ANATOMY AND PHYSIOLOGY OF EYE

Structure of the eye

ORBIT

Bony Orbit

Canals and fissures in the orbit

Bones forming the orbit
Medial wall-Ethmoid, Lacrimal, Frontal, Sphenoid

Lateral wall-Zygoma, Maxilla

Roof-Frontal

Floor-Maxilla

Orbit dimensions
Volume : 30 cm3 •

Entrance : 35 X 45 mm •

Depth : 40-45 mm (adult)

Structures passing through the orbit

• Foramina:
Optic foramen • Optic n., Ophthalmic. A.

• Ducts
Nasolacrimal duct

• Canals
Infraorbital canal

• Fissures
Superior orbital fissure

Inferior orbital fissure

Superior and Inferior Orbital Fissures
CRANIAL NERVES
Twelve Cranial Nerves

Cranial Nerves in Skull

Optic Nerve-11nd Cranial Nerve
One million cells.

Originates from Ganglion cell layer of retina.

Length 40 to 46 mm

Largest sensory nerve of the eye

Composed of retinal nerve fibers

(Intraocular part)
Exit eyeball through the optic disc

Traversus the orbit (orbital part)

Pass through optic foramen (intracanalicular part)

Enters cranial cavity (intracranial part)

 1 Intraoular part -Optic head (which is where it begins in the eyeball (globe)
with fibers from the retina;
2. Orbital part (which is the part within the orbit).
3. Intracanicular part (which is the part within a bony canal known as the optic
canal);
4. Cranial part (the part within the cranial cavity, which ends at the optic
chiasm).[2]

Functions
1. Transmits all visual information-including colour perception, brightness
perception and contrast perception.
2. Conducts visual impulses for neurological reflexes
a. light reflexes-pupils constrict when light is shorn
b. Accommodation reflex-lens swells when looking at near object

The mammalian central nervous system has limited regenerative

capabilities. Hence damage to optic nerve often results in blindness.
Visual Pathway

Anatomy of Visual Pathway

Lesions affecting visual pathway
Optic chiasma lesions

Site of lesion/pressure Field defect Typical lesions

Optic neuritis

Amaurosis fugax

Ipsilateral monocular Optic atrophy

Optic nerve
blindness
Retrobulbar optic
neuropathy

Trauma

Pituitary adenoma
Optic chiasm (central) Bitemporal hemianopia
Suprasellar aneurysm

Distension of the
3rd ventricle
Ipsilateral monocular nasal
Optic chiasm (lateral)
hemianopia Internal carotid/posterior
communicating artery
atheroma
 MCA stroke
Contralateral homonymous
Optic tract
hemianopia
Tumours

MCA stroke
Contralateral homonymous
Optic radiation Tumour
quadrantanopia
Trauma

Contralateral homonymous PCA stroke

Occipital cortex hemianopia with macular
sparing Trauma
Oculomotor Nerve- 111rd Cranial Nerve

• Origin: Mid brain

• Course: 2 Divisions

1. Superior Division: ▪ Superior Rectus ▪ Levator Palpebrae Superioris

2. 2. Inferior : ▪ Medial Rectus ▪ Inferior Rectus ▪ Inferior Oblique ▪ Motor
root to Ciliary ganglion
Trochlear Nerve-IVth Cranial Nerve
Origin-Midbrain

Supplies Superior Oblique

Abducent Nerve –VIth Cranial Nerve

Origin-Pons

Supplies-Lateral Rectus
Trigeminal Nerve-Vth Cranial Nerve

Sensory to eye orbit and face

Motor to muscles of mastication

Facial Nerve –VIIth Cranial Nerve
Origin –Pons

Supplies-muscles of facial expression and taste sensations of anterior 2/3 of

tongue

"To Zoo By Motor Car", standing for Temporal, Zygomatic, Buccal, Marginal mandibular and Cervical
branches.

CILIARY GANGLION
Ganglion formed by postganglionic parasympathetic neurons.

Located at apex of orbit between Optic Nerve and Lateral rectus muscle.

3 mm size

Nerves from Ciliary Ganglion innervate sphincter pupillae (constrict pupil) and
ciliary muscles (accommodation).

Damage by injury or disease causes tonic pupil (poor pupillary reaction and loss
of accommodation)
EXTRAOCULAR MUSCLES

4 Recti-

Six muscles for eye movements-

2 Obliques

There are six extraocular muscles in each eye:

• Rectus Muscles.
Four recti-for straight movements

Superior (upward), Inferior (lower), Lateral (toward the outside, or away

from the nose), and Medial (toward the inside, or toward the nose).

• Oblique Muscles.
Two Oblique muscles that are responsible for angled movements.
Superior oblique muscles control angled movements upward toward the
right or left. Inferior oblique muscles control angled movements
downward toward the right or left.
Origin Insertion

Recti -Annulus of Zinn On sclera posterior to limbus

Superior Oblique-lesser wing of sphenoid On sclera under superior rectus

Inferior Oblique-orbital floor On sclera, under lateral rectus

1. Obliques Abduct whereas Rectii Adduct (except LR)
2. Superiors Intort whereas Inferior Extort
3. Rectii act according to their names whereas Obliques act opposite to their names.
EYELIDS

Structures that must be considered in a description of lid anatomy are the skin
and subcutaneous tissue; the orbicularis oculi muscle (shown below); the
submuscular areolar tissue; the fibrous layer, consisting of the tarsi and the
orbital septum; the lid retractors of the upper and lower eyelids; the retroseptal
fat pads; and the conjunctiva.
Eyelids
Mobile folds that cover the eyeball

1. Consist of 5 layers
i. Skin and subcutaneous tissue.
Skin is thinnest in human body. Subcutaneous tissue is losse connective
tissue without fat-hence eyelids swell with oedema or blood.
Eyelashes have glands of Moll and glands of Zeis
ii. Orbicularis oculi-Palpebral part gently closes eyelids
-Lacrimal part drains tears
 Orbital part tightly closes lids
iii. Tarsal plates
Composed of dense connective tissue. Meibomian glands lie on tarsal
plate
iv. Levator apparatus-only located in upper eyelid. Opens the eyelid
v. Conjunctiva-thin mucous membrane reflected on the sclera

2. Blood Supply
Rich blood supply

3. Nerve supply
Sensory
 Ophthalmic Nerve (V1)-upper lid
Maxillary Nerve (V2)-lower lid
Motor
Facial Nerve-orbicularis oculi
Oculomotor nerve-Levator palpebrae superioris
Sympathetic fibres-superior tarsal plate

Diseases affected by eyelid abnormalities

Ptosis Lid retraction

Chalazion Stye
Ectropion Entropion

LACRIMAL GLAND AND LACRIMAL

SYSTEM
Lacrimal gland-exocrine gland that secretes fluid onto conjunctiva and cornea.
Situated in lacrimal fossa, in superior lateral part of orbit
Lacrimal fluid –nourishes and lubricates the eyes

Lacrimal fluid produced by lacrimal gland

flow on to the conjunctiva

accumulates in medial canthus

drains into lacrimal sac

nasolacrimal duct

inferior meatus of nasal cavity

Clinical application

Dacryoadenitis -inflammation of lacrimal gland

Bacterial, viral
Inflammatory conditions-sarcoidosis, thyroid eye disease
Dacryocystitis –inflammation of lacrimal sac

Nasolacrimal duct obstruction

LAYERS OF EYEBALL
Cornea

Outer protective layer of the eye

Five layers: the epithelium, Bowman's layer, the stroma, Descemet's
membrane, and the endothelium.

Cornea functions- Cornea and sclera form protective barrier

- contribute to refractive power of the eye.
-focusses light rays onto the retina
-filters ultraviolet rays of the sun
Sclera

Extends from cornea to the optic nerve.

Less than 1 mm thick
Episclera, stroma, lamina fusca, endothelium.
Functions
Gives the eyeball the white colour
Protects from injury and supports the eye
Provides attachment for muscles which help to move the eyeball
Conjunctiva covering are clear membranes which lubricate the eyes

ANTERIOR CHAMBER
Anteriorly cornea
-angular space posteriorly iris and ciliary body
Filled with watery fluid called aqueous humor.

Aqueous humor produced by ciliary body

Posterior chamber (between iris and lens)

Anterior chamber

Functions

Provide oxygen for the eye

Nourishes cornea, iris and lens by carrying nutrients

Removes waste products from lens

Maintain intraocular pressure (and the shape of the eye)

The eye receives oxygen through the aqueous. Its function is to nourish the
cornea, iris, and lens by carrying nutrients, it removes waste products excreted
from the lens, and maintain intraocular pressure and thus maintains the shape of
the eye. This gives the eye its shape. It must be clear to function properly.

UVEAL TISSUE-Iris, Ciliary body and choroid

Iris
Pigmented muscular structure in the front part of the eye between cornea and lens

Opening in the center is the pupil.

Pigments give iris the colour.

Functions

Iris

gives colour to the iris (it is pigmented tissue)

Controls amount of light entering by varying the size of pupil (like a camera)

Responsible for near point reading (pupils must constrict to see close)

Pupil

Variable size-regulates amount of light entering the eye

Constricts-when sphincter pupillae contracts. Occurs in bright light, certain drugs,

consequence of ocular illumination

Dilates-when dilator muscle contracts. Occurs in dim light, drugs (mydriatics),

trauma
• Pupil. It is a variable-sized black circular opening in the center of the iris that regulates
the amount of light that enters the eye. The pupil needs to be round in order to
constrict.

• Constricted. A constricted pupil occurs when the pupil size is reduced to constriction
of the iris or relaxation of the iris dilator muscle. The iris constricts with bright
illumination, with certain drugs, and can be a consequence of ocular inflammation.

• Dilated. A dilated pupil is an enlarged pupil, resulting from contraction of the dilator
muscle or relaxation of the iris sphincter. It occurs normally in dim illumination, or
may be produced by certain drugs (mydriatics) or result from blunt trauma.

Focusses light onto the retina

Pliable to control refraction (less pliable with ageing leading to presbyopia)-the

lens changes its shape to change the focal distance of the eye.

Ciliary Body
Circumferential tissue (ring of tissue) between end of choroids and beginning of iris.

Functions
Ciliary muscle 70 ciliary processes

Involved in accommodation produce aqueous fluid

Control intraocular pressure

Choroid
Lies between retina and sclera.

Function

Nourishes retina through the blood vessels.

LENS
Biconvex structure

Capsule, epithelium, fibres

Held in place by zonules

VITREOUS HUMOUR (CHAMBER)
Transparent colourless gelatinous mass

Fills the rear 2/3 of eye ball (between lens and retina)

Function

Maintains the eyeball shape (eyeball will collapse otherwise)

RETINA

Innermost of the 3 coats of the eye

10 layers

Retinal pigment epithelium (RPE)

Retina
Subretinal space is in between
Adehsion between RPE and neurosensory
retina is weak

Inner neurosensory retina

Posterior pole (area centralis) is between superior and inferior temporal arteries

Macula Lutea (macula-spot. Lutea-yellow). Situated in posterior pole, lateral to

optic disc

Fovea-depression in the posterior pole

Foveola is in center of fovea-area of highest visual acuity
Foveola reflex is at the center of the fovea
Function
Light sensitive tissue that converts images from the eye, along the optic nerve to
brain

Images from the eye optical system

Converted by retina
VISION

Electrical impulses

Optic nerve