spec lenses Flashcards
1
Q
distinguish between sperical, cylindrical and toric lenses (1)
A
sphere:
- power the same in every meridian
cylinder:
- power in one meridian
toric:
- two power across two orientations perpendicular to each other
2
Q
identify the 3 forms of toroidal surfaces
A
capstan formation
barrel formation
tyre formation
3
Q
distinguish between spectacle magnification (SM) and relative spectacle magnification (RSM) (1)
A
SM - image size due to spec lens
RSM - retinal image size
4
Q
outline Knapp’s law
A
there will be no image size difference on the retina if the lens is placed at the anterior focal point of the eye
