ABO Low Vision & Rehabilitation 2 — Questions and Answers
Question 1: Which magnification formula correctly calculates the required add power for a patient with 20/200 acuity who wants to read standard newsprint (20/40 equivalent)?
- Add = 1/working distance in meters
- Add = distance acuity denominator / goal acuity denominator × 2.5D
- Add = (20/200) / (20/40) × 4D = 20D (Correct answer)
- Add = 1 / (visual acuity in decimal)
Correct answer: Add = (20/200) / (20/40) × 4D = 20D
The required magnification is 200/40 = 5×, and since 1× requires approximately 4D, the needed add is 5 × 4D = 20D.
Question 2: A patient with central scotoma due to macular degeneration is taught eccentric viewing. The preferred retinal locus (PRL) is most commonly located in which direction relative to the scotoma?
- Superior to the scotoma
- Inferior to the scotoma
- The PRL location varies by individual and must be determined clinically (Correct answer)
- Temporal to the scotoma in all patients
Correct answer: The PRL location varies by individual and must be determined clinically
The PRL develops spontaneously in a location that varies among individuals, and clinical assessment (e.g., microperimetry or scanning laser ophthalmoscopy) is needed to identify it.
Question 3: Which illumination strategy is most beneficial for a patient with retinitis pigmentosa (RP) experiencing significant glare sensitivity indoors?
- Increase overall room illumination to maximum
- Use highly directional task lighting aimed at the work surface while reducing ambient light (Correct answer)
- Prescribe photochromic lenses for indoor use
- Recommend blue-light blocking lenses only
Correct answer: Use highly directional task lighting aimed at the work surface while reducing ambient light
Directing task lighting onto the work area while keeping ambient lighting lower reduces the glare-contrast problem common in RP patients with rod depletion.
Question 4: A 68-year-old patient's best-corrected visual acuity is 20/400. When fitting a spectacle-mounted telescope for distance mobility, the clinician should prioritize which consideration?
- Maximizing magnification to achieve 20/20 equivalent
- Field of view, weight, and cosmetic acceptance in addition to acuity improvement (Correct answer)
- Binocular balance at all times
- Ensuring the telescope provides at least 10× magnification
Correct answer: Field of view, weight, and cosmetic acceptance in addition to acuity improvement
High-magnification telescopes drastically reduce field of view and are heavier, so functional factors and patient acceptance must be balanced with acuity improvement.
Question 5: Stand magnifiers are optically designed so that the image they produce is located at which focal distance?
- At infinity, requiring no additional accommodation or add (Correct answer)
- At the near point of the user's eye
- At a fixed distance equal to the magnifier's focal length beyond the lens
- At optical infinity only when the object is placed inside the focal length
Correct answer: At infinity, requiring no additional accommodation or add
A stand magnifier places the object at its focal point, producing a virtual image at optical infinity that requires no accommodation (or only the patient's habitual near add) to view.
Question 6: Which of the following best describes the purpose of a bioptic telescope system for driving?
- To be worn continuously and used as the primary viewing system while driving
- To provide a brief spotting system for signs and traffic lights while the carrier lens is used for primary driving (Correct answer)
- To replace contact lenses in patients with irregular corneas
- To provide binocular distance vision correction only
Correct answer: To provide a brief spotting system for signs and traffic lights while the carrier lens is used for primary driving
Bioptic telescopes are used intermittently as a spotting device; the driver uses the carrier lens for the majority of visual tasks and dips briefly into the telescope.
Question 7: During low vision evaluation, a patient achieves better performance on reading tasks with a typoscope. What is the primary optical or perceptual mechanism by which a typoscope aids reading?
- It magnifies text by refracting light
- It reduces glare and isolates the line of text to minimize visual crowding (Correct answer)
- It increases the contrast sensitivity of the fovea
- It shifts the image onto a healthier area of the retina
Correct answer: It reduces glare and isolates the line of text to minimize visual crowding
A typoscope is a non-optical black matte card with a window that blocks stray light (reducing glare) and limits the visible text to one line, reducing crowding effects.
ABO Low Vision & Rehabilitation 2
Which magnification formula correctly calculates the required add power for a patient with 20/200 acuity who wants to read standard newsprint (20/40 equivalent)?