Anatomy of the eye for studentss

DR. VASDEV HARANI Associate Professor

Ophthalmology

Introduction to the EyeballEyelids ConjunctivaCorneaSclera Uveal tractAqueous humorAnterior chamber angleLensRetinaOptic nerve

A spherical globe with a diameter of 24.5mm.

Consists of Skin Subcutaneous tissue Orbicularis muscle Levator palpebrae

superiorus (upper lid) Tarsal plate Palpebral conjunctiva

Protect the eye from injury

Reflex closure of eyelids occurs when some object comes close to the eye or bright light shines into eye (corneal reflex)

Regular blinking assists in distribution of tears and prevents drying of the tear film

A transparent mucous membrane that lines the inner surfaces of the eyelids and the front surface of the eyeball.

The Palpebral conjunctivaStarts at the lid margins

and is firmly attached to the posterior tarsal plate

The Fornical conjunctivaIs loose and redundant and

maybe thrown into folds

The Bulbar conjunctivaCovers the anterior sclera

and is continuous with the

corneal epithelium at the limbus

Epithelium is non-keratinizing and about

five cell layers thick Basal cuboidal cells evolve

from the surface Goblet cells are located within

the epithelium

Stroma Consists of richly vascularized

loose connective tissue Accessory lacrimal glands of

Krause and Wolfring are located deep within the stroma

The transparent dome which serves as the window of the eye.

The primary (most powerful) structure focusing light entering the eye.

Cornea is composed of 5 layers Epithelium. Bowman’s

membrane. Stroma Descemet’s

membrane. Endothelium).

No blood vessels. Transparent stroma with low level of

fluids. Endothelium cells serves as a pump that

supply oxygen and remove fluids. Tear film also supplies oxygen and keep

corneal surface smooth and clean.

The white, opaque cover of the eye.

Covers 80% of the eye’s outer layer.

Contains thick elastic collagen.

It provides protection. Serves as an attachment

for the extra-ocular muscles which move the eye.

Iris Ciliary body Choroid

The iris is composed of Endothelium Stroma Epithelium

Stroma muscles Dilator - sympathetic

innervation Constrictor – parasympathetic

innervation

Determined by the amount of pigment present in iris.

No pigment - pink iris (albino), some pigment – blue iris, increasing amounts of pigment- green>hazel> brown irides. 

The pigments: melanin (chromosome 15) and lipochrome (chromosome 19).

Heterochromia iridesHeterochromia irides: when one iris has a different color than the other iris.

The pupil is the clear area that is located in the center of the iris of the eye.

 It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye

In darkness the iris dilator muscle causes the pupil to “dilate” and allowing more light to reach the retina.

In brightness, the iris sphincter muscle (which encircles the pupil) constricts, causing the pupil to “constrict” and allowing less light to reach the retina.

Constriction also occurs during accommodation - the “near reflex.”

Pars plana – flat area continuous with the retina

Pars plicata – contains the ciliary processes that secretes the aqueous humor

Ciliary muscle runs circularly around the eye and controlles accommodation

The posterior segment of the uvea, between the sclera and the retina.

Reach in blood supply, supplies oxygen and nutrition to the outer two thirds of the retina.

Produced by the ciliary body.

Entering from the posterior chamber, it passes through the pupil into the anterior chamber and filtrates through the angle into the blood stream.

Serves to nourish ocular structures.

Iris-corneal junction

Contains the trabecular meshwork (TM )which acts like a filter for the aqueous humor.

From the TM the humor drains to schlem’s canal and then to blood stream.

Biconvex, avascular, transparent structure.

Suspends behind the iris by the zonules which are connected to the ciliary body.

Serves to converge light onto the retina.

Ciliary muscle constrict > zonular tension decreases > lens becomes more spherical > more dioptric power that converge light from a near target onto the retina.

This loss of transparency, or opacity formation is called Cataract

The innermost layer of the eye.

The retina is a multi-layered

sensory tissue that lines the back of the eye. 

 It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. 

These impulses travel along the optic nerve to the brain where they are turned into images.

Fovea: area with the highest concentration of photoreceptors.

Central retina: A circular field of approximately 6 mm around the fovea.

Peripheral retina: stretching to the ora serrata.

Phptoreceptors Cones

Concentrated in the fovea

Most active in daylight

Central vision Rods

Mostly in the peripheral retina

Most active in night vision

Peripheral vision

Consists of 1.2 million axons that arise from the retina.

Leaves the eye through the optic disc also known as the blind spot.