Unit+3+Lenses

**Unit 3: Lenses

//__PINK EYE__//**

Pink eye, also known as conjunctivitis is an infection of the conjunctiva (the outer most layer of the eye that covers the sclera) __//Symptoms//__ -Itching -Swollen eyelids -Watery discharge -Irritation -Tearing -Redness

__//Causes//__ -Allergic (seasonal) -Viral -Bacterial


 * How can it be treated**

__//Allergic//__ -Cool compresses and artificial tears (eye drops)

__//Bacterial//__ -Treated with antibiotic eye drops or oitments

//__Viral__// -Could take 3 weeks to fully recover -- Cool compresses, artificial tears, and steroid drops



When light is shown through your eye. the cornea (outer-most part of eye) focuses light through a small opening called the pupil. Behind the pupil is the lens. The lens focuses light to the back of your eye, the retina. The lens can change its shape depending on what you're trying to focus on.



Some people's cornea isn't shaped right, so light ends up short of the retina. This can be corrected by placing a concave lens in front of the cornea. This refocuses the light to be exactly on the retina. The same thing can by done with a concave lens if the image is focused behind the retina. Note: You're nearsighted if the image shows up in front of the retina, and farsighted if it shows up behind the retina.

What happens to a beam of light when the concave and convex lenses are moved closer or farther apart?
As the concave and convex lenses move closer together, the amount that the beam of light bends outward decreases.



As the concave and convex lenses move further apart, the amount that the beam of light bends outward increases.

Nearsighted and Farsighted
If you are nearsighted, the image will form before your retina because your eyes are longer than normal, so that you could not see the image clearly.



A way to treat it is to wear a concave lens so that the image will form right on your retina.



If you are farsighted, the image will form behind you retina because you eyes are shorter that normal, so that you could not see the image clearly.



A way to treat it is to wear a convex lens so the the image will form right on your retina.