Visual Deficits: Consequences and Prospects for Rehabilitation

Question 1

Nature of visual deficits arising from damage to the eye (central vision loss) and brain (hemianopia)

Answer 1

Central vision loss – the loss of detail vision, resulting in having only side vision remaining.

Hemianopia – the loss of one half of your visual field; the most common cause of this type of vision loss is stroke.
-Occurs in 15% of stroke patients. (Bahnemann et al., 2015)

Question 2

Assessment of visual fields

Answer 2

Perimetry (for plotting visual fields)

Static (target of fixed size, luminance increased until seen)

Kinetic (moving target fixed size and intensity)

Question 3

Eye movements in hemianopia
(Meienberg et al. 1981)

Answer 3

Simple eye movement task – saccades
- Move eyes to target appeared randomly left or right on horizontal axis.
- Sighted visual field (right) – normal.
- Hemianopia field (left) – staircase pattern of small saccades.

Initially small step saccades made into blind field, later start making larger saccades

Question 4

Blindsight

Answer 4

a phenomenon in which patients with damage in the primary visual cortex of the brain can tell where an object is although they claim they cannot see it.

-Some hemianopias can make accurate eye movements in their blind field.
-Forced choice- move eyes to target you have not seen.

Question 5

Reading and visual field defects

Answer 5

• Vision loss has serious consequences for reading and visual cognition.
• Visual field defects common after stroke.

Damage to:
- Projections from LGN to V1
- To primary visual cortex (V1)
- Or both

Question 6

Left vs Right hemianopia

Answer 6

Left hemianopia:
difficulty making leftward return-sweep eye movements
disorganised and multiple steps to find start next line

Right hemianopia:
difficulty shifting gaze (saccades) onto each word (left-to-right)
increased time spent fixating, small steps

Question 7

Reading deficits and abnormal eye movement behaviour in reading:

Answer 7

Hemianopia Dyslexia: Right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading.

Question 8

Therapy for reading in right hemianopias (Leff et al. 2001)

Answer 8

Therapy
-reading scrolling text - content was selected by the patients.
-Web-app presents text as single horizontal scrolling line.
-Induces optokinetic nystagmus.
-When reading scrolling text - eyes track to the left, followed by involuntary rightward saccade (OKN)

Participants and method
-33 patients (mean age- 62 years, 15 months post stroke)
-Minimum 5 hours of practice reading scrolling text.
-Speed self-controlled
-Automated visual field test
-Assessed reading speech (static lines) after 5-hour intervals.

Findings
-Reading speed improved and sig. ‘dose’ effect.
-Generalised from scrolling text to normal static text.

Question 9

Pure Alexia (AR) (Leff et al. 2001)

Answer 9

Pure Alexia – an acquired reading disorder

Alexia with Agraphia
-(Agraphia an impairment or loss of a previous ability to write)
Alexia without agraphia or Pure Alexia
-Pure Alexia – an acquired reading disorder
-Strategy of letter-by-letter reading

Rare to find a case of Pure Alexia without a right hemianopia.
Case A.R. - had pure alexia without agraphia or hemianopia.
- A.R. - left occipital haemorrhage. Visual fields, eye movements, and sensorimotor function were normal.
- Initially, he could not recognize letters, but this resolved incompletely, and he was able to read some words using an explicit letter-by-letter strategy.

Question 10

Pure Alexia and role of right visual field defects
(Pflugshaupt et al., 2009)

Answer 10

Pure Alexia
-Lesion involving the left occipital- temporal region.
-Visual word form area (left hemisphere)
-Fusiform face area in right)

(Leff et al. 2001)
92% of cases have right visual field defects but not regarded as primary cause of alexia.

Question 11

Pure Alexia vs Hemianopia dyslexia

Answer 11

A) Pure Alexia - More fixations, very long fixation durations, shorter amplitudes of rightward saccades, higher percentages of regressions and more pronounced effects of word length on fixation frequency

B) Hemianopia dyslexia - More fixations, small increase in fixation duration and shortened amplitudes of rightward saccades, Reduction in rightward saccade amplitude related to visual field loss.

Question 12

Scanning training
(Kerkhof.,1994)

Answer 12

Eye movement training
22 hemianopia patients
- No neglect
Measures:
- Search field (when searching for a light)
- Searching on slides for geometrical symbols (pointer to find shapes e.g., circles)
- Table search test (40 objects- asked to find certain object e.g., pencil)

Question 13

Reading training

Answer 13

• 57 patients with visual field defects and hemianopia alexia
  Reading speed test before/after treatment:
• Training with scrolling text to improve (rightward saccades)
• 40minsperdayx5days
• Group reading speed improved from 350sec to 150sec.

Findings
Attributed to improvement in eye movement behaviour - (fewer fixations’ regressions)

Question 14

Fresnel (or Peli) prisms

Answer 14

A Peli prism lens aims to expand your peripheral visual field if you have a homonymous hemianopia.

It works by using high powered prisms to shift the image from the side with visual field loss onto the other side where you can see it.

Question 15

Hemianopia and driving (Bowers et al., 2009)

Answer 15

Impact on driving: Poor detecting obstacles

HH - 12 people with hemianopia (no neglect)
NV - 12 normal vision (NV) controls.
Driving simulator with hazards (total 120 minutes) city and country roads
Pedestrians appeared on roadway (R-Peds) or at intersections (I-Peds)

Conclusion
- Poor detection and slow responses indicate HH problematic for driving
- Incompatible with safe driving – need to assess drivers on simulator.
- Some evidence HH drove slower – as compensation strategy.

Question 16

Hemianopia

Answer 16

A hemianopia is where there is a loss of one half of your visual field.

Hemianopia is caused by damage to the brain, for example, by a stroke, trauma or tumour. The extent of field loss can vary and depends of the area of your brain that has been affected.