PERIMETRY : PERIMETRY Dr Praveen Deshpande
PG in MS Ophthalmology
VIMS, Bellary. Normal visual field : Normal visual field Defn - as the area perceived simultaneously by a fixating eye.
Traquair –island of vision in the sea of darkness Slide 3: Light adapted state- island of vision central peak which corresponds to fovea, island slopes downwards towards periphery.
Dark adapted – rod vision predominates , contour island of vision - flat with central depression rather than peak. Hill of vision : Hill of vision Slide 6: The hill of vision is a 3-dimensional representation of the retinal sensitivities.
The x-y-plane represents location in the visual field.
The ordinate (z-axis) displays the normal threshold stimulus luminance Slide 7: Isopter –a boundary line on a visual field within which a light target of a certain size and intensity is visible.
Scotoma- area in visual field with loss of retinal sesitivity
Absolute – area of total loss in which even with largest and brightest target cannot be perceived.
Relative – area of partial loss within which a brightest or largest can be seen and smaller or dimmer target is not seen. Slide 8: Luminance –intensity or brightness of a light stimulus, measured in apostilb.
the measured light sensitivity is expressed in log units referred as decibels (db)
Visible threshold- luminance of given stimulus (asb or db) at which it is perceived 50% of time. Slide 9: Suprathreshold stimuli-
brighter than threshold, will be 50%of time.
dimmer than threshold and seen < 50% Slide 11: Decibel scale is a relative scale created to measure retinal sensitivity.
A decibel is 0.1 log unit , 10 dB represents 10 fold decrease of max stimulus and 20 db represents 100 fold stimulus attenuation.
zero dB- max intensity of stimulus Slide 14: The perimeters measures the ability of the eye to detect a diff in contrast between a test target & background luminance.
the differential light sensitivity (d.l. sensitivity) is measured in different locations of the retina in order to detect deviations values(defect).
Threshold sensitivity is highest at fovea and decreases progressively towards the periphery.
Retinal sensitivity 1/α threshold PERIMETRY : PERIMETRY Defn - Perimetry or campimetry is the systematic measurement of differential light sensitivity in the visual field by the detection of the presence of test targets on a defined background.
-Static HISTORY : HISTORY Mariotte discovered the blind spot in 1668,
clinical perimetry started Graefe in 1856.
Important further steps were made by Bjerrum in 1889
Groenouw introduced isopters in 1893 as the connection of points with the same differential light sensitivity.
The Bjerrum screen remained the popular standard in
the USA, called the Tangent Screen.
The first cupola perimeter was designed by Goldmann in 1945 Slide 17: Uses of perimetry
-glaucomatous field defects
-optic disc lesions
-optic nerve lesions
-neuro-ophthalmic lesions Slide 18: Basic principles of VF testing
-background luminance Slide 19: Stimuli – stimuli used in perimetry are spots of lights of various predefined combinations of diameter and intensity.
Visibility of stimuli depends
- distance of eye from screen
- Length of time
- Color of the stimuli & background
- Condition of the pt Slide 20: Stimulus size –standard target is white disc, it is adjusted by varying stimulus size & luminosity.
Mean retinal sensitivity increases with increasing size of the stimulus-spatial summation
Exposure time-stimulus is presented for longer peroid of time become more visible-temporal summation.
Normal-0.1 sec, HFA uses 0.2 sec .
Suprathreshold stimulus is presented for
longer time -0.5 – 1sec
Background luminance –luminance used is marginally photopic . Slide 21: Patient variables
cataract & media opacity
Pupil size-miosis depresses central and peripheral threshold sensitivity and exaggerate field defect.
mydriasis has less influence on vf. Slide 22: Age – increasing age is a/w decrease in retinal sensitivity, progresses throughout life.
Media opacity- glare and change in the intensity of stimulus. Exaggerate central or peripheral VF.
Refractive error- primarily influence the central field, myopia of < 3d no correction Kinetic perimetry : Kinetic perimetry kinetic perimetry-stimulus is moved from non seeing area to seeing are along a set meridian.
- Arc and bowl
central 30 degrees of the field.
A black felt "tangent screen", usually 4'x4', the usual location of the blind spot when tested at 1 meter and 2 meters.
Targets of various sizes and colors. Slide 24: Target size, test distance and target color :
1/1000 W = 1 mm target at 1000 mm (1 meter), white target .
Absolute scotoma (ie blind spot): double hatched lines
Relative scotoma : single hatched lines
If test performed at 2 meters .
Visual field and blind spot are expected to expand to twice the size when test distance is increased Slide 25: Arc and bowl –
-central & peripheral field
Screen – curved ribbon of metal or bowl shaped
Bowl of Goldmann - radius 300mm and extends 95* to each side of fixation
Target varied by changing size and intensity
Size: 0, I, II, III, IV, V : 0 is the smallest, V is the largest
Intensity: 1, 2, 3, 4 : 1 is the dimmest, 4 is the brightest
Intensity: a, b, c, d, e : a is the dimmest, e is the brightest Advantages of manual perimetry : Advantages of manual perimetry Better examination of peripheral field
Reveal scotomas that were missed between the testing points in static perimetry4.
Shape of the defects may also be more impressive
Sever VL test-retest variability is better
Patients with central scotomata
Neuro -ophthalmology. Slide 28: Disadvantages of manual perimetry
less reliability & reproducibility
less sensitive in detecting early VFD
lack of fixation monitoring
lack of normative data Automated Static perimetry : Automated Static perimetry standard protocol of static white –on-white stimuli known as standard automated perimetry. size of the stimulus and the locations tested remain constant.
Intensity (brightness) of the stimulus is varied in order to determine the level at which the individual sees the stimulus.
ex – Humphrey
octopus Slide 30: Advantages of static perimetry
- short duration
-no examiner bias
- availability of normative data
- higher sensitivity Slide 31: Test pattern-
central 30 or 24 deg with 6 deg separation between test location
72 points in 30 deg and 54 points in 24 deg
-central 10 deg with 2 deg
30-2 and 24-2 in early GFD
10-2 in advanced GFD,small central defect. Slide 33: Testing strategies - The method to determine the differential light sensitivity is called “test strategy”.
The Normal test strategy-stimulus luminance is varied up and down in steps the procedure is called staircasing or bracketing to find the luminance value (threshold). Slide 34: NS Normal strategy – is the standard in perimetry.
4-2-1dB bracketing procedure with two threshold crossings
Duration 10-15 minutes
Early and shallow defects with younger
LVS Low vision strategy – presents a 4-2-1 dB bracketing test method
starting with its brightest stimuli and stepping up from 0 dB thus reducing the time . Slide 35: Dynamic strategy – stands for a test procedure with varying step sizes and one threshold crossing.
The steps are small in the region of normal sensitivity and become larger toward locations where the field is depressed.
Duration reduced by a factor of two.
Early detection of visual field loss and in focal defects Slide 36: Tendency oriented perimetry(TOP) –
takes advantage of the fact that the d.l. sensitivity
of the retina is interrelated rather than having an
individual (isolated) value.
During the test, every answer at a particular point is also
taken into account in the adjustments of the
TOP a full threshold 2 min.
Depressed fields, for children, and for elderly persons Slide 37: 2-LT Two-level-testing – is a qualitative rather than a quantitative screening test.
The results give only a rough indication of the
Status of the visual field in terms of “normal,” “relative” or
1-LT One-level-test – used screening , the qualitative results are expressed as “normal”. Slide 38: Threshold programs
-fastpac full threshold
Full threshold – threshold values are defined stimuli intensity detected 50% of the time.
Threshold is crossed twice initially in 4db increments then 2db , 20 min. : Fastpac- threshold is crossed once and in 3db, this reduces test duration by 35% & also reduces the accuracy.
Swedish interactive Threshold algorithm(SITA)-
the test time is reduced by eliminating retest trials for short –time fluctuation determination & for assesing FP and FN responses.
-SITA Fast Slide 40: SITA Standard –
most accurate , most commonly used strategy and reduces duration by 50%.
SITA Fast –
reliability is worse than SITA Standard Octopus : Octopus It estimates threshold as the avg of last seen & unseen stimulus.
Intensity of suprathreshold is based on data from aged matched N subjects.
Stimulus duration -0.1 sec
Fixation monitorned with video display
Bebie curve-identification of diffuse visual field defect. Slide 42: For a strict definition of the d.l. sensitivity, certain parameters like stimulus size, background luminance, exposure time and color, need to be defined.
• background luminance: 1.27 or 10 cd/m2
• background color: white (yellow, in Blue-on-Yellow perimetry)
• stimulus size: Goldmann size III
• stimulus color: white (blue, in Blue-on-Yellow perimetry)
• exposure: 100 ms Slide 43: Program LVP characteristics
Test locations 9 points from 0 – 30°, 66 from 30 – 87°
Stimulus size Goldmann V
Stimulus duration 200 ms
Background 4 asb
Test phases 2 Slide 44: Octopus Humphrey
Bg - 4 asb 31.4 asb 31.5 asb
I-V III,V I-V
Duratn- 100ms 100ms 200ms
Test - 4-2-1 bracketing 4-2bracketing
Strategies Dynamic SITA Normal
TOP SITA FAST octopus : octopus Slide 50: Draws isopters in colors and calculates the isopter area in deg˝ to allow analysis of change
Displays age-corrected normal isopter values serving as an orientation to start the testing.
Displays and prints two fields (RE& LE) on one page. Slide 52: Reliability Factors
FIXATION LOSSES: -fixation monitoring
-heijl krakau technique(blind spot monitoring)
FALSE NEGATIVE ERRORS:
Pt doesn’t respond to stimuli > 9db than previously registered.
FALSE POSITIVE ERRORS:
Pt responds to auditory in absence of visual stimuli Slide 53: FLUCTUATION FACTORS:
It represents consistency of pt response during a single test.
LOW FLUCTUATION: < 1.5 dB
NORMAL FLUCTUATION 1.5dB TO 2 dB
MEDIUM FLUCTUATION >2 dB BUT < 3 dB
HIGH FLUCTUATION >3 dB Slide 54: GREY SCALE-
schematic representation of threshold values
it helps to appreciates general pattern of VF Slide 55: Total Deviation –
total deviation = (patient's response) - (expected normal)
pattern deviation = (total deviation) + (overall sensitivity changes) GLOBAL INDICES : GLOBAL INDICES -mean deviation
-pattern standard deviation
-corrected pattern standard deviation
Mean deviation – avg deviation of pt from the control, negative indicate depressed field and posiyive indicate higher than normal Slide 66: Pattern standard deviation-
represents the degree of irregularity in the field, increase in PSD in a glaucoma pt indicate progression.
Corrected pattern standard deviation-
eliminates irregularities in VF sec to unreliable pt response. Glaucoma hemifield test : Glaucoma hemifield test - identify localised field defect typical of glaucoma
- sup& inf hemifield - 5 zones , avg threshold
values of sup & inf mirror images are compared.
GHT within N
GHT outside N
General reduction of sensitivity
Abormal high sensitivity Andersion criteria : Andersion criteria -3 non edge adjacent scotoma in TDPPor PDPP with p values
two pt P<5%
one pt P < 1 %
-PSD P< 5%
-GHT -abnormal Short wavelength automated perimetry- : Short wavelength automated perimetry- Designed to isolate short wavelenght pathway
Large blue stimuli presented on yellow background
Detects GFD earlier than SAP
Not suitable for follow up of mod & advanced glaucoma
Difficult to diff GFD from cataract FREQUENCY DOUBLING PERIMETRY : FREQUENCY DOUBLING PERIMETRY large M type ganglion cell are affected in early glaucoma
Based on frequency doubling method
Each stimulus is a series of white and black bands
flickering at 25 h
mod & advanced glaucoma-96%
early glaucoma – 85%
Test duration – 90sec
screening programs High pass resolution perimetry : High pass resolution perimetry -stimuli-rings of diff size at diff locations
-rings – dark borders & bright high centers
-high repeatability & reliability
-detects VFD in early and mod glaucoma Random dot motion perimetry : Random dot motion perimetry -takes the advantages of reduced motion sense in glaucoma
-shift in position of dots within a defined circular area against background of fixed dots.
-pt tells the direction in which dots are moving
- glaucoma pt – abnormal motion perception, prolonged reaction time to stimulus and less precise location Slide 75: Approximately 80% of the ganglion cells are parvocellular “P” type cells sensitive to color and contrast;
5% are koniocellular “K” cells, responsive to blue-yellow opponents;
15% magnocellular “M” (My) cells –motion &temporally modulated stimuli.
K cell system: Blue-on-Yellow perimetry (B-Y)
M cell system: frequency doubling technique (FDT)
P cell system: Hi pass resolution perimetry (HRP) Visual field defect : Visual field defect Paracentral scotoma
Nasal step defect
Temporal wedge shaped defect
Blind spot changes