BRS Low Vision Aids & Devices 4 — Questions and Answers
Question 1: A patient is prescribed a 6× Keplerian telescope. Which characteristic distinguishes this device from a Galilean telescope of equal power?
- Keplerian telescopes produce an erect image without a prism
- Keplerian telescopes provide a wider field of view and higher image quality but require an erecting prism (Correct answer)
- Keplerian telescopes are always smaller and lighter
- Keplerian telescopes cannot be used as bioptics
Correct answer: Keplerian telescopes provide a wider field of view and higher image quality but require an erecting prism
Keplerian (astronomical) telescopes produce an inverted image and require an erecting prism system, but they offer superior field of view and image quality compared to Galilean designs at the same power.
Question 2: Which patient characteristic is the MOST important contraindication for prescribing a bioptic telescope for driving in states where it is permitted?
- Visual acuity worse than 20/200 through the carrier lens
- Inability to rapidly shift gaze between the carrier and telescope (Correct answer)
- Presence of any visual field restriction
- Age over 70 years
Correct answer: Inability to rapidly shift gaze between the carrier and telescope
Safe bioptic driving requires the patient to quickly and reflexively alternate between the wide-field carrier lens and the telescope, and inability to do so is a primary contraindication.
Question 3: When evaluating a patient for a video magnifier (CCTV), which feature is MOST beneficial for a patient with extreme photophobia?
- Highest available magnification level
- Reverse polarity (white text on black background) (Correct answer)
- Largest available monitor size
- Motorized XY table for smooth scrolling
Correct answer: Reverse polarity (white text on black background)
Reverse polarity displays white text on a black background, dramatically reducing the amount of light emitted from the screen and alleviating photophobia.
Question 4: A BRS recommends a portable electronic magnifier (PEM) for a patient. What is a key LIMITATION of PEMs compared to desktop video magnifiers?
- PEMs cannot display reverse polarity
- PEMs typically have smaller screens, limiting the area visible at one time (Correct answer)
- PEMs do not offer adjustable magnification
- PEMs require special lighting to function effectively
Correct answer: PEMs typically have smaller screens, limiting the area visible at one time
Portable electronic magnifiers have smaller screens than desktop units, which limits the amount of text or image visible at any magnification level.
Question 5: Which principle explains why increasing magnification with an optical device also reduces the field of view?
- The Snell-Descartes law of refraction
- The inverse relationship between magnification and angular field in telescope optics (Correct answer)
- The diffraction limit of the objective lens
- Spherical aberration increases proportionally with power
Correct answer: The inverse relationship between magnification and angular field in telescope optics
In telescope optics, field of view and magnification are inversely related — as magnification increases, the angular field of view proportionally decreases.
Question 6: A patient with hemianopia (right homonymous) is being trained to use a portable CCTV. Which compensatory strategy should the BRS emphasize?
- Increase magnification to see more detail on the left side
- Teach systematic rightward scanning to bring content from the blind field into view (Correct answer)
- Reposition the camera to capture only the left visual field
- Recommend prism relocation lenses instead of the CCTV
Correct answer: Teach systematic rightward scanning to bring content from the blind field into view
Training deliberate, systematic scanning toward the blind (right) side compensates for the missing field by actively moving the gaze to capture information in the hemianopic area.
Question 7: Which optical low vision aid is BEST suited for a patient who needs both hands free while performing crafts at near distance?
- Hand magnifier
- Stand magnifier
- Spectacle-mounted microscopic lens (Correct answer)
- Pocket telescope
Correct answer: Spectacle-mounted microscopic lens
Spectacle-mounted microscopic lenses are worn on the face, freeing both hands entirely for near tasks like crafts, sewing, or repairs.
BRS Low Vision Aids & Devices 4
A patient is prescribed a 6× Keplerian telescope.
Which characteristic distinguishes this device from a Galilean telescope of equal power?