understanding visual field

Understanding Field Loss

Presented on Friday 2 November 2007

Neurological Causes of Visual Field Loss: Epilepsy (surgical treatment), Cerebral palsy, PVL, Tumour, Stroke.

Dr Andrew Blaikie, Consultant Ophthalmologist, NHS Fife

Cerebral Palsy

Motor impairment due to some kind of brain injury
Often unknown
Often associated with other impairments
Not cause of visual impairment
It's an associated symptom

Spastic Cerebral Palsy

Children with this type may find their muscles becoming very stiff and weak, especially under effort. This can affect the way they move.

Athetoid Cerebral Palsy

Children with this type of cerebral palsy often lose control of their posture. They may also tend to make unwanted movements.

Ataxic Cerebral Palsy

Children with this type of cerebral palsy usually have problems with balance. They may also have shaky hand movements and irregular speech.

Cerebral Palsy

Visual Acuity
Visual Field
Eye Movements
CVI
Refractive Errors
Accommodation

area affected by CP

Lower field defect

field loss

May not be completely lost

partial loss

Cerebral Palsy + PVL

Patient with spastic diplegia form of CP complaining of difficulty with tasks involving lower field.

CP and PVL

Periventricular Leucomalacia PVL

Brain Damage inPremature Babies

Hypoxia
Hypo-perfusion
Leads to brain injury of Periventricular White Matter
Spastic Diplegia
Visual Impairment

brain scan

Cerebral Visual Impairment

Two streams of visual information in the brain

The ‘Where’ stream
Fast reflex unconscious information to act upon
The ‘What’ stream
Slower conscious recognition of world

dorsal and ventral

Simultanagnosia

Inability to deal with complex scenes also known as simultanagnosia
Functionally visual field becomes small
Poor attention and easily distracted
Sticky fixation

Epilepsy - Hemispherectomy

Used in intractable seizures
Surgical removal of portions of the non functioning hemisphere combined with splitting the corpus callosum.
This is the channel which allows signals to cross from one side to the other.
Stops the seizure starting at one hemisphere and travelling to the other
Mainly removes portions of the temporal lobe which can cause quadrantopias or removal of occipital lobe can results in homonymous hemianopia.

Homonymous hemianopia

homonymous hemianopia

what hemianopia sees

However, in children some functional field can still result despite removal of occipital (site of the visual cortex)

Thought to be mediated by higher cortical areas or subconscious visual pathways via the midbrain/brainstem (Werth, Reinhard , 2006)

Epilepsy

Not all children with epilepsy will have visual field loss
Usually it is the treatment (both surgical and medical) for epilepsy rather than the condition itself which gives rise to field defects.

Infantile Spasms

Fitting from early age
Difficult to control
Delays development
Often associated with structural brain problems

Medication

VIGABATRIN – anticonvulsant drug
Used in the treatment of generalized seizures and infantile spasms
Field defects noted after approx 1 year treatment
Prevalance of between 42% (Wohltab, G et al., 1999) and 71% reported (Russell Eggitt, IM et al 2000)

Vigabatrin

Atrophy of the retinal nerve fibre layer sparing macular area
Generalised constriction of visual field
May not be reversible (Hardusa P et al (2000)

constriction of visual field

Tumours

Craniopharyngioma
Pituitary
Glioma
Menigioma

Tumours

Approximately 50% of childhood intracranial tumours will have visual symptoms
Whether Benign or Malignant
Tumours create pressure on the signals within the visual pathway
Direct – within the visual pathway
Indirect – by raising the intracranial pressure – (although unlikley to be aware of field defect from enlarged blind spot)

Craniopharyngioma

craniopharyngioma

Arises from stalk of pituitary

Presses on chiasm from behind and above
Young patients present with pituitary problems or hydrocephalus
Older complain of visual disturbance

Pituitary Tumours

pituitary tumour

Craniopharyngioma and Pituitary Tumour

Field loss - bitemporal hemianopia or (quadrantopia in early stages)
CP compresses chiasm from above PT compresses from below.
Chiasmal lesion only – will give rise to a different field defect in each eye that is, loss of right field in right eye and left field in the left eye.

visual field loss