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The Open Perimetry Interface (OPI):

Glasnost and Perestroika in the Visual Field

Andrew Turpin, Melbourne

Paul Artes, Halifax

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In 1986, the Soviet Union was facing

economic, social, and moral ruin.Michael Gorbatchov came along

and proposed

glasnost - openness, transparencyperestroika - rebuilding,

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By 2010, perimetry has seriously fallen behind imaging i

terms of innovation and excitement.There has been no major innovation since SITA(1997).

The field is isolated from mainstream science (physics,

psychology, medicine)

Commercial players do their own thing. Clinicians and

scientists work largely within their own groups using

laboratory equipment. A vast resource of creativity liesunharnessed and frustrated.

It feels very different from Tbingen in 1986...

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We need to:

Creativelyseek new ways to examine visual fields.

The center as well as the peripheryWith static as well as kinetic stimuliWith threshold as well as suprathreshold strategies

With spots as well as with new types of stimuli

Efficientlycollaborate with each other,

and with industry.

Quicklytranslate new ideas into experiments.

Quicklytranslate experiments into clinical tools.

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Many current problems of perimetry have longbeen addressed in other disciplines. Perimetry

is at least two to three decades behind thestate-of-the-art.

Many talented scientists would like to work onclinically relevant problems, but lack the tools.

Industry makes beautiful hardware, but this is

inaccessible for basic experiments.Accessing clinical data is often like breakinginto the Pentagon. There are laudable

exceptions.

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sure n conven ona a u om a e per m e ry, e re a-tionship of RT to threshold must be defined. If thereis a constant relationship between reaction time andthreshold in health and disease, one would hope thisrelationship could be used to help predict thresholdin a more accurate and less variable way. Ou r goal wasto determine this relationship of reaction time to thepsychometric function in normal subjects, normal sen-sitivity test locations in patients with glaucoma, andtest locations with 10 to 20 dB loss in patients withglaucoma, as well as to investigate the relationshipsuggested by Flammer and coworkers9 of a prolongedRT associated with an increase in threshold in subjectswith glaucoma.

METHODSSubjectsTen patients with well-established primary open angleglaucoma and 10 normal volunteers gave informedconsent to participate in the study. The protocol wasapproved by the University of Iowa Institutional Re-view Board. The tenets of the Declaration of Helsinkiwere followed. Th e normals were paid volunteers whowere hospital employees or friends or family membersof eye clinic patients. The normal subjects werematched pairwise to patients by age within 5 years.Normals were included if they had no history of eyedisease except refractive error and normal results ofophthalmo logic exam ination. They all had normal au-tomated perimetry results using the H um phrey VisualField Analyzer (HVFA; Humphrey Instruments, SanLeandro, CA), program 24-2. If a potential normalsubject had th ree o r mo re adjacent po ints with a totaldeviation score at the P < 0.05 level or two adjacent

.intraocular pressure control, but none were using amiotic. Patients with primary open angle glaucomawere excluded if they had any other disease known tocause visual loss. All subjects h ad corre cted visual acu-ity of 20 /25 or better, pupil diam eter of at least 3 mmwhen tested, spectacle correction not exceeding 6.00D (equivalent sphere), and previous experience withautomated perimetric examinations.Testing StrategyConventional automated perimetry was first per-formed with the HVFA with program 24-2 using themanufacturer's recommendations (except for threesubjects in whom program 30-2 was performed).These program s test the central 21 or 27 of the visualfield with stimuli spaced 6 apart; in addition, the 24-2 program tests one stimulus above and one stimulusbelow the nasal horizontal at 27. We used a Gold-mann size III (4 mm 2) object on a 31.5-asb back-ground. The size of the stimulus was fixed, and thethreshold to differential light intensity was estimatedat each test point with a staircase procedure. Eachpatient's appropriate near correction was used. Restbreaks were given when requested.Frequency of seeing curves were measured by con-trolling the HVFA with a custom program run by apersonal co mp uter (Hewlett Packard [Palo Alto, CA]Vectra 486, 33 mHz). At two different test locations,stimuli were presented in 2-dB intervals up to andincluding 10 dB from either side of the estimated(HVFA program 24-2) threshold, with 15 repetitionsat each stimulus intensity. All presenta tions of stimulusintensity and location were random ized. To de term inefalse-positive and false-negative responses, 60-dB and0-dB stimuli were presented 20 times at each location.

The Psychometric Function and Reaction Times ofAutomated Perimetry in Normal and Abnormal Areas ofthe Visual Field in Patients With GlaucomaMichael Wall,* RichardJ. Maw* Kim E. Stanek* and Balwantray C. Chauhanf

Purpose. To study the relationship of reaction time to the psychometric function in normalsubjects, normal sensitivity test locations in patients with glaucoma, and test locations with 10to 20 dB loss in patients with glaucoma.Methods. The auth ors tested 10 patients with glaucoma and 10 age-matched normal volunteerswith the Humphrey perimeter, first with program 24-2 and then with the method of constantstimuli to generate frequency of seeing curves. At two widely separated visual field locationson the program 24-2 grid, they presented stimuli in 2-dB intervals, 10 dB either side of theprogram 24-2 threshold, at 0 dB and 60 dB (15 repetitions per intensity). For the patientswith glaucoma, they chose a visual field location with normal sensitivity and a location in anarea of 10 to 20 dB loss.Results. Analysis of variance with post hoc 22 mmHg), whereas the remaining 2 had suspect optic diskson the grounds of asymmetry with the fellow eye. Pa-tients with glaucoma had glaucomatous visual fields(with early to advanced damage) and optic disks. Allsubjects had an ophthalmic examination, visual acuityof 6/9 or better, previous experience with perimetricexaminations, pupil diameter of at least 3 mm whentested, and a spectacle correction not exceeding 4.00diopters (equivalent sphere). The study was approvedby the Camp Hill Medical Centre Research EthicsCommittee and followed the tenets of the Declarationof Helsinki. Informed consent was obtained from eachsubject.

Testing MethodsThe Humphrey Field Analyzer can be controlled ex-ternally by a personal computer through a series of

. ,fixation losses was the percentage of blind spot presen-tations reported by the subject over the total numberof blind spot presentations.Data AnalysisThe frequency-of-seeing at each stimulus intensity wascomputed. These data were subjected to a probit analy-sis, which fitted a frequency-of-seeing curve to thedata. The threshold was taken as the stimulus intensitycorresponding to the 50% frequency-of-seeing of thefitted curve. The threshold deviation was computed bysubtracting the threshold from the age-corrected nor-mal value for that specific location. The slope of thecurve was estimated by calculating the interquartilerange (stimulus intensity interval corresponding to25% to 75% frequency-of-seeing) of the fitted curve.Figure 1 shows an example of a frequency-of-seeingcurve with the calculated parameters.

Correlations between variables were examinedwith the Spearman correlation. Differences betweencorrelation coefficients were determined with stan-dard tests.10 An analysis of covariance was used to ana-lyze the pooled data. Residuals of the regressions be-tween the dependent variables and covariates weretested for normality and homoscedasticity. Where nec-essary, log transforms were performed. All statisticaltests were two tailed, and statistical significance was setat P< 0.05.3535

commands. We have written a computer program thatuses these commands and allows us to conduct manycustomized tests, including the measurement of fre-quency-of-seeing curves.In normal subjects and patients with suspectedglaucoma, we tested locations along the 45, 135, 225,

1990: The Humphrey Field Analyzer can be

controlled from an external PC (Gateway).

1993 1996

Open Perimeter Interface

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Open Perimeter Interface2006: At ARVO, Turpin, Artes, McKendrick discuss

the idea of an open-source perimeter:

A new instrument that can serve as platform for

experiments and clinical studies, and is open to all.

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But: excellent hardware already exists (Zeiss, Haag-Streit,

Heidelberg, Oculus, Tinsley, Medmont, etc).

2010: Octopus Research Group:

Uli Schiefer (Tbingen) & Matthias Monhart (Haag-Streit)First draft of OPI by Turpin (with Dietzsch and Demirel)

Open Perimeter Interface

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OPI Open Perimeter Interface

Version 0.3

1 Preamble

This document describes a standard set of R functions for interfacing with a perimeter (an instru-ment for examining visual fields). It began existence at the First Octopus Research Meeting held

in Tubingen in July 2010, which was hosted by Prof. Ulrich Schiefer (University of Tubingen),and Matthias Monhart (Haag-Streit). R code that implements this interface should provide theset of functions described.

1.1 Document History

0.0 3 Jul 2010 Began in Hotel Hospiz, Tubingen by Andrew Turpin.0.1 7 Jul 2010 Complete rewrite with feedback from Janko Dietzsch and Shaban

Demirel.0.2 17 May 2011 Redraft by Andrew Turpin based on extensive feedback over a few rounds

from Paul Artes and Shaban Demirel.0.3 9 July 2011 image added to stimuli and a few errors in examples fixed by Turpin.

1.2 Document Future

It is expected that this document will be revised at meetings of the Imaging and Perimetry Society.

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Open Perimeter InterfaceJune 2011: PHA and AT (via skype) meet with engineers

at Haag-Streit in Berne, Switzerland, to discuss the

implementation

It finally becomes clear how exactly to do this:

1) The OPI specifies specific commands

2) Manufacturers implement in any way they like

(eg. Java, C++, Python), and make available (free, or $)

3) Researchers call the OPI functions from any

programming language they like. We like

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Open Perimeter InterfaceOpen Perimeter InterfaceopiStaticStimulus

stim

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eg: Psychometric functions for static perimetry

(stimulus size, contrast, duration).

Whatwecandonow...

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Thank you!

The way forward...