PREVIOUSLY ASKED IN:
PSC Miscellaneous Prelims 2018
Answer
Cylindrical lens
Explanation
Astigmatism is a common vision condition that causes blurred or distorted vision. It occurs when the cornea or the lens of the eye has an irregular shape (not perfectly round). To correct this uneven curvature, a cylindrical lens is used in eyeglasses. Unlike spherical lenses that focus light uniformly, cylindrical lenses have different focusing powers in different meridians to compensate for the irregular shape of the eye.
Key Points
- > Astigmatism is caused by an irregularly shaped cornea or crystalline lens.
- > It is corrected using eyeglasses with Cylindrical lenses.
- > Short-sightedness (Myopia) is corrected using a Concave lens.
- > Long-sightedness (Hypermetropia) is corrected using a Convex lens.
- > Presbyopia (age-related inability to focus on near objects) is corrected using a Bifocal lens.
- > Benjamin Franklin is credited with the invention of bifocal lenses.
Additional Information
Vision Defects and Corrective Lenses
| Defect Name | Visual Problem | Corrective Lens |
|---|---|---|
| Myopia | Cannot see distant objects clearly | Concave Lens |
| Hypermetropia | Cannot see near objects clearly | Convex Lens |
| Presbyopia | Age-related loss of near focusing | Bifocal Lens |
| Astigmatism | Distorted/blurred vision at all distances | Cylindrical Lens |
Memory Tips
- Matching Trick:
- Myopia -> conCave (MC)
- Hypermetropia -> conVex (HV)
- Astigmatism -> Cylindrical (AC)