Normal Intraocular Pressure Ranges in Different Animal Species

Normal Intraocular Pressure Ranges in Different Animal Species

General Observations

As the textbook notes, The range of normal IOP in most animals is somewhere between 15 and 25 mmHg because of the conservation between species. The mean IOP and range for an individual species varies with different studies, but general values in common domestic species are 15–18 mmHg (dog), 17–19 mmHg (cat), 15–20 mmHg (rabbit), and 17–28 mmHg (horse)

Importantly, the difference in IOP between fellow eyes should be less than 8 mmHg. If this is not the case, a thorough examination of both eyes should be performed to identify any relevant pathology

Normal Intraocular Pressure Ranges in Different Animal Species

Dogs

Normal canine IOP: 15–18 mmHg

Reference: The mean IOP and range for an individual species varies with different studies, but general values in common domestic species are 15–18 mmHg (dog)

Device-specific ranges:

Tono-Pen XL: Mean IOP of 11.7 ± 2.9 mmHg and 15.6 ± 4.2 mmHg (two studies).

Recent studies report a mean IOP of 11.7 ± 2.9 mmHg (Tofflemire et al., 2017) and 15.6 ± 4.2 mmHg (Kato, 2014) when normal canine eyes were evaluated by means of the Tono‐Pen XL.

Tono-Pen Avia: 12.8 ± 2.9 mmHg (Ben-Shlomo & Muirhead, 2020).

AccuPen: 14.3 ± 4.0 mmHg (Tofflemire et al., 2017) and 13.4 ± 4.7 mmHg (Kato, 2014).

TonoVet Plus: 19.2 ± 3.1 mmHg (Ben-Shlomo & Muirhead, 2020).

Cats

Normal feline IOP: 17–19 mmHg

General values in common domestic species are…17–19 mmHg (cat)

Device-specific ranges:

Tono-Pen: Mean IOP in cats was 19.7 ± 5.6 mmHg.

TonoVet: Noted as more accurate than Tono-Pen XL in both normal and glaucomatous eyes.

Physiological notes:

IOP is considerably lower in geriatric cats than in young cats; higher in adolescent than in adult cats; and lower in young kittens within the first few weeks of life than in adolescent cats.

Rabbits

Normal rabbit IOP: 15–20 mmHg

Cited from general values in common domestic species are…15–20 mmHg (rabbit)

Horses

Normal equine IOP: 17–28 mmHg

General values in common domestic species are…17–28 mmHg (horse)

Schiøtz tonometer (older method): 14–22 mmHg (Severin, 1976).

Tono-Pen:

Mean IOP in horses: 23.3 ± 6.89 mmHg (Miller et al., 1991).

TonoVet Plus:

The IOP values in normal canine eyes were reported to be 19.2 ± 3.1 mmHg, significantly higher than with the TonoVet and TonoPen Avia (Ben‐Shlomo & Muirhead, 2020).

Other Species

Wildlife and Large Mammals

Highest mean IOP: 32.1 ± 10.4 mmHg in the rhinoceros (Ofri et al., 2002a).

Lowest mean IOP: 3 mmHg in the chinchilla (Müller et al., 2010).

Cattle, Sheep, and Goats

The reported mean IOP for the Tono-Pen Avia…is 12.8 ± 2.9 mmHg (Ben-Shlomo & Muirhead, 2020).

Tono-Pen and Mackay–Marg tonometers correlate well in the horse and in the dairy cow (Tono-Pen XL; Gum et al., 1998).

Exotic and Laboratory Animals

Prairie dog: Noted as a published range, see source for more data.

Chinchilla: Mean IOP as low as 3 mmHg.

Reptiles, Birds, and others: “Rebound tonometry has also been reported in the prairie dog, alpaca, pygmy goat, rabbit, dairy calf, birds of prey, chicken, pigeon, ducks and geese, murres, chinchilla, African giant pouched rat, turtle, gray mouse lemur, Yacare caiman, penguin, American bullfrog, and koi fish.

Bilateral Variation

Regardless of species, the difference in IOP between fellow eyes should be less than 8 mmHg. If this is not the case, a thorough examination of both eyes should be performed to identify any relevant pathology.

Device and Technique Considerations

Mean IOP values depend not only on species but also on the method of measurement. As noted:

“Calibration of the Tono‐Pen is based mainly on IOPs within the normal range and up to about 30 mmHg, and therefore it will yield lower readings than actual IOP when IOP climbs into range of 40–50 mmHg or more”

In addition, “corneal thickness has been shown to affect IOP results with both the TonoVet and the Tono‐Pen XL. For every 100 μm increase in corneal thickness, the IOP increases by 1 mmHg for the Tono‐Pen XL and 2 mmHg for the TonoVet”

Summary Table

References

Integrated and directly cited from:

Kirk N. Gelatt – Veterinary Ophthalmology Two-Volume Set-Wiley-Blackwell, Section II: Foundations of Clinical Ophthalmology, pp. 621–629.