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Blind people who still have eyes can sense the difference between light and dark.

Insects do perceive ultraviolet light, but their compound eyes don't focus as sharply as human eyes, so the energy is spread out over a larger area. The reason humans evolved to not see UV light is because the light has enough energy to damage the rods and cones. The lens absorbs it before it can reach the retina.

People don't see ultraviolet light, but the human retina can detect it.

If you wear special goggles that make you view everything upside down, after a few days your brain will adapt, again showing you the "correct" view. When the brain translates the image, it automatically flips it.

The eye acts exactly like a camera in the sense that the image formed on the retina is inverted (upside down).

The functioning of the eye is fairly simple, but there are some details you might not know: The vitreous humor is a transparent watery gel that supports the eye and allows for this distance.

Vitreous Humor: A certain distance is required to focus light.

Ciliary muscles surround the lens, relaxing to flatten it to image distant objects and contracting to thicken the lens to image close-up objects.

Lens: While most of the focusing of light is done by the cornea, the lens allows the eye to focus on either near or distant objects.

As the pupil dilates (gets bigger), more light enters the eye. The size of the pupil is determined by the iris, the contractile ring that is associated with eye color. Iris and Pupil: Light passes through the cornea and aqueous humor through an opening called the pupil.The aqueous humor helps to shape the cornea and provides nourishment to the eye. Aqueous Humor: The fluid beneath the cornea has a composition similar to that of blood plasma.The eyeball is rounded, so the cornea acts as a lens. Cornea: Light enters through the cornea, the transparent outer covering of the eye.After puberty, eye growth is negligible.To understand how the eye sees, it helps to know the eye structures and functions:

From the second year of life until puberty, eye growth progressively slows. Until after their first month of life, most newborns lack complete retinal development, especially in the area responsible for visual acuity. During the remainder of the prenatal period, eye structures continue to enlarge, mature and form increasingly complex neural networks with the visual processing regions of the brain.Īt birth, an infants eyes are about two-thirds the size of adult eyes. The major structures of the eye- the retina, lens, and eyeball coats- are initially formed by the fifth month of fetal development. The signals are then sent to the brain, which interprets them as visual images.Įye formation begins during the end of the third week of development when outgrowths of brain neural tissue, called the optic vesicles, form at the sides of the forebrain region. The eye changes the rays into electrical signals. Light rays enter the eye through transparent tissues. Instead, it receives light reflected from the objects. We use our eyes for reading, working, watching television and many other activities. "The human eyeball measures only about 1 inch" "The eyeball is roughly about an inch in diameter brimming with many specialized structures and tissues." Eye Care, Eye Glasses and Contact Lenses. "The adult human eye weighs approximately 7.5 grams and measures approximately 24.5 millimeters in its anterior-to-posterior diameter." Magill's Medical Guide Revised Edition Brain. "The dimensions of the eye are reasonably constant, varying among individuals by only a millimetre or two the sagittal (vertical) diameter is about 24 millimetres (about one inch) and is usually less than the transverse diameter." "The eyeball is about 1 inch (2.5 cm) in diameter"Įncyclopedia Britannica Macropedia: Sensory Reception.