How they see
How does a seal see the world?
A colour-blind, blue-tuned diver
A seal's eyes are made for the dim, blue-green gloom of deep water. Effectively colour-blind, it reads the underwater world in brightness and contrast, its large eyes and a bright reflective layer squeezing vision out of the faintest light far below the surface. When the water turns murky, its sensitive whiskers take over.
See through their eyes
Human ≈ 60 cpd (20/10)
How sharp is a seal's vision?
Its eyes resolve about 6 cycles per degree (20/100 (est.)), while a human reaches around 60 cpd (20/10). Its field of view spans about 180°.
How does a seal see a human?
Its eyes resolve about 6 cycles per degree against your 60, so a face has to be roughly 10 times closer for it to pick out the detail you do. Your outline and your movement read clearly; your expression does not.
Colour comparison
How each colour shifts when seen through this animal's eyes, using the same colour model as the app. Tones a screen can't emit (such as ultraviolet) are shown as an approximation.
What colours can a seal see?
Little to no colour; brightness and contrast in a blue-green sea.
Photoreceptors
Cone monochromat + rod-dominated retina
Cone peak sensitivities
- Single cone510 nm
How does a seal see in the dark?
Excellent; large eyes and a strong tapetum lucidum.
How does a seal's vision compare to a human's?
A seal sees around 20/100 to your 20/20 and, where you see millions of hues, little to no colour. Its eyes gather dim, deep-water light far better than yours, and stay in focus both under water and in air.
What is special about a seal's vision?
- Near colour-blind
- Amphibious focus
- Sensitive whiskers complement vision
What the research shows
A harbour seal's colour blindness follows from its photopigments. Griebel & Peichl (2003) measured cone spectral sensitivity and found a single cone class peaking near 510 nm, alongside rods near 496–497 nm. With only one cone type there is no second signal to compare it with, so hue cannot be discriminated at daylight levels, however bright the scene. Peichl, Behrmann & Kröger (2001) had earlier documented this kind of visual pigment loss across marine mammals, whales as well as seals, which places the harbour seal within a wider pattern rather than making it an oddity.
Spatial resolution has been measured, but in very few animals. Weiffen et al. (2006) tested two seals under water and found the finest resolvable line widths to be 5.5 and 12.7 minutes of arc, roughly 5.5 and 2.4 cpd, so two individuals differed by more than a factor of two. The 6 cpd on this page is an estimate close to the better of the two, and acuity in air is thought to be lower. The nearly spherical lens and mobile pupil are built to cope with refraction in both media, and flicker fusion is not well quantified. Because the animal has one cone type, a brightness-only rendering is among the more defensible simulations. What a screen cannot convey is the range of light the eye handles, from surface glare to dim depth, or the trail-following the whiskers perform, which is touch rather than sight.
Guides: Are animals colour blind? · Which animal has the best eyesight? · All guides
Scientific sources
- Peichl, Behrmann & Kröger (2001)
- Hanke et al. (2009)
- Weiffen et al. (2006)
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