DISPENSING

Question 1

Effect of dispensing aspheric compared to spherical

Answer 1

• flatter back surface
• reduced edge thickness
• reduced substance/ weight
• improved cosmesis
• reduced spec mag

Question 2

Importance of accurate centration

Answer 2

To avoid unwanted prismatic effect causing visual issues such as diplopia

Question 3

Calculation for new Rx with changed BVD

Answer 3

1. Put in cross cyl
2. Feff = F / 1-dF

Question 4

Calculation for aspheric saga

Answer 4

1. Radii of curvature; r = n - 1 / F
2. Sag = r/p + /(r/p)2 - y2/p

Question 5

Four classes of mechanical strength

Answer 5

F = low impact
A = high impact
B = medium impact
S = increased robustness

Question 6

British standards for safety spectacles

Answer 6

BS EN 166 and BS EN 167