ABO NOCE Basic Opticianry Applying Prentice's Rule 5 — Questions and Answers
Question 1: A lens is +2.00 -4.00 × 090. A patient looks through a point 4 mm temporal to the OC in the right eye. What is the horizontal prismatic effect?
- 0.80Δ base in (Correct answer)
- 0.80Δ base out
- 1.60Δ base in
- 0.40Δ base out
Correct answer: 0.80Δ base in
Axis 090 means the cylinder acts in the 180° (horizontal) meridian; horizontal power = +2.00 + (-4.00) = -2.00 D; Δ = 2.00 × 0.4 = 0.80Δ; minus lens with OC nasal to gaze = base in.
Question 2: Prentice's Rule states that prism is induced whenever the eye looks through any point other than the:
- Geometric center of the lens
- Optical center of the lens (Correct answer)
- Segment center of a bifocal
- Major reference point in a single-vision lens
Correct answer: Optical center of the lens
The optical center is the only point in the lens where light passes without prismatic deviation.
Question 3: A patient requires 3.00Δ base down OD and the lens power is +6.00 D. Instead of grinding prism, the OC is shifted. How far and in which direction?
- 5 mm upward (Correct answer)
- 5 mm downward
- 0.5 mm upward
- 18 mm downward
Correct answer: 5 mm upward
d = 3.00/6.00 = 0.5 cm = 5 mm; for a plus lens, shifting the OC upward places the eye below it, inducing base-down prism.
Question 4: A -8.00 D contact lens is centered on the eye. The patient then fixates 3 mm nasally from center. How much prism is induced?
- 2.40Δ (Correct answer)
- 0.24Δ
- 24.0Δ
- 0Δ
Correct answer: 2.40Δ
Δ = 8.00 × 0.3 = 2.40Δ; Prentice's Rule applies to contact lenses exactly as it does to spectacle lenses.
Question 5: When a patient's measured binocular PD exceeds the frame's optical center distance, what type of prism is induced for a plus lens wearer?
- Base in (Correct answer)
- Base out
- Base up
- Base down
Correct answer: Base in
When PD > frame OC distance, the OCs sit closer together than the pupils; the eyes look temporal to the OCs; for plus lenses, temporal gaze = OC is nasal = base in.
Question 6: A lens OC is found 2 mm above and 3 mm nasal to the MRP. Lens power is +5.00 D. What is the resultant total prismatic effect?
- 1.80Δ (Correct answer)
- 2.50Δ
- 1.00Δ
- 1.50Δ
Correct answer: 1.80Δ
Vertical Δ = 5.00 × 0.2 = 1.00Δ; horizontal Δ = 5.00 × 0.3 = 1.50Δ; resultant = √(1.00² + 1.50²) = √3.25 ≈ 1.80Δ.
Question 7: A presbyopic patient has a +2.00 D near add with the segment center 4 mm below the distance OC. Assuming zero distance power, how much vertical prism acts at the segment center?
- 0.80Δ base down (Correct answer)
- 0.80Δ base up
- 2.00Δ base down
- 0.40Δ base up
Correct answer: 0.80Δ base down
Δ = 2.00 × 0.4 = 0.80Δ; looking below the add's OC with a plus add produces base-down prism.
ABO NOCE Basic Opticianry Applying Prentice's Rule 5
A lens is +2.00 -4.00 × 090.
A patient looks through a point 4 mm temporal to the OC in the right eye.
What is the horizontal prismatic effect?