Hypermetropia, or far-sightedness, is corrected using convex lenses, which converge light rays to focus on the retina. For a hypermetropic eye with a near point of 1 meter, the required lens power is calculated using the formula P =1/f, where f is the focal length in meters. The desired near point is typically 25 cm (0.25 m), so f = 1m−0.25m = 0.75m. Thus, P = 1/0.75 ≈ +1.33 dioptres.
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Correcting Hypermetropia: An Overview
Understanding Hypermetropia: Hypermetropia, commonly known as far-sightedness, is a vision condition where distant objects are seen more clearly than close ones. This occurs because the light entering the eye focuses behind the retina, usually due to a shorter-than-normal eyeball or a lens that is too flat.
The Role of Convex Lenses
To correct hypermetropia, convex lenses are used. These lenses converge light rays, ensuring they focus directly on the retina. This correction allows for clear vision of near objects, which is typically problematic for hypermetropic individuals.
Determining the Near Point
In this case, the near point of the hypermetropic eye is 1 meter. The near point is the closest distance at which the eye can focus on an object. For normal vision, this point is typically about 25 cm (0.25 meters).
Calculating the Required Focal Length
The lens should shift the near point from 1 meter to the normal near point of 25 cm. Therefore, the required focal length (f) is the difference between these distances:
f = 1m−0.25m = 0.75m.
Computing the Lens Power
The power of the lens (P) is calculated using the formula P =1/f. For a focal length of 0.75 meters, the power is P = 1/0.75, which equals approximately +1.33 dioptres.
Conclusion: Lens Specification for Hypermetropia
To correct the hypermetropic condition of an eye with a near point of 1 meter, a convex lens with a power of about +1.33 dioptres is required. This lens will enable the person to see near objects clearly, effectively correcting the far-sightedness.