automated static stimuli humphrey statpac · brtishjournalofophthalmology1994;78: 175-184...

BrtishJournal ofOphthalmology 1994; 78: 175-184

A comparison of automated static dark stimuli withthe Humphrey STATPAC program in glaucomatousvisual field loss

Erkan Mutlukan

AbstractVisual field examination is conventionallyperformed with bright stimuli on a dark back-ground. Dark stimuli on a bright background,however, may provide different information aslight increases and decreases are subject toparallel processing in the visual pathway.Twenty five eyes with primary open angleglaucoma and visual field loss were examinedwith the Humphrey visual field analyser thres-holding program 30-2 and the computerassisted moving eye campimeter (CAMEC)using static dark stimuli at four differentWeber contrast levels of -10 (n=9), -22(n=25), -37 (n=14), and -76% (n=25) on acathode ray tube with a background luminanceof 10 cd/m2. The cumulative results obtainedwith STATPAC 'pattern deviation' empiricalprobability maps and the results from eachcontrast of the dark stimulus at identical testlocations were compared at eccentricity annulibands of 4-9, 10-20, and 21-28 degrees. Darkstimuli of lower contrast provided higherabnormal point detection rates. Furthermore,visual field defects to the low contrast darkstimuli were more extensive than those to theluminous stimuli. In conclusion, dark stimuliallowed the delineation between glaucomatousfield defects and the normal regions in thecentral visual field.(BrJ Ophthalmol 1994; 78: 175-184)

Henry Ford Hospital,Department ofOphthalmology, 2799West Grand Boulevard,Detroit, Michigan 48202,USAErkan MudukanAccepted for publication28 July 1993

Visual field examination is universally per-formed with luminous stimuli on a relatively dimbackground. However, the visual system isthought to have differential sensitivity to bothincreases and decreases in light intensity as theend result of parallel processing in 'on' and 'off'pathways respectively. These pathways start atthe bipolar cell layer' and project to central visualstructures through the on centre and off centreretinal ganglion cells2-7 to provide a maximumcontrast sensitivity function.89 'On' and 'off'pathways display several morphophysio-logical,'5-'8 psychophysical,'9123 and electro-physiological asymmetries.2425 The smallernumber of off centre retinal ganglion cells49 1126 27

suggests a smaller functional reserve (photo-receptor ganglion cell cortical neuron channels)in the visual system. Low contrast dark stimulion low photopic and mesopic backgroundsmay have higher affinity to the magnocellularsystem28 29 which processes achromatic con-trast.333 As the magnocellular system ismore vulnerable to glaucomatous neuronaldamage,36 visual field examination with dark

(negative contrast) stimuli may provide informa-tion which cannot be obtained using lightstimuli.3738The high contrast black stimulus has pre-

viously been used for blind spot detection andfixation monitoring on a hand held tangentscreen test chart.39 The black stimuli may revealglaucomatous visual field abnormalities.' Thelow, intermediate, and high contrast kinetic darkstimuli have been experimented with on a whiteBjerrum screen in the diagnosis of cone dysfunc-tion.4' The oculokinetic perimetry chart has alsobeen described with a black stimulus.42 Multipledark (negative contrast) stimuli on a tangentscreen have been further developed in screeningfor neurological and glaucomatous visual fielddefects.43 Suprathreshold testing with kineticblack stimulus" 45 and, 'delay campimetry'"which involves the recording of patient reactiontimes to static black stimuli at a number oflocations in the visual field are known to yieldadditional clinical information especially inretinal inflammatory disorders and retrobulbarneuritis, respectively. However, computerisedsuprathreshold and threshold testing with lowcontrast static dark stimuli have not beenreported until recently.47"

In this study, static dark perimetric stimuli ofvarying contrast on a cathode ray tube arecompared with conventional light stimuli of theHumphrey visual field analyser in glaucomatouseyes, using the STATPAC empirical probabilitymaps as the standard.

Materials and methodsTwenty five glaucomatous eyes (17 right andeight left) of 25 perimetrically experiencedpatients with primary open angle glaucoma

* 50-59%* 40-49%* 30-39%* 20-29%. 10-19%* 1-9%0%

* * 0 @

* *0* * @0.* * 0* 0 0 0 0 S

* * 0 0* 0A S

* . 0* * *

* * * * *

Figure I The cumulativefrequency distribution ofabnormalpoints in the central visualfields of25 glaucomatous eyesaccording to the Humphrey autoperimeter STATPAC 'patterndeviation' results. All significant deviationsfrom the normal(outsie 95% confidence interval) constitute the abnormalpoints with decreased senstttitty.

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RightAge 69Questions asked 566Fixation losses 3/28False pos errors 1/14False neg errors 1/15Test time 00:17:23

-6

4

-1-4

-7 -24-12--21-27 --24-7 -29 -3 -29-9 -32 -15 -13

1 -1 o n-3 -2 0 -2 -2-4 -1 1 -2 -2

-1 -6 -4 -1

Totaldeviation

(j8) (O 14 &21 (M) J^ o^ 1 5 1

25 (418 14116 17 10 1 2025(2) (28) (0)> (16)|1 (17' (28

22 29 (|H)l@ )A.w 7HlH

20 26 30 (i) 29 27 30 28 24

5 2 25 1229 29 28

25 221 25 -28 24 I-J {29!24-7 -24

-10-3 24 19 25 7 -13 -27 -27

-28 -11 -F + 4 -7 -29 -30

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Patterndeviation

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.

-9 -32 -151 -1 0O -2 -2 -1 -11 -2 -2 0 -2

-6 4 -1 0 0 4-1 -9 -3 t -4 -e

-1 j-1I

. *1 U .X7 * X- ::.: ,,

Greytone symbols

Fig 2A

Figure 2 The glaucomatousfield loss in the superior Bjerrum area was evident to both (A) conventional threshold light stimuliand (B) allfour contrasts ofsingle intensity suprathreshold dark stimuli in the right eye ofthis 69-year-old woman. Interestingly,a subtle inferonasal defect became more pronounced with the lower contrasts (lighter grey) ofthe CAMEC stimuli.

(POAG) (13 male and 12 female), aged between35-82 years (mean 68 years) were included in thestudy. All eyes had 6/6, N5, or better visual acuitywith correction less than ±7 00 dioptresspherical equivalent, no media opacities, andnormal (3-6 mm) pupils. None of the patientssuffered from non-glaucomatous ocular dis-orders or systemic disease.The conventional perimetry was performed

using the Humphrey visual field analyserprogram 30-2 with Goldmann stimulus size III(4 mm2) and a stimulus duration of 0-2 seconds.The patients were also tested with the computerassisted moving eye campimeter (CAMEC)which employs a moving fixation technique.49The CAMEC technique requires an IBM com-

patible desktop computer with a joystick or

mouse and a high resolution monitor. Staticstimuli are presented automatically in relation to

a randomly moving fixation target at predeter-mined locations in the central visual field. Thepatient signals awareness of the stimulus bypressing a button. Missed stimuli are presented asecond time and repeatable misses are recordedas abnormal points in the visual field. Patientresponses are processed, analysed, printed, andsaved at the end of the test. The full details ofcomputer assisted moving eye fixation are des-cribed elsewhere (Damato B E, et al, in press).The test grid designed for this study was identi-cal to the test grid of Humphrey program 30-2.The CAMEC stimulus size was compensated foreccentricity, with a surface area of 1-8 mm2 up to10 degrees, 3-1 mm' between 10 and 20 degrees,and 4-9 mmx beyond 20 degrees from fixation.These sizes of dark stimuli, in a pilot study with10 normal subjects, were detectable along thenasal horizontal meridian of the normal visual

-12 -1

-29 -20 -11 -6i-13 -11 -9 2o0 -2

-6

-2 -IO -3l

Global indicesMD -5 07 dBPSD 9 37 dBSF 149 dBCPSD 9 22 dB

p <2%p < 0.5%

p < 0.5%

. .

. .

Probability symbolsp < 5%

a p < 2%i p < 1%U p < 0.5%

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A comparison ofautomated static dark stimuli with the Humphrey STATPAC program in glaucomatous visualfield loss

Right

-22%-76%

0

-37%

Fig 2B

field (Mutlukan, unpublished data). The staticdark stimuli were presented for the defaultduration of 0-2 seconds. For calibration, theluminances of the test stimuli and backgroundwere measured at 36 different locations using aluminance meter (Minolta nt-i) and averageluminance (Weber's) contrasts (Cw) calcu-lated.5"' Dark stimulus contrasts of -76%(2 dB=20 log Cw; the darkest grey), -37%(9 dB), -22% (13 dB), and -10% (20 dB, thelightest grey) were the only suitable grey tones ofthe EGA graphics software ofCAMEC in giving a

useful stimulus range. These dark stimuluscontrasts were presented on a 10 cd/m2 back-ground. Tests were performed with singleintensity stimuli as separate examinations

in a random order either before or after theHumphrey 30-2 threshold test. All patients hadprior demonstration/training for 15 minuteswhich involved the recognition ofthe dark stimulifor each test. TheCAMEC (each) and Humphreytests took an additional average of 10 and 15minutes to complete, respectively. Patient fatiguewas minimised by a few minutes of rest after eachtest session. All tests for each individual were per-formed with full aperture near correction at a30 cm test distance and completed on the same

day.The Humphrey STATPAC 'empirical prob-

ability (p) values' as well as the dark stimulusdetection status ('seen' or 'missed') for eachcontrast at the corresponding test locations were

CAMEC2Visual field plot

° Seent3 Seen on retest

* Missed

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RightAge 71Questions asked 502Fixation losses 6/26False pos errors 0/12False neg errors 3/22Test time 00:14:40

3),1

-3-2-4

-5 -5 11-13 -4 -4 2

-7 -2 -5 -4 -3

-7 -S -2 -4 0 1-i - t

Totaldeviati(

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2? 128 26

-1 24 23)27 23 -13 -4

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-114 -4 -2 -2 -1 2 ;! ; t-144 -4 -4 -2 -2 -1 -4 -3

AN

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-2

Patterndeviation

-1 -4 o-I

-7 -2) -I -4

-8 -5 -3 Q

'Ii.I

:- .I

-1-3-4-2

0 -5O 0 -1

-1 -7-1

Global indicesMD -2-87dB p< 10%PSD 3-00 dBSF 1 76 dBCPSD 2-24 dB

Greytone symbols

Fig 3A

Figure 3 (A) The nasalfield loss to the light stimuli ofthe Humphrey thresholdingprogram appeared more extensive whencompared with (B) the lowest contrast (- 10%) dark stimuli, which also revealed double arcuate scotomas.

compared at eccentricity annuli bands of 4-9degrees, 10-20 degrees, and 20-28 degrees usingthe 'Minitab' statistical software package. Thesensitivity and specificity of the different darkstimulus contrasts were studied by performingpoint by point comparisons between theHumphrey 'total deviation' (TD), 'patterndeviation' (PD) plots, and CAMEC results,except the test locations above and below thephysiological blind spot. The threshold resultsshowing significant depression in 'TD' and 'PD'plots beyond 95% confidence interval (shownwith STATPAC symbols representing p<5%, 2%,1%, and 0-5%) were categorised as representingthe visual field abnormality, and the remaininglocations (inside 95% confidence interval,p>5%) were considered healthy parts of thevisual field.52 The TD result of STATPACindicated the areas with both homogeneous and

localised reduction in sensitivity, whereas thePD result showed only the localised componentof any field defect.52

ResultsSTATPA* evaluation of the decibel thresholdvalues revealed relative scotomas in 11 eyes(Aulhorn-Karmeyer classification, stage 1),small isolated absolute scotomas in 10 eyes (stage2) and absolute scotomas connected to the blindspot in four eyes (stage 3) with the mean globalvisual field indices of -5 2 dB mean defect(MD); 6-1 dB pattern standard deviation (PSD);5-4 dB corrected pattern standard deviation(CPSD); and 2-2 dB short term fluctuation(STF).53 5 The reliability indices from allHumphrey threshold results were within thenormal range (that is, fixation losses <20%, false

Probability symbolsp < 5%

a p < 2%M p <1%U p < 0-5%

-12 -4 -4 -2 -2 -1 -2 3 0 1

4 .-2 -3 -1 1 4

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A comparison ofautomated static dark stimuli with theHumphrey STATPAC program in glaucomatous visualfield loss

CAMEC2Visual field plot

O Seeno Seen on retest

a Missed

300

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. 0.o..oo0 o0. 0 0 0

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answers <33% of total attempts). The cumula-tive frequency of involvement of the test loca-tions in the PD plots is shown in Figure 1.

All four contrasts of static dark stimuliindicated the abnormal areas in the central visualfields of glaucomatous eyes (Fig 2). In general,lower contrasts of dark stimuli delineated moreextensive visual field abnormalities, and dis-played abnormal areas which were not detectedby the light stimulus and STATPAC (Fig 3). Thehighest contrast (-76%, black) stimuli and thelowest contrast (- 10%, light grey) stimuliidentified the normal and abnormal pointsrespectively with the best accuracy at all eccen-

tricity bands (Fig 4). For instance, the black

(-76% contrast) stimulus identified 93% of thenormal locations (true negative rate= specificity)in PD plots as such with a false positive rate of7% within 10 degrees from fixation; however, itstrue positive rate (detection of abnormality=sensitivity) for glaucomatous loss was only 49%in the same area. Both the true and false positiverates increased with increase in eccentricity.The true positive rate improved with loweringdark stimulus contrast and reached 86% at-10% contrast with a higher 'false positive' rateof 35% within 10 degree eccentricity. Thatrelation between the dark stimulus contrast andthe detection rates was evident at all eccentrici-ties. The average true and false positive detection

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g 80

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X 400a 302 20

10

--+'- r>2Odeg

,M10-20 deg-><10 deg o -10%

+ -22%* -37%A -76%_

I0 10 20 30 40 50 60 70 80 90 100

False positive result (%)

Figure 4 The percentage sensitivity (true positive result rate)and specificity (true negative result rate= I -false positive rate)ofthe dark perimetric stimuli ofvarying contrast againstSTATPAC pattern deviation results at eccentricity annuli bandsof4-9 degrees, 10-20 degrees, and beyond 20 degrees withinthe glaucomatous central visualfield at4741 test locations.

rates obtained against the PD plots within thewhole central field were higher than those againstthe TD results.

DiscussionAt present, automated thresholding perimetrywith light stimulus is the most sophisticatedapproach. It has the best sensitivity andspecificity available especially in experiencedpatients. Indeed, the Humphrey visual fieldanalyser with STATPAC has a wide acceptance forthe standardised evaluation of glaucomatouspatients. STATPAC automatically compares themeasured light threshold decibel (dB) values withthe age-expected normal dB values and indicatesthe deviations from normal. STATPAC considers agiven dB light sensitivity value abnormal (out-side 95% confidence interval) if that value is 5 dBor lower than the expected sensitivity. It enabledthe identification and classification of the normaland abnormal areas in the glaucomatous visualfields according to their defect depth and level ofstatistical significance.55 The 'total deviation'

plot reflects not only the localised defects but alsothe effect of inappropriate refractive correction,pupil size, and media opacity on visual sensi-tivity as well as the generalised loss component ofglaucomatous visual field involvement. The con-cept of a generalised (diffuse, homogeneous)sensitivity loss component in glaucoma stillremains controversial although it was reported tobe present in nearly half of the eyes withglaucomatous visual field involvement.""'8 Thefrequency of visual field abnormality in the TDplots from the eyes included in this study weresignificantly higher than that in the PD plots(p<O0OOl). This finding suggests the presence ofglaucomatous diffuse sensitivity loss in theseeyes since the field artefacts which may havebeen caused by preretinal factors wereminimised by careful selection of the patients(Mutlukan and Jay, in preparation). Slightlyhigher (an average of 3-6%) false positive ratesagainst the PD results suggest that the detectionof the dark stimuli, like the light stimuli, isinfluenced by the diffuse sensitivity loss in thevisual field.

It was previously demonstrated that thevisibility of the dark perimetric stimulus isdependent on stimulus parameters such asstimulus size, contrast, and level of backgroundluminance.59 Accordingly, eccentricity compen-sated sizes of dark stimuli follow the slope of thenormal hill of vision at all contrast levels, withthe lower contrast levels requiring higher retinalsensitivity for their detection. The results fromthis study further confirm that, similar to theconventional incremental threshold examina-tion, the decremental differential sensitivity inthe visual field can be determined and theabnormalities can be quantified with successivepresentations of different dark stimulus con-trasts in increasing or decreasing steps.47Dark stimuli of low contrast were frequently

missed in apparently normal parts of the glauco-matous visual fields, especially at the outereccentricities. This is partly due to the negativeeffect of the peripheral stimuli locations onpatient attentiveness6' as well as the possible

FigSA left FigSA right

Figure 5 (A) Asymmetrical cupping in the right eye ofa 63-year-old man suspected ofhaving glaucoma. Intraocular pressureswere 32 mm Hg in the right eye and 19 mm Hg in the left.

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A comparison ofautomated static dark stimuli wfith theHwmphrey sTATPAcprogram in glaucomatou visualfield loss

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182

Figure SC Threshold CAMEC22 Visual field plotdetemination with equal size

and duraton ofstatic darkstimuli revealedfield loss inthe right eye.

Lft

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Figure SD The totalsensitivity to the dark stinuliin the glaucomatous right eyewas 152 dB lss than that inthefellow eye (O dB=-100% contrast, blackstimulus).

Left eye

272dB 19 23 2 318dB

/ 3 23 23 23 23 23 \

/ 3 23 23 23 23 23 23 :23

19 1 1 23 23 23 23 23 19 23

23 19v 23 23 23 23 23 19 19

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Total = 1135dB

Right eye

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Total = 983 dB

Mutlukan

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A comparison ofautomated static dark stimuli with theHumphrey STATPAcprogram in glaucomatous visualfield loss

160

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156

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152 17-1

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187 202 202

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Figure SE Minimum age-expected normal dark stimulus threshold valuesfor 60years ofage in the central visualfield (95%confidence interval=mean-2 SDfor each test location; n=13).

decrease in the suprathreshold values of theselected dark stimulus sizes in glaucomatousvisual fields. The true negative rate of 71% fromthe lightest grey (- 10%) dark stimuli within 10degree eccentricity provides evidence that eventhe lowest negative contrast value employed inthis study was at least 4 dB above the equivalentlight threshold in the central visual field. There-fore, seemingly false positive results from darkstimuli also suggest that negative contrast wasdetecting early glaucomatous visual field defectswhich were being missed with the luminous(positive contrast) stimuli of the Humphreyvisual field analyser. Glaucoma is known toselectively damage retinal ganglion cells withlarge somal diameter3'4- and off centre ganglioncells are included in that morphologicalcategory.3 The results from threshold examina-tion with static dark on bright stimuli inglaucoma suspect eyes further support the con-cept that the dark stimuli may diagnose visualfield abnormalities before they become evidentto equal sizes and durations of conventionalpositive contrast stimuli (Fig 5).6'The differential involvement of the 'off path-

way in glaucoma and other neuro-ophthalmicdisease, the affinity of the dark stimuli to themagnocellular system, and the diagnosticadvantage of performing threshold determina-tion with dark on bright stimuli require furtherclinical trials.This study was conducted at Tennant Institute ofOphthalmology,University ofGlasgow, Scotland.The author was supported financially by The International

Glaucoma Association, The Royal National Institute for the Blind,The Ross Foundation of Prevention of Blindness, and McCunnTrust, and wishes to thank Dr B E Damato for his review of theearlier version of this manuscript, Mr J McGarvie and DrA Evansfor the software improvements, Drs Jay, Dutton, Dudgeon, Cant,Bronte-Stewart, McFadzean, and Professor Kirkness for theirkind permission to examine their patients.

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