The far point of a myopic person is 80 cm in front of the eye. What is the power of the lens required to enable him to see very distant objects clearly?

To determine the power of the lens required for a myopic person to see distant objects clearly, we first need to understand a few key concepts about myopia and lens power. Myopia, or nearsightedness, occurs when the eye focuses images in front of the retina, making distant objects appear blurry. The far point of a myopic person is the farthest distance at which they can see clearly, which in this case is 80 cm. To correct this vision, we need to use a lens that allows light rays from distant objects to focus correctly on the retina.

Understanding Lens Power

The power of a lens is measured in diopters (D) and is calculated using the formula:

P = 1/f

where P is the power in diopters and f is the focal length in meters. For corrective lenses, the focal length is negative for diverging lenses, which are used to correct myopia.

Calculating the Focal Length

Since the far point of the person is 80 cm, we need to convert this distance into meters for our calculations:

• 80 cm = 0.80 m

To correct the vision, we want the lens to create a virtual image at the far point of the eye, which means the focal length of the lens should be equal to the negative of the far point:

f = -0.80 m

Finding the Power of the Lens

Now, we can substitute the focal length into the lens power formula:

P = 1/f = 1/(-0.80)

Calculating this gives:

P = -1.25 D

Conclusion

The power of the lens required for this myopic person to see distant objects clearly is -1.25 diopters. This negative value indicates that a diverging lens is needed to correct their vision. By wearing glasses or contact lenses with this power, the individual will be able to focus light correctly onto their retina, allowing them to see faraway objects clearly.