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Question
Explain why the image distance in the eye does not change when we change the distance of an object from the eye?
Solution
The focal length of the human lens can change i.e., increase or decrease, depending on the distance of objects and due to this the image distance in the eye does not change when we change the distance of an object from the eye. It is the ciliary muscles that modifies the curvature of the lens to change its focal length.
For example, to see a distant object clearly, the focal length of the lens should be larger. For this, the ciliary muscles relax to decrease the curvature and thereby increase the focal length of the lens. Hence, the lens becomes thin. This enables the image to be formed on the retina of the human eye.
Now if the same object is moved closer to eye, the ciliary muscles contract to increase the curvature and thereby decrease the focal length of the lens. Hence, the lens becomes thick and we still obtain the image of the object on the retina.
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