ABO NOCE Basic Opticianry Applying Prentice's Rule 5

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?

Accepted Answer

0.80Δ base in

Answer

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:

Accepted Answer

Optical center of the lens

Answer

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?

Accepted Answer

5 mm upward

Answer

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?

Accepted Answer

2.40Δ

Answer

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?

Accepted Answer

Base in

Answer

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.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Applying Prentice's Rule 5