Special Lenses Flashcards
1
Q
What do all Spherical lenses have
A
- All meridians have the same refractive power
-when the light hits any point it will refracted by the same amount and forms a point image - all medrians pass through the centre
2
Q
Cyndrical lenses
A
A Lens where one of the principal meridians has zero refractive power.
-curved in the horizontal plane- producing refractive power
- no curve in the vertical plane- giving no refractive power
3
Q
Where are the principle medrians located to each other for the cyndrical lenses
A
The principle meridians are the horizontal and vertical which are Located at 90 degrees to each other
4
Q
What a toric lenses
A
A toric lens is where the two principal meridians have different curvatures e.g. different curvature in horizontal and vertical Plane
- a toric lens has different focal strength in the horizontal and vertical plane
5
Q
What does different shaped curves mean
A
Different refractive powers in each meridian
6
Q
What do toric lens produce
A
They produce 2 line loci at 90 degrees to each other
