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| PHOTOCHROMIC
The ability of a mineral or plastic lens to become darker or lighter depending on the amount of available light.
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PIGMENTOSA RETINITIS
A hereditary disorder in which first the peripheral rods and eventually the entire retina gradually degenerates, leading to total blindness. |
PLASTIC LENSES
Manufactured from a base of polymerized resin, plastic lenses are of very high optical quality. They are three times lighter than mineral lenses as well as shock-resistant and can be tinted or photochromic. |
PRESBYOPIA
An abnormality of vision that results when the crystalline lens thickens with age. As it becomes more rigid, it is less able to adjust and near vision deteriorates. After age forty, no one is immune from presbyopia! |
PROGRESSIVE LENSES
Lenses whose power changes progressively from far vision in the upper half of the lens to near vision in the lower half.There is no optical or aesthetic break in the lens. They include the famous Varilux lenses that provide clear vision at every distance. Progressive lenses are the modern way to correct presbyopia for those who prefer eyeglasses to contact lenses. |
PROGRESSIVE MYOPIA
A myopia that continues to increase after maturity and can reach very high values. |
PUPIL
The central opening in the iris. It acts like the diaphragm on a camera: its diameter varies with the amount of light. (see EYE) |
PUPILLOMETER
An instrument for making a monocular measurement of interpupillary distance. |
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