Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 98
Ocular Rigidity
ОглавлениеAnother key concept in the measurement of IOP is ocular rigidity (k), or the resistance offered by the fibrous tunics of the eye (i.e., sclera and cornea) to a change in intraocular volume. Ocular rigidity may also be defined as the change in IOP per incremental change in the intraocular volume; this resistance manifests as a change in IOP. Ocular rigidity is determined by Schiotz indentation tonometry, and it estimates the change in volume (open manometer system) when the instrument is placed on the cornea as well as after injections of exact volumes or preselected elevations in IOP. With applanation tonometry, ocular rigidity is not a factor! This logarithmic relationship between IOP and volume of the globe is
Table 2.10 IOPs in select animal species.
| IOP results | |||
|---|---|---|---|
| Species | Mean ± SD | Tonometer | Investigator |
| Alligator | 23.7 ± 2.1 | TonoPen | Whittaker et al. (1995) |
| Cat | 22.6 ± 4.0 | Mackay‐Marg | Miller et al. (1991b) |
| 19.7 ± 5.6 | TonoPen | ||
| Cow | 28.2 ± 4.6 | Mackay‐Marg | Gum (1990) |
| 26.9 ± 6.7 | TonoPen XL | ||
| Chinchilla | 3.0 ± 1.8 | TonoVet‐D | Müller et al. (2010) |
| 9.7 ± 2.5 | TonoVet‐D | Snyder et al. (2018) | |
| Dog | 15.7 ± 4.2 | Mackay‐Marg | Miller et al. (1991a) |
| 16.7 ± 4.0 | TonoPen | ||
| 17.8 ± 0.9 (pm) | Mackay‐Marg | Gelatt et al. (1981) | |
| 21.5 ± 0.8 (am) | |||
| Ferret | 22.8 ± 5.5 | TonoPen | Sapienza et al. (1991) |
| 15.4 ± 1.1 | TonoPen Vet | Di Girolamo et al. (2013) | |
| 14.1 ± 0.4 | TonoVet | ||
| Frog (White's tree frogs) | 16.8 ± 3.9 | TonoLab‐R | Hausmann et al. (2017) |
| 14.7 ± 1.6 | TonoVet‐D | ||
| Goat (pygmy) | 11.8 ± 1.5 | TonoVet‐D | Broadwater et al. (2007) |
| 10.8 ± 1.7 | TonoPen XL | ||
| Guinea pig | 18.3 ± 4.6 | TonoPen Vet | Coster et al. (2008) |
| 6.1 ± 2.2 | TonoVet | ||
| Horse | 25.5 ± 4.0 | Mackay‐Marg | Cohen & Reinke (1970) |
| 23.5 ± 6.1 | Mackay‐Marg | Miller et al. (1990) | |
| 23.3 ± 6.9 | TonoPen | ||
| Mouse (no anesthetic) | 14.6 ± 0.5 | TonoLab | Ding et al. (2011) |
| Nonhuman primate Rhesus (ketamine) | 14.9 ± 2.1 | Pneumatonograph | Bito et al. (1979) |
| 15.4 ± 2.6 | TonoPen XL | Komaromy et al. (1998) | |
| Tibetan monkey | 29.3 ± 0.9 | TonoVet‐P | Liu et al. (2011) |
| Rabbit | 19.5 ± 1.8 | Pneumatonograph | Vareilles et al. (1977a, 1977b) |
| 17.9 ± 2.1 | Smith & Gregory (1989) | ||
| 9.5 ± 2.6 | TonoVet | Pereira et al. (2011) | |
| 15.4 ± 2.2 | TonoPen Avia | ||
| Raptor | |||
| Red‐tailed hawk | 20.6 ± 3.4 | TonoPen | Stiles et al. (1994) |
| Golden eagle | 21.5 ± 3.0 | ||
| Great horned owl | 10.8 ± 3.6 | ||
| White‐tailed sea eagle | 26.9 ± 5.8 | TonoVet | Reuter et al. (2011) |
| Northern goshawk | 18.3 ± 3.8 | ||
| Red kite | 13.0 ± 5.5 | ||
| Eurasian sparrowhawk | 15.5 ± 2.5 | ||
| Buzzard, common | 26.9 ± 7.0 | ||
| Kestrel, common | 9.8 ± 2.5 | ||
| Falcon, peregrine | 12.7 ± 5.8 | ||
| Owl, tawny | 9.4 ± 4.1 | ||
| Owl, long‐eared | 7.8 ± 3.2 | ||
| Owl, barn | 10.8 ± 3.8 | ||
| Rat | 17.3 ± 5.3 | TonoPen | Mermoud et al. (1994) |
| 21.4 ± 1.0 | TonoPen | Sappington et al. (2010) | |
| Sheep | 10.6 ± 1.4 | Perkins | Gerometta et al. (2009) |
Table 2.11 Factors that cause short‐ and long‐term fluctuations in IOP.
| Short‐term fluctuations | Long‐term fluctuations |
|---|---|
| Diurnal changes | Aging |
| Forced eyelid closure | Race/breed |
| Contraction of retractor bulbi muscles | Hormones |
| Coughing/Valsalva maneuver | Glucocorticoids |
| Abrupt changes in blood pressure | Growth hormone |
| Pulse | Estrogen |
| Struggling/electroshock | Progesterone |
| Changes in body/head position | Obesity |
| Succinylcholine | Myopia |
| Acidosis | Gender |
| Season |
Ocular rigidity is a constant characteristic of each eye, but it also depends on IOP. Hence, the distensibility of each globe varies among individuals as well as with the IOP. Dogs and cats have greater scleral elasticity than humans, so less resistance is offered with indentation tonometry, and buphthalmia occurs more readily with prolonged, increased IOP.
