Conjunctiva — a transparent mucous membrane that covers the outer surface of the eyeball except for the cornea. It also lines the inner surface of the eyelid. Cornea — the clear cone over the front part of the eye. It is responsible for most of the optical power of the eye. Choroid — a layer of the eye found between the retina and the sclera.
It contains major blood vessels and provides nourishment to the outer layers of the retina. Fovea — is located in the center of the macula. It provides the sharpest vision. Iris — a colored circular muscle that gives us the color of our eyes. It is responsible for controlling the amount of light that gets into the eye.
Lens — is responsible for bringing rays of light into focus on the retina. It is a clear oval structure suspended behind the iris which can contract and expand as needed to provide additional focusing power.
Macula — a small central area of the retina responsible for fine central visual acuity. Optic Nerve — carries the light impulses for sight from the retina to the brain. Retina — the most active area of the eye where the rods and cones are found. Evolution Evidence 2. Natural Selection 3.
Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1.
Your rods detect colours in shades of grey and they can sense shape and movement. You have about million rods. They are densest at the edge of your retina and don't need a lot of light to work. So you use them in dim light. Your cones see colours. You have three different types of cone, each of which contains a pigment that responds to a different wavelength of light - green, red or blue.
If your brain receives impulses from more than one type of cone at the same time, you see mixed colours. You have around 7 million cones. They are densest at the centre of your retina and need bright light to function. This is why, when it's dark, you can only detect shades of grey. Before light rays touch your retina, they travel through a disc-shaped lens. Your lens bends light rays to focus them exactly on your retina.
Muscles in your eye can change the shape of your lens, thereby adjusting its light-bending power. This allows you to focus on different objects. By focussing images on your retina, your lens turns them upside down.
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