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R (Radial Keratotomy to Rod)

Radial Keratotomy

Friday, January 15th, 2010

Early form of refractive surgery involving controlled surgical incisions on the periphery of the cornea causing the surface to flatten as it heals.

Reflection

Friday, January 15th, 2010

The portion of rays not absorbed by a substance and therefore rebounded at an angle equal and opposite to the incident light except in the case of where the incident light is at 90 degrees to the plane. Here the reflected light is returned along the same path as the source.

Refraction

Friday, January 15th, 2010

Deflection of light at the point where two mediums of different density meet eg. air and water, air and glass or glass and plastic etc. The greater the difference in density the greater the angle of deflection. It is probably the single most important scientific aspect of the correction of sight. Without it optics would not exist. Term also used when referring to a sight test.

Refractive Index

Friday, January 15th, 2010

The term used when referring to the density of a substance such as glass or plastics. The more dense the material the less curvature needed to produce a given power therefore high index spectacle lenses are thinner than conventional lenses.

Retina

Friday, January 15th, 2010

The membrane at the back of the eye that receives the visual images and converts them into electrical impulses which are then transmitted to the brain along the optic nerve.

Retinal Detachment

Friday, January 15th, 2010

The painless breaking away of the retina from the wall of the eye. Often associated with an increased level of floaters and or flashing lights. Requires immediate treatment. Also see retinal hole and scleral buckle.

Retinal Hole

Friday, January 15th, 2010

With age the vitreous (the jelly like substance filling the space between the crystalline lens and the retina) becomes more fluid resulting in an increased state of movement. The effect of this is to pull away small portions of the retina causing a hole or even a detachment.

Retinitis Pigmentosa

Friday, January 15th, 2010

Atrophy and pigment changes in the retina causing night blindness and gradual loss of the visual field. Incurable and eventually leads to blindness.

Retinoblastoma

Friday, January 15th, 2010

Hereditary. A malignant tumour originating in the retinal cells. If untreated produces secondary tumours that gradually fill the eye and enter the brain via the optic nerve causing death.

River Blindness

Friday, January 15th, 2010

See onchocerciasis.

Rod

Friday, January 15th, 2010

Light sensitive retinal cells responsible for peripheral and night vision.