Early form of refractive surgery involving controlled surgical incisions on the periphery of the cornea causing the surface to flatten as it heals.
R (Radial Keratotomy to Rod)
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.
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.
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.
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.
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.
Atrophy and pigment changes in the retina causing night blindness and gradual loss of the visual field. Incurable and eventually leads to blindness.
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.
Light sensitive retinal cells responsible for peripheral and night vision.