bilaterally. Ocular lesions were considered to be vision threatening in 29.0% of the unilaterally affected birds and 29.0% of the bilaterally affected birds. The most common case outcomes were discharge from hospital to rehabilitation facility (45.6%) followed by euthanasia (43.0%). The presence of an ocular lesion or a vision-threatening ocular lesion was not significantly associated with outcome. Reference ranges are reported for B-mode ultrasound, ocular morphometrics, and horizontal corneal diameter in all species.

CONCLUSION

  Complete ophthalmic examination can be supplemented by the use of ocular morphometrics, ultrasound, and ERG in the manually restrained raptor. These advanced diagnostic techniques may be useful in developing more objective criteria for evaluating eligibility for release following rehabilitation of free-living birds of prey.

Evaluation of rebound tonometry in non-human primates

To determine the accuracy and reproducibility of intraocular pressure (IOP) measurements obtained with the TonoVet® rebound tonometer in cynomolgus macaques and to determine the effects of corneal thickness on measurements obtained by the TonoVet®. The anterior chambers of both eyes of anesthetized monkeys were cannulated with branched 23-G needles; one branch was connected to a vertically adjustable reservoir and the other to a pressure transducer. IOP was increased by 5 mmHg increments and then decreased by 10 mmHg decrements. IOP was measured using the TonoVet® at each increment and decrement by 2 independent observers and at every other increment and every decrement by a single observer using 'minified' Goldmann applanation tonometry. Central corneal thickness was measured with a PachPen(TM) ultrasonic pachymeter. TonoVet® readings correlated well with manometric IOP (slope = 0.972, r(2) coefficient = 0.955). No significant differences were observed when comparing eyes or operators; however there was a non-significant trend for TonoVet® readings taken in right eyes to be closer to manometric IOP than those taken in left eyes. The TonoVet® had a non-significant tendency to underestimate manometric IOP. TonoVet® readings obtained during the decremental phase of the experiment were significantly closer (p < 0.004) to manometric IOP than those obtained during the incremental phase. Central corneal thickness significantly increased (p < 0.0001) over the course of the experiment. The TonoVet® rebound tonometer is a reliable and accurate tool for the measurement of IOP in cynomolgus macaques. This tonometer has several advantages, including portability, ease of use, and brief contact with the corneal surface making topical anesthetics unnecessary.