Submitted On:-

Submitted By :- Supriya MohanSubmitted To :- Soya Teacher

SREE NARAYANA TRAINING COLLEGE

SREEKANDESWARAM

POWER POINT PRESANTATION : ON EYE

The Human Eye, Its Functions, And Visual Impairment

How the Human Eye Works The human eye can be compared to a

camera which gathers, focuses, and transmits light though a lens to create an image of the environment. In a camera, the image is created on film; in the eye, the image is created on the retina, a thin layer of light sensitive cells at the back of the eye. The lens of the eye bends, or refracts, light that enters the eye.

The cornea, which is a clear, transparent covering in the front portion of the eye also contributes to focusing light on the retina. Nerve fibers extending back from the retina’s nerve cells come together behind the retina to from the optic nerve, a “cable” of nerve fibers connecting the eye with the brain,

The optic nerve transmits messages about what we see from the eye to the brain. Like a camera, the human eye controls the amount of light that enters the eye through the lens under various lighting conditions.

The orbit is the bony cavity that contains the eyeball, muscles, and blood vessels, as well as the structures that produce and drain tears. Each orbit is a pear-shaped structure that is formed by several bones.

An Inside Look at the Eye

The outer covering of the eyeball consist of a relatively tough, white layer called the sclera(or white of the eye). Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin, transparent membarance ( conjunctive), which runs to the edge of the cornea. The conjunctive also covers the moist back surface of the eyelids and eyeballs.

Exterior is smooth and white Interior is brown and grooved Extremely durable Flexibility adds strength Continuous with sheath of optic nerve Tendons attached to it

SCLERA

SCLERA

The cornea is the clear bulging surface in front of the eye. It is the main refractive surface of the eye.

Primary refractive surface of the eye Index of refraction: n = 1.37 Normally transparent and uniformly thick Nearly avascular Richly supplied with nerve fibers Sensitive to foreing bodies, cold air, chemical

irritation Nutrition from aqueous humor and Tears maintain oxygen exchange and water content Tears prevent scattering and improve optical quality

THE CORNEA

THE CORNEA

ANTERIOR & POSTERIOR CHAMBERS

The anterior segment is divided into two chambers. The front (anterior) chamber extends from the cornea to the iris. The back (posterior) chamber extends from the iris to the lens. Normally, the equeous humor is produced in the posterior chamber, flows slowly through the pipil into the anterior chamber, and then drains out of the eyeball through out flow channels located where the iris meets the cornea.

The anterior chamber is between the cornea and the iris The posterior chamber is between the iris and the lens Contains the aqueous humor Index of refraction : n =1.33 Specific viscosity of the aqueous just over 1.0 (like

water, hence the name) Pressure of 15-18 mm of mercury maintains shape of

eye and spacing of the elements

Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil. The cornea serves as a protective covering for the front of the eye and also helps focus light on the retina at the back of the eye. After passing through the cornea, light travels through the pupil. The iris- the circular, colored area of the eye that surrounds the pupil – controls the amount of light that enters the eye. The pupil dilates and constricts like the aperture of a camera lens as the amount of light in the immediate surroundings changes. The iris allows more light into the eye when the environment is dark and allows less light into the eye when the environment is bright. The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle.

IRIS/PUPIL

IRIS/PUPIL

Iris is heavily pigmented Sphincter muscle to constrict or dilate the pupil Pupil is the hole through which light passes Pupil diameter ranges from about 3 - 7 mm Area of 7 – 38 square mm Eye color (brown, green, blue, etc.) dependent on

amount and distribution of the pigment melanin

IRIS/PUPIL

LENS

Transparent body enclosed in an elastic capsule

Made up of proteins and water

Consists of layers, like an onion, with firm nucleus, soft cortex

Gradient refractive index (1.38 -1.40)

Young person can change shape of the lens via ciliary muscles

Contraction of muscle cause lens to bulge

At roughly age 50 the lens can no longer change shape

LENS

VITREOUSE HUMOR

o Fills the space between lens and retina

o Transparent gelatinouse body

o Specific viscosity of 1.8 – 2.0 (jelly – like consistency)

o Index of refraction, n = 1.33

o Nutrition from retinal vessels, ciliary body, aqueous

o Floaters, shadows of sloughed off materials/debris in

the vitreouse

o Also maintains eye shape

VITREOUSE HUMOR

RETINA

The light has to pass through many layers of cells

before finally reaching the photoreceptors. The

photoreceptors are where the light is absorbed and

transformed into the electrochemical signals used by

the nervous system. This change is called transduction

The interior of the eyeball is the “inner” side and

the exterior is the “ outer” side. The nuclear layers

contain cell bodies. The plexiform layers contain the

connection between cells in the retina.

RETINA

OPTIC NERVE

The location where the optic nerve is bundled and

leaves the retina is known as the optic disk. There are

no photoreceptors at the location of the optic disk and

hence there is a blind spot. The scientific term for a

blind spot is a scotoma. So the blind spot due to the

disk is a natural permanent scotoma in normal vision.

Here is a demonstration of the natural permanent

scotoma.

OPTIC NERVE

THE FOVEA

The fovea is the location on the retina of central

gaze. when you look directly, or fixate, at a stimulus you

the retina locus of this central fixation is the fovea.

There are only cones in the human fovea (no rods).

They are thinner, elongated, any very tightly packed.

Because of this, the fovea is the location of highest

visual acuity and best color vision.

THE FOVEA

THE MACULA

Covering the fovea is a pigment called the

macula. It is thought that macula serves a protective

filter over the foviea that absorbs blue and ultraviolet

radiation. This pigment varies from observer to observer

and is a source of individual variation in color vision.

Usually we do not notice the filtering of the macula but

under special conditions we can notice its presence

causing what is known as Maxwell’s spot.

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