iCare tonometers) is gaining popularity in the clinic, especially for children and non-cooperative patients, as the tonometers are handheld devices and no topical anesthesia is required for the procedure 7. Rebound tonometry determines the IOP via induction of a current generated by the rebound effect of a small probe onto the cornea. This method is routinely used in regular clinical care, where Goldmann applanation tonometry (GAT) is the gold standard 5, 6. In applanation tonometry, the force needed to flatten the cornea is used to calculate IOP. Indentation (also known as impression) tonometry uses a plunger to measure the depth of corneal indentation, as used in the Schiøtz tonometer 4. Tonometry is an indirect non-invasive measuring method that can be divided into three different subcategories: indentation, applanation, and rebound tonometry. Although manometry is the most accurate method, it is invasive and requires trained personnel along with expensive and specialized equipment. IOP in animal experiments can be measured by manometry or tonometry. For example, in glaucoma animal models the anterior chamber of the eye can be injected with microbeads to block the outflow of aqueous humor (AH), thus increasing IOP 1, 2, 3. Animal models are routinely used to study underlying pathophysiology and are used in the development of new glaucoma therapies. Repeatable and reproducible objective measurement of IOP are of great importance for disease management. Increased intraocular pressure (IOP) and fluctuations in IOP are important characteristics of glaucoma. The impact of sedation on IOP was substantial and should be taken into account during experimentation. Our results show that among the three tonometers tested, the TonoVet tonometer is best for use in rabbits while the TonoLab should be avoided. After sedation, a significant IOP reduction (often > 25%) was observed.
The TonoLab and TonoVet showed the highest agreement (r = 0.85, R 2 = 0.73).
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). For the TonoLab (6.55%) and TonoVet (6.38%) the CoV was lower than for the TonoPEN AVIA (10.88%). Repeatability was determined using the coefficient of variation (CoV) for two observers. Additionally, the impact of sedation on IOP was investigated in 21 New Zealand White rabbits with the TonoVet tonometer. 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.
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