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Abstract and Figures

Background Currently available perimeters have limited capabilities of performing measurements of the visual field in children. In addition, they do not allow for fully automatic measurement even in adults. The patient in each case (in any type of perimeter) has at his disposal a button which he uses to indicate that he has seen a light stimulus. Such restrictions have been offset in the presented new perimeter ZERK 1. Methods The paper describes a new type of automated, computerized perimeter designed to test the visual field in children and adults. The new perimeter and proprietary software enable to carry out tests automatically (without the need to press any button). The presented full version of the perimeter has been tested on a head phantom. The next steps will involve clinical trials and a comparison with measurements obtained using other types of perimeters. Results The perimeter ZERK 1 enables automatic measurement of the visual field in two axes (with a span of 870 mm and a depth of 525 mm) with an accuracy of not less than 1o (95 LEDs on each arm) at a typical position of the patient’s head. The measurement can be carried out in two modes: default/typical (lasting about 1 min), and accurate (lasting about 10 min). Compared with available and known types of perimeters, it has an open canopy, proprietary software and cameras tracking the eye movement, automatic control of fixation points, light stimuli with automatically preset light stimulus intensity in the following ranges: 550–700 mcd (red 620–630 nm), 1100–1400 mcd (green 515–530 nm), 200–400 mcd (blue 465–475 nm). Conclusions The paper presents a new approach to the construction of perimeters based on automatic tracking of the eye movements in response to stimuli. The unique construction of the perimeter and the software allow for its mobile use in the examination of children and bedridden patients.
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Simplied automatic method
formeasuring the visual eld using the
perimeter ZERK 1
Robert Koprowski1*, Paweł Kasprowski2 and Marek Rzendkowski3
Background
Perimetry is a basic test associated with the quantitative evaluation of the visual field
[13]. is is a subjective test [4]. Various factors influence its repeatability and reliabil-
ity [5, 6]. is is mostly the cooperation of the patient with the camera, which requires
concentration. e visual field tests are now done routinely during the eye examination
Abstract
Background: Currently available perimeters have limited capabilities of performing
measurements of the visual field in children. In addition, they do not allow for fully
automatic measurement even in adults. The patient in each case (in any type of perim‑
eter) has at his disposal a button which he uses to indicate that he has seen a light
stimulus. Such restrictions have been offset in the presented new perimeter ZERK 1.
Methods: The paper describes a new type of automated, computerized perimeter
designed to test the visual field in children and adults. The new perimeter and propri‑
etary software enable to carry out tests automatically (without the need to press any
button). The presented full version of the perimeter has been tested on a head phan‑
tom. The next steps will involve clinical trials and a comparison with measurements
obtained using other types of perimeters.
Results: The perimeter ZERK 1 enables automatic measurement of the visual field in
two axes (with a span of 870 mm and a depth of 525 mm) with an accuracy of not less
than 1o (95 LEDs on each arm) at a typical position of the patient’s head. The measure‑
ment can be carried out in two modes: default/typical (lasting about 1 min), and accu‑
rate (lasting about 10 min). Compared with available and known types of perimeters,
it has an open canopy, proprietary software and cameras tracking the eye movement,
automatic control of fixation points, light stimuli with automatically preset light stimu‑
lus intensity in the following ranges: 550–700 mcd (red 620–630 nm), 1100–1400 mcd
(green 515–530 nm), 200–400 mcd (blue 465–475 nm).
Conclusions: The paper presents a new approach to the construction of perimeters
based on automatic tracking of the eye movements in response to stimuli. The unique
construction of the perimeter and the software allow for its mobile use in the examina‑
tion of children and bedridden patients.
Keywords: Image processing, Measurement automation, Segmentation,
Ophthalmology, Perimetry
Open Access
© 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and
indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdo‑
main/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
RESEARCH
Koprowski et al. BioMed Eng OnLine (2016) 15:88
DOI 10.1186/s12938-016-0210-1
BioMedical Engineering
OnLine
*Correspondence:
robert.koprowski@us.edu.pl
1 Department of Biomedical
Computer Systems, Faculty
of Computer Science
and Materials Science,
Institute of Computer
Science, University
of Silesia, ul. Będzińska 39,
41‑200 Sosnowiec, Poland
Full list of author information
is available at the end of the
article
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Page 2 of 10
Koprowski et al. BioMed Eng OnLine (2016) 15:88
performed by an ophthalmologist [79]. In special cases, they constitute an extremely
valuable source of data (visual field). ese are: glaucoma, diseases of the retina and the
optic nerve, central nervous system damage [10, 11]. During the test and in all types
of perimeters (PTS 920 from OPTOPOL Technology, AP-100-OPTOtech, Carl Zeiss
Humphrey System 740 or Heidelberg Edge Perimeter), the patient sits in front of a semi-
circular canopy resting the chin and forehead on the chin rest and the forehead rest [1,
1215]. e patient looks at the fixation point with one eye [2, 3, 16]. en the light
stimuli appear automatically on the canopy. e brightness of the light stimuli is changed
[1719]. e patient’s task is to react to the light stimuli by pressing a button [2022]. In
this way, it is possible to precisely determine and analyse the sensitivity thresholds of the
retina at various points with respect to the correct level. Additionally, on this basis, the
maps of areas of good sensitivity of vision and its defects are plotted. e information
associated with false-positive results is also stored [23, 24]. ese are those cases when
the patient presses a button signalling the presence of a light stimulus in its absence—it
may be a deliberate act or a symptom of weariness. e test lasts for a few minutes and
can be carried out in patients of any age [2528]. e criterion for exclusion from the
test concerns mentally ill people and pregnant women [26, 28].
erefore, there are three problems in perimetry that have not been solved so far:
Fully automatic measurement [2931]—understood as a method that does not
require any operator intervention and patient’s reaction to seeing a light stimulus;
Limited use in young children;
Deliberate introduction of erroneous results by the patient (by pressing the button
routinely when the frequency of stimuli is constant).
e perimeter ZERK 1 described in this paper is devoid of the above-mentioned
problems.
Material
e developed software of the perimeter ZERK 1 was tested on the Intel® Core i7 com-
puter-3770 CPU 3.4GHz, 10GB of RAM. e eye movements were monitored by a sys-
tem of EyeTribe and Genius Eye trackers. For instance, the EyeTribe tracker system is a
Danish company producing modules for tracking the position of eyeballs. Tracking the
eye movement involved a typical measurement consistent with the Declaration of Hel-
sinki, and was performed in 20 healthy volunteers as part of routine applications of the
EyeTribe tracker. On this basis, two perimeters were constructed. e first one, designed
to test adults, had a chin rest and a forehead rest, and the other one, intended for meas-
urements in young children, was movable and without the rest. e construction of
the perimeter is described in detail in the following sections. Currently, the authors are
at the stage of submitting an application to the ethics committee to get permission to
test the entire system. Moreover, a utility model application has been filed at the Euro-
pean Patent Office. No research was carried out on humans as part of this work. All the
results were obtained from routine tests performed with the EyeTribe tracker and (in the
case of the full perimeter) tests on a phantom head (EYE Examination Simulator MB2A,
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Koprowski et al. BioMed Eng OnLine (2016) 15:88
Manikin size 42×21×38cm, 2kg)—in the case of testing the perimeter intended for
children and adults.
Methods
e perimeter ZERK 1 was created based on the two premises mentioned in the Intro-
duction. e first one is the ability to perform measurement of the visual field in young
children. Accordingly, the presented perimeter cannot have a closed canopy. e child
needs to see the carer/parent, which reduces the fear of examination and prevents move-
ments during the test. e second premise is the total automation of the examination.
Owing to the built-in eye trackers, the patient’s reaction to the light stimulus is recorded.
As a result, the patient does not press any button to signal that he sees the stimulus.
e perimeter ZERK 1 is made up of four basic elements—Fig.1:
Vertical and horizontal arms containing RGB LEDs (WS2812 Intelligent control
LED integrated light source, power supply voltage 6.5 V, red 620–630 nm, 550–
700mcd, 20mA, green 515–530nm, 1100–1400 mcd, 20mA, blue 465–475 nm,
200–400mcd, 20mA) placed at a linear distance from each other every 10mm. e
arms have a span of 870mm (from the outermost left–right or up–down points) and
a depth of 525mm. e horizontal arm has a total of 190 LEDs, 95 LEDs arranged
every 1° on each side. e vertical arm has 135 LEDs attached every 1°. In this way,
the arms cover the full visual field;
e fixation point placed in the main axis of the perimeter containing a colour
marker. In the case of children, it is a colourful contour of a favourite character from
a fairy tale or an animal. e size of the fixation point is about 20×20mm;
A system of EyeTribe trackers;
A PC with windows operating system and developed software that enables to track
the movement (location) of the eye in response to a light stimulus.
Fig. 1 The perimeter ZERK 1: a Schematic diagram, b Image of the created perimeter. The numbers indicate:
1 central fixator, 2 LEDs, 3 eye tracking, 4 vertical arm, 5 horizontal arm, 6 base, 7 vertical guides, 8 computer
with dedicated software
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e task of the perimeter ZERK 1 is to preset light stimuli covering the full range of
the visual field both vertically and horizontally. e analysis of the patient’s response to
the light stimulus was carried out on the basis of the EyeTribe tracker which tracks the
eyeball reaction. ZERK 1 can be removed from the base and placed directly next to a
bedridden patient (child). e individual LEDs are controlled via USB as well as a micro-
controller 89c2051 and USB converter. e test is carried out with the dedicated soft-
ware in 2 modes:
Simplified, fast mode—allowing for a 1-minute rough assessment of the visual field.
Accurate, full mode—allowing for a 10-minute accurate assessment of the visual
field.
In each test mode, the brightness (in the range of 550–700mcd) and the order of stim-
uli are random. e interval between stimuli is also random and ranges from 0.5 to 5s.
e random position of the next stimulus and different length of the interval between
stimuli prevents the patient from getting used to a scheme, prevents his weariness dur-
ing the test, and thus reduces the number of false positive results (when the patient
moved the eyeball out of habit although there was no stimulus). Figure2 shows a simpli-
fied block diagram of ZERK 1. e two main blocks are presented in the diagram. e
first one is responsible for processing the eyeball movement. After acquisition, the image
LGR AY is calibrated to the image LC (the head movement and uneven illumination are
Fig. 2 A simplified block diagram of the perimeter ZERK 1. The diagram shows the two main blocks. The first
one is responsible for processing the eyeball movement. After acquisition, the image is calibrated (the head
movement and uneven illumination are deleted). Next, the image is subjected to median filtering to detect
the eye movement in the thus analysed eye movement image. The second block is responsible for control‑
ling LED strips. It includes a microprocessor which controls the LEDs and brightness at random (pulse‑width
modulation). Explanations of variables LGRAY, LC, LMED, LE, MSE, NSE and LHC are presented in the text
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Koprowski et al. BioMed Eng OnLine (2016) 15:88
deleted). Next, the image is subjected to median filtering [3234] (image LMED) to detect
the eye movement (LE) (after earlier covering of the left or right eye). e second block
is responsible for controlling LED strips. It includes a microprocessor which controls
the LEDs and brightness at random (pulse-width modulation—PWM). e merger of
these two blocks results in a map (the patient’s visual field) created in an application
developed in C++. Communication with the PC was realized via USB 2.0. It is two-
way communication. e information about the eyeball movements is obtained from the
eye tracker, whereas the information which LED, with what intensity, and where exactly
on the perimeter is to shine, is returned. e methods of image analysis and processing
shown in Fig.2 provide the time of analysis of the response to a single stimulus of less
than 10ms, and are virtually negligible (do not affect significantly the overall result of
the measurement time for the patient). It should be noted that the presented methods
of analysis are one of the possible proposals for their implementation. Other methods
of image analysis and processing can involve advanced morphological methods [29, 30],
statistical methods [31, 32], or artificial intelligence methods and others [33, 35, 36].
Discussion andresults
e obtained results relate to the part of data analysis directly associated with the eye
tracker. e data were collected retrospectively and relate to the assessment of the prac-
tical usefulness of data analysis methods and software. Figure3 shows an example of
the extreme positions of the patient’s eye and the results obtained. e images from
Fig.3a to f are the subsequent positions of the left eye: starting with the central position,
then down, right, up, left and back to the central position. e part g shows a sample
graph of stimulus brightness changes (red) from 0 to 220mcd for the position changes
of the perimeter by the angle of 35° (green background), 40° (yellow background), 55,
60 and 60° (red background) as well as 60° (blue background). e changes over time
of the angular shift of the left eye acquired from the eye tracker are marked in blue. e
response of the eye differs depending on the duration of the light stimulus. Because
this is not the aim of the present study, this information has been omitted. However,
Fig. 3 Examples of the extreme positions of the patient’s eye and the results obtained. The images from a to
f are the subsequent positions of the left eye: starting with the central position, then down, right, up, left and
back to the central position. g A sample graph of stimulus brightness changes (red) from 0 to 220 mcd for the
position changes of the perimeter by the angle of 35° (green background), 40° (yellow background), 55°, 60°
and 60° (red background) as well as 60° (blue background). The changes over time of the angular displace‑
ment of the left eye are marked in blue
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it has been noted that there is a linear relationship between the light stimulus duration
and the accuracy of localization (the angular accuracy of the eye movement toward the
stimulus).
e full system of ZERK1 has been compared with the Heidelberg edge perimeter [4,
8, 22] and the artificial, preset map of the defects in the visual field. e selection of the
Heidelberg Edge Perimeter resulted from the possibility of obtaining digital reference
data concerning the measurement results. e angular accuracy of measurement with
ZERK1 has been shown schematically in Fig.4a. e preset defects in the visual field
are shown in Fig.4b together with the results obtained from the Heidelberg edge perim-
eter and ZERK1. e numerical comparison presented in Table1 provides the following
results related to the usability of ZERK1:
Fully automatic measurement—owing to the use of the system for tracking the eye-
ball movement;
Quantitative results of the defects in the visual field horizontally and vertically with
an angular accuracy of at least 1°;
e possibility of obtaining additional parameters such as the speed of the patient’s
eyeball response to a stimulus;
Elimination of the human factor (cheating during measurement) owing to a random
change of the stimulus location, a random change in its brightness and the analysis of
the eyeball movements which do not result from the stimulus.
e limitations of ZERK1 should be also mentioned here:
Measurement in only two axes—horizontally and vertically;
e impact of the perimeter position on the results obtained (the absence of the chin
rest is an option which results in difficulty in obtaining reproducible results—based
Fig. 4 A comparison of the visual field for two types of perimeters: a Explanation of the angular accuracy of
ZERK1 where 1 arms of ZERK1, 2 visual field, 3 the area of one LED, 4 position of patient’s eye; b Imposition of
the results for the phantom where, 5 results obtained from the Heidelberg edge perimeter, 6 reference area
for defects in the visual field, 7 results obtained using ZERK1, 8 colour palette of the threshold of eye sensitivity
to stimuli expressed in dB
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on the measurements performed on the phantom, the error was ±10% in the meas-
urement of the distribution and the brightness level of the response to a stimulus);
e need for fixation of the patient in the central position of the perimeter—and dif-
ficulty in staying focused on this point;
e dependence on external illumination due to the open construction of the perim-
eter.
An example of a report (phantom) from tests performed with ZERK1 is shown in
Fig.5. e upper section contains the logo and information such as the patient’s name,
identification number, start and stop of the test, test type and the number of false posi-
tive and false negative results. e lower section (Fig.5) provides the numerical results
in a simplified version (right) and full version (left) in gray levels and as a histogram.
At the current stage, the authors plan thorough clinical trials in adults and children
with various diseases, both those involving various types of defects in the visual field and
those directly related to extra ocular muscle dysfunctions. ey can reduce the possibil-
ity of carrying out measurements or exclude the patient from the test.
Conclusion
e paper presents a new approach to the construction of a perimeter based on auto-
matic tracking of eye movements in response to stimuli. Owing to this unique solution,
the patient does not have to press any button to signal seeing the stimulus. e unique
construction of the perimeter allows for its mobile use for the examination of children
and bedridden patients. Currently, the authors intend to carry out detailed clinical tri-
als of the created perimeter and compare the results with the results obtained using
other perimeters. It is already known, on the basis of the presented preliminary results,
that the new type of the perimeter will work perfectly in basic diagnostics of visual field
Table 1 Comparison ofthe basic parameters ofthe Heidelberg edge perimeter andZERK1
Parameter Heidelberg edge perimeter ZERK1
Confirmation of seeing the stimulus Manual (button) Automatic
Measurement time (precise) 3 min 10 min
Measurement time (rough) 1 min
Measurement area Central 10, 24 and 30° visual field Central 10, 24 and 30° visual field—
but only in two axes
Number of points 100 190 + 135
Analysis of the duration of the eye‑
ball response to a stimulus
Possibility of measuring the visual
field in children
Possibility of measuring the visual
field in bedridden people
Angular resolution
Archiving results √ √
Possibility of displaying a multicol‑
oured stimulus
Sensitivity From 0 to 25 dB From 0 to 25 dB
Dependence of the results obtained
on external lighting
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Koprowski et al. BioMed Eng OnLine (2016) 15:88
(glaucoma, diabetes) in adults as well as in screening tests in children. e scope of diag-
nostic procedures will comprise monitoring the speed of the eyeball response and the
assessment of sensitivity to a light stimulus. To conclude, the presented perimeter does
not constitute competition for the known types of perimeters, it only completes the
market in the area of fully automatic measurement, examination of bedridden patients
and additional analysis of movement parameters (speed of response) of the eyeball.
Abbreviations
AMD: age‑related macular degeneration; ROI: region of interest; PWM: pulse width modulation.
Authors’ contributions
RK suggested the algorithm for image analysis and processing, implemented it and analysed the images. PK proposed to
use the EyeTribe tracker to build the perimeter and conducted his research using human volunteers, MR is the originator
of the perimeter, he was also responsible for carrying out the tests on the human phantom. All authors have read and
approved the final manuscript.
Fig. 5 Example of a report (phantom). The upper section contains the logo and information such as the
patient’s name, identification number, start and stop of the test, test type and the number of false positive
and false negative results. The lower section provides the numerical results in a simplified version (right) and
full version (left) in gray levels and as a histogram
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Author details
1 Department of Biomedical Computer Systems, Faculty of Computer Science and Materials Science, Institute of Com‑
puter Science, University of Silesia, ul. Będzińska 39, 41‑200 Sosnowiec, Poland. 2 Institute of Informatics, Silesian Univer‑
sity of Technology, Akademicka 16, Gliwice 44‑100, Poland. 3 Individual Specialist Medical Practice, Gliwice, Poland.
Acknowledgements
The authors thank Mr. Piotr Jura for the possibility to perform the measurements of the outcome of his thesis entitled
“Perimeter controlled with a microprocessor”.
Competing interests
The authors declare that they have no competing interests.
Funding
We acknowledge the support of Silesian University of Technology grant BK/263/RAu2/2016.
Received: 20 June 2016 Accepted: 19 July 2016
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... pus and the medial temporal lobe structures (Grossman and Blake, 2002;Gibson, 2014). Eye tracker may also be used simultaneously together with other diagnostic devices like MRI (Alichniewicz et al., 2013;Ettinger et al., 2004) or deep brain stimulation (Antoniades and FitzGerald, 2016) or perimeter for vision field measuring (Koprowski et al., 2016). ...
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Purpose: To determine if the relationship between retinal sensitivity and macular inner retinal layer thickness differs between primary open-angle glaucoma (POAG) with mild and advanced central visual field (VF) damage. Methods: One eye of 153 POAG patients was included. Using spectral-domain optical coherence tomography, we measured the average thickness of the macular ganglion cell-inner plexiform layers (GCIPLT) and the macular nerve fiber layer/GCIPL (ganglion cell complex [GCCT]) in a 0.9-mm-diameter ganglion cell displacement-adjusted circular area corresponding to the four central test points of the Humphrey Perimeter 24-2 program and correlated the results with the average retinal sensitivity (1/Lambert) at the corresponding test points, with adjustment for other confounding factors. Results: Ninety-three eyes had mild central and 60 eyes advanced central VF damage with an average total deviation (TD) of the four test points of greater than or equal to -4 decibels (dB) (mild group) and less than -4 dB (more severe group), respectively; the average mean deviations were -3.0 and -9.8 dB, respectively. In the mild group, the GCCT and GCIPLT were correlated significantly and positively with the average retinal sensitivity with partial regression coefficient of 0.007 and 0.005, respectively, and in the more severe group with partial regression coefficient of 0.019 = 0.007 + 0.012 (P = 0.007) and 0.010 = 0.005 + 0.005 (P = 0.078), respectively. The axial length and disc size were correlated with GCIPLT with marginal significance (P = 0.052 and P = 0.042). Conclusions: The relationship between the macular GCC and GCIPL thickness and retinal sensitivity at the corresponding retinal areas differed between POAG with mild and advanced central VF damage.
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Purpose: To compare keratocyte activation, cellular morphologic changes and wound healing after SMILE and PRK procedures using transmission electron microscope (TEM). Methods: In this study, 22 New Zealand white rabbits (10- to 15-week old) were used. The right eyes of all animals underwent SMILE procedure and the left eyes underwent PRK procedure. Cornea samples taken 1 day and 1 week postoperatively were examined using TEM. Results: Using TEM 1 day after SMILE procedure, the organization of collagen fibers seemed to have been preserved without thermal alterations. Keratocyte activation was observed in the anterior stroma. Disrupted collagen arrangement and debris of cells are visible in the area of damage, and some phagocytic cells and a large number of secondary lysosomes are visible in those cells. At the perimeter zone of the interface, many coenocytes and collagen fragments could be found within the phagocytic cell. One week after SMILE procedure, potential lacuna could be discerned. A large part of the interface of the lenticule extracted had an appearance of clearly being adhered to some mucus secretions. One day after PRK procedure, an irregular epithelial surface was visible using TEM. Keratocytes had been activated and the rough endoplasmic reticulum in those cells had expanded. One week after PRK procedure, the epithelial surface still was irregular and keratinization of the epithelium was still visible in some areas. Corneal endothelium cells were mildly damaged and some vacuoles within the cytoplasm could be discerned. In the anterior stroma, some unhealthy activated keratocytes could still be observed. New collagen fibrils were found present near the activated keratocytes. Conclusion: Using TEM, keratocyte activation could still be observed after SMILE compared to after PRK procedure. Fewer cellular ultrastructural changes were seen after SMILE procedure. Unlike in PRK procedure, no damaged epithelium and endothelium were found after SMILE.
Article
Purpose: To investigate the level of test-retest variability in the Medmont M700 automated perimeter. We compare the retest variability of the outer 20° test points of one test method to test points in the inner 10° of two test methods to determine whether test points from different tests and regions exhibit different retest variability. We also generate some clinically applicable coefficient of repeatability (CoR) values for M700 Overall Defect (OD) and Pattern Defect (PD) indices. Methods: Twenty-four glaucoma patients with varying degrees of field loss were enrolled, and 21 patients (40 eyes) had usable results. The Central (30°) test and the Macula (10°) test were performed on each eye on the same day. To determine retest variability, the tests were repeated 1 week later at the same time of day. Results: Test points from 5 to 20 dB in the outer 20° of the 30° test showed lower retest variance than points of equal decibel value in the central 10° of the same test. For the 30° test, the OD CoR was 2.4 dB. The PD retest CoR varied with glaucoma severity, ranging from 1.24 dB for PD less than or equal to 2.8 to 3.1 dB for PD more than 5.7. The 10° test CoR for OD was 2.1 dB, and PD retest CoR ranged from 1.58 for PD less than or equal to 2.8 to 2.4 for PD more than 5.7. Conclusions: In glaucoma patients, retest variance for some decibel values does not seem to increase with increasing eccentricity in the M700. The OD values as graded by the M700 do not appear to correspond well with the amount of visual field loss and are not directly comparable to mean deviation results reported by other perimeters. Pattern defect values in the M700 seem to correlate well with the degree of field loss.