Do you know eyes can live even after our death!! Donating eyes after death can light the life of another person. Know that one pair of eyes gives vision to two corneal blind people. Hence, it is one of the vital sensory organs of the human body. The colourful world we see is the result of the beautiful creation of the body – The human eye.
The eye lens is composed of fibrous, jelly-type material. The curvature of the eye lens can be adjusted to a certain level with the aid of ciliary muscles. A change in the curvature of the eye lens can change its focal length. The eye lens becomes thin, and the focal length increases when the muscles of the eyes are relaxed. The objects at a distance can be viewed clearly when the focal length increases. To see the objects that are close by, the ciliary muscles contract and increase the curvature of the lens and hence decrease the focal length. The ability of the eye lens to adjust its focal length is called accommodation.
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Defects of Vision And Their Correction
Defects in the eye happen due to many reasons. Due to growing age, the vision also decreases, and when the focal length alters, the vision also alters. We know that cataract is a common defect seen in the eye. Cataracts cause partial or sometimes complete vision loss when not treated properly. When the crystalline lens at old age becomes milky and cloudy, it is known as a cataract. When a person undergoes cataract surgery, the vision can be restored.
When the eye loses its ability to adjust its focal length, problems appear like a person cannot see the image correctly (blurring of vision), unable to view nearby objects or far away objects. When the defect in the refractive index occurs, the person cannot see the objects comfortably and distinctly. If not taken timely care of, the eyes might completely lose the power of accommodation. In this article, let us learn about various vision defects and their correction.
Read More: The Human Eye
Refractive Defects of Vision
Some of the common defects of vision are:
(i) Myopia or near-sightedness
(ii) Hypermetropia or far-sightedness
Myopia or Near-Sightedness
Myopia is commonly known as near-sightedness. In this condition, the person can see the objects nearby but cannot see distant objects clearly. Faraway objects appear blurry, and a person will not be comfortable seeing them. Myopia condition takes place when the shape of the eyes leads the light rays to bend in a wrong way, focusing images in front of the retina rather than focusing on the retina.
Myopia is explained in the figure below.
- Blurry vision.
- Difficulty in seeing while driving, particularly during night times.
- Headaches due to eyestrain.
Correction : When a concave lens of suitable power is used, it assists in focusing the image onto the retina.
Hypermetropia or Far-Sightedness
Hypermetropia is commonly known as far-sightedness. In this condition, the person can see objects at a distance but cannot see nearby objects clearly. Usually, the person with this disorder squints to see nearby objects. Hypermetropia is caused when the light rays from a closeby object are focussed at a point behind the retina. The condition of hypermetropia is clearly explained in the figure below.
- Blurry vision.
- Headaches due to eyestrain.
Correction : Using spectacles with a converging lens imparts additional focusing power and thus helps form the image on the retina.
We know that along with age, the power of the accommodation factor to adjust the focal length also decreases. People have difficulties viewing nearby objects clearly without the assistance of corrective eyeglasses. This condition is referred to as presbyopia. Presbyopia happens when the ciliary muscles weaken and diminish the elasticity of the eye lens. Presbyopia can be seen in people above the age of 40 years.
Blurred vision due to ageing.
Headaches due to eyestrain.
Correction : This condition can be corrected by using proper eyeglasses or contact lenses. Minor surgery also helps in restoring the vision with better clarity. Advancement in technology has made it easy to correct the refractive defects with contact lenses or through surgical interventions.
Person With Myopia and Hypermetropia Disorders
We can see some people who suffer from myopia and hypermetropia disorders. In such conditions, it is advised to use bifocal lenses. Usually, bi-focal lenses consist of concave as well as convex lenses. The bi-focal lens has a concave lens in the upper portion and a convex lens in the lower portion to facilitate distant vision and near vision.
When to See a Physician?
As soon as you feel blurry close-up vision while reading or while performing other activities, a physician can help diagnose the disorder. Sometimes you might also have a loss of vision in one eye with or without eye pain. Some symptoms which are common and yet not to be ignored are: seeing black spots or halos around lights and flashes of light. People might also experience double vision but do not think the symptoms are common. Approach the doctor and seek medical help immediately.
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Read more: Difference between concave and convex lens
Frequently Asked Questions – FAQs
What is a cataract?
When the crystalline lens at old age becomes milky and cloudy, it is known as a cataract.
Name some of the defects that take place in the eye due to refractive property.
Common refractive defects of vision are:
State True or false: Myopia is known as far-sightedness.
False. Myopia is known as near-sightedness.
What is a bi-focal lens?
A bi-focal lens consists of a concave lens in the upper portion and a convex lens in the lower portion.
What is the reason for hypermetropia?
The light rays from a nearby object are focussed at a point behind the retina. Hence the person cannot see the objects nearby distinctly.
Watch the video and solve the previous year questions in the chapter The Human Eye and Colorful World Class 10
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