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Lecture: 4
The Sense of Vision
Dr. Eyad M. Hussein
Ph.D of Neurology
Consultant in Neurology Department,
Nasser Hospital,
Assistant Professor,
Faculty of Medicine, Islamic University
Faculty of Dentistry, University of Palestine
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‫الصامت مع الشكر الرجاء تحويل الجوال إلى وضع‬
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Components of the Visual System
I.
Accessory structures (the adnexa of the eye):
includes eyebrows, eyelids, eyelashes, lacrimal
apparatus, conjunctiva, extrinsic eye muscles. Help
protect the eyes from direct sunlight and damaging
particles.
II. Eyes: is the organ of vision.
III. Optic nerve, tract, and pathway.
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I. Accessory structures of the Eyes
1. Eyebrows: protects eyes - to prevent sweat, water, and
other damaging particles from falling down into the eye.
2. Eyelid (Superior and Inferior Palpebra): for blinking
“average blinking = 25B/min”.
Function:
• Protects the eye from foreign objects, sun, bright
light and from sweat.
• Help spread tears over surface of eye (moist &
comfort).
• They keep the eyes from drying during sleep.
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3. Eyelash:
• Protects the eye from foreign objects.
• Lubricates lids and restrains tears from flowing over
the margin of the eyelids.
4. Medial and lateral commissure: angels where the eyelids
join at the medial and lateral margins of the eye.
6. Conjunctiva: thin, clear layer of skin covering of the front
of eye (covers the sclera and the inside of the eyelids).
Function:
• Helps lubricate the eye by producing mucous.
• Immunological function: helps to prevent the entrance
of microorganism into the eye.
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Lacrimal Apparatus
Lacrimal Gland: located lateral to eye and secretes
tears.
Superior and inferior lacrimal canals (Canaliculi):
collect tears.
Lacrimal sac: collects tears from lacrimal canals.
Lacrimal punctum: opening of each lacrimal canal.
Nasolacrimal duct: collects tears from lacrimal sac and
empties tears into nasal cavity.
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Extrinsic Eye Muscles
1. Lateral rectus muscle: abducts (laterally) the eyeball.
2. Medial rectus muscle: adducts (medially) the eyeball.
3. Superior rectus muscle: elevates, adducts and rotates medially.
4. Inferior rectus muscle: depresses, adducts and rotates medially.
5. Superior oblique muscle: depresses, abducts and rotates
laterally.
6. Inferior oblique muscle: elevates, abducts and rotates laterally.
7. Orbicularis oculi: close the eyes.
8. Levator palperbrae superiosis muscle: open the eyes.
9. Muller’s muscle (Superior tarsal muscle): is a smooth muscle,
that helps to raise the upper eyelid with the levator palpebrae
superioris muscle.
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II. The Eyeball
The eyeball consists of three tunics (layers):

External (fibrous) tunic: consists of the
cornea (anterior) and the sclera (posterior).
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Middle tunic-Uvea (vascular and smooth
muscle layer): consists of the ciliary body,
iris (anterior) and the choroid coat (posterior).

Internal tunic (nervous layer): consists of the
retina.
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Layers of the Eyeball
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External (Fibrous) Tunic
1. Cornea:
• Clear transparent layer.
• Anterior portion.
• Located in front of the iris.
• Only organ that has no blood vessels.
• One of the first organs transplanted.
Function:
• Light transmission.
• Light refraction (focus light as it enters eyes).
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2. Sclera:
• “White of the eye”.
• Posterior portion.
• Surrounds the eye and gives
the eye its shape.
• The sclera is attached to the
extraocular muscles.
Functions:
• Protection.
• Muscle attachment.
• Shape of the eye.
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Middle (Vascular) Tunic
1. Iris:
Ring shaped tissue.
 Anterior portion.
 Pigmented part of eye.
 Contains blood vessels, pupillary muscles.
 The iris divided the space between the lens and cornea into
anterior and posterior chambers.
Function: controls the amount of light that enters the eye
(light intensity function).
Pupil: central opening of iris.
Two smooth (intrinsic) muscles:
1. Circular muscles: Constrictor (sphincter) pupillae muscle.
2. Radial muscles: Dilator pupillae muscle.
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Intrinsic Eye Muscles
Anisocoria
Double of iris and pupils
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2. The ciliary body :
• “Ciliary muscle and process”.
• Anterior portion.
• Pigmented ring of smooth muscle around the lens.
Function: regulates the shape of the lens for
accommodation.
3. Choroid Coat:
• Posterior portion.
• Vascular layer of the eye, containing connective tissue,
and lying between the retina and the sclera.
Function: Provides blood supply to the outer layers of
the retina.
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
Lens:
• Clear, flexible structure.
• Behind the iris & pupil.
• Surrounded by a ring of
muscular tissue – ciliary
body.
Function:
• Light transmission.
• Light refraction.
• the lens & ciliary body help
control fine focusing of
light and images on retina.
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Chambers of the Eye
1. Anterior Chamber:
• Fluid-filled “Aqueous humor” space.
• Behind the cornea & infront of the iris.
• Aqueous humor helps nourish the cornea & the lens.
2. Posterior Chamber (PC):
• Fluid-filled “Aqueous humor” space.
• Behind the iris & infront of the lens.
3. Vitreous Chamber:
• located behind the lens & infront of the retina.
• Filled with a gel-like fluid called the vitreous humor.
• The vitreous help maintain the shape of the eye.
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Inner (Nervous) Tunic

Retina:
◦ Consists of a specialized layer of cells (nervous tissue).
◦ Contains light sensitive photoreceptors (cones and rods
of the retina).
◦ Converts light signals into nerve signal then send these
signals to the optic nerve “Acts like the film in a
camera to create an image”.
◦ Continuous with optic nerve.
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Histology of the Retina of the Eye
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‫هذا ساليد غريب يحتاج إلى إنسان رايق جدا وفصل‬
‫كامل لفهمه‬
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The Nerve Supply of the Eye
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The Optic Nerve II: enters the orbit through the optic
foramen and passes to the light receptor cells in the retina.
The Oculomoter Nerve III: control the movement of the
eyeball. it enters the orbit through the superior orbital fissure.
The Abducent Nerve VI: enters through the superior orbital
foramen.
The Trochlear Nerve IV: enters through the superior orbital
foramen.
The Trigeminal Nerve V: send branches to the eye.
Opthalmic and maxillary divisions (zygomatic nerve).
The Facial Nerve VII: temporal and zygomatic branches
innervates the orbicularis oculi.
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III. Visual Pathway
The Optic Nerve
 Optic Nerve: (Latin for "to see").
• A bundle of 1 million nerve fibers.
• Responsible for transmitting nerve signals from
the retina to the brain.
• The optic disc is the front surface of the optic
nerve.
Function: Special sensory nerve (Sense of vision).
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Pathway of the Vision
Receptors of light are rods and cones of retina → optic
nerve → optic canal of the sphenoid bone → optic
chiasma (the nasal or medial fibers decussate to the
opposite optic tract, while the temporal or lateral fibers
continue in the same optic tract → optic tract (gives
fibers to Edinger-Westphale nucleus in midbrain) → relay
in the lateral geniculate body → thalamus → posterior
limb of internal capsule → optic radiation → end in areas
17, 18, 19 of occipital lobes.
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The Visual Pathway
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The Visual Pathway
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Visual Acuity
Acuity of vision:
with a Snellen chart.
The normal acuity is
6/6 to 6/9 in each eye.
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Visual Field Defects
Checked by confrontation, if abnormal recorded with
Goldman screen
Perimeter
Confrontation Test
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Fundus Examination
(Ophthalmoscopy)
Normal optic nerve disc
Papilledema
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Color Blindness Test
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Visual Pathway and Visual Field Defect
Left
Right
Lesions:
A. Blindness in one eye (Left).
B. Bitemporal hemianopsia.
C. Contralateral homonymous
hemianopsia (Right)
D. Quadrantanopsia
E. Contralateral homonymous
hemianopsia (Right).
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Light Reflex
•Direct Light Reflex: Light in one eye leads to constriction
(miosis) of the same eye
• Indirect Light Reflex : Light in one eye leads to constriction
(miosis) of the opposite eye
Pathway of Light Reflex
Fibers from rods and cones of retina → optic nerve → optic
chiasma → optic tract → before reaching the lateral geiculate
body → they pass to the third cranial (oculomotor) nerve
nucleus (Edinger-Westphal nucleus) in midbrain of both side
→ through oculomotor nerve → ciliary ganglion → supply the
constrictor pupillae muscle
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Accommodation and Convergence Reflex
for Near Vision
Patient is asked to follow your finger from a far point to
a near one:
 Ciliary muscles contraction leads to change the shape
of lens (becomes thicker and rounder due to its
elasticity).
 Miosis (contraction of constrictor pupillae muscle).
 Convergence (contraction of both medial recti muscle).
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Accommodation of the Lens for Far Vision
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Ciliary muscles relaxes and lens becomes thinner
(flatter) due to its elasticity.
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Mydriasis (contraction of dilator pupillae muscle).
a. Accommodation of the lens to far vision.
b. Accommodation of the lens to near vision.
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