The retina of the eye acts like the ........ of a camera.

To remove myopia (short-sightedness),a lens of power $0.66 \, D$ is required. The far point of the eye is approximately ....... $cm$.

The least distance of distinct vision of a long-sighted person is $60 \ cm$. By using a spectacle lens, this distance is reduced to $12 \ cm$. The power of the lens is

The least distance of distinct vision for a long-sighted person is $x \ m$. He wants to read a newspaper placed at a distance $(x/2) \ m$. The power of the spectacle lens used by him is $x \ D$. What is the value of $x$?

$A$ person can see objects clearly when they lie between $40 \ cm$ and $400 \ cm$ from his eye. In order to increase the maximum distance of distant vision to infinity, the type of lens and power of the correction lens required respectively are

$A$ person is suffering from the defect astigmatism. Its main reason is