Interpreting VF

Kinetic:

• moving target

• finds peripheral extent of field

• lines linking points = isopter ( more closley spaced = sharper drop in sensitivity)

• quick easy testing with gross perimetry

• unit of measurement: eccentricity( distance from fixation point) + meridian

Static:

• lights presented at fixed points at decresing brightness until no longer seen

• unit of measurement: threshold measured in (cdm^-2) or (asb) or log10

  • 1 cdm^-2 = 3.14asb

  • 1 log unit = 10x/ decibels ( dB)

• Full or supra threshold

1. Confrontation fields

2. Arc perimetry

3. Bjerrum screen

4. Goldmann bowl perimeter

Confrontation fields:

• working in a plane so:

  • can’t assess temporal field

  • variable target distance

• assumes your fields is at least equal to pxs

Arc:

• record unlike confrontation, results not dependant on examiner's facial contours

• red targets favoured as ONH disease causes red to become desaturated.

Screens:

• not good for small areas of VF loss ( glaucoma)

• 1m testing distance

Goldmann:

• 6 different sized stimuli ( O to V)

• 4 different intensities ( 1-4)

High threshold= better sensitivity = dimmer lights seen

normal range = 0 to 30dB

can find depth of defect eg.

Supra:

• good to use when expect px to be normal

• identify defects you didnt expect

Full:

• good to use when you know defect is there

• good to monitor VF loss progress

• necessarily complex if px is normal

• the fixation loss number should be low eg. 2/10 means px was fixating on the point 8 out of 10 times so the test is pretty accurate