The Human Eye and the Colourful World Practices

A set of vocabulary flashcards covering the anatomy of the human eye, vision defects, and optical phenomena such as dispersion, refraction, and scattering of light.

Retina

A light-sensitive screen upon which the eye's lens system forms an inverted real image of an object.

Cornea

A thin membrane that forms the transparent bulge on the front surface of the eyeball through which light enters the eye.

Eyeball diameter

The approximately spherical shape of the eye has a diameter of about $2.3\,cm$.

Iris

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

Pupil

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

Crystalline lens

The part of the eye that provides the finer adjustment of focal length required to focus objects at different distances on the retina.

Ciliary muscles

Muscles that modify the curvature of the eye lens to change its focal length for focusing on near or distant objects.

Accommodation

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

Least distance of distinct vision

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.

Near point

Another term for the least distance of distinct vision; the closest point at which an object is seen clearly.

Far point

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 because the image is formed in front of the retina.

Hypermetropia

Also known as far-sightedness; a defect where a person can see distant objects clearly but cannot see nearby objects distinctly because the image is focussed at a point behind the retina.

Presbyopia

A vision defect arising due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens with aging, making it difficult to see nearby objects clearly.

Bi-focal lenses

Corrective lenses consisting of both concave (upper portion for distant vision) and convex (lower portion for near vision) lenses.

Angle of the prism

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

Angle of deviation ($\angle D$)

The angle between the direction of the incident ray and the direction of the emergent ray.

Spectrum

The band of the coloured components of a light beam, typically identified by the acronym VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, and Red).

Dispersion

The splitting of white light into its seven component colours by a prism.

Rainbow

A natural spectrum caused by the dispersion of sunlight by tiny water droplets in the atmosphere, always formed in a direction opposite to the Sun.

Atmospheric refraction

The refraction of light caused by the Earth’s atmosphere, which has a gradually changing refractive index.

Twinkling of stars

A phenomenon due to atmospheric refraction where the apparent position of a star fluctuates and the amount of starlight entering the eye flickers.

Tyndall effect

The phenomenon of scattering of light by colloidal particles in a heterogeneous mixture, making the path of the light beam visible.