Animal vision

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Animal vision

• Björn Ekesten
• Department of Clinical Sciences, SLU
• 2006

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Why do we have eyes?

• Predator detection
• Detection of prey / food
• Orientation
• Communication

3
Is animal vision important?

• What is normal vision for different species?
• How is vision affected by different diseases?
• When are performance and safety affected?

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What is vision?

• Detection of light
• Detection of movements
• Other properties
• Focus and accommodation
• Visual field
• Depth vision
• Retina and postretinal pathways
• Visual acuity
• Night vision
• Day and color vision

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Photon capture

• Phototransduction cascade
• Dark-current and hyperpolarization

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Retinal circuitry

• Graded responses
• Amplification and modulation

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Rods and cones

• 6 x 106
• 200 photons
• Rapid responses
• Tolerates bright back-grounds, gt 103 cd/m2
• Hyperpolarize

• 108
• Single photon
• Slow responses
• Saturated in daylight, 101 cd/m2
• Hyperpolarize

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Brightness contrast

• Cones - detect increments and decrements in light
  over a wide range
• Rods - detection of light against a dark bakground

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Movements

• Different pathways
• Magnocellular
• Parvocellular
• Peripheral retina

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Movement detection

• Dogs
• Still 585 m
• Movements 810-900 m
• Horses
• Still 500 m

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Focus and accommodation

• Very limited ability to accomodate
• Usually emmetropic
• Refractive errors not uncommon
• Myopia - dogs horses
• Hyperopia - dogs horses
• Astigmatism

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Myopia
Myopic
Emmetropic
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Visual perspective
Dachshund
Grand Danois
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Visual field
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Limitations of visual field
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Depth vision

• Uniocular clues
• Realtive size
• Interposition
• Perspective
• Texture
• Binocular clues
• Horizontal displacement on the retina
• Horse 9 cm at 2 m

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Retina and postretinal pathways

• Photoreceptors
• Rod dominated
• lt10 cones
• Ganglion cells
• Visual streak / area centalis
• Central 6000 cells/mm2
• Peripheral 500 cells/mm2
• Convergence and image size

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Visual acuity

• Optics
• Image size and brightness on the retina
• Distance between photoreceptors
• Convergence toward ganglion cells
• Visual acuity
• Man 1.0
• Horse 0.7 0.8
• Dog 0.25-0.3

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Night vision

• Rod dominated
• Rhodopsin
• Tapetum lucidum
• Horse / cattle - fibrous
• Cat / dog - cellular
• Corpora nigra

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Spectral sensitivity
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Daylight and color vision

• Humans and Old World primates are trichromats
• Cats, dogs, cattle, horses and pigs are
  dichromats
• Blue cones ( 435 nm)
• Green cones ( 545 nm)

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Color contrast

• Comparison between 2 cone mechanisms
• Low resolution

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Colors that are easy/difficult to distinguish

• Blue
• Green / yellow
• Black
• White

• Greenish-yellow
• Yellow
• Orange
• Red

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At last

• Predators and prey have different visual fields
• Excellent night vision
• Fair central vision
• Limited color vision
• Refractive errors occur