7.1.7: Understands special examination needs of px w/ severe VF defects

Question 1

What eye test adaptations do you need to make for pxs with severe visual field defects?

Answer 1

• logMAR at closer distance
• Uniform lighting
• Refract over px’s glasses
• Bracket & use high lenses as starting point
• Use trial frame and full aperture lenses - avoid phoropter
• Encourage eccentric viewing
• iCare or Perkins tonometry
• Direct ophthalmoscopy
• Big fixation targets - ‘O’ letteer for cyl
• Rely on objective methods

Question 2

How do you interact with pxs who have severe VF defects?

Answer 2

• Guide px on affected side into room & seat
• Approach, talk and test px on unaffected side
• Move trip hazards, obstacles, chairs
• Make sure well-lit room
• Downstairs access for pxs with mobility issues

Question 3

Describe visual field defects and what they look like? Paracentral scotoma, nasal step, arcuate scotoma, monocular defect, bitemporal hemianopia, binasal hemianopia, central vision loss, homonymous hemianopia, inferior quadrantopia, cecocentral scotoma, peripheral vision loss.

Answer 3

• Paracentral scotoma: loss of nerve fibres in central 10-20 deg of fixation, respects horizontal midline
• Nasal step: step-like defect along horizontal midline due to asymmetric loss of nerve fibre bundles in uperior & infeiro hemifields
• Arcuate scotoma: coalescence of arcuate scotoma & nasal step, follows arcuate pattern of nerve fibre layer.
• LE monocular defect: lesion at optic nerve
• Bitemporal hemianopia: chiasm lesion
• Binasal hemianopia: pituitary tummour. Nasal fibres are lower and pituitary right beneath them. Vigabatrin toxicity (epilepsy med).
• Central vision loss: AMD, stargardts or Best Vitelliform –> macular disorder
• Right homonymous hemianopia: lesion in left LGN or left visual cortex
• Right inferior quadrantopia: left optic radiation
• Cecocentral scotoma: optic neuritis
• Peripheral vision loss: glaucoma or retinitis pigmentosa

Question 4

What should the VF defect be on the screener machine?

Answer 4

• Reproducible
• Consistent with optic disc appearance/relevant structures
• Reliable: <20% fixation losses, <33% false +ves (trigger happy)/false -ves (px does not respond to brighter stimulus even though seen dimmer)

Question 5

Describe the Humphrey VF Analyser: Targets, test patterns?

Answer 5

Near add worn - distance 30cm
Targets:
- central target: yellow light in bowl’s centre
- small diamond: for pxs who cannot see centre target e.g. AMD. Px looks in centre of 4 lights.
- large diamond: for pxs who can’t see above two.
- Test –> Fixation target –> select central, small diamond, large diamond

Test Patterns:
- 10-2: measures 10° temporally & nasally. Tests 68 points. Used for macula, retinal & neuro–ophthalmic conditions and advanced glaucoma.
- 24-2: measures 24° temporally & 30° nasally & tests 54 points. Used for neuro-ophthalmic conditiosn & general screening as well as early detection of glaucoma.
- 30-2: measures 30° temporally & nasally and tests 76 points. Used for general screening, early glaucoma & neurological conditions
- Estermann: used to test functionality of px’s vision to ensure they are safe to drive. Binocular.
- C76: supra-threshold - pass/fail on each spot. Does not change brightness of stimulus. General screening.

Question 6

What is mean deviation? Pattern standard deviation? Glaucoma Hemifield Test?

Answer 6

MD:
- average difference from normal expected value in px’s age group. Representation of depressed vision for each point when compared with age-matched controls
- it does not account for global depression e.g. cataract or vitreous haem
- -2.00 or less could indicate glaucoma

PSD:
- provides info on localised loss
- high PSD: non uniform sensitivity loss (not diffuse like cataract or vit haem)
- as glaucoma progresses, PSD may seem to improve due to global depression of hill of vision

GHT:
- compares points in upper field to corresponding points in lower field
- only on 30-2 & 24-2
- “outside normal limits” - may signify glaucoma
- “borderline”
- “within normal limits”

Question 7

Describe confrontation as VF measure?

Answer 7

• test 33cm away
• move target from not seen to seen
• compare px’s VF to own
• 15mm red target
• v gross result
• useful for pxs with mobility issues who cannot get on Humphrey VFA

Question 8

Describe coloured targets as a measure in neurological conditions?

Answer 8

• In chiasmal lesions due to pituitary tumours, coloured desaturation occurs across vertical midline
• Only suitable for identifying gross VF defects rather than exact positionings & finer details

Question 9

Describe Amsler to measure scotomas?

Answer 9

• used monocularly to assess for changes at macula
• near correction worn
• chart used at 30cm (subtends 20° of central VF)
• each sqaure represents 1°
• px fixates central dot & notes:
  1. is central dot visible?
  2. see 4 corners & 4 sides of grid whilst focussinng on dot in centre?
  3. any blank or blurry sections of grid while focussing on centre?
  4. any wavy lines (horizontal & vertical) of grid while focussing on centre?
  5. any moving lines, shiny sections or vibrations noted in grid while focussing on centre?

-For pxs with central scotoma, use grid with cross
- To identify disorders associated w/ red desaturation, use red grid e.g. pituitary tumour causing partial blindness, toxic maculopathy or toxic optic neuropathy
- To detect paracentral scotomas (blindspot or distortion) use white dots grid on black background
- To detect distortion in specific meridian use horizontal lines grid –> useful if reading difficulties
- To identify fine visual distortions near centre of VF e.g. metamorphopsia use: narrow horizontal lines grid. Line 1° above and below fixation
- To identify subtle macular degeneration use grid with smaller grid around large central dot.

Question 10

Describe frequency doubling technology (FDT)?

Answer 10

• A low spartial frequency sinusoidal grating (<1 cycle/°) that undergoes high temporal frequency counterphase flicker (>15Hz) appears to have ~2x as many light and dark bars than are physically present –> phenomenom known as frequency doubling –> Spatial frequency appears to be doubled
• Magnocellular pathway carries info about large, fast things (low spatial frequency, high temporal frequency) & colourblind. This pathway is what FDT tests and is damaged in early stage of POAG.
• C-20 presentation tests central 20° with 17 stimulus locations made up of 4 10° targets per quadrant & one circular 5° central one.
• N-30 presentation tests above points plus 2 additional points, one presented above & other below horizontal midline positioned below 20° & 30° in nasal field. Nasal points go beyond FDT screen widt, need to adjust fixation.
• -5 screening test presents target at contrast level that 95% of healthy, age-matchedd subjectes expected to detect. If seen, not retested & labelled as normal at P ≥ 5. If unseen, retested at same contrast.
• If 2nd target not seen, then presented at contrast level that 98% (P of 2%) of healthy subjects expected to see - labelled as P<5 if seen.
• Retested 1 more time at higher contrast level of P of 1% (expected to be seen by 99% of healthy subjects) if seen P<2% - not seen P<1%
• Higher sensitivity at deteting early defects at expense of lower specificity

+ves: quick test, detects early glaucomatous defects
-ves: pxs find difficults, does not store data so no statistical analysis, points are tested in central 20/30° with large targets - representation of extent of defect is limited

Screening: C-20-5 (test always selected, if failed, repeated - if failed again Humphrey), N-30-5
Threshold: C-20, N-30