Light and Human Vision

Light

Radiant energy that enables us to see. A form of energy transmitted by radiation. The eye is sensitive to it.

Radiant Energy

The energy of electromagnetic waves that can be visible or invisible to the human eye. It is the radiation emitted from the source.

Cornea

The dome shaped tissue covering the front of the eye and accounts for about 2/3 of the eye's optical power. Focuses the light entering the eye. Washed with tears to keep moist and provide a smooth first optical surface that light strikes.

Pupil

The aperture that allows light into the eye. Opening in the center part of the iris.

Iris

The colored portion of the eye. Regulates the size of the pupil.

Lens

The clear, curved, disk that sits behind the iris that bends and focuses light on the retina and accounts for about 1/3 of human visual ability. As we age it gradually hardens and becomes less flexible.

Vitreous Humor

The gel-like fluid within the eye that maintains the shape of the eye.

Retina

A thin layer of tissue that lines the back of the interior of the eye. It receives the light that the lens has focused, converts the light to neural signals and sends these signals through the optic nerve to the brain for visual recognition.

Sclera

The white of the eye. Provides protection and controls the eye's movements.

Adaptation

The change in the pupil size in reaction to the amount of light present. The pupil dilates to allow more light into the eye in low light conditions, and contracts in high

Accommodation

The ability to adjust the focus of the eyes as the distance between the individual and the object changes.
•Cornea bends light rays.
•The iris adjust the size of the pupil to control amount of light.
•Lens flexes and changes shape to focus the image on retina.

Rods

Sensitive to quantity of light and change. Provide for slightly off-axis and peripheral vision. Especially effective in medium and low light levels. No rods at the fovea.

Cones

Responsible for color vision. Especially effective for direct vision; highly concentrated at the fovea, provided visual acuity. Especially effective in medium and high light levels.

Fovea

A depression is a depression in the retina that contains only cones (not rods) and that provides our most acute eyesight.

Intrinsically Photosensitive Retinal Ganglion Cells (ipRGC)

Respond to optical radiation and contain melanopsin and affect the human circadian pacemaker (the day/night cycle). Discovered in 2007.