Normal Human Electroretinogram*

COATS' DISEASE

865

27. Paufique, L., Ravault, M. P., Mireille Bonnet, and Istre : L'angiomatose miliaire rétinienne de Leber. Ann. Oculist. (Paris), 197:937, 1964. 28. Ricci, A.: La photocoagiilation dans un cas de microanevrisnie de Leber. Ophthalmologica (Basel), 145 .-427-430, 1963.

NORMAL HUMAN

ELECTRORETINOGRAM*

A. D. RUEDEMANN, J R . , M . D . Detroit, Michigan T h e purpose of this paper is to report the results of several statistical tests applied to the data obtained by standard electroretinographic techniques from a series of individuals with normal eye examinations. M o r e adequate interpretation of the normal E R G is desirable, particularly if one is to evaluate the abnormal E R G . Statistical tests applied to physiologic data tend to improve confidence in evaluation of function. INTRODUCTION

Since 1956, when the Electroretinography Laboratory at the Kresge E y e Institute was put in operation, certain basic requirements were laid down. T h e laboratory was set u p with the expressed purpose of performing clinical electroretinograms. A standard testing procedure was instituted, using both light-adapted and dark-adapted conditions. This has been described previously. 1 , 2 Equipment was standardized and maintained under conditions that would allow repetition of a standard test. F o r example, a standard contact lens corneal electrode was developed by trial and error techniques. This contact lens has been utilized since routine testing was instituted ( 1 9 5 6 ) . U n d e r visual control, air bubbles, poor contact, excessive lid blinking or lid activity can be held to the minimum and repetitive responses can be obtained without undue stress on the patient. ( I t is worthy of note that to date no patient has * From the Kresge Eye Institute, Wayne State University, and the Department of Ophthalmology, Detroit Receiving Hospital. This study was supported in part by the Detroit Receiving Hospital Research Corporation.

suffered corneal abrasion or severe ocular discomfort.) Instrumentation was standardized as to amplifiers, headband, filters, oscilloscope and recording apparatus. T h e same type of photic stimulator has been used since 1956.t T h e testing procedure was so standardized as to allow a short test period with little stress on the patient. T h e test is nearly always performed by a technician. T h e technician is particularly trained to handle the electronic equipment, the placement and removal of contact lenses, and the proper measurement and evaluation of results. Interpretation of results is always performed by the supervising physician. Clinical history and eye examination are obtained from the referring physician. Visual fields and color vision are tested in the laboratory prior to the electroretinographic test. F u n d u s photos are taken immediately after the test is completed. It has been the purpose of the laboratory to maintain a procedure which is so standardized that a test performed under regular conditions in one year can be compared to a test performed under similar conditions in another year. T h e patient is treated as if the test is a standard procedure. F o r a number of years a standard electroretinographic procedure has also been performed with portable equipment under hospital conditions. The main differences between the two tests would appear to involve control of excessive extraneous current in the environment and uncontrolled light sources which prevent adequate dark adaptation. t Bulb changed August, 1959.

Λ. D. RUKDEMANN, JR.

866

Otherwise, the tests are in every way comparable to an RRG performed in a shielded room. Over a period of two years ERGs were performed on normal and abnormal individuals both in and out of the shielded room, using similar equipment. The results were found to be everywhere comparable to the degree that no statistical analysis was felt necessary. At this time over 1,100 patients have been tested utilizing the standard ERG test. Some patients have been tested as many as 10 times. METHOD

The standard ERG procedure already mentioned has been discussed in previous publications.1'2 In review, the test consists of maximum dilatation of the pupils of the testée in a room maintained under reduced illumination. This allows for an adaptation period from outside illumination which may vary from day to day and time to time. After approximately 40 minutes to one hour of reduced illumination while mydriasis is taking place, the testing method is explained to the patient who is comfortably seated in a chair. The contact lenses are placed, the headband is put into position, and connections are tested. Pupil size is measured and noted on the record. The patient is first tested in a dimly lighted room (0.4 foot-candles) with a low intensity (No. 1) xenon flash, no filter, in the light ( L ) , (Grass Photic Stimulator PS1), followed in 10 seconds by a maximum stimulus (TOI6). This is followed in 30 seconds with a 20/second flicker at intensity setting No. 4 ( L 0 4 20/sec). The patient is then dark adapted for five minutes and a standard procedure consisting of a low intensity flash (No. 1) in the dark ( D O l ) , followed in 30 seconds by a medium intensity (No. 4) ( D 0 4 ) , and after one minute a maximal flash (No. 16) D 0 1 6 ) . The oscilloscope screen sweep speed is then accelerated to spread out the response across the os-

cilloscope screen. This allows for better interpretation of the components of the a-waves and b-waves. The DO 16 is repeated in one minute with two different sweep speeds, 10 and five milliseconds per centimeter at one-minute intervals. The patient is then stimulated with a blue light CDB16), followed in one minute by a green light (DG16), and in two minutes by a red light (DR16). With the room illumination again at 0.4 foot-candles, the patient's eyes are then stimulated a number of times utilizing a number of different stimuli (usually L016 and L 0 4 20/sec.) which are then relayed to a computer. The results are then subjected to analysis utilizing basic computer technique. All data regarding oscilloscope, computer and other equipment settings are recorded. Time and amplitude calibration sweeps are recorded for each patient. T H E NORMAL

ERG

In previous reports abnormal ERGs have been compared to a so-called "normal" series. The "normal" series consisted of 55 patients of various ages, race and sex, who had a normal eye examination with no evidence of ocular disease. The ERGs of these patients were subjected to standard statistical analysis. A mean for each amplitude, latency and peak time was obtained and standard deviations computed. The range from one standard below the mean to one above was called "normal" range.* A second series of 13 normal individuals, all were 20 to 26 years of age except two in their 30's, were tested on 10 consecutive occasions by the standard electroretinographic technique already noted. The results were then investigated by standard statistical methods as follows: First, comparison of the "normal" range. The "normal" range obtained from the 55 * The change in bulb intensity would indicate a shift to the right of all the amplitudes in the first normal series.

NORMAL HUMAN ELECTRORETINOGRAM

normal individuals from the first series is compared to the 13 normals tested 10 consecutive times. Second, a comparison of the values obtained from the right and left eyes of each of the 13 normal individuals on 10 successive tests. Third, the mean absolute difference over the mean (variation coefficient) was determined to get some idea of the variation of the ERG with repetitive testing of the various responses. Finally, the association or comparison between the various responses was made to determine the possible relationship or lack of relationship between the a- and b-waves of various responses. It has been obvious from the very beginning of testing that a need for "normal" range of function is essential in order to evaluate the abnormal. A normal physiologic function may vary from day to day, or for that matter from hour to hour, or minute to minute. The necessity of appreciating this particular feature of normal function is obvious. One must have some idea of normal values or relationships in order to analyze the abnormal properly. RESULTS

1. The "normal" range of the first series as compared to the "normal" range of the second series. In both the first and second series two standard deviations of the mean were determined. The first standard deviation was declared the "normal" range. The "normal" range for all of the amplitudes in microvolts for each of the standard stimuli is given in Table 1. The "normal" range for latencies and peak times are also noted. The method used to determine the standard deviation of the mean and standard deviation is noted in Table 2 for the components of aand b-waves for DO 16, fast sweep speed. The results noted in Table 1 would indicate that in our laboratory the "normal" range for all components of the routine ERG tests is rather stable.

867

2. Mean absolute difference/mean (variability coefficient). The variability coefficient is a statistical test which gives the percent of variation of each response from the mean on repetitive testing. The method used to determine the result or percent variation is noted in Table 3, the a-wave amplitude for L016 of patient K23S as tested on 10 occasions. The results obtained for all the components are noted in Table 4 and will be discussed. 3. Correlation between the ERG of the right eye and left eye of a normal subject (table 5). The basic question would be: "Is it possible to test one eye and predict that the other eye will give similar results?" It would be expected that even in normal circumstances the right and left eyes of an individual would not be exactly similar. It is well known that there are definite variations from the normal in varying conditions and circumstances. Even though positive correlation was not expected the statistical tests were performed to aid in determining the actual differences which might take place and the effectiveness of the ERG method when subjected to this type of statistical study. The statistical correlation used was one which determines the relationship between two variables. The amplitudes, peak times, and latencies were determined and calculated from the 10 tests. The raw values were then placed in rank order. The difference between the ranks were squared and using a formula from the above correlation, K was determined and from this a probability p. The rank correlation coefficient (r*) was than calculated, which is an indication of the degree of association between the two variables. The results of this correlation, noted in Tables 6, 6A, 6B and 6C, generally indicate a positive relationship of the two eyes. 4. Correlation between components of various responses. The obvious function of this test was to determine the possible relationship of various components of the different stimuli to one another, a-wave am-

A. D. RUEDEMANN, JR. plitude DO 16 to a-wave amplitude DB16 (table 7). A very high correlation figure (0.0838) would indicate a negative relationship while a low figure (0.0010 ) would indicate that

the two components are related; for example, there is less than 0.1% chance that the two components are not related. The reliability (r') of this data was determined in each case, for example, for D016 and DB16

TABLE 1 AMPLITUDES IN MICROVOLTS

1st Normal Series

2nd Normal Series

Peak Times and Latency (in milliseconds)

87-149 164-284

107-161 193-305

2 0 - 24 3 9 - 45

10- 24 58-124

3 4 - 52

2 1 - 25 5 1 - 61

3 9 - 77

4 8 - 70

a-wave b-wave smooth

16- 32 284-452

232-346

3 6 - 44 7 1 - 91

a-wave b-wave sharp b-wave smooth

55-117 330-510 302-514

60-106 309-511 352-508

29- 33 4 8 - 58 5 7 - 77

a-wave b-wave sharp b-wave smooth

168-268 385-595 376-580

192-280 395-569 408-564

2 4 - 28 4 6 - 56 6 2 - 80

a-wave b-wave sharp b-wave smooth

83-165 392-618 337-545

102-200 388-522 380-536

2 9 - 33 5 1 - 59 5 9 - 77

a-wave b-wave sharp b-wave smooth

74-148 383-559 336-546

95-149 393-489 380-544

3 0 - 34 5 0 - 60 6 1 - 77

a-wave b-wave sharp b-wave smooth

14- 38 5 1 - 97 103-267

17- 47 3 3 - 69 144-232

2 1 - 25 4 5 - 55 90-138

42-104

Not in protocol

141-251 131-241 172-276 119-283 265-425

161-227 156-222 211-285 103-197 258-386

Description L016

LOI

a-wave b-wave sharp a-wave b-wave smooth

L 0 4 20/sec. b-wave sharp DOl

D04

D016

DB16

DG16

DR16

D 0 4 20/sec. b-wave sharp Fast S'iveep Speed Components ni Pi n2 P2 P3

D016

1520242934-

19 24 28 35 40

Latency a-wave

4-

5

NORMAL HUMAN ELECTRORETINOGRAM

869

TABLE 2 n AND p AMPLITUDES IN MICROVOLTS

Case

ni

Pi

n2

P2

225 235 529 532 542 609 611 612 615 616 617 621 626

174 244 153 182 148 239 246 191 181 154 190 191 228

174 235 143 172 148 239 246 182 181 154 181 191 209

235 261 267 220 200 325 282 282 208 199 208 267 264

139 157 143 191 139 248 200 155 109 109 109 105 200

Σχ Σχ' X χ' X2

Σ — Ν <Γ

Ν" Standard Deviation = σ Range Range

296 348 315 392 305 439 437 319 208 281 281 267 300

=

2 ,521 503,409 193. 92 37 ,604.97

2,455 477,599 188.85 35,664.32

3,218 814,822 247.54 61,276.05

2,004 332,418 154.15 23,762.22

4,188 1,402,560 322.15 103,780.62

=

38 ,723. 76

36,738.38

62,678.61

25,570.61

107,889.23

1 ,118.79

1,074.06

1,402.56

1,808.39

4,108.61

=

86. 06

82.62

107.89

139.11

316.05

= =

33. 4

32.7

37.4

42.5

64.0

=

=

2

σ2

P3

=

258-386 161--227 156-222 211-285 103-197 M e a n ± one standard deviation; x = each numerical value; x = mean; N = number of cases

a-wave amplitude there is less than one chance in a thousand that the two components are not related in 94 percent of the cases. An example of the correlation is noted in Table 7. The results of all the correlations are noted in Table 8. This test was utilized to answer several questions : a. Does the a-wave correlate with the fawave of any responses? In this series only several examples were attempted. There was such a high negative correlation that the entire series was not completed. It was concluded that the a-wave and the b-wave for any stimulus did not relate and therefore measured different functions. A special example of this is noted in Table 8. Fast sweep speed amplitudes (D016) n 1; p 1( n2 are awavelets, while p 2 , p 3 are b- wavelets. There is a notably higher negative correlation of

ii! to p 2 or p 3 as compared to Pi or n2. The most significant difference is noted between n2 and p2, p 3 . b. If one stimulus gives essentially the same information as another stimulus, could one or the other then be dropped from the standard test ; for example, D 0 4 and DG16, DB16? Of eight determinations, six were at the < 0.001 level, indicating a strong positive correlation. The other two determinations were for b-wave peak time smooth where the determination is particularly difficult to make. One could assume that for purposes of the routine clinical ERG that the three stimuli were an evaluation of a similar function. c. Does the a-wave of L 0 1 6 correlate to the a-wave DR16 or with D016? In other words, do supposedly photopic functions correlate with one another and not with scotopic functions ? Do the components of dark-

870

Λ. D. R U E D E M A N N , JR.

adapted responses correlate with one another and not with photopic functions ? The stimuli utilized to evaluate photopic functions are LOI, L016, L 0 4 20/sec and DR 16. LOI has no measurable a-wave and a variable b-wave smooth. It would appear to have a reasonably high correlation to most dark-adapted stimuli indicating a measurement of a similar function. The relationship to the red response indicates a reasonably low correlation (0.2236). Although it is possible that the results have some significance, the extreme variability of LOI makes it difficult to evaluate. From the standpoint of a-wave amplitude (L016, DG16), b-wave amplitude sharp (L016, L 0 4 20/sec, DR16) there would appear to be reasonably high correlations of the photopic stimuli. The dark-adapted stimuli are generally well correlated, indicating similar functions. Contrariwise, the photopic to scotopic correlations are generally not well correlated, indicating that the various components do not measure similar functions (table 8).

TABLE 3 A-WAVE AMPLITUDE.

Case 235

Test No.

L016

m

+d

1 2 3 4 5 6 7 8 9 10

138 107 169 178 172 149 144 135 154 102

144.8 144.8 144.8 144.8 144.8 144.8 144.8 144.8 144.8 144.8

6.8 37.8 24.2 M. 2 27.2 4.2 0.8 9.8 9.2 42.8 196.0

1448 2n

mad

19.6

N

m

144.8

1448

19.6

10

144.8

i(+d) 196 10

.1354

= mad

= 19.6

n = e a c h numerical value; N = n u m b e r of tests; m = mean; mad = mean absolute difference.

TABLE 4 MAD : T H I R T E E N ' 'NORMAL" INDIVIDUALS

M b-smooth LOI DOl D04 Ü016 DB16 ÜG16 DR16

0.158 0.141 0.069 0.075 0.063 0.073 0.133

b-smooth LOI DOl D04 D016 DB16 DG16 DR16

0.071 0.056 0.065 0.043 0.053 0.048 0.054

b-sharp L016 L 0 4 20/sec D016 DB16 ÜG16 DR16

b-sharp L016 D016 DB16 DG16 DR16

AMPLI TUDES

»

0.071 0.150 0.074 0.079 0.064 0.141

a- wave L016 D04 D016 DB16 DG16 DR 16

P E A K TIME

0.024 0.039 0.037 0.044 0.049

Fast Sweep Speed 0.124 0.173 0.114 0.146 0.144 0.167

0.135

Pi

0.141

n2

0.111

Ps

0.097

P3

0.086

Fast Sweep Speed

n2 LOI L016 DOl D04 D016 DB16 DG16 DR16

111

0.104 0.074 0.067 0.044 0.051 0.043 0.059 0.086

Hi

0.037

Pi

0.042

P2

0.030

P3

0.025

NORMAL HUMAN ELECTRORETINOGRAM TABLE 5 A-WAVE AMPLITUDE

Case 235 L016

Test No.

O.D.

O.S.

Rank O.D.

Rank O.S.

1 2 3 4 5 6 7 8 9 10

138 107 169 174 172 149 130 135 154 102

129 99 151 178 163 107 144 107 154 98

5 2 8 10 9 6 3 4 7 1

5.0 2.0 7.0

10.0

9.0 3.5 6.0 3.5 8.0 1.0

d2 0.0 0.0 1.0 0.0 0.0 2.5 3.0 0.5 1.0 0.0

0.00 0.00 1.00 0.00 0.00 6.25 9.00 0.25 1.00 0.00

n(ii + l)(n-l)-62d2±l)

K=

η(η + 1 ) ν Ί ι - 1 K=-

K=

10(H)(9)-6(17.50 + 1) 10(11)V9

990-111 330

K =;2.663 =1

p=.0078 62d2

n(n + l ) ( n - l ) 105 r' = l — 990 r' 1 — .1061 r' .8939 d. Correlations of latencies and peak times. Latencies and peak times are generally well correlated except in those cases where times are more difficult to m e a s u r e ; b-wave peak time smooth, n 2 latencies correlating L O I to the other stimuli b-wave peak time sharp, D R 1 6 to the other stimuli. These findings would be expected in the evaluation of a physiologic function. T h e time of onset of any given response would be expected to relate rather constantly to one another. DISCUSSION

1. "Normal" range. F r o m Table 1 one may see that the comparison of an average range as determined from the first standard deviation of the 68 percentile group for each

component of the E R G in both series is everywhere comparable. T h e first normal series was taken from 55 normal subjects of varying age over a period of several years. T h e second series was performed over a period of three months. Naturally, there is slight variation in techniques and conditions. T h e validity of the results would seem to be strengthened by this study. F o r instance, the a-wave amplitude normal range for D O 16 first normal series was 168 microvolts to 268 microvolts, for the second normal series the range was 192 to 280 microvolts.* In the first normal series 55 measure-

* The bulb change noted would tend to bring the two normal ranges closer together.

A. D. RUEDEMANN, JR. TABLE 6 A-WAVE AMPLITUDE

L016

D04

D016

DB16

DG16

DR16

225

r' P

0.6182 0.0672

0.2697 0.4296

0.5152 0.1286

0.3031 0.3734

0.3061 0.3682

-0.2515 -0.4412

235

r' P

0.8938 0.0078

0.8636 0.0102

0.4292 0.2340

0.4152 0.2186

0.9839 0.0078

0.6875 0.0548

529

r' P

0.5209 0.1498

0.5000 0.1388

0.7250 0.0434

0.4667 0.1770

0.8516 0.0114

0.8929 0.0324

532

r' P

0.2758 0.4238

0.3910 0.2502

0.8000 0.0174

0.0750 0.8494

0.4667 0.1736

0.5959 0.0950

542

r' P

0.7727 0.0214

0.5167 0.1498

0.3061 0.3682

0.1848 0.5892

0.7411 0.0768

0.6061 0.0718

609

r' P

0.6576 0.0536

0.2500 0.8026

0.9524 0.0132

0.9643 0.0208

0.7411 0.0768

—

611

r' P

0.2334 0.5352

0.4910 0.1470

0.6576 0.0572

0.2061 0.5486

0.5334 0.1388

0.3576 0.2938

612

r' P

0.7879 0.0192

0.7262 0.0602

0.8061 0.0164

0.7425 0.0278

0.7000 0.0512

0.4420 0.3030

615

r' P

0.5485 0.1052

0.6061 0.0718

0.7213 0.0324

0.5546 0.1010

0.6143 0.1936

0.4715 0.3270

616

r' P

0.7485 0.0264

0.8061 0.0164

0.9209 0.0102

0.8375 0.0192

—

0.7584 0.0340

617

r' P

0.6792 0.0588

0.8243 0.0142

0.9000 0.0074

0.7819 0.0204

0.5061 0.1336

—

621

r' P

0.5667 0.0930

0.7834 0.0286

0.9084 0.0110

0.1429 0.7338

0.1584 0.6744

0.9000 0.0892

626

r' P

0.4042 0.2670

0.3155 0.4239

0.9355 0.0088

0.7182 0.0332

0.5607 0.0960

0.6250 0.0962

Case

ments were made, in the second normal series 13 subjects were tested 10 times so 130 measurements were made. Mean Absolute Difference Mean

(MAD) _ sy[\ ~

Variation Coefficient

This test gives the percent variation from the mean of each response on repetitive testing. The results would seem to verify the reliability of the ERG on repetitive testing. The percent variation from the mean amplitudes varies from a low of 6.3% for bsmooth (DB16) to a high of 17.3% for the a-wave amplitude ( D 0 4 ) . Of 25 variation coefficients determined, only three show more than 15% variation while 10 of 24

show less than 10% variation. Twenty-one of 24 variation coefficients vary less than 15%. Peak times and latencies are all less than 10% except for the latency of n2 for LOI. This happens to be a particularly difficult latency to measure since the a-wave is practically nonrecordable in all cases. 3. Right and left eye correlation. The results would indicate that the right and left eye of a normal subject are positively correlated to the greater number of stimuli. Inasmuch as there are normal variations which can be expected under physiologic conditions, it is not feasible to predict that the left or right eye of a normal subject can be evaluated by ERG and to accept the values as similar for both eyes. It would appear

NORMAL HUMAN ELECTRORETINOGRAM

873

TABLE 6A B-WAVE AMPLITUDE SMOOTH

Case

LOI

DOl

D04

D016

DB16

DG16

DR16

225

r' P

0.6061 0.0718

0.8334 0.0132

0.8576 0.0108

0.7819 0.0204

0.6970 0.0384

0.8152 0.0156

0.5000 0.7114

235

r' P

0.9394 0.0052

0.6516 0.0524

0.5894 0.0802

0.1625 0.6600

0.7381 0.0548

0.3125 0.4716

0.7768 0.0628

529

r' P

0.8940 0.0078

0.6459 0.0718

0.0477 0.9282

0.0792 0.8414

0.7125 0.0512

0.4000 0.4840

0.3620 0.7040

532

r' P

0.2879 0.4010

0.8459 0.0182

0.4940 0.1442

0.6576 0.0512

1.0000 0.0574

0.8483 0.0466

0.6500 0.3422

542

r' P

0.9000 0.0074

0.8626 0.0072

0.9334 0.0088

0.7024 0.0688

1.0000 0.2892

0.7000 0.1936

0.8000 0.2262

609

r' P

0.6875 0.0548

0.6000 0.3898

—

—

0.8000 0.2262

0.1000 0.9204

—

611

r' P

0.7334 0.0292

0.8459 0.0182

0.5394 0.1096

0.7042 0.0500

0.5536 0.1528

0.9643 0.0120

0.6425 0.0514

612

r' P

0.5061 0.1336

0.8000 0.2262

-0.3214 -0.7437

0.6000 0.2040

1.0000 0.2892

0.2500 0.8026

—

615

r' P

—

0.8125 0.0574

0.1910 0.5814

0.0576 0.2938

0.7182 0.0332

0.5959 0.0970

0.6750 0.2112

616

r' P

0.7500 0.0524

0.9524 0.0132

0.4879 0.1498

0.6500 0.0702

0.6191 0.1096

0.7917 0.0404

—

617

r' P

0.6122 0.0702

0.6370 0.0990

0.7334 0.0292

0.4875 0.1770

0.7970 0.0178

0.6584 0.0672

—

621

r' P

0.9197 0.0228

0.9858 0.0324

0.4500 0.2150

0.3000 0.4122

0.4465 0.2938

0.4750 0.1868

—

626

r' P

0.7947 0.0628

0.0858 0.9124

0.1167 0.7642

0.4733 0.2758

0.5584 0.1212

0.8625 0.0160

—

necessary to continue testing both eyes even though there is a positive correlation with reasonable reliability in the greater number of instances. 4. Correlation between components of various responses. In Table 8 it can be noted that several questions are answered by this particular statistical test. a. There is a very strong positive correlation between the various b-wave amplitudes to different stimuli. A negative correlation between the a-wave and the b-wave is noted by the results of DO 16 (fast sweep speeds) ; for example, negative correlation between n2 (a-wave) and p2 (b-wave). Components of the a-wave generally correlate more strongly with other a-wave components than

-

components of the b-wave ; for example, ni (a-wave) to n2 (a-wave) and p x (b-wave) to p2 or p 3 (b-wave) versus nx (a-wave) to p 3 (b-wave) or n2 (a-wave) to p 2 or p 3 (b-wave). b. Several stimuli give obviously similar responses. For instance, there is a strong positive correlation of the a-wave of D04, DB16 and DG16. This is also true of the b-wave of DOB4, DB16 and DG16. c. The strongest positive correlation appears to occur in those components which are thought to relate particularly to photopic function; for instance, b-wave sharp L016, b-wave sharp L 0 4 20/sec, and b-wave sharp DR16. Blue and green do not correlate well with red. Other dark-adapted re-

A. D. RUEDEMANN, JR

874

TA I ÎLE 6B B-WAVE AMPLITUDE SHARP

L016

L 0 4 20/sec.

D04

D016

DB16

DG16

DR16

225

r' P

0.6091 0.0718

0.8819 0.0088

0.7667 0.0324

0.8788 0.0090

0.7637 0.0232

0.7000 0.0376

0.3970 0.2420

235

r' P

0.8576 0.0180

0.8182 0.0146

1.0000 0.2892

0.2230 0.5486

0.4438 0.2186

0.6598 0.0542

0.4138 0.2542

529

r' P

0.8042 0.0244

0.7792 0.0292

—

0.8483 0.0272

0.7203 0.0688

—

0.7441 0.0536

532

r' P

0.4728 0.1616

0.4091 0.2302

—

0.4910 0.1470

0.6000 0.2040

—

0.4459 0.2186

542

r' P

0.6940 0.0394

0.5179 0.1802

—

0.8091 0.0160

0.8690 0.0238

0.8571 0.0458

0.1545 0.6600

609

r' P

0.7349 0.0278

0.6518 0.1212

._

0.5953 0.1236

0.5000 0.7264

—

0.4554 0.2846

611

r' P

0.1375 0.7188

0.3607 0.2892

—

0.7304 0.0300

—

—

0.5849 0.0836

612

r' P

0.3576 0.2938

0.7054 0.0854

0.5000 0.7264

0.4788 0.1586

0.1042 0.7872

615

r' P

0.4879 0.1498

0.9243 0.0060

—

0.5500 0.1260

—

616

r' P

0.5485 0.1052

0.8697 0.0096

0.7858 0.0658

0.7091 0.0358

617

r' P

0.7584 0.0340

0.9834 0.0060

0.7233 0.0854

621

r' P

0.5091 0.1336

0.6727 0.0818

626

r' P

0.6125 0.0892

0.4000 0.2714

Case

-0.0450 -0.1060

0.7542 0.0358

—

0.6965 0.1052

0.7947 0.0628

0.8215 0.0548

0.8607 0.0104

0.5292 0.1416

0.9121 0.0068

0.8091 0.0164

—

0.8143 0.0802

0.9250 0.0096

0.2572 0.6100

0.5983 0.1556

0.6000 0.2040

—

0.7679 0.0466

1.0000 0.2892

—

0.3334 0.4010

sponses do not correlate well with lightadapted responses and vice versa. The a-wave L016 has a negative correlation with darkadapted a-wave components except DO 16. Dark-adapted a-wave amplitudes correlate well except for DR16 (photopic). The p values and their reliabilities obtained between the various a- or b-wave amplitudes for different stimuli (light or dark adapted) not only tend to bear out the reliability of the test itself but also to show that similar functions are measured though different stimulus intensities may be used. For instance, the generally positive correlations noted between various b-wave amplitudes.

d. The onset of response to any given stimulus which can reasonably be compared would indicate that the time factors are the most constant part of the routine ERG test. CONCLUSIONS

1. A series of statistical tests were set up lo evaluate the results obta'ned from a series of normal individuals tested by standard (to the Electroretinography Laboratory, Kresge Eye Institute) ERG techniques. The results indicate that the ERG techniques utilized are statistically adequate. 2. A number of statistical studies have been performed on a series of 13 normal subjects tested 10 times. The normal range

NORMAL HUMAN ELECTRORETINOGRAM

875

TABLE 6C Π AND p AMPLITUDE

D016 Case

Π)

Pi

Il 2

P2

P3

225

r' P

0.7182 0.0332

0.7182 0.0332

0.5637 0.0950

0.4667 0.1676

0.8515 0.0114

235

r' P

0.8213 0.0146

0.7819 0.0204

0.7849 0.0198

0.5516 0.1032

0.5546 0.1010

529

r' P

0.5759 0.0892

0.5879 0.0818

0.5729 0.0892

0.3819 0.2628

0.4334 0.2006

532

r' P

0.7819 0.0204

0.8667 0.0098

0.6455 0.0562

0.4970 0.1416

0.8000 0.0174

542

r' P

0.6031 0.0734

0.6152 0.0688

0.3364 0.3222

0.9182 0.0064

0.9122 0.0068

609

r' P

0.5091 0.1336

0.5394 0.1096

0.2516 0.4654

0.5209 0.1498

0.3096 0.4354

611

r' P

0.4970 0.1416

0.4061 0.2302

0.4243 0.2112

0.2273 0.5092

0.2000 0.5620

612

r' P

0.6000 0.0750

0.7304 0.0300

0.6213 0.0658

0.6455 0.0562

0.8758 0.0094

615

r' P

0.7273 0.0308

0.8334 0.0132

0.5031 0.1362

0.1273 0.7188

0.6334 0.0602

616

r' P

0.9425 0.0052

0.9292 0.0094

0.8667 0.0156

0.8959 0.0124

0.8792 0.0138

617

r' P

0.9677 0.0040

0.9788 0.0036

0.9394 0.0052

0.6243 0.0644

0.8213 0.0146

621

r' P

0.7750 0.0308

0.7750 0.0308

0.3792 0.2858

-0.0580 -0.1650

0.8792 0.0138

626

r' P

0.8091 0.0164

0.5637 0.0950

0.8455 0.0120

0.7970 0.0178

0.8546 0.0110

of a previous normal series of 55 patients

TABLE 7

has been compared to the normal range ob-

EXAMPLE OF CORRELATION

tained from the 13 retested normal subjects. T h e two ranges compare favorably. 3. T h e mean average difference over the mean or variation coefficients of the 13 normal subjects showed a percentage variation from the mean of less than 1 5 % in 21 of 24

a-wave amplitude a-wave amplitude

n(n + l)(n-l)-6(2d 2 ±l) K= —— 11(11 + 1 ) ^ 1 1 - 1 2

2d = 22

amplitude determinations and less than 1 0 % in all but one of the various peak time or latency measurements. I n any measurement of physiologic function tested repetitively in which a percentage variation from the mean

K=

2,184-126

of function. I t is also a reliable indicator of

630.4665

K = 3.29

of less than 1 5 % can be obtained, the test can be considered a reasonable measurement

DO 16 OB 16

r'=l

p=<0.0010 132

2,184

= 0.940

A. D. RUEDEMANN, JR.

876

TABLE 8 p VALUES

a-wave amplitudes L016 L016

r' P

D04

r' P

D016

r' P

DB16

r' P

D04

D016

DB16

DG16

DR16

0.394 0.0838

0.696 0.0057

0.485 0.0455

0.405 0.0793

0.798 0.0028

0.863 0.0014

0.951 <0.0010

0.957 <0.0010

0.495 0.0427

0.940 <0.0010

0.857 0.0014

0.703 0.0071

0.935 <0.0010

0.602 0.0183

DR16 b-wave amplitudes sharp L016 L016

r' P

L 0 4 20/S

r' P

D016

r' P

DB16

r' P

DG16

r' P

L 0 4 20/S

D016

DB16

DG16

DR16

0.615 0.0202

0.775 0.0036

0.527 0.0465

0.373 0.1170

0.806 0.0026

0.318 0.1423

0.188 0.2810

0.104 0.3707

0.695 0.0104

0.882 0.0026

0.850 0.0035

0.631 0.0143

0.936 0.0015

0.409 0.0951 0.282 0.1814

DR16 b-wave amplitudes smooth LOI

LOI

r' P

DOl

r' P

D04

r' P

D016

r' P

DB16

r' P

DG16

r' P

DR16

DOl

D04

D016

DB16

DG16

DR16

0.647 0.0156

0.752 0.0062

0.832 0.0041

0.769 0.0052

0.734 0.0071

0.277 0.2236

0.929 <0.0010

0.529 <0.0010

0.929 <0.0010

0.896 <0.0010

0.833 0.0125

0.929 <0.0010

0.973 <0.0010

0.979 <0.0010

0.762 0.0202

0.966 <0.0010

0.952 <0.0010

0.691 0.0314

0.979 <0.0010

0.691 0.0314 0.739 0.0239

NORMAL HUMAN ELECTRORETINOGRAM

877

TABLE 8 {Continued) Fast sweep speedI amplitudes D016 ni ni

r' P

Pi

r' P

ils

r' P

P2

r' P

Pi

0..962 < 0 .0010

n2

P2

ps

0.825 0.0021

0.660 0.0110

0.495 0.0427

0.819 0.0022

0.594 0.0192

0.396 0.0838

0.319 0.1335

0.369 0.1003 0.830 0.0020

Ρ3

Π2 latencies a-wave LOI LOI

r' P

L016

r' P

DOl

r' P

D04

r' P

DQ16

r' P

DB16

r' P

DG16

r' P

L016

DOl

D04

D016

DB16

DG16

DR16

0 .341 0 .1170

0.094 0.3707

0.149 0.3015

0.172 0.2743

0.143 0.3085

0.831 0.2776

0.099 0.3632

0.816 0.0023

0.846 0.0016

0.842 0.0017

0.860 0.0014

0.861 0.0014

0.569 0.0239

0.910 <0.0010

0.907 <0.0010

0.907 <0.0010

0.899 <0.0010

0.626 0.0146

0.930 <0.0010

0.968 <0.0010

0.968 <0.0010

0.648 0.0019

0.903 <0.0010

0.954 <0.0010

0.593 0.0197

0.994 <0.0010

0.627 0.0146 0.581 0.0217

DR16 b-wave peak time sharp L016 L016

r' P

D016

r' P

DB16

r' P

DG16

r'

DR16

P

D016

DB16

DG16

DR16

0 .522 0 .0344

0.123 0.0367

0.439 0.0901

-0.114 0.3520

0.477 0.0643

0.371 0.1292

-0.0625 0.4207

0.922 0.0027

0.125 0.3466 0.146 0.3264

A. D. RUEDEMANN, JR.

878

TABLE 8 (Continued)

LOI

r' P

DOl

r' P

D04

r' P

D016

r' P

DB16

r' P

DG16

r' P

b--wave peak time smoothI LOI

1DOl

D04

D016

DB16

DG16

DR16

0 .255 0 .1922

0.147 0.3050

0.213 0.2389

0.089 0.3783

0.254 0.1894

0.262 0.2358

0.386 0.0885

0.301 0.1562

0.225 0.2177

0.430 0.0681

0.691 0.0314

0.650 0.0139

0.760 0.0041

0.768 0.0038

0.834 0.0129

0.651 0.0150

0.730 0.0075

0.857 0.0107

0.817 0.0023

0.643 0.0148 0.619 0.0475

DR16 Fast sweep speed latencies D016 Hl

ni

r' P

Pi

r' P

P2

r' P

Pi

0 .887 < 0 .0010

Pi

pa

0.794 0.0029

0.654 0.0016

0.860 0.0014

0.756 0.0043 0.935 <0.0010

Ps

variation from the normal within the limits of normal physiologic variation. F r o m the standpoint of determining function, it would not seem necessary to retest individuals except when possible loss or gain of function might be expected. 4. Positive correlation between the right and left eyes of a normal subject is noted. Although the organs are paired it is not reasonable to consider them everywhere similar even though a positive correlation is noted. F o r this reason simultaneous testing of both eyes will be continued in this laboratory.

5. A positive correlation was noted between certain responses. A negative correlation was noted between the a- and the b-waves. This indicates that separate retinal functions are being tested. Those responses related to dark-adapted stimuli demonstrated a positive correlation. A positive correlation was also noted between those responses related to light-adapted stimuli. Light-adapted stimuli generally did not correlate with dark-adapted stimuli. 690 Mullett

Street

(26).

REFERENCES

1. Ruedemann, A. D., Jr., and Noell, W. K. : A contribution to the electroretinogram of retinitis pigmentosa. Am. J. Ophth., 47:564-573 (Jan. Pt. II) 1959. 2. Ruedemann, A. D., Jr.: The electroretinogram in hereditary visual cell degeneration. Tr. Am. Acad. Ophth., 63:141-160 (Mar.-Apr.) 1959.