Visual Impairments or Defects of Vision
The conditions when the eye’s adjustment capacity becomes weak, then the objects do not appear clear is called visual impairments. In these cases, the reflection of the object does not form an image on the retina, but rather in the front or back. This condition is called Visual Impairments or vision defects, depending on the state of reflection, it is of the following type:
1. Myopia, a Very Common Visual Impairments
The person suffering from myopia has obvious near-visible objects but the distant object is not clear because the image of distant objects is formed before the retina. The distant point of the eye with this defect does not come to infinity but comes close.
Causes of Myopia Defect
1. Due to an increase in curvature of the eye lens due to some reason, its focus distance is reduced.
2. Increasing the diameter of the eye lens ball.
For these reasons, the image of a distant object is formed before the retina, so that it is not visible clearly.
Remedy to Remove Myopia
To remove close vision defect, concave lens glasses with proper focus distance are used so that the rays of light moving from a distant object come from the distant point of the eye after refraction from the concave lens, and the reflection of the object forms on the retina.
2. Far-Sightedness or Hypermetropia, a Very Common Visual Impairments
The person suffering from far-sightedness sees the distant objects clearly but the nearby objects are not clear because their image is behind the retina. The near point of the eye with this defect goes more than 25 centimeters away, so the person suffering from this defect is not seen clearly in the 25 centimeters and the objects near it.
Causes of Far-Sightedness or Hypermetropia
1. Increased focus distance due to reduced curvature of the eye lens for some reason.
2. Decreasing the diameter of the eyeball due to the weakening of the muscles of the eye.
For these reasons, the object is not clearly visible due to the reflection of objects located close behind the retina.
Remedy to Remove Far-Sightedness
Convex lens glasses with the proper focus distance are used to correct far-sight defects so that the rays of light moving from a distant object appear to come from the point near the eye after refraction from the convex lens. These rays, after refraction from the eye lens, focus on the retina, making the object visible.
The collapsed capacity of the eye decreases due to the weakening of the ciliary muscles of the eye and lack of flexibility in the eye lens. Such a person does not see the objects of both far and near places clearly. This is called presbyopia.
Prevention of Presbyopia
A two-focal lens is used to correct presbyopia. It consists of both concave and convex lenses which help to create a reflection of objects located near and near the retina.
In this defect, horizontal and vertical objects located at equal distances together are not clearly visible. The main reason for this is an irregularity in rounding of the cornea.
Rectification of Astigmatism
Cylindrical lenses with proper focus distances are used to correct this vision defect. Lenses (temporary) or refractive surgery (permanent) are used to correct astigmatism.
In this type of defect, humans can see properly but they cannot differentiate between certain colors. The most common type of color blindness makes it hard to tell the difference between red and green. Another type makes it hard to tell the difference between blue and yellow. But in total color blindness, people can not differentiate in any color but that’s not very common. This defect is congenital in the human eye and it is incurable. The major cause of color blindness is the lack of conical cells in the eye.