Variable focal length of the eye and its role in accommodation:

The variable focal length of the eye is responsible for the accommodation of the eye. Accommodation refers to the ability of the eye to adjust its focal length in order to focus on objects at different distances. This allows us to see objects clearly, whether they are near or far.

Process of accommodation:

Accommodation is achieved through the adjustment of the shape of the lens in the eye. The lens is a flexible and transparent structure located behind the iris and the pupil. It changes its shape to adjust the focal length and bring objects into focus on the retina.

Role of the lens:

The lens in the eye has the ability to change its shape due to the action of ciliary muscles. When we look at distant objects, the ciliary muscles relax, causing the lens to flatten. This decreases its refractive power, allowing the eye to focus on distant objects.

On the other hand, when we look at nearby objects, the ciliary muscles contract, causing the lens to become more rounded. This increases its refractive power, allowing the eye to focus on nearby objects. This adjustment of the lens shape is crucial for clear vision at different distances.

Importance of variable focal length:

The variable focal length of the eye is essential for providing clear and focused vision at different distances. Without accommodation, our vision would be blurry and objects at different distances would appear unfocused.

Relation to other options:

Persistence of vision refers to the phenomenon where an image continues to be perceived by the brain even after it has been removed from the visual field. This is not directly related to the variable focal length of the eye.

Colour blindness is a condition where individuals have a decreased ability to perceive certain colors. It is caused by a deficiency in the normal functioning of the color-sensitive cells in the eye, not the variable focal length.

The least distance of distinct vision refers to the minimum distance at which the eye can see objects clearly without any strain. This is not directly related to the variable focal length of the eye.

Therefore, the correct option is 'A' - accommodation of the eye. The variable focal length of the eye allows for the adjustment of the lens shape, enabling clear vision at different distances.