Kinds of lens
Progressive lens
A lens whose power changes gradually from distance at the top to reading at the bottom, with no visible line.
Illustrative · the shape of the principle, not measured data
In more depth
A progressive lens changes power smoothly down its face: distance through the top, an intermediate corridor, and reading at the bottom, with no line anywhere. You choose a distance by where you look through the lens, lowering the eyes to read and raising them to see across a room.
Changing power continuously has a geometric price — softer areas either side of the corridor — so the design, and how precisely the lens is fitted to your pupil, decide how wide and calm the clear zones feel. Two progressives with the same prescription can wear very differently.
Related terms
CorridorThe channel of clear vision running down the center of a progressive, connecting the distance and reading zones.Peripheral distortionThe soft, swimming zones beside a progressive's corridor — a geometric consequence of continuous power change, present in every progressive ever made. Better designs manage it; none eliminate it.Fitting heightThe vertical distance from your pupil center to the bottom of the lens in your chosen frame. The most common cause of progressive remakes when wrong.Addition (ADD)The extra reading power added to the lower part of a progressive or bifocal. Typically starts near +1.00 in the early forties and usually settles near +2.50 (up to +3.00 for close working distances).