Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 113
Vitreous
ОглавлениеThe next refractive tissue is the vitreous. Though there is little refraction as light passes from the lens into the vitreous (due to their similar refractive indices), the vitreous plays an important role in refractive development of the eye. Vitreous elongation increases the axial length of the eye, thereby increasing the refractive path of light and inducing myopia, or nearsightedness (Figure 2.11). In certain fish, this mechanism serves to increase ocular refraction and compensate for loss of corneal refractive power. In different goldfish strains, for example, the vitreous body can contribute anywhere from 37% to 70% of the total axial length of the eye.
Table 2.14 Eye size (ascending order) and corneal power (descending order) in selected animal species.
| Species | Axial length (mm) | Corneal power (D) | References |
|---|---|---|---|
| Goldfish | 4.2 | 129 (in air) | Hughes (1977) |
| Rat | 6.3 | 112.7 | Hughes (1977) |
| Chicken | 8.9 | 108 | Cohen et al. (2008) |
| Guinea pig | 8.9 | 83.9 | Howlett & McFadden (2007) |
| Sea otter | 14.0 | 59.2 | Murphy et al. (1990) |
| Rhesus monkey (4 months) | 16.3 | 56 | Qiao‐Grider et al. (2010) |
| Rabbit | 18.0 | 44.6 | Hughes (1977); Wang et al. (2014) |
| Cat | 21.3 | 43.0 | Habib et al. (1995) |
| Dog | 19.5–21.9 | 37.8–43.2a | Gaiddon et al. (1991); Nelms et al. (1994); Rosolen et al. (1995) |
| Ostrich | 38/0 | 25.3 | Martin et al. (2001) |
| Elephant | 38.8 | 21.3 | Murphy et al. (1992a) |
| Horse | 39.2 | 16.5 | McMullen & Gilger (2006) |
| 43.7 | 15.7–19.5 | Farrall & Handscombe (1990); Miller & Murphy (2017) |
a The range of values in the dog probably reflects a breed difference, because larger breeds have flatter corneas.
