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

$A$ person's near point is $50 \, cm$ and his far point is $3 \, m$. The power of the lenses he requires for $(i)$ reading and $(ii)$ seeing distant stars are:

$A$ person cannot see objects clearly placed at a distance of more than $40 \, cm$. He is advised to use a lens of power:

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 $x$?

Myopia is a defect of the eye due to which a person experiences difficulty in seeing .......

$A$ presbyopic patient has a near point of $30 \ cm$ and a far point of $40 \ cm$. The dioptric power of the corrective lens required for seeing distant objects is: (in $D$)