ABO NOCE Basic Opticianry Ophthalmic Optics 4 — Questions and Answers
Question 1: A patient's prescription is OD -4.00 -1.50 x 090. What is the power in the 180 meridian?
- -4.00 D
- -5.50 D (Correct answer)
- -1.50 D
- -2.50 D
Correct answer: -5.50 D
In a minus-cylinder prescription, the sphere power acts along the axis meridian (090), and the full cylinder power is added 90° away (180°): -4.00 + (-1.50) = -5.50 D.
Question 2: Which surface of a meniscus lens is typically convex?
- The back (ocular) surface
- Both surfaces are convex
- The front (object-side) surface (Correct answer)
- Neither surface is convex
Correct answer: The front (object-side) surface
In a standard ophthalmic meniscus lens, the front (convex) surface curves toward the world and the back (concave) surface curves toward the eye.
Question 3: What does 'base curve' refer to in ophthalmic lens terminology?
- The curvature of the back surface of the lens
- The reference surface curvature, usually the front convex surface (Correct answer)
- The prismatic base direction
- The minimum edge thickness
Correct answer: The reference surface curvature, usually the front convex surface
The base curve is the reference surface power of an ophthalmic lens, most commonly expressed as the front (convex) surface power in diopters.
Question 4: A cylinder lens with axis at 45° corrects astigmatism in which meridian?
- The 45° meridian
- The 135° meridian (Correct answer)
- Both the 45° and 135° meridians equally
- The 90° meridian
Correct answer: The 135° meridian
A cylinder lens with axis at 45° has no power along the 45° meridian (the axis) and full correcting power in the 135° meridian (perpendicular to the axis).
Question 5: The spherical equivalent of -3.00 -2.00 x 090 is:
- -3.00 D
- -4.00 D (Correct answer)
- -5.00 D
- -2.00 D
Correct answer: -4.00 D
Spherical equivalent = sphere + (cylinder/2) = -3.00 + (-2.00/2) = -3.00 + (-1.00) = -4.00 D.
Question 6: Which type of lens has exactly the same power in all meridians?
- Toric lens
- Cylindrical lens
- Spherical lens (Correct answer)
- Aspheric lens
Correct answer: Spherical lens
A spherical lens has a single uniform power in every meridian because it is formed by a section of a sphere.
Question 7: The back vertex power of a lens is measured from:
- The front surface to the rear focal point
- The rear surface to the rear focal point (Correct answer)
- The lens center to the rear focal point
- The front surface to the front focal point
Correct answer: The rear surface to the rear focal point
Back vertex power is the vergence of light leaving the back (ocular) surface when parallel light enters the front surface, measured from the back surface to the rear focal point.
ABO NOCE Basic Opticianry Ophthalmic Optics 4
A patient's prescription is OD -4.00 -1.50 x 090.
What is the power in the 180 meridian?