Eye and Eye Sight

Introduction To Eye

Eye is a very sensitive organ of our body and it plays an important role for us. At the back of eye there is a membrane called retina which contains photoreceptor nerve cells. These photoreceptor nerve cells detect light and changes them into elctrical impulses which are then send through the optic nerves to the visual areas of the brain. As a result, an image is produced in the brain which we can see through our eyes.



Structure of eye

The human is wrapped of three layers of tissues:


The Sclerotic Coat

This layer covers the white part of the eye except in the front where a transparent layer known cornea is formed. The cornea allows the light to pass through it and bend light rays to such an extent that they can become focused.
The surface of the cornea is kept moist and dust-free by secretions from the tear glands.

The Choroid Coat

This is the middle layer of eye pigmented with a chemical melanin which reduces the reflection of stray light within the eye. This choroid layer forms iris in the front of eye and it is responsible for eye colour. The opening and closing of iris controls the size of eye which varies with specific conditions.In dim light, the pupil opens wider letting more light into the eye. In bright light the pupil closes down. This not only reduces the amount of light entering the eye but also improves its image-forming ability.

The Retina

Retina is the third and inside layer of the eye.It contains the light receptors, called the rods and cones. Some interneurons are also present in the retina which process the signals in the rods and cones before it passes to the brain.

The rods and cones are not at the surface of the retina but lie underneath the layer of interneurons.





Anterior Chamber

The cavity in the front part of the eye between the lens and cornea is called the Anterior
Chamber. It is filled with Aqueous, a water-like fluid. This fluid is produced by the ciliary
body and drains back into the blood circulation through channels in the chamber angle. It is
turned over every 100 minutes.


Chamber Angle

Located at the junction of the cornea, iris, and sclera, the anterior chamber angle extends 360
degrees at the perimeter of the iris. Channels here allow aqueous fluid to drain back into the
blood circulation from the eye. May be obstructed in glaucoma.


Ciliary Body

A structure located behind the iris (rarely visible) which produces aqueous fluid that fills the
front part of the eye and thus maintains the eye pressure. It also allows focusing of the lens.


Conjunctiva

A thin lining over the sclera, or white part of the eye. This also lines the inside of the eyelids.
Cell in the conjunctiva produce mucous, which helps to lubricate the eye.


Cornea

The transparent, outer "window" and primary focusing element of the eye. The outer layer of
the cornea is known as epithelium. Its main job is to protect the eye. The epithelium is made
up of transparent cells that have the ability to regenerate quickly. The inner layer of the cornea
is also made up of transparent tissue, which allows light to pass.


Hyaloid Canal

A narrow channel that runs from the optic disc to the back surface of the lens. It serves an
embryologic function prior to birth but none afterwards.


Iris

Inside the anterior chamber is the iris. This is the part of the eye which is responsible for one's
eye color. It acts like the diaphragm of a camera, dilating and constricting the pupil to allow
more or less light into the eye.


Pupil

The dark opening in the center of the colored iris that controls how much light enters the eye.
The colored iris functions like the iris of a camera, opening and closing, to control the amount
of light entering through the pupil.


Lens

The part of the eye immediately behind the iris that performs delicate focusing of light rays
upon the retina. In persons under 40, the lens is soft and pliable, allowing for fine focusing
from a wide variety of distances. For individuals over 40, the lens begins to become less
pliable, making focusing upon objects near to the eye more difficult. This is known as
presbyopia.


Macula

The part of the retina which is most sensitive, and is responsible for the central (or reading)
vision. It is located near the optic nerve directly at the back of the eye (on the inside). This
area is also responsible for color vision.


Optic Disc

The position in the back of the eye where the nerve (along with an artery and vein) enters the
eye corresponds to the "blind spot" since there are no rods or cones in these location.
Normally, a person does not notice this blind spot since rapid movements of the eye and
processing in the brain compensate for this absent information. This is the area that the
ophthalmologist studies when evaluating a patient for glaucoma, a condition where the optic
nerve becomes damaged often due to high pressure within the eye. As it looks like a cup
when viewed with an ophthalmoscope, it is sometimes referred to as the Optic Cup.


Optic Nerve

The optic nerve is the structure which takes the information from the retina as electrical signals
and delivers it to the brain where this information is interpreted as a visual image. The optic
nerve consists of a bundle of about one million nerve fibers.


Retina

The membrane lining the back of the eye that contains photoreceptor cells. These
photoreceptor nerve cells react to the presence and intensity of light by sending an impulse to
the brain via the optic nerve. In the brain, the multitude of nerve impulses received from the
photoreceptor cells in the retina are assimilated into an image.


Sclera

The white, tough wall of the eye. Few diseases affect this layer. It is covered by the episclera
(a fibrous layer between the conjunctiva and sclera ) and conjunctiva, and eye muscles are
connected to this.


Vitreous

Next in our voyage through the eye is the vitreous. This is a jelly-like substance that fills the
body of the eye. It is normally clear. In early life, it is firmly attached to the retina behind it.
With age, the vitreous becomes more water-like and may detach from the retina. Often, little
clumps or strands of the jelly form and cast shadows which are perceived as "floaters". While
frequently benign, sometimes floaters can be a sign of a more serious condition such as a
retinal tear or detachment and should be investigated with a thorough ophthalmologic
examination.




Eyesight

Eyesight can be defined as the ability of a person or animal to see. Whatever we see, it depend on our eyesight that how clearly can we see it. Problems with eyesight can lead us to very uncomfortness. If we are not able to see or watch properly it affects our daily life activities. However life is not complete without an eyesight. Some eyesight problems are mild and sometimes it is very severe such as blindness, when a person is completely not able to see.

Eyesight Problems

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Short-sightedness (myopia)

Short sight occurs when light is focused in front of the retina causing distance vision to become blurred. Near vision, however, is usually clear. Short sight normally develops in childhood or adolescence and is often first noticed at school. Glasses may need to be worn all the time or just for driving, watching TV or sports.

Long-sightedness (hypermetropia)

Long sight occurs when light is focused behind the retina rather than on it, and the eye has to make a compensating effort to re-focus. This can cause discomfort, headaches or problems with near vision. Glasses may need to be worn all the time or just for close work, such as reading, writing or computer use. In older people, as re-focusing becomes more difficult, distance vision may also become blurred.

Astigmatism

Astigmatism occurs when the curvature of the cornea or lens is not perfectly round. It is sometimes described as the eye being shaped like a rugby ball rather than a football. Most people have a small amount of astigmatism, which may not need correcting. If vision is blurred or headaches occur, your optometrist may recommend glasses are worn all the time or just for specific tasks.

Presbyopia

Presbyopia is the loss of focusing ability that occurs naturally with age. In younger people, the lens is very flexible and the eye has a wide range of focus from far distance to close up. As you get older, the lens slowly loses its flexibility leading to a gradual decline in ability to focus on near objects. Presbyopia is not a disease but a normal and expected change which sooner or later affects everyone, whether you already wear glasses or contact lenses or not. Around the age of 40-45, you will begin to notice that you are holding the newspaper further away or need more light to read small print. There is no advantage in delaying using reading glasses, or changing to bifocals or varifocals. They will not make the eyes lazy. Your optometrist will advise you on the best form of vision correction to suit your individual lifestyle and occupation.

Regular examinations are important throughout life, whether or not you are experiencing problems with your eyesight. Your optometrist will not only test your vision and, if necessary, prescribe glasses or contact lenses, but will also check closely for any early signs of eye disease or other medical condition.



Treatment and Cure

Eyesight can be treated through various ways. Consultation from a doctor should be the first step for the treatment of eyesight.

Glasses

One easy way to cure eyesight is wearing contact lenses or glasses. This is a common way to control eyesight. There are different glasses short-sightedness and for long-sightedness there are different glasses. People usually make use of glasses because it costs cheaper. Some people also feel uncomfortable wearing glasses.

Laser Surgery

Another major treatment for weak eyesight is laser surgery. In recent years laser surgery have been used to reduce the need for glasses. Usually laser surgery involves the re-shaping of cornea, the transparent area at the front of eye. Different laser surgeries are used to treat short, long sightedness.

Types of surgery

There is now a wide range of techniques available. The most common are:

LASIK (laser in situ keratomileusis)

This type of surgery is not used for those who have severe eyesight problems. In this a cut is made across the cornea and a part of damaged tissue is raised. The exposed surface is then re-shaped by using excimer laser and the part of tissue is replaced.

PRK (photorefractive keratectomy)

PRK has been performed since the late 1980s but since the development of LASIK and LASEK is now mainly used for correcting low prescriptions. In this cornea is re-shaped but without cutting any tissue.

LASEK (laser epithelial keratomileusis)

LASEK is similar to PRK but the surface layer (epithelium) of the cornea is retained as a flap. Retaining the epithelium is thought to prevent complications and speed up healing.

Wavefront-guided LASIK

Wavefront-guided LASIK is a technique used to reduce the natural irregularities of the eye that can cause light rays to focus incorrectly. This improve the visual result of the eye.


However, you must contact an optometrist, who will decide treatment for your eyesight and discuss the advantages and disadvantages of spectacles, contact lenses and refractive surgery.



Looking after your eyes - Five Top Tips

• Include eye healthy food in your diet such as fruits(orange, apple) and vegetables(carrots).
• Visit an optometrist regularly. Optometrists are professionally trained not only to test sight and prescribe glasses and contact lenses; they can also spot eye problems and treat infections.
• Be "eye aware" - make sure to check each of your eyes one at a time, and if you notice any changes, consult your optometrist.
• Parents, keep an eye on your children - don't forget, they don't know what "normal" vision is, so watch out for signs that there may be problems. These include instances where children's eyes appear not to work together, if they rub their eyes often or if they seem to shut one eye to see more clearly.
• Contact lens wearers - never wear anyone else's lenses, wash them in tap water or sleep in them.
  
• Buy good quality, dark sunglasses - Sunlight can damage the retina and the lens of the eye, and we risk causing long-term damage to our eyesight.