ABO OPHTHALMIC DISPENSING
MIDTERM EXAM QUESTIONS AND
ANSWERS 100% VERIFIED. JUST
RELEASED
1. Which of the following describes the transposition of the prescription +2.00 -1.50 x 045?
A. +0.50 +1.50 x 045
B. +0.50 -1.50 x 135
C. +2.00 +1.50 x 135
D. +0.50 +1.50 x 135
Answer: D
Conceptual Explanation: To transpose, add the sphere and cylinder to get the new sphere
(+0.50), change the sign of the cylinder (+1.50), and change the axis by 90 degrees (135).
2. Using Prentice’s Rule, calculate the induced prism for a +4.00 D lens decentered 5mm
inward.
A. 0.2 prism diopters Base Out
B. 2.0 prism diopters Base In
C. 2.0 prism diopters Base Out
D. 0.2 prism diopters Base In
,Answer: B
Conceptual Explanation: Prism = Power x Decentration (in cm). 4.00 x 0.5cm = 2.0 prism
diopters. For a plus lens, decentering inward (toward the nose) creates Base In prism.
3. What is the standard index of refraction for CR-39 (Plastic) lenses?
A. 1.586
B. 1.498
C. 1.600
D. 1.523
Answer: B
Conceptual Explanation: CR-39, the standard plastic material, has a refractive index of
approximately 1.498. 1.523 is Crown Glass and 1.586 is Polycarbonate.
4. A patient’s RX is -10.00 D at a 12mm vertex distance. If the frame sits at a 17mm vertex
distance, what is the effective power?
A. -9.52 D
B. -10.50 D
C. -11.25 D
D. -9.25 D
Answer: A
, Conceptual Explanation: When a minus lens moves further from the eye, it loses power
(becomes less minus). Formula: F_new = F / (1 + dF). The change in distance is 0.005m. -10
/ (1 + (0.005 * -10)) = -.95 = -10.52 D? Wait, minus lens moving away needs MORE
minus to maintain effectivity. Actually, for the eye to perceive the same power, the lens
power must be adjusted. A minus lens moving away becomes WEAKER, so we need a
STRONGER minus. However, the question asks for effective power of the existing lens: F_eff
= F / (1 + dF) = -9.52 D.
5. The ‘Abbe Value’ of a lens material refers to its:
A. Impact resistance
B. Specific gravity
C. Refractive index
D. Dispersive power (chromatic aberration)
Answer: D
Conceptual Explanation: The Abbe value (or v-value) is a measure of the material’s
dispersion. A lower Abbe value indicates higher chromatic aberration.
6. What is the ‘Boxing System’ term for the horizontal distance between the vertical lines
tangent to the edges of the lens?
A. B measurement
B. DBL
C. A measurement
MIDTERM EXAM QUESTIONS AND
ANSWERS 100% VERIFIED. JUST
RELEASED
1. Which of the following describes the transposition of the prescription +2.00 -1.50 x 045?
A. +0.50 +1.50 x 045
B. +0.50 -1.50 x 135
C. +2.00 +1.50 x 135
D. +0.50 +1.50 x 135
Answer: D
Conceptual Explanation: To transpose, add the sphere and cylinder to get the new sphere
(+0.50), change the sign of the cylinder (+1.50), and change the axis by 90 degrees (135).
2. Using Prentice’s Rule, calculate the induced prism for a +4.00 D lens decentered 5mm
inward.
A. 0.2 prism diopters Base Out
B. 2.0 prism diopters Base In
C. 2.0 prism diopters Base Out
D. 0.2 prism diopters Base In
,Answer: B
Conceptual Explanation: Prism = Power x Decentration (in cm). 4.00 x 0.5cm = 2.0 prism
diopters. For a plus lens, decentering inward (toward the nose) creates Base In prism.
3. What is the standard index of refraction for CR-39 (Plastic) lenses?
A. 1.586
B. 1.498
C. 1.600
D. 1.523
Answer: B
Conceptual Explanation: CR-39, the standard plastic material, has a refractive index of
approximately 1.498. 1.523 is Crown Glass and 1.586 is Polycarbonate.
4. A patient’s RX is -10.00 D at a 12mm vertex distance. If the frame sits at a 17mm vertex
distance, what is the effective power?
A. -9.52 D
B. -10.50 D
C. -11.25 D
D. -9.25 D
Answer: A
, Conceptual Explanation: When a minus lens moves further from the eye, it loses power
(becomes less minus). Formula: F_new = F / (1 + dF). The change in distance is 0.005m. -10
/ (1 + (0.005 * -10)) = -.95 = -10.52 D? Wait, minus lens moving away needs MORE
minus to maintain effectivity. Actually, for the eye to perceive the same power, the lens
power must be adjusted. A minus lens moving away becomes WEAKER, so we need a
STRONGER minus. However, the question asks for effective power of the existing lens: F_eff
= F / (1 + dF) = -9.52 D.
5. The ‘Abbe Value’ of a lens material refers to its:
A. Impact resistance
B. Specific gravity
C. Refractive index
D. Dispersive power (chromatic aberration)
Answer: D
Conceptual Explanation: The Abbe value (or v-value) is a measure of the material’s
dispersion. A lower Abbe value indicates higher chromatic aberration.
6. What is the ‘Boxing System’ term for the horizontal distance between the vertical lines
tangent to the edges of the lens?
A. B measurement
B. DBL
C. A measurement
