BRS Evaluation of Visual Impairment 4 — Questions and Answers
Question 1: A client with retinitis pigmentosa (RP) undergoes dark adaptation testing. Compared to a normal observer, a client with RP would most likely show:
- Normal cone phase but absent or severely elevated rod threshold in the rod phase (Correct answer)
- Absent cone phase but normal rod threshold after 30 minutes of dark adaptation
- Normal rod and cone thresholds with only color confusion errors
- Elevated thresholds only under photopic conditions with normal scotopic thresholds
Correct answer: Normal cone phase but absent or severely elevated rod threshold in the rod phase
RP primarily affects rod photoreceptors, so cone-mediated early dark adaptation may be relatively preserved while the rod phase shows absent or markedly elevated thresholds.
Question 2: A BRS specialist notes that a client reads at 40 words per minute with a stand magnifier but 95 words per minute with a CCTV at the same magnification level. This discrepancy most likely reflects:
- A difference in the client's intellectual ability between testing sessions
- The CCTV's broader field of view and better contrast enhancement allowing faster reading (Correct answer)
- The stand magnifier providing a higher level of actual magnification
- A spontaneous improvement in the client's retinal function between tests
Correct answer: The CCTV's broader field of view and better contrast enhancement allowing faster reading
CCTVs typically offer a wider field of view and adjustable contrast/brightness, which reduces crowding effects and fatigue, enabling faster reading than equivalent optical magnifiers.
Question 3: Legal blindness in the United States is defined as best-corrected visual acuity of 20/200 or worse in the better eye, OR a visual field:
- Of 30 degrees or less in the better eye
- Of 20 degrees or less in the better eye (Correct answer)
- Of 10 degrees or less in the better eye
- Showing any hemianopic defect in either eye
Correct answer: Of 20 degrees or less in the better eye
U.S. legal blindness criteria include a visual field of 20 degrees or less (diameter) in the better eye, in addition to the acuity criterion.
Question 4: When evaluating a client with cortical visual impairment (CVI), which behavioral feature would most suggest CVI rather than an ocular cause of visual impairment?
- Reduced acuity that improves with increased letter size and high contrast
- Visual responses that vary significantly with fatigue, illness, or sensory overload and improve with familiar stimuli (Correct answer)
- A central scotoma on confrontation visual field testing
- Stable visual acuity that does not fluctuate between visits
Correct answer: Visual responses that vary significantly with fatigue, illness, or sensory overload and improve with familiar stimuli
CVI is characterized by highly variable visual function influenced by fatigue, health status, and environmental complexity, with better responses to familiar or high-interest stimuli.
Question 5: The Smith-Kettlewell Edge Test (SKET) is designed to evaluate:
- Reading acuity at near distances
- Detection of edges and targets relevant to mobility tasks under low contrast conditions (Correct answer)
- Binocular vision and stereopsis
- Scotopic sensitivity using a standardized dark-room protocol
Correct answer: Detection of edges and targets relevant to mobility tasks under low contrast conditions
The SKET assesses a client's ability to detect edges and objects at low contrast levels that simulate conditions relevant to independent mobility and safe travel.
Question 6: A client reports that vision is clearest when not looking directly at a target (off-axis viewing). This is most consistent with a deficit in which retinal region?
- Peripheral retina only
- The fovea/macula (central retina) (Correct answer)
- The optic nerve head
- The pars plana
Correct answer: The fovea/macula (central retina)
When off-axis viewing improves clarity, the fovea is dysfunctional and the client has spontaneously developed eccentric (parafoveal or peripheral) fixation.
Question 7: In low vision evaluation, the term 'equivalent viewing distance' (EVD) helps clinicians determine:
- The working distance a client must use to achieve equivalent acuity with a given magnifier compared to a normal reference distance (Correct answer)
- The distance at which a client becomes legally blind
- The maximum distance a telescopic device can focus
- The distance between the client and a Pelli-Robson chart for contrast testing
Correct answer: The working distance a client must use to achieve equivalent acuity with a given magnifier compared to a normal reference distance
EVD quantifies how close a person with low vision must place a target (or how a magnifier reduces effective distance) to achieve the same acuity as the reference standard.
BRS Evaluation of Visual Impairment 4
A client with retinitis pigmentosa (RP) undergoes dark adaptation testing.
Compared to a normal observer, a client with RP would most likely show: