The Human Eye and the Colourful World

Vocabulary flashcards covering the anatomy of the human eye, vision defects, and optical phenomena such as dispersion, atmospheric refraction, and the Tyndall effect.

Retina

A light-sensitive screen in the human eye on which the lens system forms an image.

Cornea

A thin membrane through which light enters the eye, forming a transparent bulge on the front surface of the eyeball.

Eyeball diameter

The human eyeball is approximately spherical in shape with a diameter of about $2.3\,cm$.

Iris

A dark muscular diaphragm behind the cornea that controls the size of the pupil.

Pupil

A structure in the eye that regulates and controls the amount of light entering the eye.

Power of Accommodation

The ability of the eye lens to adjust its focal length using the ciliary muscles.

Near point of the eye

The minimum distance at which objects can be seen most distinctly without strain, which is about $25\,cm$ for a young adult with normal vision.

Far point of the eye

The farthest point up to which the eye can see objects clearly, which is infinity for a normal eye.

Cataract

A condition at old age where the crystalline lens becomes milky and cloudy, causing partial or complete loss of vision.

Myopia

Also known as near-sightedness, a defect where a person can see nearby objects clearly but cannot see distant objects distinctly.

Hypermetropia

Also known as far-sightedness, a defect where a person can see distant objects clearly but cannot see nearby objects distinctly.

Presbyopia

A defect of vision caused by ageing where the power of accommodation decreases and the near point gradually recedes.

Bi-focal lenses

Commonly used to correct both myopia and hypermetropia, consisting of a concave lens in the upper portion for distant vision and a convex lens in the lower part for near vision.

Angle of the prism

The angle between the two lateral faces of a triangular glass prism.

Angle of deviation

The angle at which the emergent ray bends relative to the direction of the incident ray when passing through a prism.

Spectrum

The band of the coloured components of a light beam.

Dispersion

The splitting of white light into its seven component colours (VIBGYOR).

Tyndall effect

The phenomenon of scattering of light by colloidal particles, making the path of the beam visible.

Atmospheric refraction

The refraction of light by the earth's atmosphere due to gradually changing refractive index.

Advance sunrise and delayed sunset

Phenomena caused by atmospheric refraction where the Sun is visible about $2$ minutes before actual sunrise and $2$ minutes after actual sunset.