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Optical Glossary

Fri 24th Aug 2007 - 2:53 pm - Back to Article Selection

Aqueous Humour

Aqueous humour is a thick watery substance located in the anterior segment or front third of the eye and provides nutrients to the lens and cornea. The pressure from the aqueous humour helps maintain the shape of the cornea. Normally the aqueous and vireous humour do not mix as the lens and zonule of zinn are located between the two areas.

Ciliary Zone

The ciliary zone is the region of the iris which does not comprise the pupillary zone and extends to the ciliary body.

Dilator Pupillae

The dilator pupillae is a muscle of the iris which functions to dilate the pupil.


A dioptre is a unit of measurement used to quantify the optical power of a lens and is equal to the reciprocal of the focal length (m) of that lens.


The fovea or fovea centralis is a region of the eye located in the centre of the macula which allows sharp vision such as is required where high definition information is needed ie. reading. The fovea is densely packed with light sensitive cells and while it occupies only 1% of the total retina over 50% of the visual cortex is involved in processsing the information it provides.

Intraocular Lens

Intraocular lenses are implanted into the eye usually as a replacement for the existing lens as a treatment for cataracts or to correct vision problems.


The macula or macula lutea is a structure near the centre of the human retina with a diameter of approximately 1.5mm which houses the fovea and foveola.

Pupillary Zone

The pupillary zone is the innermost region of the iris and forms the boundary of the pupil.

Refractive Power

Refractive power, otherwise known as optical power or dioptric power is the degree of convergence or divergence a lens or curved mirror applies to light which interacts with it and is equal to the reciprocal of the focal length (m) of he device. Refractive power is most commonly measured in dioptre.


The scotoma, otherwise known as the blind spot is present in all normal mammalian eyes. The blind spot is the area of the visual field where there are no photoreceptor cells on the retina, the point at which the optic nerve passes through the retina and interfaces with the retinal nerves. The blind spot is not normally noticeable as the brain is able to "e;fill in"e; the blank spot using information from the other eye and surrounding areas of the retina.

Sphincter Pupillae

The sphincter pupillae is a muscle of the iris which functions to constrict the pupil.

Suspensory Ligament

The suspensory ligament is the collective term for the zonular fibres which connect the lens to the rest of the eye.

Visual Cortex

The visual cortex is the region of the brain responsible for interpreting visual information from the eyes. The visual cortex is comprised of a number of regions including the primary visual cortex (V1) and the extrastriate visual cortical areas (V2, V3, V4, V5). The visual cortex is supplied with blood by a branch of the posterior cerebral artery.

Zonule of Zinn

The Zonule of Zinn is a ring surrounding the lens comprised of fibrous strands which connect the ciliary body to the lens. The zonular fibres maintain the position of the lens in 3 dimensional space and allow the focusing power of the eye to be changed by varying the tension of the fibers through dilation or contraction of the ciliary muscle.

Disclaimer: The author is not a medical doctor, optician, ophthalmologist or any other medical professional, this article has been compiled using a variety of internet reference sources and while every effort has been made to ensure accuracy this cannot be guaranteed. No preference for product or brand is inferred or intended and the contents of this article are not to be used in whole or in part to inform a decision regarding any aspect of contact lens use.

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