The Human Eye and the Colourful World

Vocabulary flashcards covering key terms and concepts from The Human Eye and the Colourful World (Chapter 10).

Retina

The light-sensitive membrane at the back of the eye where the image is formed; it converts light into electrical signals sent to the brain via the optic nerve.

Cornea

The transparent front membrane of the eye through which light enters; most refraction of light occurs at its outer surface.

Iris

The dark muscular diaphragm behind the cornea that controls the size of the pupil and thus the amount of light entering the eye.

Pupil

The opening in the iris that regulates the amount of light entering the eye.

Crystalline lens

The natural lens of the eye whose curvature is adjusted by ciliary muscles to focus on objects at different distances.

Ciliary muscles

Muscles that change the curvature of the lens to adjust focal length during accommodation.

Accommodation

The ability of the eye to adjust its focal length by changing the lens curvature to focus on near or distant objects.

Near point

The closest distance at which an object can be seen clearly without strain; about 25 cm for a normal young adult.

Far point

The farthest distance at which the eye can see clearly; for a normal eye this is infinity.

Myopia

Near-sightedness: distant objects are blurred because the image forms in front of the retina; corrected with concave (diverging) lenses.

Hypermetropia

Far-sightedness: near objects are blurred because the image forms behind the retina; corrected with convex (converging) lenses.

Presbyopia

Age-related loss of accommodation; near point recedes, making close reading difficult; corrected with bifocal or reading lenses.

Cataract

Clouding of the crystalline lens due to aging, causing partial or complete vision loss; surgically treatable.

Bi-focal lenses

Eyeglass lenses with two sections: an upper concave portion for distance vision and a lower convex portion for near vision.

Concave lens

A diverging lens used to correct myopia by spreading light rays so the image moves onto the retina.

Convex lens

A converging lens used to correct hypermetropia by bending light to form a focus on the retina.

Prism

A triangular glass block used to refract light; its angle defines dispersion and deviation effects.

Angle of incidence (i)

The angle between the incoming ray and the normal to the refracting surface.

Angle of refraction (r)

The angle between the refracted ray and the normal at the refracting surface.

Angle of emergence (e)

The angle between the emergent ray and the normal after leaving the second surface of a prism.

Angle of deviation (D)

The angle by which the incident ray is deviated from its original direction after passing through a prism.

Spectrum

The band of colours produced when white light is dispersed by a prism (VIBGYOR: Violet to Red).

Dispersion

Splitting of white light into its component colours due to different refraction for different wavelengths.

VIBGYOR

The sequence of colours in the visible spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red.

Tyndall effect

Scattering of light by colloidal particles, making the beam visible (e.g., sunlight through smoke or mist).

Scattering

The redirection of light by particles; causes blue colour of the sky because shorter wavelengths scatter more.

Atmospheric refraction

Refraction of light by Earth's atmosphere due to varying refractive index, causing apparent position shifts and sunrise/sunset timing changes.

Twinkling

Apparent flickering of stars caused by continuous refraction of starlight by the Earth's atmosphere.

Eye bank

An organization that collects, evaluates, and distributes donated eyes for transplantation and research; donor and recipient identities are confidential.

Corneal transplantation

Surgical replacement of a damaged cornea with a donor cornea to restore vision in corneal blindness.