The Eye
The light enters through the cornea which protects the eye.
Pupil - the adjustable opening in the center of the eye through which light enters. The pupil is a hole.
Iris - a ring of muscle tissue that forms the colored portion of the eye (its a muscle) around the pupil and controls the size of the pupil opening, thus controlling the amount of light entering the eye.
Lens - The transparent structure behind the pupil that changes shape to help focus images on the retina.
Accommodation - the process by which the eye’s lens changes shape to focus near or far objects on the retina.
Retina - The light-sensitive inner surface of the eye containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
Acuity - The sharpness of vision.
Nearsightedness - a condition in which nearby objects are seen more clearly than distant objects because distant objects focus in front of the retina.
Farsightedness - a condition in which faraway objects are seen more clearly than objects because the images of near objects are focused behind the retina.
The Retina
Rods - retinal receptors that detect black, white and gray; necessary for peripheral and twilight vision, when cones don’t respond.
Cones - Receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions; detect fine detail and give rise to color.
Light energy strikes the rods and cones producing chemical changes that generate neural signals.
The neural signals activate the bipolar cells which then activate the ganglion cells.
Axons of the ganglion cells converge to form the optic nerve (the nerve that carries neural impulses from the eye to the brain).
Blind Spot - the point at which the optic nerve leaves the eye, creating a “blind spot” because no receptor cells are located there.
Fovea - the central focal point in the retina, around which the eye’s cones cluster.
Actually part of the brain that migrates to the eye during fetal development.