Optics and Refraction Flashcards
6 cards from real Vision and Ophthalmology practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Optics and Refraction flashcards as text
What is the purpose of a lensometer (lensmeter)?
Answer: Measure the power of a fabricated spectacle lens
A lensometer (lensmeter or focimeter) measures the prescription (sphere, cylinder, axis, and prism) of a finished spectacle or contact lens.
Irregular astigmatism, unlike regular astigmatism, cannot be fully corrected by:
Answer: Spectacle lenses with cylindrical correction
Irregular astigmatism has principal meridians that are not perpendicular and cannot be fully corrected with spectacle cylindrical lenses; rigid lenses neutralize the irregular surface.
Snellen visual acuity of 20/40 means the patient can see at 20 feet what a normal eye can see at:
Answer: 40 feet
20/40 acuity means the patient must be at 20 feet to resolve detail that a person with normal vision can resolve at 40 feet.
What is the near point of accommodation in a fully accommodating emmetropic eye?
Answer: Approximately 7–10 cm (varies by age)
In young emmetropes with maximal accommodation, the near point can be approximately 7–10 cm, with amplitude of accommodation decreasing with age.
Which test uses polarized filters to measure stereoacuity (depth perception)?
Answer: Random dot stereotest (e.g., Randot)
Random dot stereotests like the Randot or TNO test use polarized or anaglyph filters to present disparate images to each eye, testing stereoscopic depth perception.
Base-out prism correction for esotropia works by:
Answer: Displacing the image toward the base, reducing the convergence demand
Base-out prism displaces images toward the base (outward), reducing the convergence required and alleviating the esotropia-related binocular dysfunction.