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C
- carrier
- central field
- centration distance CD
- centration error of the instrument
- centration point CP
- clear lens
- coated lens
- combination frame
- concave lens
- condensing lens
- continuously-indicating focimeter
- contrast
- converging lens
- convex lens
- corneal plane
- Corneal Refraction
- corrective lens
- curved-form lens
- curved-top bifocal
- curved-top segment
- cylinder
- cylinder axis
- cylindrical lens
- cylindrical power
- cylindrical surface
- cylindrical test lenses
centration distance CD
Required horizontal distance between the centration points of a pair of lenses. NOTE1: This may be specified by monocular values, measured from the assumed centreline of the bridge of the nose or spectacle frame. NOTE2: If an inter-pupillary distance only is specified, this is taken to be the centration distance.