COT Refraction and Retinoscopy 5 — Questions and Answers
Question 1: If a spectacle Rx is −10.00 D at a vertex distance of 12 mm, what is the approximate contact lens power needed?
- −9.00 D (Correct answer)
- −10.00 D
- −11.00 D
- −8.50 D
Correct answer: −9.00 D
For high minus lenses, moving the lens to the cornea reduces effective power; the CL power is approximately −9.00 D at the corneal plane.
Question 2: During retinoscopy, the reflex in the 90° meridian neutralizes with +1.00 D and the 180° meridian with +3.00 D. The resulting refraction in plus cylinder form is:
- +1.00 +2.00 ×090 (Correct answer)
- +3.00 −2.00 ×090
- +1.00 +2.00 ×180
- +2.00 +1.00 ×090
Correct answer: +1.00 +2.00 ×090
The least plus meridian (90°) becomes the sphere (+1.00), and the cylinder is the difference (+2.00) with axis at the least plus meridian (090).
Question 3: A patient's cycloplegic refraction is +2.00 D OU. After cycloplegia wears off, they accept only +0.50 D during manifest refraction. The remaining +1.50 D is called:
- Latent hyperopia (Correct answer)
- Absolute hyperopia
- Facultative hyperopia
- Manifest hyperopia
Correct answer: Latent hyperopia
Latent hyperopia is the portion of total hyperopia that cannot be relaxed voluntarily and is only detected under cycloplegia.
Question 4: Which instrument performs an objective, automated refraction by measuring wavefront aberrations or Purkinje images?
- Autorefractor (Correct answer)
- Lensometer
- Keratometer
- Pachymeter
Correct answer: Autorefractor
An autorefractor objectively measures the refractive error by analyzing reflections from the retina or measuring wavefront errors without patient response.
Question 5: When refining cylinder axis with the Jackson cross cylinder, the patient reports that flip position 1 and flip position 2 look equally blurry. This means:
- The axis is correctly positioned (Correct answer)
- The axis must be rotated toward the minus dot
- The axis must be rotated toward the plus dot
- The cylinder power is too low
Correct answer: The axis is correctly positioned
Equal blur in both JCC positions means the cylinder axis is correctly placed at the midpoint between the two flip orientations.
Question 6: A hyperopic child accommodates to achieve clear distance vision. The glasses correction that relaxes this accommodation and may reveal the full hyperopia is called a:
- Cycloplegic refraction (Correct answer)
- Manifest refraction
- Dry refraction
- Subjective refraction
Correct answer: Cycloplegic refraction
Cycloplegic refraction uses a cycloplegic drug to paralyze accommodation, revealing the full hyperopic correction that would otherwise be masked.
Question 7: The 'against motion' reflex seen on retinoscopy can be eliminated by adding which type of lens in front of the eye?
- Minus (concave) lenses (Correct answer)
- Plus (convex) lenses
- Prism lenses
- Plano lenses
Correct answer: Minus (concave) lenses
Against motion indicates myopia beyond the working distance; adding minus lenses moves the far point back toward the examiner to achieve neutralization.
COT Refraction and Retinoscopy 5
If a spectacle Rx is −10.00 D at a vertex distance of 12 mm, what is the approximate contact lens power needed?