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Access Excellence Classic Collection

How We See:
The First Steps of Human Vision:


Astigmatism: A defect of the lens resulting in blurred vision due to the fact that the lens does not focus light rays to a focal point.

Aqueous humor: The fluid that fills the space in the vertebrate eyeball which is in front of the lens.

Chromophore: A term used to describe a molecule that appears to be colored because it absorbs light in the visible region.

Cone Cells: One of two types of light-sensitive cells in the retina. Responsible for vision in bright light and allowing detection of colors.

Cornea: A transparent covering at the front of the vertebrate eye. Covers the iris and the pupil. Its surface curves slightly to bend light rays as they pass through.

Iris: The doughnut shaped colored part of the eye. The iris regulates the amount of light entering the eye.

Lens: A transparent biconvex disk consisting of a firm but elastic jelly type material. Works with the cornea to focus light onto the retina. The lens changes thickness depending on whether the eye is looking at an object up close or an object in the distance.

Night Blindness: A term used to describe the condition of having decreased visual acuity at low light levels. Often results from defects in the rod cells.

Optic Disk: Portion at the back of the eye at which the neurons in the retina attach to the optic nerve.

Optic Nerve : The nerve that emerges from the optic disk and goes to the brain. This nerve carries the impulses made in the retina to the brain.

Photo-excitation: The process a molecule undergoes when it absorbs light energy.

Photoreceptors: Cells in the retina that receive light that enters the eye. The photoreceptors are responsible for changing light into impulses that are sent to the brain.

Photosensitive: A term used to describe a molecule or material that responds to light.

Pupil: Hole in the center of the iris, through which the light enters. Can be either round, as in humans, or slit-shaped, as in many nocturnal animals.

Retina: The innermost layer of the eyeball. Light is imaged onto the retina by the lens. The retina contains three layers of neurons, including the photoreceptor neurons. The other neurons in the retina are responsible for sending impulse signals to the brain.

Rhodopsin: A protein found in the membrane of rod cells that is responsible for the absorption of light, thus leading to our ability to see.

Rod Cells: Cells in the retina that detect light. Rod cells are responsible for seeing at low light levels.

Spectroscopic: The term refers to the use of light (either lasers or lamps) to examine the molecule. The light interacts with the molecule to excite either the molecule's motions or electrons. This interaction provides a signature response that can be measured with laboratory equipment. The signals provide information about the molecule's motion, or structure or electronic states.

Transduction: The process of changing from one form of energy to another form of energy. In this unit transduction refers to the transformation of light energy into chemical energy.

Visual Pigment: The molecule in the retina that make it appear colored.

Vitreous Humor: Liquid contained in the space behind the lens of the vertebrate eyeball. Helps focus the light onto the retina.

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