Sight

By Valerie Tema

How the eye works

• CORNEA: Light first enters a person’s eye through his/her cornea. The Cornea bends the light to go on the the pupil.

• PUPIL/IRIS: The pupil is the black part in the middle of the eye. The iris is the colored part surrounding it. These allow the light to pass farther into the eye.

• LENS: The lens, like the lens of a camera, brings the light into focus.

• RETINA: The retina is at the back of the eye. It contains photoreceptor nerve cells. Those take the light and make them into electrical impulses. The impulses are sent to the OPTIC NERVE of the eye, and the optic nerve transmits the information

to the brain. That’s how you see.

Here’s a picture.

How dogs see

• Dogs aren’t colorblind in the sense that they can only see black, white and gray colors. They have trouble seeing greens and reds, and see mostly in blues and yellows.

• They can see flickering light better than humans can. For example, on TV we see continuous action, but dogs may see a serious of moving frames.

• Their vision isn’t as sharp and detailed as humans’, however they can detect motion and see in the dark much better than humans can.

Cataracts

• A CATARACT is a clouding the lens. The lens is contained in a capsule. When old cells die, they become trapped in the capsule. When the old cells accumulate, they start to cloud up your lens and make all the images you see blurry.

• Cataracts are a natural result of aging. Diabetes and alcoholism have also been known to cause cataracts.

Causes of visual impairments

• The number one cause of visual impairment is Cataracts (47%).

• Behind it are glaucoma (12.3%), age-related macular degeneration (AMD) (8.7%), corneal opacities (5.1%), diabetic retinopathy (4.8%), childhood blindness (3.9%), trachoma (3.6%), and onchocerciasis (0.8%).

Seeing stars

• Do you ever see stars after you sneeze, when you have a headache, or when you get up quickly after lying down?

• There is a thick gel in our eyeballs that keeps them nice and plump. This gel can rub against the retina, stimulating the part of the eye that is responsible for creating images in out brain. Whether or not any actual light is entering the eye, any stimulation of the retina will be translated as light.

• Sneezing could cause pressure on the eye or stimulate the nerves that have to do with it.

• After you stand up quickly, blood pressure might drop and deprive your brain of oxygen, changing the eye’s environment or affecting

the optic nerve. • This is also why you see a kind of light show when you shut your

eyelids really tight.

Myths about Vision

• Myth: Sitting too close the to TV is bad for the eyes. Parents have been saying this forever, but there’s never been any actual evidence that sitting close to the TV is damaging.

• Myth: Using the computer for too long will damage the eyes. This also isn’t true. But, it has been shown that when you sit in front of the computer for awhile, you blink less, which may dry out your eyes and/or cause a strain on them.

References

• http://www.ehow.com/how-does_4564351_the-eye-work.html• http://www.blundelloptometry.com/images/eye_diagram.gif• http://www.vetinfo.com/dogsee.html• http://www.stlukeseye.com/Conditions/Cataracts.asp• http://www.who.int/blindness/causes/en/• http://www.livescience.com/mysteries/080414-llm-stars-sneeze.html• http://kidshealth.org/parent/general/eyes/vision_facts_myths.html• http://www.graphicsdb.com/data/media/580/3D%20Waves%20Optical

%20Illusion.jpg• http://www.wildlifeonline.me.uk/images/graphics/dog_vision.jpg• http://www.j9sk9s.com/_borders/How_Dogs_See.jpg• http://harvardeye.com/cataract/images/imgCataract.jpg

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