PC - Visual Fields - Week 3 Flashcards
How can the visual field be represented?
Island of vision in a sea of blindness.
What are Amsler grids used for? What is it used to regulate?
Central scotoma/distortions. Used to regulate AMD.
Describe what Amsler grids are, and how they work.
Consists of a grid, each square is 5mm, with a focus point in the middle. If the lines appear blurry or are missing, or are black, suggests a disorder.
How do metamorphosia, scotoma, and AMD appear on an Amsler grid?
Metamorphosia - a distortion in the lines
Scotoma - blind spot, lines disappear
AMD - distorted lines with a black spot.
Under what conditions should Amsler grid testing be conducted?
Fully corrected, and bright conditions. No squinting, and the head/chart must both be straight.
What is the best way to know what the patient is seeing when they look at an Amsler chart?
Ask them to draw what they see.
If a patient has AMD in one eye, what is the chance of them having it in the other?
40%
Can a confrontation test detect glaucoma?
No.
Is confrontation done under habitual vision?
Yes.
Describe a facial Amsler test.
Ask the patient to look at your face from 75cm away, if your features are blurry etc.
Explain what distances are used during a confrontation test.
Heads are held 75cm apart.
Hands are held 50cm away from the patient.
Both heads must be eye level and straight.
Describe the confrontation test.
Ask patient to cover their eye entirely with their palms. Ask them to fixate on your corresponding open eye.
Hold up a given number of fingers in the quadrant being tested, and ask them to add them without looking at your fingers. They should be fixating on your open eye.
Test both hemifields twice for confirmation, then repeat for the other eye.
Define Neglect and Extinction.
Neglect - when you present fingers in two quadrants, they neglect one quadrant
Extinction - you present fingers in two quadrants, but they get the total wrong, but individual quadrants correct
Describe the red cap test.
Hold the cap at 40cm with monocular viewing.
Have the patient tell you the colour of the cap.
Move the cap to the various quadrants, and judge the caps dimness/brightness on a 1-10 scale, assuming when centre-held it is 10.
Describe kinetic red cap testing.
Have the patient tell you when the cap changes colour or they can no longer see it.
What tests are essential for glaucoma?
kinetic and static perimetry
Describe standard automated perimetry.
Is computerised, measuring sensitivity to small white lights presented on a dimly lit background. Performance is compared to a normal curve.
Describe the Humphrey notation for perimetry.
Specified as X-Y
X - extent of coverage
Y - 1 if on the midline, 2 if offset from the midline
Describe the Medmont notation for perimetry.
Specified as Annn A can be -M for macula - 10 degrees -C for central - 30 degrees -G for glaucoma - 30 + 50 degrees nasal -P for peripheral - 50 degrees nnn is the number of test points.
Between Humphrey and Medmont perimetry, which is a grid and which is radial? Does the pattern have any effect?
Humphrey - grid
Medmont - radial
Pattern has no effect.
Compare static perimetry screening with static perimetry threshold - advantages.
Screening Good for the elderly Cortical defects Learning/training Threshold Confirming a defect Monitoring for stability
Compare static perimetry screening with static perimetry threshold - disadvantages.
Screening Early subtle defects Defects Monitoring disease progression Threshold Patients with limited attention spans Disabled
Name the five visual field defects, and damage to the appropriate structure to induce it.
- Total blindness of ipsilateral eye - optic nerve
- Bitemporal homonymous hemianopia - optic chiasm
- Contralateral homonymous hemianopia - optic tract
- Contralateral homonymous superior quadrantonopia - temporal lobe
- Contralateral homonymous inferior quadrantonopia - parietal lobe
Describe what the output values are for perimetry, and where they are.
Top left - threshold values
Top right map - greyscale map
Top left map - numerical total deviation map
Middle 2 maps - numerical pattern deviation maps
Under greyscale map - glaucoma hemifield test
Under GHT - VF indices, significant if there is a P value
Bottom 2 maps - total deviation probability maps - most accurate
