The mechanism of vision

The mechanism of vision

The curvature of the lens of the eye changes when we look at a distant or at a near object, to ensure a sharp image.

Biology

Keywords

eye, imaging, vision, sensory organ, optic nerve, short-sightedness, hyperopia, visual acuity, color vision, vision problem, iris, pupil, lens, ciliary body, cornea, vitreous chamber, macula lutea, scotoma, sclera, choroid, retina, visual cortex, anterior chamber, stimulus, light, cone cells, rod cells, pigment, receptor, signal, glasses, contact lenses, human, biology

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  • - It is the continuation of the choroid. Its smooth muscle ensure the adaptation to changing levels of light: in strong light the pupil contracts, while in weak light it dilates. It contains pigments which give the human eyes their individual color.
  • - It is the eye’s aperture and the iris acts like a shutter that controls the amount of light that falls on the retina. In strong light the iris is contracted by its smooth muscles, in weak light it dilates. The pupillary light reflex is an unconditioned reflex, its center is located in the brain stem. Abnormal operation of the pupillary reflex therefore indicates the injury of the brain stem.
  • - It is a convex lens with variable focal distance. Its flexibility allows it to become more curved when looking at a nearby object, while it can be flattened by the ciliary zonules. This provides a sharp image on the retina. As we age, the lens loses its flexibility and therefore looking at nearby objects becomes more difficult in old age (as this requires the lens to become more curved). This is called presbyopia. A cataract is a gray clouding that develops in the lenses making it opaque, which may lead to blindness.
  • - It contains aqueous humor. When there is too much of this liquid, ocular hypertension occurs which causes glaucoma. This in turn, may lead to blindness as hypertension can destroy the retina.
  • vitreous humor - A chamber filled with a transparent gel called the vitreous humor. Light reaches the retina through this chamber.
  • - The area of the retina responsible for visual acuity. The inverted miniature image of objects is formed here. In the center of the macula there are only cone cells, towards the edge the number of rod cells increases.

  • - It is a convex lens with variable focal distance. Its flexibility allows it to become more curved when looking at a nearby object, while it can be flattened by the ciliary zonules. This provides a sharp image on the retina. As we age, the lens loses its flexibility and therefore looking at nearby objects becomes more difficult in old age (as this requires the lens to become more curved). This is called presbyopia. A cataract is a gray clouding that develops in the lense making it opaque, which may lead to blindness.

  • - It is a convex lens with variable focal distance. Its flexibility allows it to become more curved when looking at a nearby object, while it can be flattened by the ciliary zonules. This provides a sharp image on the retina. As we age, the lens loses its flexibility and therefore looking at nearby objects becomes more difficult in old age (as this requires the lens to become more curved). This is called presbyopia. A cataract is a gray clouding that develops in the lense making it opaque, which may lead to blindness.

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