The Human Eye

The eye is like a camera: Light enters, is focused on a surface, and a picture is made.

Parts of the Human Eye

Light enters your eye through a clear portion of the sclera. The Sclera is the tough, white, outer covering of the eye

The cornea is a clear curved, tissue covering the front of the eye. It slightly bends the light as it goes through.

The pupil is simply a hole in the iris. It changes size to let different amounts of light in.

The iris is the colored part of the eye.

The iris is also a muscle that controls the size of the pupil. In bright light, the iris expands and the pupil gets smaller In low light, the iris contracts and the pupil gets bigger

The Eyelid is a thin pieces of skin that keeps the eye clean and protects. It also helps to spread our tears to all parts of the eye.

Directly behind the iris is the lens. The lens changes shape to focus the light that is coming into our eyes. Its shape is convex, meaning it curves outward on both sides.

Behind the lens is a clear gel called the vitreous humor. The Vitreous Humor is a thick transparent liquid that fills the center of the eye. It gives the eye its shape Mostly made of water.

The retina is the tissue that lines the back of the eye. Its job is to converts light rays into electrical signals to send to the brain It contains two types of light-sensitive cells: rods and cones.

Rod shaped cells sense black and white and work in low light. Cone shaped cells sense color and must have more light than rods to work. Three kinds of cones: L-cones M-cones S-cones

The rods and cones send messages to the brain through the optic nerve. The brain makes sense of all the information it is receiving and tells us what we are seeing

. In your brain, the sight center is in the back, between your ears. This location explains why a blow to the back of your head might cause blindness, even though your eyes are fine.

Two Causes of Color Blindness Genetic (you are born with these types) Sometimes a cone is missing, or the cone does not recognize the correct wavelengths of light. L- and M-cone problems result in red-green color blindness, the most common. (left) Color Vision Test: If you see “5” = normal color vision; if you see “2” = red/green color deficiency (right) Color Vision Test: If you see “45” = normal color vision; if you see “spots” = red/green color deficiency Most people with color blindness are able to distinguish a small range of colors, so really, the term "color-deficiency" is more appropriate than "color-blindness."

2. Non-Genetic (these types occur after birth) Accidents that damage the vision center of the brain, cataracts, glaucoma, Parkinson’s Disease can cause S-cone problems, diabetic retinopathy can affect color vision