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The patient with 20/20 vision who cant read

• UBC Clinical Neuroophthalmology Day
• Jason Barton

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What do you need to read? 1. Low-level visual
processes - intact central 5 degrees 2. Eye
movements - steady fixation and accurate
saccades 3. Attention 4. Higher level
visual processes - to decode form into letters
and words 5. Linguistic analysis - generating
meaning and pronunciation from word forms that
are seen Conclusion reading can be derailed by
a wide variety of problems. A systematic
approach to acquired reading disorders is useful.
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1. Visual fields and reading A. hemianopic
dyslexia - central 5 degrees. Left hemianopia
trouble finding the beginning of lines, since the
left margin disappears into the field defect as
they scan rightwards. Marking their place
with an L-shaped ruler helps. Right hemianopia
prolongs reading times, with increased numbers
of fixations and reduced amplitude of reading
saccades to the right. Smaller type and
learning to read obliquely with the page turned
nearly 90 degrees may help. Reading
performance can improve with time as both types
of patients learn adaptive strategies
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Hemianopic dyslexia- eye movements Trauzettel-Kl
osinski S, Brendler K. Eye movements in reading
with hemianopic field defects the significance
of clinical parameters. Graefes Arch Clin Exp
Ophthalmol 1998 236 91-102
Left hemianopia
Right hemianopia
Normal
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Case Hemianopic dyslexia 37 year old man in MVA
with brief LOC. Complains of difficulty
reading. 20/20 ou.
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1. Visual fields and reading B. hemifield slide,
with bitemporal hemianopia absence of
overlapping regions of binocular visual field
leads to unstable binocular alignment with
transient duplication or disappearance of words
during reading.
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Case Hemifield slide. 35 year old woman with 3
days of episodic diplopia with reading, letters
suddenly double, at other times they disappear.
across the room vertical steps appear in
windowsills and doorframes. She denied any
visual loss. 20/20 OU. no RAPD. bilateral optic
disc pallor.
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2. Eye movements and reading. A. Inability to
maintain steady fixation (i) Nystagmus in
primary position - congenital (usually with
reduced acuity) - acquired - vestibular
(usually too dizzy to read) - central
(downbeat! - worse in downgaze) (ii) Saccadic
intrusions - opsoclonus and ocular flutter -
square wave jerks - PSP
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2. Eye movements and reading. B. Inability to
make accurate saccades (i) Saccadic dysmetria
(cerebellar lesions) (ii) Saccadic gaze palsy
- acquired ocular motor apraxia (bilateral
frontal/parietal lesions) - supranuclear
downgaze palsy (PSP, paramedian infarct)
Note smooth pursuit is irrelevant to reading
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Case Saccadic dysmetria and macrosaccadic
oscillations 33 year-old woman with multiple
sclerosis, presenting 12 years prior with optic
neuritis, now with 3 years of imbalance and poor
writing, difficulty reading. ?
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3. Attention and reading. Neglect
dyslexia. Left hemi-neglect, right parietal or
frontal lesions space-centered deficit omit
left side of lines or pages. object-centered
deficit omit left side of words. - omissions
('bright' 'right'), - additions ('right'
'bright') - substitutions ('right' 'light').
vertically printed text is not affected. may
occur without other signs of hemi-neglect
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4. Higher level visual processes Pure alexia
(alexia without agraphia) Spectrum of
severity global alexia cannot read numbers,
letters and other abstract symbols (musical
notation, road signs and map symbols)
letter-by-letter reading slow reading with
occasional errors, decipher words one letter at
a time characteristic word-length
effect reading time correlates with the number
of letters in the word
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Associated signs (not invariable) right
hemianopia/superior quadrantanopia anomia for
colours and sometimes other visual objects.
impaired verbal memory, other visual agnosias,
optic ataxia right hand has difficulty reaching
to left visual field Left medial
occipitotemporal lesion (PCA infarct)
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Two major explanations exist for pure alexia. 1.
Disconnection alexia Most commonly, a) left
occipital lesion complete right hemianopia.
Therefore no visual input to left language
areas from the left brain. AND b)
splenium/forceps major/periventricular white
matter occipital horn, interrupt callosal fibers
from the intact right occipital lobe. Therefore
no visual input to left language areas from the
right brain. Support unusual cases with
combination of a splenial lesion and right
hemianopia from left non-occipital lesions, e.g.
LGN.
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Two major explanations exist for pure alexia. 2.
Word form agnosia visual agnosia from
dysfunction of the left ventral extrastriate
cortex fMRI shows activation of left visual
fusiform word area by reading. associated with
impaired processing of local texture,
identification of complex objects in drawings
Support pathologic reports showing left
fusiform and lingual gyral lesion but no splenial
degeneration
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5. Central (linguistic) dyslexia Most often
associated with aphasia, dementia Alexia with
agraphia - left angular gyrus lesion may be
associated with other signs of Gerstmanns
syndrome (acalculia, right-left
disorientation) Linguistic variants
Phonological dyslexia - patients have lost the
spelling rules but not their dictionary. problems
only emerge when they have to spell novel words
or pseudo-words (grickle, centus). Surface
dyslexia - patients have lost the dictionary but
not the rules patients can only read if they can
sound it out. Hence they have trouble with
irregular words (yacht, colonel) Deep
dyslexia - patients have lost spelling rules and
also make semantic errors (reading cat for
dog)
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Alexia with agraphia 55 year-old right-handed man
with several weeks of daily headaches. Subtotal
resection of left angular gyrus mass
glioblastoma. Exam fluent speech, normal
comprehension, mild anomia. trouble with
calculations, right/left orientation. 20/30 od,
20/20 os. macular-splitting right hemianopia.
Fundi normal. Difficulty reading- made semantic
errors (beautiful pretty, but
and) Difficulty writing - spider sitre,
kite kibe, hammer harer
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SUMMARY When reading doesnt work Low-level
visual processes hemianopic dyslexia (central 5
degrees) hemifield slide Eye
movements fixation - nystagmus, saccadic
intrusions saccades - dysmetria or palsy
Attention hemineglect dyslexia Higher level
visual processes pure alexia (disconnection,
word-form agnosia) Linguistic
analysis alexia with agraphia, central dyslexias