AOA Optics and Refraction 1 — Questions and Answers
Question 1: In an eye with simple myopia, the far point is located:
- At a finite distance in front of the eye (Correct answer)
- At optical infinity behind the retina
- On the retina itself
- At the anterior focal point of the eye
Correct answer: At a finite distance in front of the eye
In myopia the parallel rays from infinity focus in front of the retina; the far point (where diverging rays appear to come from) is at a finite real distance anterior to the eye.
Question 2: When performing retinoscopy, a 'with' reflex indicates that the eye's far point is:
- Behind the examiner (hyperopia or low myopia) (Correct answer)
- In front of the examiner (high myopia)
- At the examiner's working distance (neutrality)
- Unrelated to the far point location
Correct answer: Behind the examiner (hyperopia or low myopia)
A 'with' motion reflex during retinoscopy means the far point is beyond the examiner's working distance, indicating hyperopia or myopia less than the working lens.
Question 3: The principal effect of a minus cylinder lens is to:
- Reduce power in one meridian while leaving the other unchanged (Correct answer)
- Increase power equally in all meridians
- Rotate the axis of astigmatism by 90°
- Reduce power equally in all meridians
Correct answer: Reduce power in one meridian while leaving the other unchanged
A minus cylinder lens has zero power along its axis meridian and maximum minus power 90° away, selectively reducing power in one meridian.
Question 4: Chromatic aberration in the eye is primarily responsible for which clinical phenomenon?
- Blue light focusing slightly anterior to red light (longitudinal chromatic aberration) (Correct answer)
- Prism effect at the lens periphery causing rainbows
- Increased glare sensitivity in mesopic conditions
- Reduced contrast sensitivity at spatial frequencies above 10 cpd
Correct answer: Blue light focusing slightly anterior to red light (longitudinal chromatic aberration)
The ocular media have higher refractive index for shorter wavelengths; blue light focuses about 2D anterior to red, a phenomenon used in the duochrome (red-green) test.
Question 5: The power of a thin lens required to correct a 4D myope is:
- -4.00 D (Correct answer)
- +4.00 D
- -2.00 D
- +2.00 D
Correct answer: -4.00 D
To move the far point from 25 cm in front of the eye to optical infinity, a diverging lens of -4.00 D (focal length -25 cm) is required.
Question 6: Astigmatism is defined as a refractive condition in which:
- The eye has different powers in different meridians (Correct answer)
- The eye has no definite focal point
- Both eyes have equal refractive errors
- The cornea is uniformly too steep for the axial length
Correct answer: The eye has different powers in different meridians
Astigmatism occurs when the refracting surfaces of the eye have different curvatures in different meridians, preventing parallel rays from converging to a single point focus.
AOA Optics and Refraction 1
In an eye with simple myopia, the far point is located: