1. Sense Organs: The Eye
Anatomy by Melissa Olman
Physiology by Layleeta Prasad
Genetics by Louis Truong
Evolution by Thomas Rhodes
Biology 347
Dr. Kusanda
Collaboration Project

2. The Anatomy of the
Eye

4. Iris – Regulates the
diameter of the pupil and
also gives the eye its color
Pupil – Opening in the
center of the iris that lets
light into the interior of the
Eye

5. -The iris works in conjunction with
the pupil to control how much light
enters the eye
-The iris has tiny muscles which
enable it to dilate and constrict the
pupil to allow more or less light into
the eye

8. Physiology of the eye

9. Process of vision
• Refraction- bending of light through cornea to
the retina
• Accommodation
-for objects of closer vision, ciliary muscles
contracts, making the lens more convex
-for objects of further vision, ciliary muscles
are relaxed and the lens is flatter.

10. Processing visual information to the
brain
• Retinal Neurons :
- photoreceptors, bipolar,
ganglion, horizontal and amacrine
cells.
• photoreceptors produce nerve
impulses in response to the light
• photoreceptors and ganglion cells
synapse with bipolar cells
• Horizontal and amacrine cells
also synapse with the other
neurons to assist in the
integration of visual information
• nerve signals formed by these
synapses, exit the eye via the
optic nerve and travels to the
optic chiasm
bio1152.nicerweb.com

11. Processing visual information to the
brain
• nerve signals formed
by the synapses, exit
the eye via the optic
nerve and travels to the
optic chiasm
• Visual cortex receives
information
http://www.glaucoma-eye-
info.com/meningioma.html

12. Photorecption
• Scotopic photoreception
- rods- the receptors for night vision
• Photopic photoreception
-cones –daytime vision and color vision
-3 cones: blue green and red
• Visual pigements:
- retinal
- the light absorbing molecule in both rods and cones.
-It is bound to the protein opsin.
-when opsin and retinal combine in rods, it forms the visual
pigment rhodopsin.

13. Depth perception
• Monocular vision:
-visual fields do not overlap
-each eye is used separately
-this type of vision is rare
• Binocular vision:
-the two visual fields overlap
-allows for objects to be seen in three dimensions
-also allows for increase depth perception.
- Stereoscopic vision is within this area of overlap

14. Refraction disorders
• Myopia-
-nearsightedness
-lens is too thick causing the image to focus in
front of the retina
• Hyperopia-
-farsightedness
-lens is too thin causing the image to focus
behind the retina

15. Age related disorders
• Cataracts
- caused by hardening of the lens
-involves cloudiness of the lens that blocks light from reaching the retina
• Glaucoma
- caused by buildup of aqueous humor due to drainage problems
- results in damage to the cells of the retina and optic nerves fibers
causing blindness
-For glaucoma it is common to get surgery to correct the drainage
problems.
• Dry eyes
- caused by a reduction of secretions causing the conjunctiva to become
dry
• Presbyopia
-caused by a loss of elasticity and thickening of the lens

16. Genes controlling eye
development
Homology? Or Analogy?

17. Mutation of Pax6
• Drosophila= eyeless (ey)
– total loss of eye facets on both sides of the head
• Mice= “small eyes” (pax6)
– Homozygous “small eye” embryos are eyeless, noseless and
suffer from brain damage
– Heterozygous mutation develop on adult mice had reduced eyes
• Human= Aniridia
– Similar to mice
– Heterozygous Aniridia patient, has a reduced or no iris
– Homozygous mutant human fetus, was born with no eyes, nose
and also suffer from brain damage. Fetus dies prior to birth

18. Pax6 gene
• Is the master control gene in the eye
development.
• Controls position of the eyes on the body plan
• This gene is universal in all Bilateria
• This gene has a critical affect on the eye
development but not solely to eyes. It is also
involved with the formation of nervous
system, brain and nose.

19. Pax6 Gene
• Pax6 Gene in mouse placed in Drosophila
antenna

20. Induced Ectopic Eyes

21. Precursor of Pax6
• It is found that in Cnidarians have less
classes of Pax genes than in bilaterian . a
duplication of the Pax genes in ancestral
bilateria resulted in the product Pax6
• Although they do not have Pax6
Cnidarians such as box jellyfish have
complex eye with lens which has both
visual and the shielding pigments
• PaxA and PaxB from Cnidarians are
expressed in the eyes
• Like Pax6 they can also induce ectopic
eyes in drosophila which may suggest
that they were precursor of Pax6 in
humans

22. Hox Gene
• Hox genes is regulatory
gene commanding
secondary genes in
formation of body parts
• function controls the
organization along of
animal’s posterior and
anterior axis
• Sets up Bilateral
symmetry (giving us a
pair of eyes)

23. Evolution of the Eye

24. Light Sensitive Proteins
• Also called eye spots
• Used by unicellular organisms
– Detection of light and dark
• No specific direction
• Introduced Circadian Rhythms
http://wikis.lib.ncsu.edu/index.php/Ancestry

25. Light Sensitive Proteins (Stigma)
• Light sensitive patch near the flagella
– Stimulation of flagella in response to light
– Light dependent movement
• Photosynthesis
• Spawning
http://www.studyblue.com/notes/note/n/lab-quiz-2-ecology--protists/deck/1199028

26. Multicellular “Cup Formation”
• Shallow depression where light sensitive cells
– Allowed detection of light direction
• Light had 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

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

28. Cambrian Explosion and Light switch
Theory
• Introduction of Visual field with simple brains
– Needed the ability to process the interaction of
light and cells to form an image
• First visual field was just shadows
• Light Switch Theory
– Andrew Parker
• Proposed that the sudden explosion in Cambrian fossil
records was a result in vision and increased Pedation
• Caused raid evolution and development

29. Separation from the Environment
• Transparent overgrowth of cells on the top of
cup depression
– Separation of light sensitive cells and external
environment
• Protection
• Specialization
– Higher refraction index
– Color filtering
– Blocks UV

30. Separation from the Environment
• Also allowed for the operation of the sense
organ in Aquatic and Terrestrial environments
– Major step in Evolution

31. Lens formation and diversification
• Evolved independently from multiple linages
– Originally used for seeing in darker waters
• Separation into 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 recoreds

32. Developments due to selective
pressures
• Color vision
– Advantage 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

33. 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

34. http://en.wikipedia.org/wiki/File:Diagram_of_eye_evolution.svg

35. References
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Ings S. 2008. Darwin 200: An eye for the eye. Nature 456(7220):304-9.
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Piatigorsky J. 2007. Gene sharing and evolution the diversity of protein functions /. Cambridge, Mass.: Harvard University Press.
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Virtual Medical Centre (Internet) c2002. Virtual Medical centre; (Last updated 4 Dec 2012; Cited 4 Dec 2012) Available from:
http://www.virtualmedicalcentre.com/