• $summary_{type}$: application
• $word_{count}$: 150

The human eye has a near point of 25 cm and a far point at infinity. Myopia (short-sightedness) occurs when the far point is at a finite distance — distant objects focus before the retina. Corrected by a concave lens of power P = -1/far point (in metres). Hypermetropia (far-sightedness) occurs when the near point exceeds 25 cm — nearby objects focus behind the retina. Corrected by a convex lens: 1/f = $\frac{1}{-near point}$ - $\frac{1}{-25 cm}$. Presbyopia (age-related loss of accommodation) often requires bifocal lenses. Astigmatism (non-uniform corneal curvature) is corrected by cylindrical lenses. JEE questions typically provide the defective near/far point and ask for the power of the corrective lens.