3.1.5 Investigates visual fields of patients with all standards of acuity and analyses and interprets the results Flashcards
What is visual field and what should it subtend?
Visual Field – The visual field is everything that an eye can see in any given instant in time (limited by facial
anatomy: forehead, eyebrows, nose, cheek bone)
o Superior – 60 degrees
o Inferior – 70 degrees
o Nasally – 60 degrees
o Temporally – 100 degrees
* Central Visual Field – Central field subtends 30 degrees, peripheral field subtends >30 degrees
What is cone density? Where is the physiological blind spot? What is a visual field defect?
Cone Density – Max density at fovea diminishing in periphery – no sensitivity at blind spot (ONH) – hill of vision
* Physiological Blind Spot – 15 degrees temporal
* Visual field defect – a departure from the topography of the hill of vision normal limits
Who needs visual fields?
- Unexplained H/A and Migraines
- Unexplained reduced/blurred vision
- Complaining of VF loss
- Raised IOPs
- Blurred Disc Margins
- FH of glaucoma
- Stroke
What is isolated visual field loss? What is generalised visual field loss?
- Isolated visual field loss – Focal VF loss – Termed Scotoma
o Relative Scotoma – light perception is present within an area of focal loss
o Absolute Scotoma – no light perception within the area of focal loss - Generalised visual field loss – Diffuse VF loss
o Diffuse – Diffuse VF loss is sometimes called a generalised reduction or a depression
What should you include in your description of field loss?
- Shape – Quadrantanopia. Hemianopia, Altitudinal Defect, Arcuate Scotoma, Nasal Step, Junctional Scotoma
- Comparison between eyes – Heteronymous (opposite half of VF), Homonymous (same half of VF), Macular
Sparing. - Location – Superior, Inferior, Nasal, Temporal, Central, Paracentral, Peripheral
- Overlapping Homonymous Hemianopia – Incongruent (Partial overlap), Congruent (Complete overlap). The
degree of congruence gives an indication of the anatomical location of the lesion causing the VF defect
Describe field loss associated with the retina?
Retina – Horizontal Raphe (Division between superior and inferior fibres), Vertical Demarcation Line – Superior
(Nasal, Temporal) fibres, Inferior (Nasal, Temporal) Fibres, Macular Fibres (papillomacular bundle).
o Damage to Bundle of NF – VF defect follows shape of bundle (Arcuate Defect – Complete), Partial damage
and loss of function (Hypoxia) can result in partial defect along the NF bundle (Paracentral defect, Nasal step)
(Signs of glaucoma)
o Optic Disc Drusen – enlargement of the blind spot, inferonasal arcuate scotoma (mimic glaucoma)
o ONH Coloboma – Due to incomplete closure of embryonic fissure and build-up of glial tissue (mimic
glaucoma) – most occur inferiorly, Large colobomas lead to superior altitudinal defect, stable over time
o Vascular Damage – (BRVO) – Deep scotoma, sharply defined margin, respect horizontal midline,
o Toxicity – (Vigabatrin) – Used to treat epilepsy – concentric nasal visual field defect
o ARMD – Central visual field loss (drusen and geographic atrophy)
Describe field loss associated with the optic nerve?
o Optic Nerve Fibre Arrangement – ONH greater distribution of macular fibres (temporal edge). ONH to Chiasm
reorganisation of NF. At chiasm Macular fibres centrally, ST superiorly, IT nasally and temporally, SN and IN
inferiorly.
o Lesion – Uncommon, tend to present as damage of the papillomacular bundle due to the greater distribution
of the ONH being for papillomacular fibres. VF defect extend from blind spot to fixation.
o ON Compression – no characteristic defect and depends on fibre affected – Meningiomas most common
cause of compression – these are tumours arising from uncontrolled multiplication of the arachnoid cells.
Compression present as a reduction of VA due to swelling of the ONH leading to atrophy.
Describe damage to lateral geniculate nucleus?
Vascular damage is the most likely cause of the LGN lesion because the blood supply
is comprised of thin networking vessels. The boundary between the lobes where these vessels terminate is the
most vulnerable to damage. Relative high congruency but not complete
o Hourglass defect – damage to the ventral boundary
Describe damage to optic radiations?
Optic radiation can be damaged by compressive tumours or more commonly by vascular
damage – very congruent defect.
o Stroke – Obstruction of blood flow and oxygen to brain, damage depends on location within brain. Px
unaware of defect and not always investigated for defect. Most common is homonymous hemianopias. Most
have some form of VF defect.
o Parietal Lobe (Pie on Floor) – Lesion to this area causes an inferior quadrantanopia
o Temporal Lobe (Meyers Loop) (Pie in Sky) – Lesion to this area causes a superior quadrantanopia
Describe damage to striate cortex?
central 30 degrees of VF represented by 80% of the striate cortex
o Macular Sparing – difficult to demonstrate clinically – 30-2 will not show macular sparing. 10-2 will show
macular sparing
o Temporal Lobe Lesion – Complete Congruency
What are common types of visual field defects?
Paracentral Scotoma: A loss of nerve fibres in the central 10-20o of fixation,
respects the horizontal midline
* Nasal Step: A step-like defect along the horizontal midline due to asymmetric loss
of the nerve fibre bundles in the superior and inferior hemifields.
* Arcuate Scotoma: Coalescence of arcuate scotoma and nasal step, follows the
arcuate pattern of the NFL
* Ring Scotoma: If the arcuate scotoma involves the upper and lower quadrants. It
can be macula sparing as the papillomacular bundle is the last to be affected
* LE monocular defect: Lesion at Optic Nerve
* Bitemporal Hemianopia: Chiasm lesion
* Central Vision loss: AMD, Stargardts or Best Vitelliform à macula disorder
* Right Homonymous Hemianopia: Lesion in Left LGN or Left Visual Cortex
* Right inferior Quadranopia: Left Optic Radiation
* Cecocentral Scotoma: Optic Neurits
* Peripheral Vision Loss: Glaucoma or Retinitis Pigmentosa
