Vision

Sclera

'White of the eye'.

Fovea Centralis

A small depression in the retina of the eye where visual acuity is highest. The centre of the field of vision is focused in this region, where retinal cones are particularly concentrated.

Macula

An oval yellowish area surrounding the fovea near the centre of the retina in the eye, which is the region of keenest vision.

Rod Cell

BLACK AND WHITE. Function in less intense light. The optic discs of the cell contain photopigments. Used in night vision. In dim light, maximum visual acuity is at the periphery of the field (i.e. rods are located in the periphery of the retina).

Photopic

Eye works in high light intensities. These types of cones are concentrated at the fovea centralis.

Scotopic

Eye works under low light intensities.

Rhodospsin

Light-sensitive receptor protein involved in visual phototransduction. Found in the rods of the retina - extremely sensitive to light, therefore working best in low-light conditions.

Photopsin

Photoreceptor proteins found in the cone cells of the retina that are the basis of colour vision.

Vitreous Humor

Posterior chamber of eye (main cavity). Filled with intraocular fluid which contains collagen - liquid produced by ciliary body. With age, the gel shrinks and liquifies.

Cone Cell

Responsible for colour vision and function best in bright light. These cells are tightly packed in the fovea centralis, a rod-free area with thin, densely packed comes which reduce in numbers towards the periphery of the retina. Most of these cells are found towards the macula. Three different types of cone cells: Blue, Green and Red.

Photoreceptor Cell

Specialized neuron found in the retina that is capable of phototransduction (light converted into electrical signals). Proteins within this cell absorb photons, triggering a change in the cell's membrane potential.

Refraction

The bending of light as it enters a medium of different density. The curved surfaces of cornea and lens refract incoming light. Focuses onto retina. Objects at the centre of the visual field focus onto the fovea centralis. The Image is inverted and reversed.

Phototransduction

The process through which photons, elementary particles of light, are converted into electrical signals. Visual phototransduction occurs in the retina through photoreceptors, cells that are sensitive to light.

Retina

Third and inner coat of the eye. Layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. These are mainly of two types: the rods and cones.

Cornea

Transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, it refracts light - 'transparent window that lets light into the eye'.

Choroid

Vascular layer of the eye - lies between the retina and sclera. It provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract.