How can defects of the eye be corrected

Bifocal lenses consists of concave on the upper portion and convex on the lower portion. Concave supports distinct vision and convex supports near vision Refractive eye defects can also be corrected using contact lenses or through specific surgical procedures. Defects of Vision and their Correction. Knowing the focal length of the concave lens, we can calculate its power. Hypermetropia or long-sightedness is that defect of vision due to which a person cannot see the nearby objects clearly though he can see the distant objects clearly.

For example: A person having the defect hypermetropia cannot read a book clearly and comfortably though he can read the number of a distant bus clearly. The near-point of a hypermetropic eye is more than 25 cm away.

The defect of eye called hypermetropia or long- sightedness is caused. The ciliary muscles attached to the eye- lens become weak and cannot make the eye-lens thicker to increase its converging power. So, due to the low converging power of eye-lens in an eye suffering from hypermetropia, the image of nearby object is formed behind the retina and hence the eye cannot see it clearly.

In an eye suffering from hypermetropia, the eye-ball is too short due to which the retina is at a smaller distance from the eye-lens. This condition also results in the formation of the image of a nearby object behind the retina.

The diverging rays of light coming from a nearby object O placed at the normal near point N are converged to form an image I behind the retina due to which the eye cannot see the nearby object clearly.

The image is formed behind the retina either due to low converging power of eye- lens or because of eye-ball being too short. When a convex lens converging lens L of suitable power is placed in front of the hypermetropic eye, then the diverging rays of light coming from the nearby object are first converged by this convex lens. The whole purpose of using a convex lens here is to increase the converging power of the eye-lens.

The focal length of convex lens needed to correct hypermetropia or long-sightedness can be calculated by using the lens formula:. In this formula, the object distance u is to be taken as the normal near point of the eye and the image distance v will be the distance of the near point of the length of the convex lens, its power can be calculated. In old age, due to ciliary muscles becoming weak and the eye-lens becoming inflexible or rigid , the eye loses its power of accommodation.

Because of this an old person cannot see the nearby objects clearly. Presbyopia is that defect of vision due to which an old person cannot see the nearby objects clearly due to loss of power of accommodation of the eye. Presbyopia occurs in old age due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye-lens. The near-point of the old person having presbyopia gradually recedes and becomes much more than 25 centimetres away.

Presbyopia defect is corrected in the same way as hypermetropia by using spectacles having convex lenses. A person suffering from myopia as well as hypermetropia uses spectacles having bifocal lenses in which upper part consists of a concave lens to correct myopia used for distant vision and the lower part consists of a convex lens to correct hypermetropia used for reading purposes.

It is possible to correct the refractive defects of the eye such as myopia and hypermetropia by using contact lenses or by undergoing surgical procedures. The medical condition in which the lens of the eye of a person becomes progressively cloudy resulting in blurred vision is called cataract.

Cataract develops when the eye-lens of a person becomes cloudy or even opaque due to the formation of a membrane over it. Cataract decreases the vision of the eye gradually. It can even lead to total loss of vision of the eye. Another way to correct this defect is to alter the refractive power by surgery like Lasik surgery. Hypermetropic eye has positive power like or as corrective powers. This indicates that the corrective lens required is convex.

Such lenses are mostly used during reading or using laptops, etc. The near-point of the old person having presbyopia gradually recedes and becomes much more than 25 centimeters away. A person who cannot distinguish between various colours but can see well otherwise, is said to be colour-blind. The vision becomes blurred due to the refractive defects of the eye.

There are three common refractive defects of vision. The images of distant objects are not formed at the right spots of rods and cones and hence appear blurred. A person with Myopia cannot see the distant objects clearly though he can see the nearby objects clearly. Far off objects cannot be seen as the eye lens does not produce a long focal length. However, nearby objects can be clearly seen. In a myopic eye, the parallel rays of light coming from the distant object at infinity are converged to form an image.

The image is formed in front of the retina due to which the eye cannot see the distant object clearly. This clouding results in blurred images. Age-related macular degeneration ARMD. This is a degenerative condition of the macula the central retina. It is caused by the hardening of the arteries that nourish the retina. This deprives the retinal tissue of the nutrients and oxygen that it needs to function and causes a deterioration in central vision.

Glaucoma: The eye produces a clear fluid aqueous humor that fills the space between the cornea and the iris.