visual fields recap Flashcards
what is the incidence of visual field loss in the general public
3-5%
name the two basic classifications of visual field methods
static and kinetic
how is the kinetic visual field assessment carried out
start from a non seeing area and move in until px detects the target
what is static perimetry the best technique for
the detection and investigation of early field loss
why is detection of early field loss crucial
to detect primary open angle glaucoma
name the two classifications/strategies of static perimetry
threshold and supra threshold
name the two types of threshold static perimetry
full threshold and SITA/ZATA
how does the full threshold strategy work
each location is thresholded sing a staircase procedure
how does the SITA/ZATA strategy work
it is a quicker version of the full threshold strategy
how does the supra threshold strategy work
stimuli are first presented at an intensity that is calculated to be above the patient’s threshold, if the stimuli are seen, then it is assumed that no significant defect exists
list 7 advantages of the threshold strategies for testing visual fields
- sensitive to shallow field loss and early fluctuations in glaucomatous VF loss
- visual field progression (glaucoma)
- allows statistical analysis
- diagnostic information
- provides information about reliability of the data
- highly skilled perimetrist not needed
- reproducible VF test/testing conditions
name a disadvantage of the threshold strategy for testing visual fields
time consuming
name 3 advantages of the supra threshold strategy for testing visual fields
- multiple or single stimulus has enabled speed up of investigation and able to assess visual fields on every visit
- good screening test
- no need for highly trained perimetrist
name a disadvantage of the supra threshold strategy for testing visual fields
insensitivity to shallow visual field defects = poor detection of early POAG
name 3 types of visual field equipments for kinetic perimetry
- gross perimetry/confrontation
- arc perimeters
- certain bowl perimeters e.g. goldman, octopus
name 2 types of static perimeters and give examples of the manufacturers that do them
- automated perimeter - Humphrey field analyser and modern Henson models
- automated/semi-automated perimeters - Henson for supra threshold testing
explain how the automated static perimeter works
the decision making process of the examination strategy is exclusively controlled by the computer and does not require intervention of the operator
explain how the semiautomated static perimeter works
some field tests require the operator to control the examination strategy
e.g. we have to find the patients threshold, or during multiple stimulus when we have to ask the patient how many lights they can see
what test strategy will you use on a patient who has family history of glaucoma
SITA/ZATA fast threshold
when would it be useful to carry out gross perimetry/confrontation test on a patient
in investigating patients who will benefit from a more detailed investigation of their peripheral fields
what is found to be low with gross perimetry/confrontation test
sensitivity
if a patient has poor visual acuity, which test is best to analyse their visual fields
gross perimetry/confrontation test
if you require further peripheral investigation after using the gross perimetry/confrontation test on a patient, what other 2 options can you use
- kinetic methods on a bowl perimeter
- peripheral static methods on a HFA
should a rx be worn for gross perimetry/confrontation test and why
no prescription should be worn for a peripheral fields, because:
- peripheral acuity is poor whether the refractive error is corrected or not
- frames and the periphery of lenses can interfere with peripheral field
in which case may it be worth doing a peripheral field with and without the rx
very high refractive error: +/- 8D or more, too see if there is any difference
when carrying out static perimetry, and measureing the central 30 degrees of visual field, when must an rx be worn
if the rx is above -5,00D
what add should be used on top of a distance rx for a 40-44 y/o
+1.50
what add should be used on top of a distance rx for a 45-49 y/o
+2.00
for what age group should a +2.50 add be used on top of a distance rx
50-54
for what age group should a +3.00 add be used on top of a distance rx
55-59
for what age group should a +3.50 add be used on top of s distance rx
60-64
what add should be used on top of a distance rx for a +64 y/o
+4.00
when will you use BVS and when will you not, when using a patient’s rx during visual fields
BVS is cyl is less than 1.00DC and use cyl in lens holder or use px own rx if cyl more than 1.00DC
what rx will you use on a px who is fully cyclopeged during visual fields
full add
which type of lenses should be used only as a last resort when during visual fields
bifocals, progressives and tinted glasses
list the three different levels of investigations available with the Henson supra threshold programme and the amount of patterns for each level of investigation
- 26 retinal locations in 8 patterns
- 68 retinal locations in 20 patterns
- 136 retinal locations in 40 patterns
what is a disadvantage to using the 26 retinal locations level in the Henson
you can miss an error/scotoma in visual fields
when will you decide to use the 136 retinal locations level in the Henson
if missed lights in the 68 retinal point setting and want to establish the extent of the defect
when will you decide to use the 68 retinal locations level in the Henson
for patients where the field defect is suspected other reasons for performing a more rigorous test
why will you measure a patients threshold instead of setting it by age on the Henson
because the vf machine will assume that everyones threshold is the same
list the 4 types of supra threshold strategies available on the humphrey
- threshold related
- three zone
- quantify defect strategy
- age reference strategy
how does the threshold related type of supra threshold strategy work on the humphrey
an expected hill of vision is calculated and the stimulus intensity is set 6DB brighter than expected at each location
how does the three zone type of supra threshold strategy work on the Humphrey
the expected hill of vision is calculated as in threshold related e.g. 6DB brighter than expected at each location and the defects are classified as relative or absolute
what does relative and absolute stand for in the three zone type of supra threshold strategy on the Henson
- relative defect = if point missed the first time then the vf machine shows a brighter stimulus, if the patient gets the brighter stimulus then it is a relative defect
- absolute defect = if the patient misses the stimulus a second time which is at a brighter level than the first, then the brightest stimulus will be shown, if the patient misses this then it is classified as an absolute defect
how does the quantify defect type of supra threshold strategy work on the humphrey
locations missed twice at screening level are thresholded, so the depth of the scotoma is assessed by establishing the threshold
how does the age reference type of supra threshold strategy work on the Humphrey
the expected hill of vision is estimated from the patient’s birth date
which programme requires both eyes to be tested at the same time
estermann vf test
what is the estermann vf test used for
ascertaining whether fit to drive
what correction will you use with the estermann vf test
no trial lenses are used, if px requires an rx to function daily then use actual glasses, if does not require an rx to function daily then do not use an rx, the same applies to tinted specs.
other than drivers, who else is the estermann vf test used on
fire fighters
what visual field test will you do if a patient has symptoms or has a FHG
SITA fast 24-2
when will you use an amsler chart
if you see a suspicious macula, or if you are unable to see the macula
at what distance is the amsler chart designed for
28-32cm, so the patient should be corrected for this distance
name 2 limitations of the amsler chart as a screening tool
- only detects 50% of patients with macular disease = poor sensitivity
- will incorrectly identify about 2% of patients as having a scotoma when they do not have one
