The Human Eye and the Colorful World

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The cornea is a thin transparent membrane that forms the bulge on the front surface of the eyeball. Most of the refraction for light rays entering the eye occurs at the outer surface of the cornea. It…

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Accommodation is the ability of the eye lens to adjust its focal length to focus objects at different distances on the retina. When ciliary muscles relax, the lens becomes thin (for distant objects).

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The near point is the minimum distance at which objects can be seen most distinctly without strain. For a young adult with normal vision, the near point is about 25 cm. This is also called the least d…

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Myopia (near-sightedness) is a defect where a person can see nearby objects clearly but cannot see distant objects distinctly. The image forms in front of the retina. It is corrected using a concave l…

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Hypermetropia (far-sightedness) is a defect where a person can see distant objects clearly but cannot see nearby objects distinctly. The image forms behind the retina. It is corrected using a convex l…

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Presbyopia is a vision defect that occurs with aging when the eye gradually loses its power of accommodation. The near point recedes away, making it difficult to see nearby objects clearly. It is caus…

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Bi-focal lenses consist of both concave and convex lenses in one spectacle. The upper portion has a concave lens for distant vision, and the lower part has a convex lens for near vision. They are used…

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The angle of deviation is the angle between the direction of the incident ray and the emergent ray when light passes through a prism. Due to the prism's shape, the emergent ray bends at an angle to th…