Board Certified Ophthalmologist FREE Board Certified Ophthalmologist Optics and Refraction Principles Questions and Answers 2 — Questions and Answers
Question 1: A patient with a keratometry reading of 44.00 D in one meridian and 46.00 D in the perpendicular meridian has what type and amount of corneal astigmatism?
- 2.00 D with-the-rule astigmatism (Correct answer)
- 2.00 D against-the-rule astigmatism
- 2.00 D oblique astigmatism
- 4.00 D irregular astigmatism
Correct answer: 2.00 D with-the-rule astigmatism
The 2.00 D difference between meridians with the steeper curvature at 90 degrees indicates with-the-rule astigmatism.
Question 2: What is the critical angle for total internal reflection at a crown glass-air interface if the refractive index of crown glass is 1.52?
- 41.1 degrees (Correct answer)
- 48.8 degrees
- 33.3 degrees
- 56.4 degrees
Correct answer: 41.1 degrees
The critical angle is calculated as arcsin(1/1.52), which equals approximately 41.1 degrees.
Question 3: A patient wearing a +10.00 D aphakic spectacle correction at a vertex distance of 12 mm requires what equivalent contact lens power?
- +11.40 D (Correct answer)
- +10.00 D
- +8.93 D
- +12.50 D
Correct answer: +11.40 D
Using the vertex distance formula, moving a plus lens closer to the eye requires increasing its power, yielding approximately +11.40 D.
Question 4: In Gullstrand's schematic eye, what is the approximate total refractive power of the eye?
- +58.6 D (Correct answer)
- +43.0 D
- +63.0 D
- +20.0 D
Correct answer: +58.6 D
Gullstrand's schematic eye has a total refractive power of approximately +58.6 diopters combining corneal and lenticular contributions.
Question 5: Which aberration causes a point source of light to appear as a comet-shaped blur when imaged through the peripheral portion of a spherical lens?
- Coma (Correct answer)
- Spherical aberration
- Chromatic aberration
- Distortion
Correct answer: Coma
Coma produces an asymmetric, comet-shaped blur pattern for off-axis point sources passing through different lens zones.
Question 6: A prism with an apical angle of 10 degrees and refractive index of 1.5 produces approximately how many prism diopters of deviation?
- 5 prism diopters (Correct answer)
- 10 prism diopters
- 15 prism diopters
- 7.5 prism diopters
Correct answer: 5 prism diopters
Using the thin prism approximation, deviation = (n-1) × apical angle = (1.5-1) × 10 = 5 prism diopters.
Board Certified Ophthalmologist FREE Board Certified Ophthalmologist Optics and Refraction Principles Questions and Answers 2
A patient with a keratometry reading of 44.00 D in one meridian and 46.00 D in the perpendicular meridian has what type and amount of corneal astigmatism?