Refraction and Retinoscopy Flashcards
7 cards from real COT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Refraction and Retinoscopy flashcards as text
If a spectacle Rx is −10.00 D at a vertex distance of 12 mm, what is the approximate contact lens power needed?
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.
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:
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).
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:
Answer: Latent hyperopia
Latent hyperopia is the portion of total hyperopia that cannot be relaxed voluntarily and is only detected under cycloplegia.
Which instrument performs an objective, automated refraction by measuring wavefront aberrations or Purkinje images?
Answer: Autorefractor
An autorefractor objectively measures the refractive error by analyzing reflections from the retina or measuring wavefront errors without patient response.
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:
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.
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:
Answer: Cycloplegic refraction
Cycloplegic refraction uses a cycloplegic drug to paralyze accommodation, revealing the full hyperopic correction that would otherwise be masked.
The 'against motion' reflex seen on retinoscopy can be eliminated by adding which type of lens in front of the eye?
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.