ABO Ametropia/Ophthalmic Optics 3 — Questions and Answers
Question 1: A spectacle lens with a base curve of +6.00 D and back surface power of -2.00 D has a front vertex power of approximately:
- +4.00 D (Correct answer)
- +8.00 D
- +6.00 D
- +2.00 D
Correct answer: +4.00 D
In a thin lens approximation, total power = front surface + back surface = +6.00 + (-2.00) = +4.00 D.
Question 2: The far point of a 5.00 D myope is located:
- 20 cm in front of the eye (Correct answer)
- 20 cm behind the eye
- At infinity
- 50 cm in front of the eye
Correct answer: 20 cm in front of the eye
Far point distance = 1/F = 1/5.00 = 0.20 m = 20 cm in front of the eye for a myope.
Question 3: Chromatic aberration in the eye causes violet light to focus:
- Behind red light
- At the same point as red light
- In front of red light (Correct answer)
- Only on the peripheral retina
Correct answer: In front of red light
Short wavelength (violet) light is refracted more strongly than long wavelength (red) light, so it focuses anterior to red.
Question 4: A +3.00 D thin lens in air has a focal length of:
- 3 cm
- 33.3 cm (Correct answer)
- 30 cm
- 0.33 cm
Correct answer: 33.3 cm
Focal length f = 1/F = 1/3.00 = 0.333 m = 33.3 cm.
Question 5: Which condition is characterized by a refractive error caused by increased axial length without any change in corneal or lenticular power?
- Refractive myopia
- Axial myopia (Correct answer)
- Index myopia
- Curvature myopia
Correct answer: Axial myopia
Axial myopia results specifically from an elongated globe, placing the retina behind the focal point of the optical system.
Question 6: When converting a minus cylinder prescription to plus cylinder form, the new axis is:
- Rotated 45 degrees
- Unchanged
- Rotated 90 degrees (Correct answer)
- Rotated 180 degrees
Correct answer: Rotated 90 degrees
Transposing a prescription requires rotating the axis by 90 degrees, changing the cylinder sign, and algebraically combining cylinder with sphere.
Question 7: The index of refraction of CR-39 plastic is approximately:
- 1.50 (Correct answer)
- 1.60
- 1.67
- 1.74
Correct answer: 1.50
CR-39 (allyl diglycol carbonate) has an index of refraction of approximately 1.50, making it the standard plastic lens material.
ABO Ametropia/Ophthalmic Optics 3
A spectacle lens with a base curve of +6.00 D and back surface power of -2.00 D has a front vertex power of approximately: