Defects in vision
People with 20/20 vision can comfortably focus on distant and on near objects, clearly seeing both. Others can clearly see either distant or near objects, not both. Such people have a defect in vision.
Those able to clearly see only nearby objects are near-sighted.
Those able to clearly see only distant objects are far-sighted.
As the ciliary muscles become weaker with age, they are less able to change the shape of the lens to focus on near and distant objects. This defect is known as lack of accommodation.
Those able to clearly see only nearby objects are near-sighted.
Those able to clearly see only distant objects are far-sighted.
As the ciliary muscles become weaker with age, they are less able to change the shape of the lens to focus on near and distant objects. This defect is known as lack of accommodation.
Normal, Near-sighted and Far-sighted vision.
A person with normal (20/20) vision is able to clearly see both near and distant objects. In both circumstances, the light comes to focus on the retina.
A person who is near-sighted (a defect known as myopia) can only clearly see nearby objects. The light rays from nearby objects come to focus on the retina. Distant objects however are not clearly seen. The light rays from distant objects come to focus in front of the retina. (See Figure 1) A diverging lens (concave lens) is used to correct this.
A person who is far-sighted (a defect known as hyperopia) can only clearly see distant objects. The light rays from distant objects come to focus on the retina. Nearby objects however are not clearly seen. The light rays from nearby objects come to focus behind the retina. (See Figure 1) A converging lens (convex lens) is used to correct this.
A person who is near-sighted (a defect known as myopia) can only clearly see nearby objects. The light rays from nearby objects come to focus on the retina. Distant objects however are not clearly seen. The light rays from distant objects come to focus in front of the retina. (See Figure 1) A diverging lens (concave lens) is used to correct this.
A person who is far-sighted (a defect known as hyperopia) can only clearly see distant objects. The light rays from distant objects come to focus on the retina. Nearby objects however are not clearly seen. The light rays from nearby objects come to focus behind the retina. (See Figure 1) A converging lens (convex lens) is used to correct this.