Anatomy - Comparison of the eye between animals

Comparison of the eye between animals

Visual fields

Figure 1: Visual field of a carnivore (cat) and a herbivore (horse). a: Frontal position of cat's eyes results in narrow monocular visual field and wide binocular visual field. b: Lateral position of horse's eyes results in wide monocular visual field and narrow binocular visual field.
Source: Sjaastad O.V., Sand O. and Hove K. (2010) Physiology of domestic animals, 2nd edn., Oslo: Scandinavian Veterinary Press.

• Animals eyes protrude from skull more
• Carnivores and primates
• Forward facing eyes
• Binocular visual field > monocular visual field
• Depth perception (stereoscopic vision)
• Concentration on near objects
• Herbivores
• Laterally positioned eyes
• Binocular visual field < monocular visual field
• Panoramic vision

Orbit

Figure 2: Skulls of a carnivore (dog) and a herbivore (sheep). a: open orbit in dog. b: closed orbit in sheep.
Source: Sjaastad O.V., Sand O. and Hove K. (2010) Physiology of domestic animals, 2nd edn., Oslo: Scandinavian Veterinary Press.

• Carnivores: 
• Open orbit
• Lateral orbital ligament
• Herbivores: 
• Closed orbit
• Lateral bony orbital margin 

Pupil shape

• Round: birds, dog, pig
• Vertical slit: cat
• Horizontal slit: large herbivores
• All circular when dilated  

Anterioposterior flattening of eyeball

• Horses and cattle
• Ramp retina
• Little accomodation is required for focusing on close objects

Tapetum 

• Nocturnal adaptation
• Reflection of incident light increases stimulation of light-sensitive receptor cells in retina à aids vision in dark
• Ungulate: tapetum fibrosum - dense connective tissue
• Carnivores: tapetum cellulosum - reflective cells
• Diurnal species: lack tapetum

Pecten 

Figure 3: Transverse section of Avian eye
Source: Proctor N.S. and Lynch P.J. (1993) Manual of ornithology: Avian structure and function, 1st edn., New Haven: Yale University Press.

• Birds 
• Projection of retina into posterior chamber
• Highly vascular 
• Supply nutrients to retina

References

1. Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
2. Proctor N.S. and Lynch P.J. (1993) Manual of ornithology: Avian structure and function, 1st edn., New Haven: Yale University Press.
3. Samuelson D.A. (2007) Textbook of veterinary histology, 1st edn., Missouri: Saunders Elsevier.
4. Sjaastad O.V., Sand O. and Hove K. (2010) Physiology of domestic animals, 2nd edn., Oslo: Scandinavian Veterinary Press.