Glossary

Refraction - Determination of the refractive power of the eye and the degree to which this differs from the normal eye by presenting a series of graded lens powers to give the clearest vision. This will determine whether a spectacle or contact lens prescription is required and the strength needed. This is usually performed by an Ophthalmologist or Optometrist.

Refractive Error - Defect of the eye's focusing system resulting in a blurred image on the retina. This can be due to astigmatism, myopia or hyperopia and can usually be corrected by glasses, contact lenses, or refractive surgery.

Refractive Surgery - Correction of refractive error by surgical means. This can be by laser (LASIK and LASEK) or by clear lens extraction (CLE).

Retina - The light sensitive membrane that lines the interior of the eye and covers the rear two-thirds of the eyeball. It converts images from the eyes optical system into electrical impulses that are sent to the brain via the optic nerve. The retina is made up of 10 different layers containing nerve cells, neurons and photoreceptors. The outer part of the retina next to the choroid is pigmented and called the retinal pigment epithelium (RPE). The inner part of the retina contains the photoreceptors (rods and cones) and their associated nerve fibres.

Retinal Detachment - Separation of the retina from the underlying retinal pigment epithelium (RPE). Commonly occurs due to holes or tears in the retina allowing fluid from the vitreous cavity to accumulate under the retina. Vision is lost in the affected part of the retina. Immediate surgical repair is needed.

RPE - Retinal Pigment Epithelium - The pigmented cell layer that forms the outer part of the retina and nourishes the retinal visual cells (photoreceptors). It lies firmly attached to the underlying choroid and overlying photoreceptors. The RPE is composed of a single layer of hexagonal cells densely packed with pigment granules to prevent stray light passing through the eyeball.