The document summarizes the evolution of eyes across different organisms. It discusses how eyes evolved independently over 40-60 times from light-sensitive cells. Early eyes were simple pits that could detect light and dark, evolving into pinhole eyes and eventually camera-style eyes with lenses. Compound eyes also evolved multiple times. The molecular basis of eye evolution involves genes like Pax6 and Hox genes. Across species, eye structures adapted for different environments and lifestyles, with variations in pupil shape, color vision, and retina anatomy in fish, amphibians, reptiles, birds, and mammals.

1. Evolution of eye
MPhil First years
– Bhandary Shashank Kishore
– Rinu Thomas
– Greeshma G

2. Biological evolution
• 5 billion years ago
• Evolution of vision – consequence of light on earth
• Paleontological evidence
– Eyes evolved independently in different organisms
– 40-60 times
– Image forming eyes arose in
• Cnidarians
• Molluscans
• Arthropods
• Chordates
• Pax6 – molecule (role in evolution)

3. Darwin’s theory of evolution
Evolution - “descent with modification”
Similarities among
organisms is from a
common ancestor Differences among
organisms is the result of
natural selection, which
adapted them to different
environments
1
2

4. 4
Fossil Evidence of Evolution

7. Human eye

8. Types of eyes
• Simple eye
– Camera eyes
– Concave mirror eye
– Pinhole eyes
• Compound eyes
– Apposition Eye
– Superposition Eye
o Ommatidia receptors

9. Compound eyes

10. How Could Eyes Evolve?
• Eyes evolved from light sensitive neurons
• Light sensitive spot to a fully developed lens eye

11. Process of evolution

12. Light sensitive proteins
• Eye spots
• Unicellular organisms
– Detection of light and dark
Eyespot – photosynthesis

13. Multicellular “Cup formation”
• Shallow light depression where light sensitive cells.
-Allowed detection of light direction
• Light has to be angled into cup, stimulating only a
portion of cells.
-As depression became deepened, the sense of direction
became finer
-Possibility formation before appearance of the brain
• No need for processing

14. Pit and Pinhole eyes
• Formation of deeper depressions and
narrow openings.
-Less ambient light giving finer sensitivity.

15. Cambrian explosion and light
switch theory
• Introduction of visual fields with simple brains.
-Needed the process of interaction of light and cells
to form an image.
• First visual field was just shadows.

16. Separation form the environment
• Transparent outgrowth of cells on the top of cup
depression.
-Separation of light sensitive cells and external
environment.
• Protection
• Specialization
– Higher refractive index
– Color filtering
– Blocks UV

17. Separation form the environment
• Also allowed for the operation of the sense organ in
Aquatic and Terrestrial environments.
-Major step in evolution.

18. Lens formation and diversification
• Evolved independently form multiple linages.
-originally used for seeing in darker waters.
• Separation of double layer with aqueous middle
- Allowed for waste removal and nutrient supply.
- Increased protection, optical power, viewing angle, and resolution
- Could not be found in fossil records.

19. Developments due to selective pressures
• Color vision
-Advantages for finding food, mates and avoiding prey.
• Focusing
-Environmentally dependent
• Amount of light in environment
• Location
-Non predatory animals typically have eyes on the side of the
head.
• Increased visual range for detection of predators.

20. Developments due to selective
pressures.
• Location
-Predators have eyes located on the front of the head.
• Increased depth perception.
• Muscle attachments
-Movement of the eye.

21. Structural Evolution of the Eye: Nilsson
• Spatial recognition-Light sensitive
patch of cells resting on a dark
pigmented back ground
• Centre patch – Depression
• Edges started constricting and raising
• Cupping occurred - Molluscans

22. Structural evolution of the Eye
• Pinhole eye was formed
– No good resolution
– Dim image
• Any change that improves clarity
and illumination will be favored
• Secondary assumption
– Development of a lens
– Increase in the size of the eye
• Progress from a light sensitive disk
to a camera-eye

23. The fact………….

27. What is the genetic factor
behind ?????

28. Pax6 gene
• It is the master control in the gene development
• Controls position of the eyes on the body plain
• This gene is universal in all bilateria
• This gene has a critical affect on the eye development
is not solely to eyes
• Also in formation of nervous system, brain and nose

29. 9

30. Precursor of Pax6 gene
• Cnidarians: Less classes of Pax genes
• Duplication of Pax genes resulted in the formation of
Pax6 genes

31. Hox gene
• Responsible for the bilateral symmetry
• Paired eyes

32. Discovery of similarities
• Walter Gehring and Rebecca Quiring
• Similar genes of PAX-6 gene in mice and Aniridia in humans
• Mutations in these analogues can truncate the development of
eyes in mice and cause serious defects in the human eye.

33. Annelids eye

34. Annelid eye
• A- transparent cornea
• B, C- granular tissue enclosing globe of
eye
• D- external surface of reticular pigment
epithelium
• F- internal surface of reticular pigment
epithelium
• E- iris
• G- crystalline lens, optic nerve
• K- vascular trunks around base of eyeball

35. Eye of Arthropods

36. Ommatidia are the functional units of insect eyes. Ommatidia contain receptor cells
that send axons to the CNS.
Lens
Receptor
cells
Ommatidia
Axons
Insects appear to have two eyes also, but they are compound!
Each ommatidium sends separate information to their brain.

38. Spider eye

40. 40Eyes of vertebrates
Anatomical Evidence for Evolution

41. 41Eyes of Mollusks
Anatomical Evidence for Evolution

43. Cornea Lens
Retina
(photoreceptors
are on the inside
surface)
Sensory
nerves to
brain
The Cephalopod Eye
This “design” is “more intelligent” than that of mammals (humans) because it lacks the blind spot
and maximizes light exposure to receptors

44. Molluscans
• Horseshoe crab eyes

45. Evolution of eye in vertebrates

47. Anatomy of fish eye

48. Fish
• Fish eyes have spherical lens along with rods and
cones
• Most species have colour vision
• Complete fish eye could have evolved in less than
350,000 years
• Fish can be sensitive to polarized and ultraviolet light
• The first ancestor to conquer the world was the fish
before amphibians, reptiles, birds

49. • Most fishes have fixed pupil size either circular or slit-
like.
• Lens of the fish works more than other optical parts of
the eye.
• Free from spherical aberration.
• Foveas are highly sensitive to light to dark waters in
the water bed.

50. Eye working in water
• Water absorbes light, light is decreased as it is deeper.
• Fixed pupil size in most fishes
• Sharks and rays with muscular iris
• Photoreceptors are deeper inside the eye and are very sensitive in
absorbing wavelength
• Layers of rods and cones arranged irregularly
• Irregularity changes with development
• Tapetum layer for absorbance of sensitive light

51. • Visual stabilization by vestibule-ocular reflex
• Accommodation controlled by lens
• Bony fishes have retractor lentis for near vision
• Cartiliangous fishes have the protractor lentis for far
vision

53. Zones where different types of fish are
present
• surface waters or the sunlit zone.

54. Four eyes
• Four eyed fish have raised above the top of the head and divided
in two different parts, so that they can see below and above the
water surface at the same time.
• Eye of a four-eyed fish
1) Underwater retina 2) Lens 3) Air pupil
4) Tissue band 5) Iris 6) Underwater pupil
7) Air retina 8) Optic nerve

55. Mesopelagic fishes
• Deep water fish
• Light does not support photosynthesis
• Adapted for an active life under low light conditions
• Big lenses and rods
• Very Sensitive to light signals

56. The bathypelagic fishes
• Below 1000 meters
• Ocean is pitch black
• Very little food and no sunlight
• Bioluminescence

57. Fishes inside caves
• Heat shock protein 90 (HSP90) stress
• Cavefish habitats, including pH, oxygen content and temperature.
• Conductivity much lower in the caves
• Eye-size variation
• Adaptive small-eye phenotype.

58. Barrel eyes
• They have large telescopic eyes.
• No cone cells
• Fish has property of avoiding stings from other fishes
• Deepwater fishes, like this Antarctic toothfish, often have large,
upward looking eyes, adapted to detect prey
• The telescope fish has large, forward-pointing telescoping eyes
with large lenses

60. Amphibians
• The eyes of amphibians also can function in two
environments: in air and in water.
• Eye focusing performed in the same way as in a camera: the
lens moves along the optic axis of the eyeball toward or
from the retina.
• For protection of the eyes’ surface from drying, there are
eyelids
• Some kinds of amphibians — mainly terrestrial ones —
have also lachrymal glands.
• It is interesting that frogs perceive by eyes moving objects
only. Shrubs, trees, sky they perceive as background.

61. Frog eye
• Choice of food is determined only by size and movement.
• Can be fooled easily not only by a piece of dangled meat but by
any moving small object.
• Large round lens of the frog
• The frog is naturally nearsighted (myopic) to -6 diopters giving it
a focus of approximately 6 inches.
• Frogs and toads can change their focus by moving the lens out
towards the cornea.
• In frogs the focus range is a few diopters and in toads the focus
range is 5 diopters giving a best myopia of -1 diopters.
• The advantage of nearsightedness is that it blurs the background
clutter making foreground object characterization much easier.
• Only 75% of the light intensity entering the eye reaches the retina

62. Retinal anatomy
• The optic nerve of the frog consists of approximately 470,000
unmyelinated fibers and 15,000 myelinated fibers.
• In the toad it consists of 320,000 unmyelinated fibers and 10,000
myelinated fibers.
• The frog Rana pipiens has approximately 440,000 small ganglion
cells (7 to 10 microns in diameter) and 12,000 of the larger
ganglion cells 14 to 20 microns in diameter.
• The frog brain consists of only 16 million neurons one can see that
the retina makes up a significant portion of its brain's total neuron
number.

63. • The frog retina has three cell layers as shown in figure 3: the
outer, middle, and inner granular layers, and two fiber layers: the
inner and outer plexiform layers.
• The frog has a limited color discrimination as indicated by the red
and green rods.
• Only the ganglion cells from the inner granule layer send axons to
the brain
• Some of the thick arbors tend to separate into two vertical layers

64. Reptiles
The pupil is elliptical or round and may give an indication of habitat
and lifestyle.
Round pupils and nocturnal species have vertical pupils.
Coral snakes and all New World non-venomous snakes, except the
boa constrictor have round pupils, while pit vipers have vertical slit
pupils.
• Sclera - The eye has no ossicles (unlike other reptiles) and the
sclera is composed entirely of tendinous connective tissue.
• Posterior segment - The retina is usually grey mottled with white
or red spots and appears with semi-opaque nerve fibres radiating
uniformly outwards from the optic disc that is obscured in families
having a conus

65. Birds
• Birds have a total of six pigments: four cone pigments plus pinopsin (a pineal
photoreceptive molecule) and rhodopsin for black and white vision.
• Chickens, humans and mice all have the rhodopsin pigment; mice in addition have blue
and green; humans have blue, green, and red; and birds have these three pigments plus
violet and pinopsin.
• For every colour that humans perceive, birds can see very distinct multiple colours,
including ultraviolet light. Birds use infrared light (which we sense as heat) for night
vision, allowing them to rapidly visualize their young in a dense, dark tree.

67. • The four pigments in estrildid finches' cones extend the range of
colour vision into the ultraviolet
• There are two sorts of light receptors in a bird’s eye, rods and
cones.
• Most birds are tetrachromatic, possessing four types of cone cells
each with a distinctive maximal absorption peak.
• Pigeons probably have an additional pigment and therefore might
be pentachromatic

68. Perception
• Birds can resolve rapid movements better than humans, for whom
flickering at a rate greater than 50 Hz appears as continuous
movement.
• Humans cannot therefore distinguish individual flashes of a
fluorescent light bulb oscillating at 60 Hz, but budgerigars and
chickens have flicker thresholds of more than 100 Hz.
• A Cooper's hawk can pursue agile prey through woodland and
avoid branches and other objects at high speed; to humans such a
chase would appear as a blur.

70. MAMMALIAN EYES

71. Till now

72. Few drops from plenty
• Mice
• Cat
• Horse
• Monkey

73. Ocular Dimensions

74. Mice

75. Holangiotic Retina:3-4 major venules and
arteries radiating to optic disc.
Mouse eyesight is as good as what human
see in far off peripheral vision

77. Cat
• Cat eye has Tapetum Lucidum -a reflective layer behind the
retina
• Ability to see in dark
• Decrease visual acuity

78. • Pupil size minimizes to streak or round under bright
illumination

79. • Visual field 2000 -eyes face forward
• Cats have central band known as visual streak instead of
fovea.
• Eye colour gold,green,orange
• They don’t blink frequently squint their eyes to
communicate with other cats
• Third eyelid (nictating membrane) thin cover closes from
sides.
• Partially closes when cat is sick.

81. Sight at night.
• Visual streak: A region with few and smaller retinal
vessels recognized as horizontal band dorsal to the disc
representing area of higher ganglion cell and cone
density for improved visual acuity.
• They have more number of cones and rods

82. • Only 2 cones cells were evolved till then
• They distinguish among blue and violet colours rather than
colours near red spectrum

83. Horse
• Lateral placement of eyes, horizontally elongated,
rectangular pupil-able to see broad wide range landscape.
• Almost 360 degrees each eye view separately
• In addition to these photo-receptors and other mechanisms
for adjusting to light, the horse has one of the largest eyes
among land mammals, which allows more light to enter the
eye.
• Less steropsis,Very sensitive to motion

85. How do they see
• Horses have amazing field of vision and they see everything
except those in their centre hence they look down as they
walk

86. Monkey
• Apes and old monkeys were trichromats and the new world
monkeys are colour blind,more common in males than
females

87. Vertebrate Retina
cone
rod
light

89. THANK YOU