Documenta Ophthalmologica 40, 2:342 254, 1976. AUTOMATION OF PERIMETRY E. L. GREVE, M. T. GROOTHUYSE & W. M. VERDUIN
fA msterdam) INTRODUCTION For over a year, the W.A.G.O. (Werkgroep Automatisering Gezichtsveldonderzoek - Dutch Team on Automation of Perimetry) have been working on a pilot study concerning the question: is automation of perimetry possible? This study was started for the following reasons: 1. Determination of the visual field is necessary in numerous ophthalmological and neurological disorders. 2. Determination of the visual fields is often only useful if the performance is of high quality (Greve, 1973). 3. High-quality determination of the visual field requires knowledge, time and money; this knowledge and time are usually lacking, and it is doubtful whether adequate perimetry will ever be possible in a private ophthalmological practice. One solution of the problem might be to train specialized T.O.A.'s (= technical ophthalmological assistants). Preferably, such TOA's would work in a center tor penmetry uncler the supervision of a perimetrologist. 4. Such training of specialized TOA's would take a long time and it seems doubtful whether it would be possible to train enough TOA's for the required amount for perimetrical examination. 5. As soon as we think of a center, the possibility of automation is to be considered. 6. Determination of the visual field is a procedure suitable for automation. 7. Automatic processing of the perimetric data would afford great relief. The study of the possibility of automated determination of the visual field has a number of aspects of a rather varied nature: 1. The conditions to be fulfilled by the perimetric examination as regards equipment and technique (cf. Spahr, 1973). 2. Study of the patient's behavior in the course of automated examination of the visual field. :
Eye Clinic of the University of Amsterdam, 104 le Helmersstraat, Amsterdam (The Netherlands).
243
3. A search for new methods of stimulation, more suitable for use with automation. 4. Elaboration of computer programs, to be followed later by mechanical recording of the results, data storage and semi-automatic diagnosis. 5. Study of the efficiency of automated perimetry. The second aspect, the patient's behavior, will be considered in this first part. We are convinced that automation of perimetry will be restricted by human factors (possibilities of patient's participation), rather than by technical elements. EQUIPMENT In order to find an answer to question number 2, we devised a construction in which the patient and the stimulation part of the perimetric examination were kept separate from the control and analytical part (Figs. 1 and 2). For the stimulation part we used a modified Visual Field Analyser:
Fig. 1. Photograph of the patient's department with the modified Visual Field Analyser and the patient's chair with the operation-handle.
244
OPERATIONHANDLE PATIENTSSEAT
r--PATIENT
V.F.A.-
TAPE RECOE R-
/ EXAMINATOR
J INTERCOM
SEATOF THE EXAMINATOR
OPERATIONPANEL
INTERCOM
Fig. 2. Schematic drawing of the examination-room. There is a separate department for the patient and for the examinator. 1. Addition of an extra disc allowed simple switching from multiple-stimulus to single stimulus study. 2. Remote control was rendered possible. 3. For the communication between the patient and the analytical part, use was made of a numerical indicator located at the fixation point, with a control handle for number selection. 4. The patient was sitting in a comfortable chair, and the modified Visual Field Analyser was hanging from an adjustable stand. PROCEDURE OF THE EXAMINATION All the test subjects underwent a normal perimetric examination as described elsewhere (Greve, 1973). Immediately prior to the semi-automated perimetric examination, they were examined with a non-modified Visual Field Analyser. This was followed by an instruction by means of a tape recorder. After this instruction, a number of supraliminal test stimuli were presented, in order to familiarize the patient with the equipment, especially the number indicator and the control lever. Automated perimetry may, as in non-automated perimetry, be subdivided into a detection phase and an assessment or evaluation phase (Greve, 1973).
245
In the detection phase, the multiple stimulus method was used. The isolated test subject was simultaneously shown 2, 3 or 4 stimuli, and with the aid of the control lever had to select the number corresponding to the number of stimuli he had seen. This study was carried out in stages of 0.2 and 0.4 log. units. A difference in threshold level between a number of simutaneOusly presented stimuli amounting to over 0.4 log. units was interpreted as a defect, and as a reason to switch to the assessment phase. During the assessment phase, the intensity and the topography of a defect were determined in more detail by means of the single stimulus method.
Method in case o f normal visual field: The threshold was determined from the infraliminal to the supraliminal level, in stages of 0.2 and 0.4 log. units (Figs. 3a and 3b).
Methods in case o f visual field defects: 1st method: Identical to an examination of normal visual fields (Fig. 3c). The number of failures was very large here, owing to the zero fear (see below). 2nd method: The saw tooth method. The threshold was approached from the infraliminal as well as from the supraliminal region (Fig. 3d). With this method, also, the zero fear was still found to cause an excessive proportion of failures. 3rd method: The first few stimuli were offered with maximal luminance. If one or several stimuli were missed, this meant the presence of a defect for maximal luminance, permitting an immediate switch to the assessment phase. If no stimuli were missed at maximal luminance (Fig. 3e), the stimuli were offered at a lower level of luminance, etc. As much as possible the threshold was approached from the supraliminal level. Advantages: 1. time was saved 2. the zero fear played a less important part.
246
Ll i
il
INFRA THRESHOLD THRESHOLD
SUPRA THRESHOLD
1I~
MAX. L
2L
3I~
4Iu
---.---]I,"rIME
Fig. 3a. Method I; subjects with a normal visual field.
Fig. 3 abcde. Grafical representation of the method of examination;abscissa: successive presentations of a group of stimuli; ordinate: luminance steps of 0,2 log units. The dotted area indicates thresholdlevel. - indicates that no stimulus is seen; + indicates that some stimuli of a simultaneously presented group are seen; + indicates that all stimuli are seen. For example in Fig. 3a the stimuli are not seen at the first (1 ~ presentation; some, but not all of the simultaneously_presented stlmuh are seen at the second ( 2 ) presentation; none is seen at the thtrd ( 3 ) presentation and all are seen at the fourth ( 4 ) presentation. There is no defect if the distance between - and + is no more than 0.4 log units. 9
9
,
.
u
.
o
,
.
I
I
1~
2~
TIME
Fig. 3b. Method I; subjects with a normal visual field. In the ideal case the first presentation is infra-threshold and the second one supra-threshold.
247
INFRA THRESHOLD
THRESHOLD
? SUPRA THRESHOLD
MAX. L
! Io
!
20
I
3~
I
4o TIME
Fig. 3c, Method I; patients with a defect visual field. Luminance steps of 0.2 and 0.4 log units. Twice a -I- with a distance of 0.2 log units indicates a defect. The question marks indicate that in the detection phase the exact thresholdievel of a visual field defect is not known. This is determined in the assessmentphase.
L; INFRATHRESHOLD
=============================== ::::~
; :::~g:~::~::: ::::::::::::::::::::::
THRESHOLD
+
SUPRA THRESHOLD
MA•
I
I
I
1
1o
2~
3~
4~
Fig. 3d. Method II; patients with a defect visual field. Decreasing luminance steps in successive presentations.
248
INFRA THRESHOLD
THRESHOLD
SUPRA THRESHOLD
MAX. L 1o
2~
3~
4~ TIME
Fig. 3e. Method III; patients with a defect visual field. First presentation at maximum luminance. RESULTS AND DISCUSSION Examinations were made of: 112 eyes of test subjects with normal fields of vision, and 114 eyes of patients with visual field defects. Table 1 lists the results of the examination of normal test subjects. The first column shows the age distribution, the second the number of eyes examined. The third column shows how many groups of stimuli had to be studied further with the single-stimulus method. The fourth column shows the number of test stimuli regarded as necessary to familiarize the test subject with the method of examination. The fifth column lists the number of errors made with these test stimuli, and the sixth and seventh columns show the partial and complete failures (see criteria). Finally, the eight and ninth columns show the test subjects' reactions to two questions they were asked in regard to the semi-automatic examination in general and the control lever in particular. The criteria applied to failures were the following: Complete failure: This category consisted of the patients whose automated perimetric examination was discontinued. Examination with the nonmodified Visual Field Analyser had been successful in these test subjects. Partial failures: Automated determination of the visual field was very difficult. This table shows that the number of failures has been small (3.6 % total and 3.6 % partial failures). Of the total number of eight failures, five occurred in the age group between 61 up to and including 70 years. The following factors caused difficulties in the examination:
249
t~
C)
34
6
14
27
23
8
112
31-40
41-50
51-60
61-70
"-~71
Total
Number of eyes
~30
Age
3.3
2.9
4.9
3.2
2.5
3.7
3.7
Assessment
5.6
6.4
7.4
7.0
5.3
5.0
4.3
N u m b e r of trials/patient
1.3
1.1
2.2
1.5
1.6
1.2
1.1
N u m b e r of mistakes
4 = 3.6 %
0
2
1
0
0
1
Complete failure
4 = 3.6 %
0
3
1
0
0
0
Partial failure
1 : 2.6
1:4.0
1 : 1.5
l : 4.0
1 : 2.0
1 : 3.0
1 : 3.0
Examination difficult: No difference/Easy
1
0
1
1
1
0
1
8.0
5.0
11.0
11.0
6.0
3.0
4.0
Handle difficult: No difference/Easy
TABLE 1. RESULTS OF THE EXAMINATION OF PATIENT'S WITH A NORMAL VISUAL FIELD.
1. Zero fear This is the principal cause of failure of automated perimetric examination. The number zero is not regarded as a number. When a patient sees nothing, he selects no number or a wrong one. Moreover, the continual 'seeing nothing' has a depressive effect.
2. Nervousness The test subject is sitting alone in the dark. Nervous people, in particular, worry about committing errors during the automated examination of the field of vision, and it is precisely this worrying that may cause failure.
3. Age The older age groups experience more difficulty with automated perimetry. They are more nervous, less quick-minded and tire sooner. Also, the incidence of such disorders as deafness, rheumatism, hernia, etc. is higher in these groups.
4. Local adaptation This difficulty could be minimized by having more intervals and by allowing the patients to blink during the examination. The instructions, and the presentation of test stimuli are of great importance. The test subject has to get used to the system of numbers, indicator and lever. The advantage of this system is that it stimulates fixation and holds the attention. The number of times that the answers of the detection phase had to be checked during the assessment phase is between the limits of normal, considering the equipment and method used. In general, the majority (75 %) of the test subjects did not consider the automated examination difficult. It was only a stuN1 proportion of the subjects (12.5 %) who condidered the answering of questions by the lever-numbers indicator system difficult. Table 2 lists the results of the automatic examination of patients with visual field defects, in a similar way as Table 1. Naturally, the number of times when switching to the assessment phase was necessary is much greater. Since the topography and intensity of the defects are not known, the number of test stimuli was also larger.
251
Number of eyes
7
8
13
18
61
7
114
Age
430
31-40
41-50
51-60
61-70
~71
Total
7.0
9.2
7.8
8.4
5.6
6.1
4.0
Assessment
8.1
10.0
9.0
10.5
6.2
7.1
5.6
Number of trials/patient
1.7%
2.7%
18 = 1 5 . 9 %
3=
13 = 1 1 . 5 %
2=
0
0
0
Complete failure
11 = 9 . 6 %
1 = 0.9%
8 = 7.0%
2 = 1.7%
0
0
0
Partial failure
1 : 1.5
1:0.6
1:0.8
1:6.5
1 : 2.6
1 : 5.0
1 : 1.5
Examination difficult: No difference/Easy
6.0
1.5
4.0
1.2
1 : 2.4
1:
1 :
1 : 14.0
1 : 10.0
0:
1 :
Handle difficult: No difference/Easy
TABLE 2. RESULTS OF THE EXAMINATION OF SUBJECTS WITH A DEFECT VISUAL FIELD.
TABLE 3. RESULTS OF THE LAST 51 PATIENT'S, EXAMINED WITH METHOD III. Age
Number of eyes
Complete failure
Partial failure
25
1 =
0
>61
26
8 = 31.0%
2 = 7.8%
Total
51
9 = 17.6 %
2 = 4.0%
~61
4.0 %
The distribution of the patients over the various age groups was unequal. Of the total number of 114 subjects, 68 belonged to the age groups over 60 years and 46 were 60 years old or younger. All subjects were patients of our ophthalmological clinic, which implies an unfavorable selection. As Table 2 shows, all failures occurred in the age group over 60 years. The proportion of total failures amounted to 15.9 % of the total number of patients examined, but to 27 % of the older age groups. In the course of the study of the patients with defects of the visual field, the examination method has been adapted twice. Table 3 lists the results of the last 51 patients, who have been examined by an improved method (method III). We find that the proportion of total failures has not decreased, but that the proportion of partial failures has grown less. In automated examination of patients, a proportion of failures of approx. 30 % has to be expected in the older age groups. Possibly, this proportion will be slightly reduced by further refinement of equipment and technique. CONCLUSION Automation of perimetry is quite feasible in normal subjects (3.6 % failures). It is equally feasible in patients with visual field defects not over 60 years of age (0 % failures). Automated examination ends in failure in 30 % of the patients in the older age groups seen in our clinic. This means that automated perimetry is particularly suitable for purposes of screening, i.e. to distinguish between subjects with and without visual field defects.
253
A u t o m a t e d p e r i m e t r y also allows p e r f o r m a n c e o f an accurate assessment phase, b u t in 16 % of the cases the e x a m i n a t i o n will have t o be p e r f o r m e d b y a perimetrist. To a Center for p e r i m e t r y , this still m e a n s a considerable lightening t h e w o r k load. In general, a u t o m a t i o n of p e r i m e t r y m e a n s that t h e possibility o f examin a t i o n o f the visual field is m a d e available t o large groups o f people.
REFERENCES Greve, E. L. Single and multiple stimulus static perimetry in glaucoma; the two phases of visual field examination, (thesis). Doc. O~phthal.-36 : 1-355 (1973). Norren, D. Van et al. Automatisering van gezichtsveldonderzoek - de Scoperimeter - (will be published). Spahr, J. Zur Automatisierung der Perimetrie. I. Graefes Arch. Ophthal. 188 : 323338. (1973). DISCUSSION Van Balen: I suppose the intention is to render the perimetric examination less timeconsuming. Have you beefi able to check this yet by comparison with the normal Friedman examination?
Answer: Our goal is not so much a shorter duration of the examination but rather an increase of the capacity. No comparison with the normal Freedman examination is yet possible, owing to the prehminary nature of the apparatus used. Von Winning: a. Does the small group of bad results also include cases with good cooperation but with incorrect visual fields, different from the visual fields obtained in the standard manner? b. With all forms of perimetry you warn against the assumption of simple relations between the stimulus and the result of the examination; corrections are necessary, depending among other things on summation. Now is the stimulus repeated after a very short interval, equivalent without any correction to enhanced intensity of the stimulus? c. Supposing you prefer perimetry to campimetry, would optic enlargement of the angle at which the screen is viewed be worth considering? (cf. the paper by Migchelsen & Jonkers).
Answer: a. No, the bad results have all been due to lack of understanding, zero fear, etc. as stated. b. The method of intensifying the stimulus by increasing the number of impulses within the critical interval is entirely equivalent to increasing the intensity with constant light sources, within the critical interval, the form of presentation exerts no influence. c. Such optic enlargement is not advisable for automated determination of the visual field, owing among other things to highly critical distance between eye and the magnifying glass. Moreover, by moving the fixation point over the display, the visual field to be examined will be magnified further.
254
fA msterdam) INTRODUCTION For over a year, the W.A.G.O. (Werkgroep Automatisering Gezichtsveldonderzoek - Dutch Team on Automation of Perimetry) have been working on a pilot study concerning the question: is automation of perimetry possible? This study was started for the following reasons: 1. Determination of the visual field is necessary in numerous ophthalmological and neurological disorders. 2. Determination of the visual fields is often only useful if the performance is of high quality (Greve, 1973). 3. High-quality determination of the visual field requires knowledge, time and money; this knowledge and time are usually lacking, and it is doubtful whether adequate perimetry will ever be possible in a private ophthalmological practice. One solution of the problem might be to train specialized T.O.A.'s (= technical ophthalmological assistants). Preferably, such TOA's would work in a center tor penmetry uncler the supervision of a perimetrologist. 4. Such training of specialized TOA's would take a long time and it seems doubtful whether it would be possible to train enough TOA's for the required amount for perimetrical examination. 5. As soon as we think of a center, the possibility of automation is to be considered. 6. Determination of the visual field is a procedure suitable for automation. 7. Automatic processing of the perimetric data would afford great relief. The study of the possibility of automated determination of the visual field has a number of aspects of a rather varied nature: 1. The conditions to be fulfilled by the perimetric examination as regards equipment and technique (cf. Spahr, 1973). 2. Study of the patient's behavior in the course of automated examination of the visual field. :
Eye Clinic of the University of Amsterdam, 104 le Helmersstraat, Amsterdam (The Netherlands).
243
3. A search for new methods of stimulation, more suitable for use with automation. 4. Elaboration of computer programs, to be followed later by mechanical recording of the results, data storage and semi-automatic diagnosis. 5. Study of the efficiency of automated perimetry. The second aspect, the patient's behavior, will be considered in this first part. We are convinced that automation of perimetry will be restricted by human factors (possibilities of patient's participation), rather than by technical elements. EQUIPMENT In order to find an answer to question number 2, we devised a construction in which the patient and the stimulation part of the perimetric examination were kept separate from the control and analytical part (Figs. 1 and 2). For the stimulation part we used a modified Visual Field Analyser:
Fig. 1. Photograph of the patient's department with the modified Visual Field Analyser and the patient's chair with the operation-handle.
244
OPERATIONHANDLE PATIENTSSEAT
r--PATIENT
V.F.A.-
TAPE RECOE R-
/ EXAMINATOR
J INTERCOM
SEATOF THE EXAMINATOR
OPERATIONPANEL
INTERCOM
Fig. 2. Schematic drawing of the examination-room. There is a separate department for the patient and for the examinator. 1. Addition of an extra disc allowed simple switching from multiple-stimulus to single stimulus study. 2. Remote control was rendered possible. 3. For the communication between the patient and the analytical part, use was made of a numerical indicator located at the fixation point, with a control handle for number selection. 4. The patient was sitting in a comfortable chair, and the modified Visual Field Analyser was hanging from an adjustable stand. PROCEDURE OF THE EXAMINATION All the test subjects underwent a normal perimetric examination as described elsewhere (Greve, 1973). Immediately prior to the semi-automated perimetric examination, they were examined with a non-modified Visual Field Analyser. This was followed by an instruction by means of a tape recorder. After this instruction, a number of supraliminal test stimuli were presented, in order to familiarize the patient with the equipment, especially the number indicator and the control lever. Automated perimetry may, as in non-automated perimetry, be subdivided into a detection phase and an assessment or evaluation phase (Greve, 1973).
245
In the detection phase, the multiple stimulus method was used. The isolated test subject was simultaneously shown 2, 3 or 4 stimuli, and with the aid of the control lever had to select the number corresponding to the number of stimuli he had seen. This study was carried out in stages of 0.2 and 0.4 log. units. A difference in threshold level between a number of simutaneOusly presented stimuli amounting to over 0.4 log. units was interpreted as a defect, and as a reason to switch to the assessment phase. During the assessment phase, the intensity and the topography of a defect were determined in more detail by means of the single stimulus method.
Method in case o f normal visual field: The threshold was determined from the infraliminal to the supraliminal level, in stages of 0.2 and 0.4 log. units (Figs. 3a and 3b).
Methods in case o f visual field defects: 1st method: Identical to an examination of normal visual fields (Fig. 3c). The number of failures was very large here, owing to the zero fear (see below). 2nd method: The saw tooth method. The threshold was approached from the infraliminal as well as from the supraliminal region (Fig. 3d). With this method, also, the zero fear was still found to cause an excessive proportion of failures. 3rd method: The first few stimuli were offered with maximal luminance. If one or several stimuli were missed, this meant the presence of a defect for maximal luminance, permitting an immediate switch to the assessment phase. If no stimuli were missed at maximal luminance (Fig. 3e), the stimuli were offered at a lower level of luminance, etc. As much as possible the threshold was approached from the supraliminal level. Advantages: 1. time was saved 2. the zero fear played a less important part.
246
Ll i
il
INFRA THRESHOLD THRESHOLD
SUPRA THRESHOLD
1I~
MAX. L
2L
3I~
4Iu
---.---]I,"rIME
Fig. 3a. Method I; subjects with a normal visual field.
Fig. 3 abcde. Grafical representation of the method of examination;abscissa: successive presentations of a group of stimuli; ordinate: luminance steps of 0,2 log units. The dotted area indicates thresholdlevel. - indicates that no stimulus is seen; + indicates that some stimuli of a simultaneously presented group are seen; + indicates that all stimuli are seen. For example in Fig. 3a the stimuli are not seen at the first (1 ~ presentation; some, but not all of the simultaneously_presented stlmuh are seen at the second ( 2 ) presentation; none is seen at the thtrd ( 3 ) presentation and all are seen at the fourth ( 4 ) presentation. There is no defect if the distance between - and + is no more than 0.4 log units. 9
9
,
.
u
.
o
,
.
I
I
1~
2~
TIME
Fig. 3b. Method I; subjects with a normal visual field. In the ideal case the first presentation is infra-threshold and the second one supra-threshold.
247
INFRA THRESHOLD
THRESHOLD
? SUPRA THRESHOLD
MAX. L
! Io
!
20
I
3~
I
4o TIME
Fig. 3c, Method I; patients with a defect visual field. Luminance steps of 0.2 and 0.4 log units. Twice a -I- with a distance of 0.2 log units indicates a defect. The question marks indicate that in the detection phase the exact thresholdievel of a visual field defect is not known. This is determined in the assessmentphase.
L; INFRATHRESHOLD
=============================== ::::~
; :::~g:~::~::: ::::::::::::::::::::::
THRESHOLD
+
SUPRA THRESHOLD
MA•
I
I
I
1
1o
2~
3~
4~
Fig. 3d. Method II; patients with a defect visual field. Decreasing luminance steps in successive presentations.
248
INFRA THRESHOLD
THRESHOLD
SUPRA THRESHOLD
MAX. L 1o
2~
3~
4~ TIME
Fig. 3e. Method III; patients with a defect visual field. First presentation at maximum luminance. RESULTS AND DISCUSSION Examinations were made of: 112 eyes of test subjects with normal fields of vision, and 114 eyes of patients with visual field defects. Table 1 lists the results of the examination of normal test subjects. The first column shows the age distribution, the second the number of eyes examined. The third column shows how many groups of stimuli had to be studied further with the single-stimulus method. The fourth column shows the number of test stimuli regarded as necessary to familiarize the test subject with the method of examination. The fifth column lists the number of errors made with these test stimuli, and the sixth and seventh columns show the partial and complete failures (see criteria). Finally, the eight and ninth columns show the test subjects' reactions to two questions they were asked in regard to the semi-automatic examination in general and the control lever in particular. The criteria applied to failures were the following: Complete failure: This category consisted of the patients whose automated perimetric examination was discontinued. Examination with the nonmodified Visual Field Analyser had been successful in these test subjects. Partial failures: Automated determination of the visual field was very difficult. This table shows that the number of failures has been small (3.6 % total and 3.6 % partial failures). Of the total number of eight failures, five occurred in the age group between 61 up to and including 70 years. The following factors caused difficulties in the examination:
249
t~
C)
34
6
14
27
23
8
112
31-40
41-50
51-60
61-70
"-~71
Total
Number of eyes
~30
Age
3.3
2.9
4.9
3.2
2.5
3.7
3.7
Assessment
5.6
6.4
7.4
7.0
5.3
5.0
4.3
N u m b e r of trials/patient
1.3
1.1
2.2
1.5
1.6
1.2
1.1
N u m b e r of mistakes
4 = 3.6 %
0
2
1
0
0
1
Complete failure
4 = 3.6 %
0
3
1
0
0
0
Partial failure
1 : 2.6
1:4.0
1 : 1.5
l : 4.0
1 : 2.0
1 : 3.0
1 : 3.0
Examination difficult: No difference/Easy
1
0
1
1
1
0
1
8.0
5.0
11.0
11.0
6.0
3.0
4.0
Handle difficult: No difference/Easy
TABLE 1. RESULTS OF THE EXAMINATION OF PATIENT'S WITH A NORMAL VISUAL FIELD.
1. Zero fear This is the principal cause of failure of automated perimetric examination. The number zero is not regarded as a number. When a patient sees nothing, he selects no number or a wrong one. Moreover, the continual 'seeing nothing' has a depressive effect.
2. Nervousness The test subject is sitting alone in the dark. Nervous people, in particular, worry about committing errors during the automated examination of the field of vision, and it is precisely this worrying that may cause failure.
3. Age The older age groups experience more difficulty with automated perimetry. They are more nervous, less quick-minded and tire sooner. Also, the incidence of such disorders as deafness, rheumatism, hernia, etc. is higher in these groups.
4. Local adaptation This difficulty could be minimized by having more intervals and by allowing the patients to blink during the examination. The instructions, and the presentation of test stimuli are of great importance. The test subject has to get used to the system of numbers, indicator and lever. The advantage of this system is that it stimulates fixation and holds the attention. The number of times that the answers of the detection phase had to be checked during the assessment phase is between the limits of normal, considering the equipment and method used. In general, the majority (75 %) of the test subjects did not consider the automated examination difficult. It was only a stuN1 proportion of the subjects (12.5 %) who condidered the answering of questions by the lever-numbers indicator system difficult. Table 2 lists the results of the automatic examination of patients with visual field defects, in a similar way as Table 1. Naturally, the number of times when switching to the assessment phase was necessary is much greater. Since the topography and intensity of the defects are not known, the number of test stimuli was also larger.
251
Number of eyes
7
8
13
18
61
7
114
Age
430
31-40
41-50
51-60
61-70
~71
Total
7.0
9.2
7.8
8.4
5.6
6.1
4.0
Assessment
8.1
10.0
9.0
10.5
6.2
7.1
5.6
Number of trials/patient
1.7%
2.7%
18 = 1 5 . 9 %
3=
13 = 1 1 . 5 %
2=
0
0
0
Complete failure
11 = 9 . 6 %
1 = 0.9%
8 = 7.0%
2 = 1.7%
0
0
0
Partial failure
1 : 1.5
1:0.6
1:0.8
1:6.5
1 : 2.6
1 : 5.0
1 : 1.5
Examination difficult: No difference/Easy
6.0
1.5
4.0
1.2
1 : 2.4
1:
1 :
1 : 14.0
1 : 10.0
0:
1 :
Handle difficult: No difference/Easy
TABLE 2. RESULTS OF THE EXAMINATION OF SUBJECTS WITH A DEFECT VISUAL FIELD.
TABLE 3. RESULTS OF THE LAST 51 PATIENT'S, EXAMINED WITH METHOD III. Age
Number of eyes
Complete failure
Partial failure
25
1 =
0
>61
26
8 = 31.0%
2 = 7.8%
Total
51
9 = 17.6 %
2 = 4.0%
~61
4.0 %
The distribution of the patients over the various age groups was unequal. Of the total number of 114 subjects, 68 belonged to the age groups over 60 years and 46 were 60 years old or younger. All subjects were patients of our ophthalmological clinic, which implies an unfavorable selection. As Table 2 shows, all failures occurred in the age group over 60 years. The proportion of total failures amounted to 15.9 % of the total number of patients examined, but to 27 % of the older age groups. In the course of the study of the patients with defects of the visual field, the examination method has been adapted twice. Table 3 lists the results of the last 51 patients, who have been examined by an improved method (method III). We find that the proportion of total failures has not decreased, but that the proportion of partial failures has grown less. In automated examination of patients, a proportion of failures of approx. 30 % has to be expected in the older age groups. Possibly, this proportion will be slightly reduced by further refinement of equipment and technique. CONCLUSION Automation of perimetry is quite feasible in normal subjects (3.6 % failures). It is equally feasible in patients with visual field defects not over 60 years of age (0 % failures). Automated examination ends in failure in 30 % of the patients in the older age groups seen in our clinic. This means that automated perimetry is particularly suitable for purposes of screening, i.e. to distinguish between subjects with and without visual field defects.
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A u t o m a t e d p e r i m e t r y also allows p e r f o r m a n c e o f an accurate assessment phase, b u t in 16 % of the cases the e x a m i n a t i o n will have t o be p e r f o r m e d b y a perimetrist. To a Center for p e r i m e t r y , this still m e a n s a considerable lightening t h e w o r k load. In general, a u t o m a t i o n of p e r i m e t r y m e a n s that t h e possibility o f examin a t i o n o f the visual field is m a d e available t o large groups o f people.
REFERENCES Greve, E. L. Single and multiple stimulus static perimetry in glaucoma; the two phases of visual field examination, (thesis). Doc. O~phthal.-36 : 1-355 (1973). Norren, D. Van et al. Automatisering van gezichtsveldonderzoek - de Scoperimeter - (will be published). Spahr, J. Zur Automatisierung der Perimetrie. I. Graefes Arch. Ophthal. 188 : 323338. (1973). DISCUSSION Van Balen: I suppose the intention is to render the perimetric examination less timeconsuming. Have you beefi able to check this yet by comparison with the normal Friedman examination?
Answer: Our goal is not so much a shorter duration of the examination but rather an increase of the capacity. No comparison with the normal Freedman examination is yet possible, owing to the prehminary nature of the apparatus used. Von Winning: a. Does the small group of bad results also include cases with good cooperation but with incorrect visual fields, different from the visual fields obtained in the standard manner? b. With all forms of perimetry you warn against the assumption of simple relations between the stimulus and the result of the examination; corrections are necessary, depending among other things on summation. Now is the stimulus repeated after a very short interval, equivalent without any correction to enhanced intensity of the stimulus? c. Supposing you prefer perimetry to campimetry, would optic enlargement of the angle at which the screen is viewed be worth considering? (cf. the paper by Migchelsen & Jonkers).
Answer: a. No, the bad results have all been due to lack of understanding, zero fear, etc. as stated. b. The method of intensifying the stimulus by increasing the number of impulses within the critical interval is entirely equivalent to increasing the intensity with constant light sources, within the critical interval, the form of presentation exerts no influence. c. Such optic enlargement is not advisable for automated determination of the visual field, owing among other things to highly critical distance between eye and the magnifying glass. Moreover, by moving the fixation point over the display, the visual field to be examined will be magnified further.
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