Question

What are defects of vision ? What are their types ? How are the defects resolved ?

Hint:

For quick recall, create a table: \[\begin{array}{rl} \bullet & \text{Myopia: Sees NEAR, Image IN FRONT of retina, Corrected by CONCAVE lens.} \\ \bullet & \text{Hypermetropia: Sees FAR, Image BEHIND retina, Corrected by CONVEX lens.} \\ \bullet & \text{Presbyopia: AGE-related, problem with NEAR vision, Corrected by CONVEX/BIFOCAL lens.} \\ \end{array}\]

Answer 1

Defects of Vision
Defects of vision are conditions where the eye loses its ability to focus light correctly on the retina, leading to blurred or impaired vision.

Types of Defects and their Resolution
The three common refractive defects of vision are:
\begin{enumerate} \item Myopia (Nearsightedness): \[\begin{array}{rl} \bullet & \text{Condition: A person can see nearby objects clearly but cannot see distant objects distinctly. The image of a distant object is formed in front of the retina.} \\ \bullet & \text{Resolution: This defect is corrected by using a concave lens of a suitable power. The concave lens diverges the light rays before they enter the eye, allowing the eye lens to focus them correctly on the retina.} \\ \end{array}\] \item Hypermetropia (Farsightedness): \[\begin{array}{rl} \bullet & \text{Condition: A person can see distant objects clearly but finds it difficult to see nearby objects. The image of a nearby object is formed behind the retina.} \\ \bullet & \text{Resolution: This defect is corrected by using a convex lens of a suitable power. The convex lens converges the light rays, providing the additional focusing power needed to form the image on the retina.} \\ \end{array}\] \item Presbyopia: \[\begin{array}{rl} \bullet & \text{Condition: This is an age-related defect where the eye's power of accommodation decreases. It becomes difficult to see nearby objects comfortably and distinctly.} \\ \bullet & \text{Resolution: It is corrected using a convex lens for near vision. Sometimes, a person may suffer from both myopia and hypermetropia, in which case bifocal lenses (containing both concave and convex parts) are used.} \\ \end{array}\] \end{enumerate}