Ophthalmic Optics and Principles Questions and Answers Flashcards
6 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Ophthalmic Optics and Principles Questions and Answers flashcards as text
What is the prismatic effect at a point 4 mm below the optical center of a -3.00 D lens?
Answer: 1.2Δ base up
Using Prentice's Rule: P = d × F = 0.4 cm × 3.00 = 1.2Δ. For a minus lens, the prism base is toward the optical center (base up when point is below OC).
What is the power cross for the prescription +2.00 -1.50 × 090?
Answer: +0.50 D at 090 and +2.00 D at 180
The axis is 090, so no cylinder acts at 090. Power at 090 = sphere = +2.00 + 0 = +2.00. Wait — at axis 090, cylinder = 0, so power = +2.00. At 180 (perpendicular to axis), power = +2.00 + (-1.50) = +0.50.
Transposing the prescription +3.50 -2.00 × 045 to plus-cylinder form gives:
Answer: +1.50 +2.00 × 135
To transpose to plus cylinder: new sphere = old sphere + old cylinder = +3.50 + (-2.00) = +1.50. New cylinder = -old cylinder = +2.00. New axis = old axis ± 90° = 045 + 90° = 135°.
When two thin lenses are placed in contact with each other, the combined power is:
Answer: The algebraic sum of their individual powers
For thin lenses in contact (zero separation), the combined power equals the algebraic sum: F_total = F1 + F2.
What is a prism diopter (Δ) and how is it defined?
Answer: A unit of prism power equal to 1 cm of displacement at 1 meter; P = d × F
A prism diopter (Δ) is defined as 1 cm of linear displacement of a ray at a distance of 1 meter from the prism. Equivalently, P = d(cm) × F(D) by Prentice's Rule.
What is the difference between back vertex power and front vertex power of a thick lens?
Answer: Back vertex power is measured from the back surface; front vertex power from the front surface; they differ for thick lenses due to lens thickness
For thick lenses, back vertex power (neutralizing power) and front vertex power differ because the lens thickness creates a gap between surfaces. Prescriptions are specified as back vertex power.