Visual perception
Visual perception is the ability to interpret the surrounding Biophysical environment, environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the ...
in animals plays an important role in the animal kingdom, most importantly for the identification of food sources and avoidance of predators. For this reason, blindness in animals is a unique topic of study.
In general,
nocturnal or
subterranean animals have less interest in the visual world, and depend on other
sensory modalities Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, ...
.
Visual capacity is a continuum, with humans falling somewhere in the center.
Totally blind species
*
Marsupial moles
* ''
Sinopoda scurion'' (blind huntsman spider)
*
Thaumastochelidae
The family Thaumastochelidae contains five known species of deep-sea lobsters, three in the genus ''Thaumastocheles'', and two in the genus ''Thaumastochelopsis''. The fifth species was discovered in the ten–year Census of Marine Life. These c ...
(blind deep-sea lobsters)
*
Blind cave fish
*
Cave cricket
The orthopteran family Rhaphidophoridae of the suborder Ensifera has a worldwide distribution. Common names for these insects include cave wētā, cave crickets, camelback crickets, camel crickets, Hogan bugs, spider crickets (sometimes shorte ...
s
*
Texas salamanders
* Blind
flatworms
The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
* ''
Tasmanipatus anophthalmus'' (blind velvet worm)
* ''
Typhloperipatus''
*
Eyeless shrimp
*
Eyeless fish
*
Cave beetles
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
* Cave
crayfish
* Some
bristletails,
isopods
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and ...
and
copepods.
* ''
Martialis heureka
''Martialis heureka'' is a species of ant discovered in 2000 from the Amazon rainforest near Manaus, Brazil. It was described as a new species and placed as the sole member of a new subfamily, Martialinae. The generic name means "from Mars ...
''
*
Caecilians
*
Polychelidae
The family Polychelidae contains thirty-eight extant species of blind, benthic lobster-like crustaceans. They are found throughout the world's tropical, sub-tropical and temperate oceans, including the Mediterranean Sea and the Irish Sea.
Anato ...
*
Olm
The olm or proteus (''Proteus anguinus'') is an aquatic salamander in the family Proteidae, the only exclusively cave-dwelling chordate species found in Europe. In contrast to most amphibians, it is entirely aquatic, eating, sleeping, and br ...
(also known as a Proteus)
*
Scolecophidia
The Scolecophidia, commonly known as blind snakes or thread snakes, are an infraorder of snakes. They range in length from . All are fossorial (adapted for burrowing). Five families and 39 genera are recognized. The Scolecophidia infraorder is mo ...
(blind snakes)
*
Faceless cusk
The faceless cusk (''Typhlonus nasus'') is a genus of cusk-eel found in the Indian and Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to th ...
(''Thyphlonus nasus'')
* ''
Typhlonesiotes
''Typhlonesiotes'' is a genus of ground beetles in the family Carabidae
Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,7 ...
'' ''swaluwenbergi'' (a blind ground beetle from the subfamily
Trechinae
Trechinae is a subfamily in the ground beetle family, Carabidae.
Genera
The subfamily includes the following genera:
* '' Accoella'' Uéno, 1990
* '' Acheroniotes'' Lohai & Lakota, 2010
* '' Adriaphaenops'' Noesske, 1928
* '' Aepiblemus'' Bel ...
)
*
Yeti crab
''Kiwa'' is a genus of marine decapods living at deep-sea hydrothermal vents and cold seeps. The animals are commonly referred to as "yeti lobsters" or "yeti crabs", after the legendary yeti, because of their "hairy" or bristly appearance. The ...
*
Bythograeid crabs (''family Bythograeidae'')
*
Blind mole
The blind mole (''Talpa caeca''), also known as the Mediterranean mole, is a mole found in the Mediterranean region. It is similar to the European mole, differing most prominently in having eyes covered with skin. It is found in Albania, France, ...
(''Talpa caeca'')
*
Golden moles (''family Chrysochloridae'')
*
Blind mole-rats (''subfamily Spalacinae'')
*
Blind worm lizard (''Amphisbaena caeca'')
* ''
Tauredophidium hextii'' (spiny blind brotulid)
* ''
Typhlopseudothelphusa'' (blind cave Pseudothelphusid crabs)
*
Sessile
Sessility, or sessile, may refer to:
* Sessility (motility), organisms which are not able to move about
* Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant
* Sessility (medicine), tumors and polyps that ...
animals
* ''
Typhliasina pearsei''
* ''
Dorylus
''Dorylus'', also known as driver ants, safari ants, or siafu, is a large genus of army ants found primarily in central and east Africa, although the range also extends to southern Africa and tropical Asia. The term siafu is a loanword from Swah ...
'' worker ants
Animals that live only in caves, called
troglobites
A troglobite (or, formally, troglobiont) is an animal species, or population of a species, strictly bound to underground habitats, such as caves. These are separate from species that mainly live in above-ground habitats but are also able to live u ...
(meaning 'cave dwellers'), are adapted to life in the dark. Many such species are blind or have poor vision.
Though it is less common, this may also be the case for
fossorial animals, such as
Marsupial moles.
Causes of blindness in animals
Blindness in animals can be caused be the result of environmental adaptations over time, or due to various conditions of the eyes. Many blind species have been able to adapt, navigate and survive in their environment by relying on their other
senses
A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...
. Some species are born without eyes such as the
kauaʻi cave wolf spider
The Kauai cave wolf spider (''Adelocosa anops'', the only species in the genus ''Adelocosa''), also known to local residents as the blind spider, is only known to occur in a few caves in a lava flow with an area of in the Kōloa– Poipū regi ...
,
olm
The olm or proteus (''Proteus anguinus'') is an aquatic salamander in the family Proteidae, the only exclusively cave-dwelling chordate species found in Europe. In contrast to most amphibians, it is entirely aquatic, eating, sleeping, and br ...
and the Mexican tetra.
Cataracts in Animals
Cataracts
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...
are the result of the opacification or cloudiness of the lens in the eye. Cataracts can be developed through old age, diseases or trauma to the eye. Some animals that are prone to the development of cataracts are dogs, elephants, horses, pandas and seals. Cataracts are less common in cats in comparison to dogs, where it is fairly common. Just like with humans, cataract extraction surgery can be performed on cats and dogs.
Glaucoma in Animals
Glaucoma is a progressive condition the eye causes damage to the optic nerve. The damage to the optic nerve is usually caused by intraocular pressure of the eye being elevated. Glaucoma can be seen in dogs, and less commonly, cats. Treatment can be in the form of ocular medication, like prescription eye drops.
Infant blindness
Blindness at birth serves to preserve
the young who are dependent on their parents. (If they could see, they could wander off.) Rabbits are born with eyes and ears closed, totally helpless. Humans have very poor vision at birth as well. See:
Infant vision
Infant vision concerns the development of visual ability in human infants from birth through the first years of life. The aspects of human vision which develop following birth include visual acuity, tracking, color perception, depth perception, a ...
Statements that certain species of
mammals are "born blind" refer to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the
rabbit. In humans the eyelids are fused for a while before birth, but open again before the normal birth time, but very premature babies are sometimes born with their eyes fused shut, and opening later.
Colour blindness
Primates (including humans) are unique as they possess trichromatic color vision, and are able to discern between violet
hort wave (SW) green
edium wave (MW) and yellow-green
ong wave (LW) Mammals other than primates generally have less effective two-receptor
color perception
Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...
systems, allowing only
dichromat
Dichromacy (from Greek ''di'', meaning "two" and ''chromo'', meaning "color") is the state of having two types of functioning photoreceptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats requir ...
ic color vision;
marine mammal
Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
s have only a single cone type and are thus
monochromats.
Honey- and bumblebees have trichromatic color vision, which is insensitive to red but sensitive in ultraviolet to a color called ''bee purple''.
Other animals, such as tropical
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
and
birds, have more complex color vision systems than humans. There is evidence that
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
light plays a part in color perception in many branches of the
animal kingdom, especially for
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s; however, there has not been enough evidence to prove this. It has been suggested that it is likely that
pigeon
Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primarily ...
s are
pentachromats. ''Papilio'' butterflies apparently have tetrachromatic color vision despite possessing six photoreceptor types. The most complex color vision system in animal kingdom has been found in
stomatopod
Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in length ...
s with up to 12 different spectral receptor types which are thought to work as multiple dichromatic units.
Natural selection
Darwin cites
moles Moles can refer to:
* Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain
* The Moles (Australian band)
*The Moles, alter ego of Scottish band Simon Dupree and the Big Sound
People
*Abraham Moles, French engin ...
as an example of mammals that have organs that have become
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
and are being phased out by
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
:
The eyes of moles and of some burrowing rodents are rudimentary in size, and in some cases are quite covered by skin and fur. This state of the eyes is probably due to gradual reduction from disuse, but aided perhaps by natural selection. In South America, a burrowing rodent, the tuco-tuco, or Ctenomys, is even more subterranean in its habits than the mole; and I was assured by a Spaniard, who had often caught them, that they were frequently blind. One which I kept alive was certainly in this condition, the cause, as appeared on dissection, having been inflammation of the nictitating membrane. As frequent inflammation of the eyes must be injurious to any animal, and as eyes are certainly not necessary to animals having subterranean habits, a reduction in their size, with the adhesion of the eyelids and growth of fur over them, might in such case be an advantage; and if so, natural selection would aid the effects of disuse. (Charles Darwin, The Origin of Species
''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
)
Research
The blind forms of the
Mexican tetra
The Mexican tetra (''Astyanax mexicanus''), also known as the blind cave fish, blind cave characin, and blind cave tetra, is a freshwater fish of the family Characidae of the order Characiformes. The type species of its genus, it is native to th ...
have proven popular subjects for scientists studying
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
: A recent study suggests that there are at least two distinct genetic lineages among the blind populations, arguing that these represent a case of
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
.
One theory is that because of its dark habitat, the fish embryo saves energy it would normally use to develop eyes to develop other body parts, and this developmental choice would eventually dominate the population. This is called
economical adaptation. However, studies have shown that blind cave fish embryos begin to grow eyes during development but then something actively stops this process and flesh grows over the partially grown eyes. Another theory is that some Mexican tetra randomly don't develop eyes (which is represented by broken genes in the fish's genome), and this lack of eyes spreads to the rest of the population despite having no advantage or disadvantage. This is called the
unified neutral theory of biodiversity
The unified neutral theory of biodiversity and biogeography (here "Unified Theory" or "UNTB") is a theory and the title of a monograph by ecologist Stephen P. Hubbell. It aims to explain the diversity and relative abundance of species in ecolo ...
.
In one experiment studying eye development,
University of Maryland
The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of M ...
scientists transplanted
lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
es from the eyes of sighted surface-form
embryos into blind cave-form embryos, and vice versa. In the cave form, lens development begins within the first 24 hours of embryonic development, but quickly aborts, the lens cells dying; most of the rest of the eye structures never develop. Researchers found that the lens seemed to control the development of the rest of the eye, as the surface-form tetras which received cave-form lenses failed to develop eyes, while cave-form tetras which received surface-form lenses grew eyes with
pupil
The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...
s,
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...
s, and
iris
Iris most often refers to:
*Iris (anatomy), part of the eye
*Iris (mythology), a Greek goddess
* ''Iris'' (plant), a genus of flowering plants
* Iris (color), an ambiguous color term
Iris or IRIS may also refer to:
Arts and media
Fictional ent ...
es. (It is not clear whether they possessed sight, however.)
The
evolution of trichromatic color vision in primates occurred as the ancestors of modern monkeys, apes, and humans switched to
diurnal (daytime) activity and began consuming fruits and leaves from flowering plants.
Steven Pinker
Steven Arthur Pinker (born September 18, 1954) is a Canadian-American cognitive psychologist, psycholinguist, popular science author, and public intellectual. He is an advocate of evolutionary psychology and the computational theory of mind.
...
. '' How the Mind Works'', 1997. p. 191. .
(''see-
Evolution of color vision,
Evolution of color vision in primates
The evolution of color vision in primates is highly unusual compared to most eutherian mammals. A remote vertebrate ancestor of primates possessed tetrachromacy, but nocturnal, warm-blooded, mammalian ancestors lost two of four cones in the retina ...
'')
Injury, disease and disability
![One-Eyed Cat](https://upload.wikimedia.org/wikipedia/commons/4/47/One-Eyed_Cat.jpg)
Blindness often afflicts pets, especially
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
in old dogs.
In literature
The theme of blind animals has been a powerful one in literature.
Peter Shaffer
Sir Peter Levin Shaffer (; 15 May 1926 – 6 June 2016) was an English playwright, screenwriter, and novelist. He wrote numerous award-winning plays, of which several were adapted into films.
Early life
Shaffer was born to a Jewish family in L ...
's Tony Award-winning play,
Equus, tells the story of a boy who blinds six horses.
Theodore Taylor's classic young adult novel, ''
The Trouble With Tuck
''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the ...
,'' is about a teenage girl, Helen, who trains her blind dog to follow and trust a seeing-eye dog. In non-fiction, a recent classic is
Linda Kay Hardie's essay, "
Lessons Learned from a Blind Cat," in ''
Cat Women: Female Writers on their Feline Friends''.
See also
*
Sudden acquired retinal degeneration, a disease that causes blindness in dogs
References
{{DEFAULTSORT:Blind Animals