https://nabeelbeeran.blogspot.com/ Eye - Introduction

1. SPECIAL SENSES
DR. NABEEL BEERAN
MBBS, MD
13/03/2020
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2. eye
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3. Specific Learning Objectives
At the end of this class, student should be able to:
• Appreciate the functional anatomy of eye.
• List the layers of sclera, cornea and retina and
mention their functions.
• Understand the role of choroid, ciliary body and
iris in visual function.
• Differentiate between rods and cones.
• Explain the composition, formation, drainage
and functions of aqueous humor.
• Give the significance of intra ocular pressure.
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4. • EYE has 2 major parts:
1. Optical system
Helps to focus and form an image on the
receptor cells- light rays fall.
2. Neural system
Transmits optical signal in the form of
action potential along the optic nerve to visual
cortex.
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5. Anatomy of Eye
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7. The wall of the eyeball is composed of 3 layers:
• Outer fibrous coat
• Middle vascular layer
• Inner nervous coat
Interior of the eyeball is divided into 3 spaces:
• Anterior chamber
• Posterior chamber
• Posterior cavity
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8. Outermost layer:
1/6th portion transparent anteriorly- cornea.
5/6th portion opaque area – sclera.
• Anterior part of sclera and posterior part of
eyelids are covered by mucous membrane :
conjunctiva.
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9. Sclera
• White avascular fibrous coat- composed of
collagen fibers.
• Shape to eyeball.
• Protective function.
• Extraocular muscles- regulates the eyeball
movement.
• Central portion of eye- transparent cornea.
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10. Layers of Cornea
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11. Lacrimal gland
• Lateral corner of eye.
• Secretes tear
• Keeps cornea moistened.
• Prevent infection.
• Drained through naso-lacrimal duct.
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12. Middle vascular area:
The middle layer surrounds the eyeball completely
except for a small opening in front known as the
pupil.
Comprises 3 structures:
1. Choroid
2. Ciliary body
3. Iris
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13. Choroid
• Posterior 2/3rd of eyeball.
• Nourishes blood vessels.
• Nourishes structure of eyeball.
• Front thickened portion- ciliary body- absorb
extra amount of light.
Ciliary body
• 2 parts: ciliary muscle and ciliary processes.
• Attached to suspensory ligament at one end.
• Other end- crystalline lens.
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14. Iris
• Thin, pigmented, circular, contractile diaphragm that
hangs over the anterior surface of the lens.
• Colour to the eye.
• Central aperture- pupil- light enters the eye.
• 2 types of smooth muscle: Circular (sphincter pupillae)
and radial (dilator pupillae).
• Accommodation for near vision.
Functions:
• Regulates intensity of light.
• Absorbs extra amount of light.
• Prevents entry of light through periphery of lens.
• Increases the depth of focus by constriction of pupil. 14

15. Inner most layer:
• Retina: photoreceptors rods and cones.
light is focused on retina – stimulates photoreceptors
Signal to optic nerve
Information reaches visual cortex
Generates visual sensation
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17. Layers of Retina
1. Pigmented epithelium
2. Layers of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer synaptic layer
6. Inner nuclear layer
7. Inner synaptic layer
8. Ganglion cell layer
9. Optic nerve
10. Internal limiting membrane
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18. Outer pigmented epithelial layer:
• Rich in melanocytes.
• Prevents scattering of light
• Phagocytosis
• Storage of vitamin A
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19. • Rods and cones- Photoreceptors.
• Each rod and cone is divided into outer
segment, inner segment and a synaptic zone.
• Rods: thin, rod- like appearance.
• Cones: conical outer segment.
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21. Functions of Retina:
1. Visual functions:
• Light sense: Help to perceive light.
• Form sense: Appreciate the shape.
• Color sense: Perceive and recognize different
color and different intensities of the same color
• Sense of contrast: Perceive changes in the
luminance between two regions.

22. 2. Reflexes:
• Light reflex.
• Accommodation reflex.
3. Help to maintain the Tone ,Posture and
Equilibrium.
4. In animals it has a role in the sexual cycle.

23. Rods :
1. 120 million.
2. Mainly in peripheral
retina.
3. Slender ,Elongated,
Rod like.
4. More pigments/rod.
5. Only one type of
pigment-Rhodopsin.
6. Cannot detect color.
7. Functions better in
dim light.
8. Loss- Night blindness
Cones:
1. 6million
2. Mainly in the central
retina.
3. Conical shape.
4. Less pigments/cone.
5. Three types:
Porphyropsin,
Iodopsin,
Cyanopsin.
6. Can detect color.
7. Functions better in day
light
8. Loss-functional blindness.23

24. Lens divides the cavity of eye into 2 compartments
• Anterior compartment: Aqueous humor
• Posterior compartment: Vitreous humor
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25. Fluids in the eye:
• Aqueous Humor
• Vitreous Humor
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27. Outflow of Aqueous Humor:
Aqueous Humor is formed in ciliary processes
Into the anterior chamber
Through the pupil
Anterior to the lens
The angle between cornea and the iris
Canal of Schlemm
Extra ocular veins 27

28. Functions of Aqueous Humor:
• Provides nutrition to all the avascular
structures of the eye.
• Maintain the intraocular pressure.
• Maintain the shape of the eye.
• Acts as a refractive medium
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29. Functions of vitreous humor:
• Prevent the wall of eyeball from
collapsing.
• It maintain the intraocular pressure and
keep the intraocular structures in
position.
• Acts as a refractive medium.
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31. Glucoma/Ocular Hypertension:
• Pressure increase to 60-70 mm of Hg.
• Normal :15mm of Hg (12-20mm of Hg)
• Pressure above 25-30 mm of Hg can
cause blindness if maintained for long
duration.
Causes:
• Blockage of canal of Schlemm
• Excessive production of the fluid
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32. 2 types:
Primary:
• Open angle: after 40yrs
• Closed angle: after 60yrs.
Secondary :
Cataracts, Trauma, Intraocular haemorrage.
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34. Treatment OF GLAUCOMA:
• Pilocarpine: Facilitating the out flow.
• Adrenaline: Diminishes the aqueous inflow.
• Acetazolamine: Reduces the formation.
• Surgical method.
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35. References
1. Review of Medical Physiology by Ganong
24th edition
2. Textbook of Medical Physiology by Guyton
and Hall 13th edition
3. Textbook of Medical Physiology by G.K.Pal
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36. THANK YOU