This ppt helps to understand students basic concepts of eye with the best diagram, Students preparing for +1,+2, NEET, CSIR-NET can prepare from this ppt

1. Eye--- Structure, Composition of
eye and biochemical events of
visual transduction
By :Harjinder Kaur

2. Structure of eye:

3. External structures of the eye
includes:
• Eyelids
• Eye- lashes
• Eyebrows
• The lacrimal (tearing)
apparatus
• Extrinsic eye muscles
Figure showing Surface
structure of the right eye.

4. Eyelids
• Two eyelids are present :
 Upper eyelid
 Lower eyelid
• Each eyelid consists of :
 Epidermis
 Dermis
 Subcutaneous tissue
 Fibers of the orbicularis
oculi muscle
 A tarsal plate
 Tarsal glands
 Conjunctiva
• Upper eyelid is more
moveable than lower eye lid
Figure showing detailed structure of
eyelid

5. Eyelash and Eyebrow
• Eyelashes-----project from
the border of each eyelid
• Eyebrows------arch
transversely above the upper
eyelids
• Function:
 Help protect the eyeballs from
foreign objects, perspiration,
and the direct rays of the sun.
Figure showing eyebrow
and eyelash

6. Lacrimal apparatus and Extrinsic Eye
Muscles
Lacrimal apparatus Extrinsic Eye Muscles
• Consisting of the
 Lacrimal gland
 The lacrimal lake
 The lacrimal duct
 The lacrimal sac
 The nasolacrimal duct.
• Secretes and drains tears into
the nasal cavity,
• Six extrinsic eye present each
eye:
 the superior rectus,
 inferior rectus,
 lateral rectus,
 medial rectus, superior
oblique,
 and inferior oblique
• These muscles are capable of
moving the eye in almost any
direction.

7. Figure showing lacrimal
apparatus
Figure showing
Extrinsic Eye Muscles

8. PUPIL:BLACK CENTRE
It contract and dilate depending
upon amount of light.

9. Internal structure of Eye: Eyeball
• Eyeball
 Each being suspended by
extraocular muscles and
fascial sheaths in a
quadrilateral pyramid- shaped
bony cavity called orbit.
• Each eyeball consist of 3
layers:
 Fibrous tunic
 Vascular tunic
 Retina
Figure showing three layers and important
structure of Eyeball

10. Figure showing detailed structure of
the Eye

11. Fibrous tunic
• Cornea:
 Glassy transparent external
surface covering one sixth of
eye.
 Function---- Admits and
refracts (bends) light.
• Sclera:
 White part of the eye
 It covers the entire the eyeball,
except the cornea.
 Function-----Provides shape
and protects inner parts.

12. Vascular tunic
• Iris:
 Located between the cornea and
lens.
 Function----Regulates amount
of light that enters eyeball and
gives color to eyes
• Ciliary body:
 Located in the anterior region of
the vascular tunic
 Function----- Secretes aqueous
humor and alters shape of lens
for near or far vision
(accommodation).
• Choroid:
 Highly-vascularized, darkly-
pigmented membrane
 Function: Provides blood
supply and absorbs scattered
light.

13. Retina:
 Sensory membrane that lines
the inner surface of the back of
the eyeball.
 Composed of several layers,
including one that contains
specialized cells called
photoreceptors.
 Function: Receives light and
converts it into receptor
potentials and nerve impulses.
Output to brain is via axons of
ganglion cells, which form the
optic (II) nerve.

14. Microscopic view of retina:

15. Photoreceptor cells of retina
Rod cells Cone cells
• Cylindrical or rod-shaped
• Light sensors
• 120 million in number
• Functions in less intense light
• Used in peripheral vision
• Responsible for night vision
• Detects black, white and
shades of grey
• Pigment id Rhodopsin
• Tapered or cone-shaped
• Detects colour
• 7 million in number
• Highest concentration at fovea
centralis
• Functions best in bright light
• Perceives fine details
• 3 types of cone cells, each
sensitive to one of the three
primary additive colours: red,
green, and blue

17. Lens
Anterior cavity or aqueous
chamberLens are tranaparent,
biconvex and crystalline
structure
Behind the pupil and iris,
within the cavity of the
eyeball, is the lens.
Lacks blood vessels
Function: Refracts light.
The space in the eye that is
behind the cornea and in front of
the lens is called anterior chamber.
Function: Contains aqueous
humor that helps maintain shape of
eyeball and supplies oxygen and
nutrients to lens and cornea.

18. Macula Lutea
• Small yellowish area of the retina near the optic
disc ("yellow spot").
• Area that provides the most acute vision (clear
vision)
• When the gaze is fixed on any object, the centre
of the macula, the centre of the lens, and the
object are in a straight line

19. Fovea centralis
• Contains no rod cells
• A pit in the centre of the macula lutea
• Has high concentration of cone cells
• Recall: cones are associated with colour vision
and perception of fine detail
• No blood vessels to interfere with vision
• Provides sharp detailed vision (e.g. needed
during reading, driving etc.)

20. Blind spot:
• Optic disc: where the optic nerves converge and
exit the eye
• No light-sensitive cells to detect light rays
• Results in a break in the visual field, known as a
blind spot

21. Vitreous Chamber
Larger posterior cavity of the eyeball is the
vitreous chamber, which lies between the lens
and the retina.
vitreous chamber contain vitreous fluid a
transparent jellylike substance.
Function--- Vitreous humour holds the retina
flush against the choroid
 Give the retina an even surface for the reception
of clear images.

22. Optic nerve:
 Bundle of axons from the retina
Function----Transfer visual information from
the retina to the vision centers of the brain via
electrical impulses.
Blind spot is caused by the absence of
specialized photosensitive (light-sensitive) cells,
or photoreceptors, in the part of the retina where
the optic nerve exits the eye.

23. Composition of eye

24. Composition of cornea
Biochemical component Percentage
 Water 78%
 Collagen 15%
Type I 50-55%
type III <1%
Type IV 8-10%
 TypeVI 25-30%
other protein 5%
Keratan sulphate 0.7%
Chondroitin/dermatan sulphate 0.3%
Hyaluronic acid and salts 1%

25. Cornea
• Storma
 Collagen fibrils 70%
 soluble proteins (Ig G, A, M)
Proteoglycans: Keratin
sulphate,
 Enzymes
 Matrix metalloproteinases
(MMP-1, MMP-2, MMP-3)
Electrolytes
• Epithelium
 Water 70%
 Enzymes necessary for
metabolism
 Acetylcholine
 Electrolytes (Na+, K+, Cl-)

26. Aqueous humor
• Water 99.9%
• Proteins 5-16 mg%
• Amino acid 5mg/kg water
• Non colloid constituent in millimols/kg water are:
• Glucose(6)
• Urea (7)
• AscorbaTE(0.9)
• LACTIC ACID(7.4)
• Inositol(0.1)
• Na+

27. • Anterior chamber
 Lesser bicarbonate
 Higher chloride
 Lesser ascorbate
 pH 7.6
• This digfference is due to
diffusional difference across
the iris.
• Posterior Chamber :
 Higher bicarbonate •
 Lower chloride
 Higher ascorbate
 pH 7.57
 Iris vessels are permeable to
anioins and non electrolytes.
Aqueous Humour :It fills 0.25ml
anterior and 0.06ml posterior chamber.

29. Lens
• Lens water — Dehydrated
• Soluble Crystallins and insoluble albumiboids
• Amino acids
• Carbohydrates
• Lipids
• Electrolytes
• Glutathione
• Proteins
• Vitamin C, vitamin E , and carotenoids

30. Lens…..
• High concentration of glutathione

32. Vitreous Humor
• Collagen is the main content of insoluble
proteins in vitreous humor
• Hyaluronic acid is glycosaminoglycan. It adds
viscosity to the gel. It forms a water binding
meshwork around collagen fibers
• Soluble proteins has mainly glycoprotein and
albumin
• Sugar
• Ascorbic acid
• Amino acids
• Electrolyte

33. Metabolism and energy acquiring
mechanism of eye

34. Metabolism in cornea:
• Most actively metabolising layer of cornea are
Epithelium
Endothelium(requires larger supply of
metabolites).
Cornea is a avascular structure so source of
nutrients are:
Soultes such as glucose (by diffusion or active
transport)
Oxygen (by active transport through tear film).

35. Glucose metabolism in cornea:
 Much of the glucose is metabolised by the hexose
monophosphate pathway (the pentose shunt) with no
production of ATP.
The products are ribose-5-phosphate and NADPH (2)
The corneal epithelium is permeable to oxygen give rise to
reactive oxygen species - oxidise the sulfhydryl (-SH) groups
of proteins

36. Glucose metabolism in lens
• Three main pathways :
 Glycolysis (80-85%)
 TCA (Krebs) cycle (-5%)
 Hexose monophosphate (pentose shunt) (10— 15%)
• Glucose yields —2 ATP under aerobic condition and 36
ATP under anaerobic condition
• The maintenance of the lens structural integrity
requires:
 Osmotic balance provided by Na+,K+-ATPase
Redox balance provided by glutathione (and GSH
reductase)
 Protein synthesis necessary for growth and maintenance
of the tissue.

37. • GSH maintains unaggregated state of lens proteins by
reducing or reversing oxidative damage by UV.
• HMP in the lens provides the NADPH required by GSH
reductase, which is important in maintaining GSH and redox
balance.
• Glucose can be converted to sorbitol by auto-oxidation or
enzymatically by aldose Reductase which utilises NADPH
supplied by HMP.
• Sorbitol can be converted to fructose by sorbitol
dehydrogenase.
• The ratio of the two enzymes in the human lens favours
sorbitol production.
• Less than 5% of glucose is converted to sorbitol.
• It slowly diffuses out to the aqueous humour and doesn't
accumulate in the lens

38. • High external glucose concentrations lead to
increased lens glucose, which saturates the
normal metabolic pathways, leading to increased
sorbitol synthesis.
• Sorbitol accumulation leads to increased
osmolarity of the lens -affects the structural
organisation of crystalline and promotes
denaturation and aggregation, leading to
increased scattering of light and cataract

39. Diabetic eye disease:
• Diabetic retinopathy affects blood vessels in the retina that lines the
back of the eye. It is the most common cause of vision loss among
people with diabetes and the leading cause of vision impairment and
blindness among working-age adults.
• Diabetic macular edema (DME). A consequence of diabetic
retinopathy, DME is swelling in an area of the retina called the
macula.
• Cataract is a clouding of the eye's lens. Adults with diabetes are 2-5
times more likely than those without diabetes to develop cataract.
Cataract also tends to develop at an earlier age in people with
diabetes.
• Glaucoma is a group of diseases that damage the eye's optic nerve—
the bundle of nerve fibers that connects the eye to the brain. Some
types of glaucoma are associated with elevated pressure inside the
eye. In adults, diabetes nearly doubles the risk of glaucoma..

40. • One of the most metabolically active tissues .
• The blood—retinal barrier is overcome by carrier-
mediated facilitated diffusion through specific plasma
membrane glycoproteins, the glucose transporters
GLUT 1 and GLUT 3.
Glucose metabolism in retina:

42. • In the absence of glucose (hypoglycemia,
aglycemia) the retina can metabolise exogenous
lactate or pyruvate • The hexose monophosphate
pathway (HMP) is also active in the retina:
produce NADPH for Glutathione and Ribose
phosphate for DNA and RNA

43. Biochemical events visual
transduction:

44. Vitamin A absorption, metabolism and
delivery to the eye: vitamin A (retinol) plays
very imp. Role in visual transduction:

45. Flowchart showing vitamin A :
Transport from dietary intake
to photoreceptor cells
Change in retinol:

46. Rhodopsin
• Rhodopsin, a specialized 7TM receptor, absorbs
visible light.
• consists of the protein opsin linked to 11-cis-retinal,
a prosthetic group.
• Absorbs light upto 500nm.
• Color of rhodopsin and its responsiveness to light
depend on the presence of the light-absorbing group
(chromophore) 11-cis-retinal.
• Light absorption results in the isomerization of the
11-cis-retinal group of rhodopsin to its all-trans
form.

47. VISUAL CYCLE: Coversion of Cis-retinal into trans
retinal: refer slide 48 for more understanding:
• In darkness, retinal has a bent shape, called cis-
retinal, which fits snugly into the opsin portion
of the photopigment. When cis-retinal absorbs a
photon of light, it straightens out to a shape called
trans-retinal. This cis-to-trans conversion is
called isomerization and is the first step in visual
transduction. After retinal isomerizes, several
unstable chemical intermediates form and
disappear. These chemical changes lead to
production of a receptor potential.

48. VISUAL CYCLE Continued..
• In about a minute, trans-retinal completely
separates from opsin. The final products look
colorless, so this part of the cycle is termed
bleaching of photopigment.
• An enzyme called retinal isomerase converts
trans-retinal back to cis-retinal.
• The cis-retinal then can bind to opsin, reforming
a functional photopigment. This part of the
cycle—resynthesis of a photopigment—is called
regeneration.

49. Photopigments respond to light in this
cyclical process:

50. Visual cycle:

51. Visual Cycle : formation of nerve
impulse
1. Rhodopsin changes to metarhodopsin in light
2. Metarhodopsin activates Transducin
3. Transducin activates enzyme phospodiesterase
4. Decreased intracellular cGMP
5. Closure of Na+ channel
6. Hyperpolarisation of rod cells
7. Decreased release of neurotransmitter
8. Response in bipolar cells
9. Signals to optic nerve and then to brain

53. • The light-induced activation of rhodopsin leads
to the hydrolysis of cGMP, which in turn leads to
ion-channel closing and the initiation of an
action potential.

55. Disorders of image formation:

56. Lens to correct eye disorders: