Why contraction and expansion of pupil occur in the eye?

Answer 1

The pupil size of the eye is controlled by muscles in the iris, the coloured part of the eye. The purpose of this is to control the amount of light hitting the light-sensitive retina, at the back of the eye. Too much light can damage the retina (thats why your mum told you never look directly at the sun) and too little would mean that you couldn't see properly. That is why the pupil shrinks in bright light, and expands in low light.
Thhe adjustment of pupil size is an automatic reflex, often used to assess brain damage in hospital patients - thats why on hospital dramas they shine lights in patient's eyes - "Pupils fixed and dilated" is not a good sign!

Answer 2

Contraction Of Pupil

Answer 3

To regulate the amount of light that enters it. In low light, the pupil expands so it can receive the maximum amount of the available light so that some sight is possible. In strong light, the pupil contracts to shut some of the light out, so that harmful amounts of light don't damage the retina. This is why it hurts your eyes to turn on a light in a dark room; your pupils expanded in the dark, and then too much light enters after the light is turned on, until the pupil can contract in response to the new stimulus.

Answer 4

The abundance or lack of light. Your pupils contract in bright light to reduce the aperture of the eye to stop you from being blinded by the light. In dim conditions your pupils dilate, allowing more light to strike the receptors at the back of the eye and let you see better than you otherwise would.

Answer 5

Hi, the majority of the answers you have so far are quite right, my addition is to compare the eye with a camera lens, the film needs a certain amount of light to form an image on the film and the camera uses the iris to control it in combination with the shutter speed, our eye has to be satisfied with the iris alone, blinking doesn't work, we have to resort to obscured lenses when viewing an eclipse though, hope this helps.

Answer 6

Would guess that the iris diameter alters to keep the incident light flux impinging on the retina constant. Suggest that this is a poor/slow response mechanism..must take of the order of seconds to adjust to large changes in illumination. Suggest best solution is to alter the gain/sensitivity of the photo receptors themselves. limulus a species of 'crab' has the ability to do this and can acquire visual sensation in both bright sunlight and almost abyssal darkness..

Answer 7

depends what drugs you have been doing, ecstacy opens the pupils up where amphetamine based drugs contract the pupil....
oh sorrry no its the brains way of filtering light through the eye when its dark they expand letting as much light as possible in and when there's too much light they contract !

Answer 8

Movement of the pupil of the eye according to the amount of the light which eye exposed to it (REFLEX ACTION)
This movement according to nerve stimulation by Autonomic nervous system (Sympathetic and Parasympathetic nerves)
If light is STRONG--> your pupil will contract(Miosis) to prevent burning of the eye
If light is WEAK-->your pupil will expand (Mydriasis) to allow an enough amount of light to enter to the eye to let you see.
Also your lens in your eye contract and relax (ACCOMMODATION) for near and far vision

Answer 9

It is to vary the amount of light that reaches the retina at the back of the eye, in order to protect the optic nerves that carry visual information to the brain . You also have cells in your eyes called cones and rods that are placed at different angles from each other. Cones work in the light and rods work in the dark (night vision). They change over when you go from dark to light thats why your eyes sting when you go from a dark place to light place.

Answer 10

To control the amount of light going into the eye. Too much light can damage the eyes, therefore, we need a mechanism for light control