The Human Eye and the Colourful World – Key Vocabulary

A set of vocabulary flashcards summarising essential terms and definitions from the chapter on the human eye, vision defects, and optical phenomena such as dispersion and rainbows.

Cornea

Transparent, curved membrane at the front of the eyeball where most refraction of incoming light occurs.

Iris

Dark, muscular diaphragm behind the cornea that controls the size of the pupil and therefore the amount of light entering the eye.

Pupil

Variable opening in the centre of the iris through which light enters the eye.

Retina

Light-sensitive inner lining of the eye that contains photoreceptor cells and on which real, inverted images are formed.

Ciliary Muscles

Ring of muscles attached to the eye lens that alter its curvature to adjust focal length.

Accommodation (Power of Accommodation)

Ability of the eye lens to change its focal length to focus objects at various distances on the retina.

Least Distance of Distinct Vision (Near Point)

Minimum distance, typically about 25 cm for a normal young adult, at which an object can be seen clearly without eye strain.

Far Point

Greatest distance at which the eye can see objects clearly; infinity for a normal eye.

Myopia (Near-sightedness)

Defect in which distant objects appear blurred because images form in front of the retina; corrected with a concave lens.

Hypermetropia (Far-sightedness)

Defect in which nearby objects appear blurred because images form behind the retina; corrected with a convex lens.

Presbyopia

Age-related decrease in accommodation caused by weakening ciliary muscles and less flexible lens; often corrected with bifocal lenses.

Cataract

Condition in which the eye’s crystalline lens becomes cloudy, leading to partial or total loss of vision; treatable by surgery.

Concave Lens

Diverging lens used to correct myopia by shifting the image back onto the retina.

Convex Lens

Converging lens used to correct hypermetropia by providing extra focusing power to form images on the retina.

Bifocal Lens

Spectacle lens combining concave and convex segments to correct both distant and near vision, typically used for presbyopia.

Prism (Triangular Glass Prism)

Transparent optical element with inclined refracting surfaces that deviates and disperses light.

Angle of Prism

Angle between the two lateral refracting surfaces of a prism.

Angle of Deviation

Angle between the direction of the incident ray and the emergent ray after refraction through a prism.

Dispersion

Phenomenon in which white light splits into its constituent colours when passing through a prism.

Spectrum

Band of colours produced by dispersion of light; for white light it ranges from violet to red.

VIBGYOR

Mnemonic for the colour sequence Violet, Indigo, Blue, Green, Yellow, Orange, Red in a spectrum.

White Light

Light that contains all visible wavelengths and produces a complete spectrum like that of sunlight.

Rainbow

Natural atmospheric spectrum formed by dispersion, internal reflection, and refraction of sunlight in water droplets.

Contact Lens

Thin corrective lens placed directly on the eye’s surface, alternative to spectacles for vision correction.

Optic Nerve

Bundle of nerve fibres that transmits electrical signals from the retina to the brain for image perception.