Eye, the organ of vision

     

EYE 
(The Organ of Sight and related diseases)

How do you see the beautiful world around you?

What helps you to see things?

Yes, that are your eyes. The human eye is like a ball and is the most delicate part of the body. So, eyes need protection from the outer environment which can damage eyes. Eyes are protected by eyelids, eyelashes and tears. The eyelid covers the eyes. It covers the eyes completely when needed. Eyelashes are the small hairs on the eyelids. They protect the eye from dust particles. Special glands called tear glands are also present in eyes. They produce tears and wash the eyes when necessary, and keep them safe from drying.

STRUCTURE OF HUMAN EYE

An eye consists of an eyeball. It is

enclosed in a socket of the skull. Eyes

move where we want to see with the

help of muscle. The following are the

main parts of a human eye:

CORNEA

The transparent outer layer of the eye is the cornea. It is like a round window which covers the iris and the pupil. It is the coloured part of the eye located beneath the cornea. Cornea usually brown, black, blue or green in colour.

PUPIL

It is a small round hole in the centre of iris. Its size increases or decreases as the muscle in the iris contracts or relaxes. It widens when light is dim and contracts when light is bright.

LENS

The lens is present behind the pupil inside an inner chamber. It has muscles that help it to change shape. The lens changes shape to see the objects at different distances. If the object is near, it becomes rounded, and if far away it flattens. This process of the lens adjusting according to object distance is called accommodation. People lose the ability of accommodation of the lens as they grow older so they need glasses. Behind the lens of the eye is a vitreous chamber having a gelatinous material called the vitreous humor inside it. This gives the eye the shape it has.

RETINA

It is present at the very back of the eyeball. It has two special types of photoreceptors called rods and cones.

OPTIC NERVE

It is the nerve that connects the eye to the brain. It send the messages to the brain.

FUNCTION OF EYE

Our eyes work in a similar way as a camera. We see objects due to the reflection of the light from that object into our eyes. The visible parts of the eyes that help in the formation of an image are cornea, pupil, iris and lens. 

After light is reflected from the object, it enters our eyes through the pupil. The iris controls the amount of light entering the pupil. It works like a shutter in a camera. The size of the pupil increases or decreases according to the light intensity. The light rays then move through the lens and fall on the retina. The lens focuses the light and images on the retina. It is just like a film of the camera where an image is formed. The image made on the retina is upsidedown. The retina has millions of light sensitive nerve cells known as photoreceptors. These nerve cells are called rods and cones depending on their shape.

The cones provide clear and sharp vision when there is bright light and detect colors. Rods help us to see things in the dark or dim light. When light rays hit these photoreceptors, nerve impulses are generated that are carried to the brain through optic nerves. The brain clearly illustrate these signals. As a result, we see the object.

COMMON EYE DISEASES

GLAUCOMA

The human eye is like a tire. Some pressure inside the eye is good and safe, however, high level of pressure is harmful for the optic nerve. Glaucoma is a group of optic diseases that is responsible for this condition. Majority of glaucoma patients don't have pain or early symptoms. So it's important to look after your eyes regularly.

Causes of glaucoma

If your eye become injured, it is chance that blood vessels will blocked. Inflammation in the eyes including eye drops, lotions, ointments, lens or surgery may also cause glaucoma.

RETINAL DISORDERS

The retina is a thin lining on the back of our eyes. Retina is made up of cells that collect images and pass them into the brain. It is most frequent that the retinal problems damages the retinal cells and break up this transfer of imaging.

Retinal problems are classified as:

Age-related macular degeneration refers to a breakdown of a small part of the retina called the macula.

Diabetic retinopathy can damage to the blood vessels in your retina caused by diabetes.

Retinal detachment takes place if the retina apart from the layer underneath.

The only way to prevent yourself from retinal diseases is early diagnosis and urgent treatment.

CONJUNCTIVITIS (Pinkeye)

In this type of infection, tissue that lines the back of your eyelids and covers your sclera become  swollen. In the reaction, following symptoms occurs:

1. Redness

2. Itching 

3. Burning 

4. Tearing 

5. Rough feelings

People of all ages can get it. Easy way to protect yourself from conjunctivitis is wash your hands regularly. This may lower chance of getting it.

Causes of conjunctivitis

infection

exposure to chemicals

exposure to irritants

allergies

EYELID PROBLEMS

Your eyelids do a lot for you. They work as safeguard, for example they allow limited amount of light to enter in the eye and spread tears over its surface. If your eyelid infected, the possible symptoms  will be itching, tearing, pain and sensitivity to light. You might also have involuntary blinking spasms or inflammation of outer edges near the eyelashes.

NIGHT BLINDNESS

During this disorder, it is hard to see at night and in the dark rooms such as in a cinema hall. It is symptom and not a problem in its own. The lack of vitamin A is the main cause of night blindness. It can be fix easily if you visit doctor. 

Some human beings are born with this problem, or it would broaden from a degenerative sickness concerning the retina, and that typically can’t be treated. If you've got  it, you’ll want to be greater cautious in regions of low light.