ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 4 â Questions and Answers
Question 1: Prentice's Rule states that the prismatic effect at a point on a lens equals:
- Lens power divided by decentration in mm
- Decentration in cm multiplied by lens power in diopters (Correct answer)
- Lens power multiplied by vertex distance
- Decentration in mm divided by lens power
Correct answer: Decentration in cm multiplied by lens power in diopters
Prentice's Rule: P (prism diopters) = c (cm) Ă F (diopters), where c is decentration from optical center in centimeters.
Question 2: Which lens aberration causes the peripheral image to appear distorted in a pin-cushion or barrel shape?
- Coma
- Curvature of field
- Distortion (Correct answer)
- Spherical aberration
Correct answer: Distortion
Distortion (pin-cushion or barrel) occurs because magnification varies across the lens, causing shape distortion of the image.
Question 3: The back vertex power of a lens differs most from its true power when:
- The lens is thin
- The lens has high power and significant center thickness (Correct answer)
- The lens has low power
- The lens is made of high-index material
Correct answer: The lens has high power and significant center thickness
Thick, high-powered lenses have the greatest difference between front vertex, back vertex, and true (equivalent) power.
Question 4: A lens with a +4.00 D front surface and a -2.00 D back surface has an approximate nominal power of:
- +6.00 D
- +2.00 D (Correct answer)
- -2.00 D
- +4.00 D
Correct answer: +2.00 D
Nominal (thin lens) power equals Fâ + Fâ = +4.00 + (-2.00) = +2.00 D.
Question 5: Increasing the vertex distance of a plus lens relative to the eye effectively:
- Increases the effective power at the eye
- Decreases the effective power at the eye (Correct answer)
- Has no effect on effective power
- Increases only the cylinder component
Correct answer: Decreases the effective power at the eye
Moving a plus lens farther from the eye reduces its effective converging power at the corneal plane.
Question 6: What does the term 'transposition' mean in ophthalmic optics?
- Changing a lens prescription from one material to another
- Converting a prescription from plus cylinder to minus cylinder form or vice versa (Correct answer)
- Moving the optical center from the datum line
- Rotating the axis of a cylindrical lens
Correct answer: Converting a prescription from plus cylinder to minus cylinder form or vice versa
Transposition converts a prescription between plus and minus cylinder forms while maintaining the same optical effect.
Question 7: An image formed by a concave (minus) lens is always:
- Real and inverted
- Virtual and erect (Correct answer)
- Real and erect
- Virtual and inverted
Correct answer: Virtual and erect
A concave (diverging) lens always forms a virtual, erect, and diminished image on the same side as the object.
ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 4
Prentice's Rule states that the prismatic effect at a point on a lens equals: