ABO Ametropia/Ophthalmic Optics 2 — Questions and Answers
Question 1: A patient has a prescription of -3.00 -1.50 x 090. What is the power in the 180-degree meridian?
- -3.00 D
- -4.50 D (Correct answer)
- -1.50 D
- -1.00 D
Correct answer: -4.50 D
In the 180-degree meridian (perpendicular to axis 090), the full sphere plus cylinder power applies: -3.00 + (-1.50) = -4.50 D.
Question 2: Which type of astigmatism has one focal line in front of the retina and one behind it?
- Simple myopic astigmatism
- Compound hyperopic astigmatism
- Mixed astigmatism (Correct answer)
- Compound myopic astigmatism
Correct answer: Mixed astigmatism
Mixed astigmatism has one principal meridian focused anterior to the retina (myopic) and the other posterior (hyperopic).
Question 3: A +2.00 D lens is placed 12 mm in front of the corneal plane. What is the equivalent power at the corneal plane?
- +1.95 D
- +2.05 D (Correct answer)
- +2.10 D
- +1.90 D
Correct answer: +2.05 D
Using F' = F / (1 - dF) = 2.00 / (1 - 0.012 × 2.00) = 2.00 / 0.976 ≈ +2.05 D.
Question 4: The circle of least confusion in a Sturm's conoid is located:
- At the anterior focal line
- At the posterior focal line
- Midway between the two focal lines (Correct answer)
- At the retina in all cases
Correct answer: Midway between the two focal lines
The circle of least confusion is the round cross-section of Sturm's conoid located equidistant between the two focal lines.
Question 5: A patient with 4.00 D of axial myopia has an eye axial length that is approximately how much longer than emmetropic?
- 0.7 mm
- 1.4 mm (Correct answer)
- 2.0 mm
- 3.0 mm
Correct answer: 1.4 mm
Each diopter of axial myopia corresponds to roughly 0.35 mm of excess axial length, so 4.00 D ≈ 1.4 mm.
Question 6: Which prism effect occurs when a myopic patient looks through the upper portion of a single-vision minus lens while reading?
- Base-up prism (Correct answer)
- Base-down prism
- Base-in prism
- No prism effect
Correct answer: Base-up prism
A minus lens creates base-up prismatic effect in its upper portion due to Prentice's rule, which can cause reading difficulties.
Question 7: Which refractive condition results from a cornea with greater curvature in the vertical meridian than the horizontal?
- Against-the-rule astigmatism
- With-the-rule astigmatism (Correct answer)
- Oblique astigmatism
- Irregular astigmatism
Correct answer: With-the-rule astigmatism
With-the-rule astigmatism occurs when the vertical corneal meridian is steeper, requiring a minus cylinder axis at 180 degrees.
ABO Ametropia/Ophthalmic Optics 2
A patient has a prescription of -3.00 -1.50 x 090.
What is the power in the 180-degree meridian?