Types of VF Defect and Possible Causes
Tunnel Vision
- Glaucoma
Uniocular Aniopia
- Optic nerve lesion
Bitemporal Hemianopia
- Pituitary tumour
Binasal Hemanopia
- Carotid aneurysm
- Vigabatrin use
Homonymous Hemanopia
- Post-chiasmal lesion e.g. in stroke
Alterations to Routine for Patient with VF Defect
- Remove any obstacles
- Guide courteously
- Test slowly!
- Test chart and targets
- Patient Communication
- Objective refraction
- Subjective refraction
- Pinhole use
- Visual field testing
Remove Any Obstacles
- Most trip hazards out the way e.g. wires or chairs
- Ensure test room is accessible i.e. no stairs
- Test VIP in quietest area of practise possible
- Remove test chair if the patient is in a wheelchair
Guide Courteously
Use proper technique:
- VIP follows half a pace behind
- VIP takes arm just above the elbow, can hold arm or clothes themselves
- VIP follows in single file in a crowded space (shouldn’t really be an issue in practise)
- Keep up a running commentary about surroundings and next steps
- When dealing with doors place the VIP on the same side as hinge and hand them the door so that they can work out its placement
- When approaching seat in testroom, approach from front and place the VIPs hand in the handle or on the cushion of the seat to allow them to work out its location and where they need to sit in relation to their body. Also make aware of step
Test Slowly!
- Can be booked into double slots to allow time without patient feeling hurried
- Avoid uneccesary procedures to prevent hurrying in important parts of routine
Test Charts and Targets Adaptation
- VIP may find it difficult to find test chart if field loss is extensive
- Move test chart nearer if needs be
- The entire test chart may not be able to be seen in a homonymous hemianopia so just test using the remaining parts of the field
Snellen Chart in VIP Testing
Advantages
- Very sensitive to blur and refractive error
- Can be portable
- O letters for use in cross cyl
Disadvantages
- Crowding not constant as unequal number of letters per line
- Unequal letter size progression
logMAR Chart in VIP Testing
Advantages
- Equal amount of letters per line so crowding is consisitent
- Sensible size progression (1.25x)
- Final score takes into account all letters read
Disadvantages
- Can be larger so not as portable and easy to illuminate
- No ‘O’ letters for cross cyl
Patient Communication Adaptation
- VIP patients often old and so at risk of other barriers to communication such as hearing difficulties
- Stay in patients seeing side, but try ensure you can be heard if other ear is the better one
- Do not use gestures which the patient may not be able to see, ensure verbal communication is spot on
- Be encouraging, remember the psychological aspect of their condition
Objective Refraction Adaptation
- Takes on a new significance when there is visual impairment
- Although ability to see out is impaired, in many cases the ability to see in is retained e.g. in stroke
- Take more time to get a accurate result in these patients
Subjective Refraction Adaptation
- Use trial frame with full aperture lenses to allow for eccentric viewing and head postures
- Use preferred retinal locus using skinny teqnique and 5^ lens
- Use bracketing techniques appropriate to patient VA e.g. if seeing 6/60 then use ±1.00DS steps
- Use larger cross cyl e.g. ±0.75DC or more, Use letter O on Snellen chart for target rather than JCC circles
Pinhole Use in Visually Impaired
Beware of use in central scotomas as will result in NLP
Visual Fields in Those With a Central Defect
- Amsler charts are a good way of screening central visual field
- 10-2 visual fields screen 5x as many points in central 10 degrees as a 30/24-2 test so are good for monitoring central fields in glaucoma
- Still at risk of peripheral disease e.g. glaucoma so modify fields machine to allow fixation, e.g diamond rather than light target
Amsler Charts
- Are 7 different charts
- Include standard amsler, charts with diagonals to support those with central scotoma
- Measures 10 degrees either side of fixation
- can be used to detect preferred retinal locus
- Can be taken away for remote monitoring
Extent of Human Visual Field
- 50 degrees nasally
- 50 degrees superiorly
- 90 degrees temporally
- 60 degrees inferiorly
Visual Fields in Those With a Peripheral Defect
- 24-2 only measures 24 degrees from fixation which is far from entire field
- Gross defects can be mapped with confrontation
- Peripheral VF measurement can be achieved using Goldman VFs which is performed in a domed piece of equipment at 33cm
Visual Fields in Those With Neglect
- Binocular fields can be used with eye movements to see if training eye movements can help “enlarge” useable field
