Question A
By use of a diagram show a spherocylindrical lens design (cross section) for a negative
sphere with a positive cylinder with the axis of the cylinder being horizontal (5)
Question B
Transpose the spherocylindrical form: +3.75 / +2.25 x 67½
i. negative cylinder form
ii. crossed cylinder form
iii. toric form with a -6.00D base curve
iv. toric form with a -1.50D sphere curve (16)
Question C
The following lenses are held together in close contact, what single lens can be used to
neutralise the combination
a) +2.50 / +2.50 x 180
b) +1.50 / +1.50 x 90
c) -6.00
d) -2.00 x 180 / -3.50 x 90 (14)
Question D
The following prisms are combined, what is the single resultant prism produced
a) 4? base up
b) 3? base along 45
c) 4? base along 120
d) 6? base along 220 (20)
Question E
Describe the following terms:
i. Refractive index
ii. Curve variation factor
iii. Abbé value
iv. Specific gravity
v. Reflectance
Discuss how you would use these headings to discuss with a patient the best lens choices

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