Question

Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles. What types of lenses are required by the person suffering from this defect to see the objects clearly? Akshay, sitting in the last row in his class, could not see the words clearly written on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked. In context of the above event, answer the following questions:
(a)Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?

Answer 1

Hint:The ciliary muscle determines the focus of the eye, and may modify the thickness and curvature of the lens.Myopia is a normal state of vision in which we can easily see objects around us, but fuzzy objects further away. It happens when our eye structure allows rays to bend wrongly, reflecting images on our retina rather than in front of our retina.

Complete step by step answer:
The focal length of the eye lens is adjusted by the ciliary muscles. This property is known as the accommodation.As human age grows, presbyopia occurs due to progressive weakness of the ciliary muscles and decreasing eye lens flexibility.A typical bi-focal lens form consists of both concave and convex sections that are needed to clearly see objects.
(a)As Akshay could only see things nearby but not things far away, he suffers from myopia. This defect is fixed using the concave lens.

Additional information:
High myopia is a more serious form of the condition, where the eyeball grows more than it is meant to grow and become very long from the front to the back. It can also increase our chance of having other conditions such as detached retina, cataracts and glaucoma in addition to making it hard to see things at a distance.The symptoms of myopia are headaches, squinting, eye strain, eye fatigue etc.Far point of an eye: When the eye’s accommodation is fully comfortable, the point farthest from the eye at which an object is distinctly centred on the retina.

Note:Lenses having negative power will extend the focus of a myopic person and give them a good vision. The higher the power of the lens the more far point can be achieved for the eye.The far point of a person suffering from myopia is less than infinity. In myopia, the individual is able to clearly see near objects, but distant objects are not visible.
In eyeglasses that correct nearsightedness, concave lenses are used. Placing concave lenses in front of a nearsighted eye decreases the light refraction and the focal length is increased.