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The human electroretinogram in the first day of life
The ,[ournal of P E D I A T R I C S
733
The human electroretinogram in the first clay of life The electroretinogram is readily recordable in the first day o[ file. Apparatus by which this may be done is briefly described. A summary o/our knowledge about the neonatal E R G is presented, together with areas o[ possible clinical application in the newborn. The use of the E R G as an index o[ maturity at birth is also noted.
T. Shipley, Ph.D., * and Manuel T. Anton, M.D. 2r I A M I~
FLA.
T ~ E electroretinogram (ERG) is considered to be an objective index of retinal function, with special reference to the receptor and bipolar layers. Thus, an E R G examination of the newborn appeals as a test for retinal integrity in the presence of a dense congenital cataract, in severe uveitis, when the fundus cannot be examined directly, and in cases of congenital blindness of supraretinal origin where no lesion of the fundus is seen? In congenital nystagmus, alteration in the E R G would point to a retinal origin. In certain conditions with a normal-appearing fundus, the E R G m a y nevertheless be depressed--amaurosis congenita (Leber) and retinitis pigmentosa sine pigmento. Moreover, in primary retinitis pigmentosa, the E R G is probably affected before the characteristic fundus signs appear, though the
From the Department o[ Ophthalmology, Bascom Palmer Eye Institute, University o[ M i a m i School of Medicine. Supported by Contract DA-49-193-MD-2344 o[ the Office of the United States Surgeon General. eAddress, Detmrtment o[ Ophthalmology, Bascom Falmer Eye Institute, University o[ Miami School o[ Medicine, Miami, Florida 33136.
earliest age at which the E R G depression occurs is not yet known. Finally, in the infantile form of Tay-Sachs disease, the presence of a normal E R G confirms that the histologic manifestation of the disease is at first confined to the ganglion cells. ~ We would also like to suggest that the E R G might serve as an index of maturity at birth, provided that the means for its elicitation can be improved. Engel and Butler, 3 for example, have recently demonstrated that the visually evoked (especially posterior parietal-occipital) etectroencephalographic potential is nearly as good an index of conceptual age as is the birth weight. An analogous function might be anticipated for the ERG. As a study preliminary to the development of a standardized E R G procedure for use with premature infants, it was necessary for us to examine the E R G of term infants *Paufique, Ravault, and Picaud 2 have recently reported on the E R G of 35 p r e m a t u r e infants, between 6.5 and 7 months of age a n d weighing less than 2,200 grams. Though we have seen this paper only in abstract, it does seem important to m e n t i o n that they found the E R G in retrolental fibroplasla most commonly to be extinguished or subnormal in various stages of the disease.
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in their first day of life. Since the nature of the neonatal E R G is still in question and the instrumentation in this field is still to some extent experimental, this work also serves as a test of certain new techniques which have been devised. BACKGROUND
The electroretinogram is the electrical response of the eye to an abrupt flash of light. It is a gross, massed response involving the whole retina. ~ After a flash of light is presented to the patient, one first records a generally small negative depolarization (called the a-wave) and then a generally larger positive afterswing (called the bwave). More subtle analysis of the adult E R G wave form is not yet really possible ~n scientific and surely not in clinical terms, though a second positive b-wave can sometimes be obtained with red light from a dark-adapted eye and a final positive swing can often be elicited with flashes of long duration when the light is turned off. Given that the human retina is not fully developed at birth, especially in the macula region, 4 and that neonatal visual acuity (e.g., by optokinesis) is vastly reduced from that of the adult, 5 it is pertinent to ask whether these facts might not somehow be correlated with unambiguous changes in the ERG. ZetterstrSm 6-s and Heck and ZetterstrSm 9 undertook the first series of studies on the neonatal ERG, from which, in view of other work to be discussed below, the conclusions given in Table IA may be derived.S~" 6Despite a great many attempts to identify contributions froln separate retinal ai'eas~ such as the macula versus tile periphery, or from separate anatomlc structures, such as the rods versus the cones, or fronl separate visual processes, such as the photoplc versus the scotoplc, workers in this field have so far failed to reach even general agreement upon the proper clinical procedm'es for their distinct ellcitation. "~ZetterstrSm failed to find an a-wave in her infant responses but this finding is difficult to interpret in view" of the fact that the typical adult E R G shown by ZetterstrSm for comparison also lacks an a-wave (s, v- -"~, Jrig. :). I n fach all of the records shown in this first paper lack the fine structure which newer techniques have since revealed. I t is not clear what the source of this m i g h t be, though such findings are common with low-intensity stimulation. The time constant is given for the low-{requency end of the spectrum ( t : l . 5 , thus F : 0 . 1 since f = ~ t) but not [or the upper end.
November 1964
Since this work 7 involved as many as 30 premature infants over the range of 1 to 10 weeks before term, with some tested on the first day of life, it stands as the major contribution in this field to date. Winkelman and Horsten 1, 10, 11, 12 began the next series of studies on this problem in their belief that normal fundi in blind infants might be more common than has hitherto been suspected. They reported, for example, that an electroretinographic response was absent in a blind infant with normal photoreceptor histology, 1~ and they sought to establish whether this lack of response could be used to diagnose this amaurosis congenita or whether, as was previously held, the response was in fact absent in m a n y normally sighted infants as well. Their technique differed from the earlier work in three important ways: The light intensity was slightly greater, the low-end frequency response of the amplifier was moved from about 1 c.p.s, up to about 5 c.p.s, because " . . . m a n y curves were disturbed by movements of the babies . . . . ,,,12 and selective amplification procedures were used in association with flicker stimulation. They studied several premature infants. We summarize their findings here in Table lB. These results, together with those of ZetterstrSm and her associates, constitute the present state of knowledge on the normal human neonatal ERG, and are thus lettered in sequence. PRESENT
STUDY
The particular problems to which we directed our attention were, first, a confirmation, as far as possible, of the previous findings, and, second, the development of a regular testing procedure that could be used routinely with neonates. Quantitative comparisons of electroretinograms from one clinic to another have so far not been possible even with adult eyes, and it must be admitted that such tech-
~This infant actually had ganglion cell disease--a finding not entirely consistent with the widespread hypothesis (If the absence of a ganglionic contribution to the ERG.
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Table IA A. The ERG of the newborn is of reduced amplitudes in comparison to the ERG of adults. B. It is somewhat more difficult to elicit than in adults. C. The more premature the infant, the longer the extrauterine period needed before the Y./a+b/ response reaches some arbitrary magnitude. D. The ERG of many premature infants can be recorded well before term. E. The ERG reaches adult form well within one year after birth. F. The response tends to be somewhat more sluggish than the adult ERG in terms of its rate of afterflash recovery, as revealed by slower following of a flickering light. G. A positive off-effect can occur in the newborn, as shown in a 14-hour-old infant s, p- sot, Fig. 3 with a flash duration of 60 roses. T a b l e IB H. N o definite histological [light microscopy] criterion could be f o u n d for t h e first a p p e a r a n c e of t h e e l e c t r o r e t i n o g r a m ' l ~ serves to reiterate Z e t t e r s t r S m ' s suggestion as and 14, p. s
that retinal immaturity may best be revealed I. J.
K.
L.
on u l t r a s t r u c t u r a l or e n z y m a t i c levels. A n E R G c a n be recorded f r o m all n o r m a l infants w i t h i n a few h o u r s after birth. By the use of selective amplification, it is possible to drive t h e n e o n a t a l E R G ( N z l 0 ) up to as h i g h as 72 c.p.s, at 6 footcandles [1 footcandle = 10 lux] a n d thus well u p into t h a t p a r t of t h e a d u l t r a n g e w h i c h is generally held to be m e d i a t e d by p h o t o p i c - c o n e vision. T h e i n f a n t E R G c a n be identical in s h a p e to t h e a d u l t response, w i t h b o t h a a n d b components. N o c o m p l e x a or b waves are yet reported, b u t in H o r s t e n a n d W i n k e l m a n ' s 12 Fig. 7, a double b-wave m a y possibly be seen in a 2 89 i n f a n t at 25 lux a n d 15 m i n u t e s d a r k a d a p t a t i o n ( t h o u g h this is by no m e a n s certain since electronic noise s o m e t i m e s behaves in j u s t this f a s h i o n ) . T h e i n f a n t E R G a m p l i t u d e s are definitely dim i n i s h e d under all arousal conditions; the age
at which they attain adult values is not yet known, but it could be as much as 4 to 6 months. NI. The infant ERG is responsive to intensity changes and exhibits darkness enhancement, albeit of a somewhat small amount. niques are especially difficult to s t a n d a r d i z e with i n f a n t s ? 1, 12 Nevertheless, with certain new instrum e n t a t i o n a n d as p a r t of a larger study on E R G n o r m a l i z a t i o n in adults, a5 we do feel t h a t some progress has been m a d e in this l a t t e r direction, a n d t h a t we are therefore
Electroretinogram in newborn
73 5
justified in presenting a p r e l i m i n a r y small sample r e p o r t a t this time. METHOD
T h e e q u i p m e n t which we have used is entirely p o r t a b l e a n d is p a r t i c u l a r l y convenient for use w i t h infants because it can be b r o u g h t directly into the nursery. ~ A c o n t a c t eye electrode was specially designed for this work, a n d is shown in Fig. 1. I t is elliptical in shape, a n d the small axis is 11 ram. long, the large axis 12 ram. T h e p u p i l l a r y a p e r t u r e is 6 ram. in d i a m e t e r a n d the vertical cylinder serving to hold the eyelids open is 7 ram. in height, T h e electrode itself consists in a ring of p l a t i n u m wire e m b e d d e d flush within the i n n e r surface of the plastic eye cup. This ring just encircles the cornea when p r o p e r l y inserted. T h e stimulus light is furnished b y three small q u a r t z X e n o n discharge l a m p s giving a p p r o x i m a t e l y a 650,000 p h o t o p i c footcandle (cnd) intensity m e a s u r e d at 6 inches f r o m the l a m p ; the flash d u r a t i o n is 13 ~sec. (too short, u n f o r t u n a t e l y , to elicit t h e E R G off-effect). Stimuli were single flashes presented at 30 second intervals. F l i c k e r stimuli were not presented, since we feel t h a t the i n t e r p r e t a t i o n of the simpler single flash E R G is still itself in question. T h e visual angle is 53 degrees. T h e r e c o r d i n g system functions well over the range of a b o u t 1 (t = 0.16) to 25 (t = 0.0064) cycles per second (6 decibel d o w n ) . This low high-freq u e n c y cutoff was chosen to eliminate the large a m o u n t of "noise" w h i c h was typical of most of our infant records. This p o i n t is i m p o r t a n t since p a r t of this noise seems to be physiologic because it a p p e a r s in quiet a n d even sleeping infants. Its a p p e a r a n c e is a p a r t i a l consequence of the use of relatively high gain in the electronics (Fig. 2). T h e gains used b o t h by H o r s t e n a n d W i n k e l m a n a n d by ourselves, e.g., 50 to 100 /sv. p e r c e n t i m e t e r were a b o u t twice the usual gain used with adults. T h e testing was done on one eye of each ~Addltional information will gladly be supplied by the senior author. The manufacturer is the Cordls Corporation, 241 N. E. 36th Street, Miami, Fla.
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Fig. 1. The infant eye electrode larged).
November 1964
(greatly en-
INFAN T
ADULT
Fig. 2. Comparison of one of the best neonatal curves with a typical curve of an adult. Cal. ~- 100 #V; time z 250 msec. of 10 healthy babies in their first day of life. Six were female and four were male. One drop of mydriatic (1 per cent Mydriacyl) was first put in the eye to be tested. The baby was then dark adapted, both eyes being covered with opaque Elastoplast eye pads, for one hour before the test. When the baby was brought to the examination booth, the eye pads were taken off under deep red light and the size of the pupil was observed; with one exception it was found to be between 3 and 5 mm. before the beginning of the test. * 9 Taking 4 mm. as an average, we thus had 363.6 photopic troland seconds (pts) of illumination delivered to the eye (pts ~ photopic cnd./m-" X seconds X pupil area in square millimeters).
This small pupil size may be explained by a combination of several factors. The pupil of the newborn is well known to be quite sluggish, 16 though the reasons for this are still somewhat obscure. For example, Duke-Elder 17 states, but without reference, that "At birth the dilatator muscle is illformed and while it retains its embryonic nature throughout life the muscle does not assume its full proportions until about the 5th year; since this muscle is not functionally active until after birth, the pupil of the newborn is small." This fact, plus immature innervation, may be sufficient to account for the general finding. On the other hand, we used a mild mydriatic in weak dosage so as to avoid all possibility of poisoning. It should be emphasized that we are trying to develop a procedure applicable to all or almost all premature infants. Actually, one infant (No. 2 in Table I I ) , still had a pinpoint pupil and nevertheless gave a good response. Finally, 3 drops of 0.5 per cent Ophthaine anesthetic was applied to the eye to be tested, with 2 minute intervals between drops. No general anesthetic agent was given in any case, nor was it ever needed. The infants, as also reported by Horsten and Winkelman, a~ often fell asleep, or continued to sleep. With the head correctly supported, it was always possible to keep the pupil centered under the eye electrode. The reference electrode was on the midforehead, and the ground on the ear. The test was done first under the dark conditions just described, and then repeated after 2 minutes of light adaptation to ambient room illumination of 25 footcandles. RESULTS
The results shown in Table I I are means of at least three responses under each test condition. The data are presented in such a way as to give some idea of over-all displacement magnitudes. The mean zero to peak a-wave amplitude is 32 /~v., the mean a-trough to peak b-wave amplitude is 91 /~v. (thus, mean !a+b] = 123 ~v.). These values are somewhat larger than those reported by Horsten and Winkelman 15 (mean, Ia+b[ - -
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Electroretinogram in newborn
73 7
Table II Minutes [ a#er
birth when ERG Neonate 1 2 3 4 5 6 7 8 9 10
Sex M M F F M F M F F F
Weight (erams)
wtzs taken
3,976 2,851 3,480 2,578 2,721 3,060 3,400 3,684 2,834 3,451
398 495 600 780 824 858 1,005 1,094 1,230 t,380
Amplitudes DarkLightadapted adapted
(la+bl in (Ea+bl in #v.) 124 148 161 80 205 162 99 52 48 159
#v.) 40 --61 55 75 -30 ---
76 ~v. for seven eyes), probably both because our illumination was approximately 10 ~ times brighter than theirs (though m a n y times shorter) and because our period of dark adaptation was 1 hour while theirs was only 5 to 15 minutes. I n the light-adapted conditions, half of the cases also exhibited both a- and b-waves (mean, a = 16/zv., b = 35 /~v.; ]a+b[ = 51). A particularly good E R G on a dark-adapted infant (No. 4), is shown in Fig. 2, together with an E R G of a normal adult taken under similar test conditions. DISCUSSION Given the variables of birth weight, minutes post p a r t u m when the E R G was taken, and the mean a plus b amplitudes, a small sample statistical analysis reveals the following rank-difference correlation coefficients: grams-microvolts r =-0.030. microvolts-minutes r=0.273. grams-minutes r=0.067. O n l y the first two have physiologic relevance, and they are not statistically significant. Presumably, the first would have to be significant if the E R G were to serve as an index of maturity; but the very small
Birth Analgesia be[ore delivery Demerol-atropine Demerol-Phenergan Demerol-scopolamine Lorfan-atropine Dernerol-Phenergan Demerol-Phenergan Demerol-atropine Demerol Demerol-atropine None
history Anesthesia at delivery General (cyclopropane) Pudendal (Novocain) General (cyclopropane) None General (cyclopropane) None Pudendal (Novocain) Pudendal (Novocain) Pudendal (Novocain) Spinal for cesarean section (Novocain)
range of birth weights in our sample has probably masked whatever correlations might exist. T h e small positive correlation between minutes post p a r t u m and microvolts, though in a suggestive and reasonable direction, is not valid, for identical statistical reasons. I t is our intention to continue work along these lines, with particular attention to enlarging the range of birth weights within our sample. It is now clear that recording of the E R G in h u m a n full-term and premature infants can be a routine clinical procedure. T h e failures which we encountered resulted from using the normal adult high-frequency cutoff at 120 e.p.s. T h e y are not included in Table II. We also obtained several records so overlaid with physiologic noise that the E R G could not be distinguished; we have records where, with a reduction in frequency response, one can observe the E R G to emerge more clearly. ~ Further study might very profitably be directed toward "~Horsten and Winkelman :z used a low frequency cut-off at about 5 c.p.s. [t ~ 0.03], c o m p a r e d to ours at 1 c.p.s. T h e y do not state the upper frequency limit, t t is clear that their recordings could have been m a d e easier with the 5 cycle cutoff in view of the excess infant eye motions; their high-frequency cutoff could have been anywhere f r o m 25 to 80, j u d g i n g from the wave forms reported. L e t this note stand as a plea that workers in this field report both ends of the frequency range a n d not just the low e n d - - t h e y are equally important. Moreover, a frequency figure is m u c h m o r e meaningful than a time figure, f r o m both physiologic a n d electronic points of view.
7 3 8 Shipley and Anton
November 1964 Table IC
ascertaining the source(s) of this relatively high-frequency interference. We do not wish to give the impression that all the problems have been solved. This is by no means correct, since m a n y of the records we have are not as clear as one might wish. But we do feel that this work is no longer really experimental a n d that other E R G laboratories should be encouraged to enter this field. A n E R G , albeit of reduced m a g n i t u d e , can readily be recorded on all n o r m a l infants in the first day of life. A few of our specific findings ought to be noted. These are given in T a b l e IC, to be considered as an extension of Tables I A and IB. T w o cautions m u s t be raised concerning our i n t e r p r e t a t i o n of this type of work. M a n y workers consider that a constant-responseamplitude technique is superior to the constant-stimulus-amplitude technique which has so far been employed. T h u s the E R G response should be held constant at some a r b i t r a r y value (e.g., some just discernible threshold m a g n i t u d e of 10 to 15 ~v.), while the stimulus intensity should be varied from subject to subject a n d from condition to condition u n t i l this m a g n i t u d e is attained. Generally, this p a r t i c u l a r m a g n i t u d e is disclosed, in a given case, by extrapolation or interpolation. This m e t h o d is preferred primarily because of the greater reliability of the findings, though it is usually m u c h more difficult to employ. Now that the basic procedures for the elicitation of the n e o n a t a l E R G appear to have been worked out, future studies might well devote their a t t e n t i o n to such thresholds. I t is probable that individual differences a m o n g the n e w b o r n will be most sharply revealed by such measures. Finally, when studying the response in the light-adapted eye, it is i m p o r t a n t to realize that with the room i l l u m i n a t i o n (Io) present, the stimulus is really a AI/Io situation and is not exactly comparable to the situation for the d a r k - a d a p t e d eye, where Io is given only by the level of i n t e r n a l retinal noise. T h e control for this stimulation difference is clear, that is, one turns off the room lights at the m o m e n t of flash, and, strictly speak-
N. In some cases, e.g., Fig. 2, the neonatal ERG resembles the adult wave form almost exactly, both in terms of latencies and relative a/b ratios, as Hersten and Winkelman also found. O. But partly confirming Zetterstr6m's findings, this is not true in all cases; many infants do give slow-starting, slow-rising, and long-duration wave forms. Perhaps the maturity index for which we are searching lies hidden in this fact. P. Furthermore, one or two records (not included in Table II) exhibit what are apparently slow a-waves in the absence of any clear-cut b-wave component. Q. While we do not have sufficient evidence to suggest why these various wave-form changes may occur, we are confident that they are probably n o t due to intensity variations in the retinal light stimulation. The light energy was reasonably constant in all cases. Moreover, since it was extremely bright, albeit of short duration, small variations in pupil size from infant to infant could not have been very important. The light energy was well above the saturation point in all instances. R. This does raise the question that the optimum light time-intensity (pts.) could be somewhat different from that which we have used. It is known, for example, that adult amplitudes decrease under very bright stimulation. S. Mann~ has stressed the fact that the final histologic maturation of the rods and cones and the demarcation of the fovea in man takes place between the second and fourth postpartum months, though Horsten and Winkelman1~ have reported that the human macula does possess rudimentary cones at birth. In any case, they have observed, and we have confirmed, the existence of darkness enhancement of the ERG amplitudes in the first day of life. Considering our mean results, we find that the response amplitude after dark adaptation is about two and a half times the amplitude of the response after several minutes' exposure to light. This enhancement is quite comparable in magnitude to that which we have found in adults under similar test conditions (though with as little as 20 minutes' dark adaptation). T. Thus, marked darkness amplitude enhancement can and does take place long before the complete histologie differentiation of the human retina. U. Though duplex a and b peaks may have appeared in one of our records, and in one of Horsten and Winkelman's,12 no decisions are really possible on this point in view of the small samples involved. V. Drugs given to the mother during labor and at the moment of birth might still have been circulating in the infants when they were tested for the ERG, and so might have affected the results. As be~t we can tell. however, there is no relationship between either the analgesic or the anesthetic given to the mother and' the subsequent ERG responses of the babies (Table II, last two columns).
Volume 65 Number 5
ing, it m u s t be used when q u a n t i t a t i v e comparisons between light- a n d d a r k - a d a p t e d conditions a r e to be m a d e . I t is for this reason t h a t we have sometimes spoken of darkness e n h a n c e m e n t r a t h e r t h a n of d a r k a d a p t a t i o n p e r se ( t h o u g h the two are m u c h the same). M o r e i m p o r t a n t , this is possibly w h y we failed to o b t a i n a l i g h t - a d a p t e d response in half of our infants.
We wish to thank Dr. Lee Worley of the Department of Pediatrics, University of Miami School of Medicine, for his valuable assistance in this study.
REFERENCES
1. Winkelman, J. F., and Horsten, G. P. M.: Congenital blindness in the presence of a normal fundus, Ophthalmologica 137: 423, 1959. 2. Paufique, L., Ravault, M. P., and Picaud, C. : Eleetroretinography and ocular pathology of premature children, ISCERG Newsletter 5: 4, 1964. 3. Engel, R., and Butler, B. V.: Appraisal of conceptual age of newborn infants by electroencephalographic methods, J. PEDIAT. 63: 386, 1963. 4. Mann, I.: The develoldment of the human eye, New York, 1950, Grune & Stratton, Inc. 5. Gorman, J. J., Cogan, D. G., and Gellis, S. S.: An apparatus for grading the visual acuity of infants on the basis of optokinetie nystagmus, Pediatrics 19: 1088, 1957.
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6. Zetterstr6m, B.: The clinical electroretinogram. IV. The electroretinogram in children during the first year of life, Acta ophth. 29: 295, 1951. 7. ZetterstrSm, B,: The electroretinogram in prematurely born children, Acta ophth. 30: 405, 1952. 8. Zetterstr6m, B.: Flicker electroretinography in newborn infants, Acta ophth. 33: 158, 1955. 9. Heck, J. v., and Zetterstr6m, B.: Analyse des photopischen Flimmer-electroretinogramms bei Neugeborenen, Ophthalmologica 135: 205, 1958. 10. Horsten, G. P. M., and Winkelman, J. E.: Development of the ERG in relation to histological differentiation of the retina in man and animals, A. M. A. Arch. Ophth. 63: 232, 1960. 11. Winkelman, J. E., and Horsten, G. P. M;: The ERG of premature and full-term born infants in the first days of life, Ophthalmologica 143: 92, 1962. 12. Horsten, G. P. M., and Winkelman, J. E.: Electrical activity of the retina in relation to histological differentiation in infants born prematurely and at full-term, Vision Res. 2: 269, 1962. 13. Zetterstr~im, B.: The effect of light on the appearance and development of the electroretinogram in newborn kittens, Acta physiol. scandinav. 35: 272, 1955. 14. Zetterstr6m, B.: Studies on the postnatal development of the electroretinogram in newborn infants, Stockholm, Sweden, 1956, Tryekeri AB Thule. 15. Shipley, T.: Human electroretinography as a gauge of visual performance, Progress Report DA-49-193-MD-2344: 1, ASTIA. 16. Scharfetter, C.: Die Pupille des Neugeborenen, Monatsschr. Kinderh. l l h 94, 1963. 17. Duke-Elder, S.: System of Ophthalmology, Vol. III, Embryology, London, 1963, Henry Kimpton, p. 305.
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The human electroretinogram in the first clay of life The electroretinogram is readily recordable in the first day o[ file. Apparatus by which this may be done is briefly described. A summary o/our knowledge about the neonatal E R G is presented, together with areas o[ possible clinical application in the newborn. The use of the E R G as an index o[ maturity at birth is also noted.
T. Shipley, Ph.D., * and Manuel T. Anton, M.D. 2r I A M I~
FLA.
T ~ E electroretinogram (ERG) is considered to be an objective index of retinal function, with special reference to the receptor and bipolar layers. Thus, an E R G examination of the newborn appeals as a test for retinal integrity in the presence of a dense congenital cataract, in severe uveitis, when the fundus cannot be examined directly, and in cases of congenital blindness of supraretinal origin where no lesion of the fundus is seen? In congenital nystagmus, alteration in the E R G would point to a retinal origin. In certain conditions with a normal-appearing fundus, the E R G m a y nevertheless be depressed--amaurosis congenita (Leber) and retinitis pigmentosa sine pigmento. Moreover, in primary retinitis pigmentosa, the E R G is probably affected before the characteristic fundus signs appear, though the
From the Department o[ Ophthalmology, Bascom Palmer Eye Institute, University o[ M i a m i School of Medicine. Supported by Contract DA-49-193-MD-2344 o[ the Office of the United States Surgeon General. eAddress, Detmrtment o[ Ophthalmology, Bascom Falmer Eye Institute, University o[ Miami School o[ Medicine, Miami, Florida 33136.
earliest age at which the E R G depression occurs is not yet known. Finally, in the infantile form of Tay-Sachs disease, the presence of a normal E R G confirms that the histologic manifestation of the disease is at first confined to the ganglion cells. ~ We would also like to suggest that the E R G might serve as an index of maturity at birth, provided that the means for its elicitation can be improved. Engel and Butler, 3 for example, have recently demonstrated that the visually evoked (especially posterior parietal-occipital) etectroencephalographic potential is nearly as good an index of conceptual age as is the birth weight. An analogous function might be anticipated for the ERG. As a study preliminary to the development of a standardized E R G procedure for use with premature infants, it was necessary for us to examine the E R G of term infants *Paufique, Ravault, and Picaud 2 have recently reported on the E R G of 35 p r e m a t u r e infants, between 6.5 and 7 months of age a n d weighing less than 2,200 grams. Though we have seen this paper only in abstract, it does seem important to m e n t i o n that they found the E R G in retrolental fibroplasla most commonly to be extinguished or subnormal in various stages of the disease.
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in their first day of life. Since the nature of the neonatal E R G is still in question and the instrumentation in this field is still to some extent experimental, this work also serves as a test of certain new techniques which have been devised. BACKGROUND
The electroretinogram is the electrical response of the eye to an abrupt flash of light. It is a gross, massed response involving the whole retina. ~ After a flash of light is presented to the patient, one first records a generally small negative depolarization (called the a-wave) and then a generally larger positive afterswing (called the bwave). More subtle analysis of the adult E R G wave form is not yet really possible ~n scientific and surely not in clinical terms, though a second positive b-wave can sometimes be obtained with red light from a dark-adapted eye and a final positive swing can often be elicited with flashes of long duration when the light is turned off. Given that the human retina is not fully developed at birth, especially in the macula region, 4 and that neonatal visual acuity (e.g., by optokinesis) is vastly reduced from that of the adult, 5 it is pertinent to ask whether these facts might not somehow be correlated with unambiguous changes in the ERG. ZetterstrSm 6-s and Heck and ZetterstrSm 9 undertook the first series of studies on the neonatal ERG, from which, in view of other work to be discussed below, the conclusions given in Table IA may be derived.S~" 6Despite a great many attempts to identify contributions froln separate retinal ai'eas~ such as the macula versus tile periphery, or from separate anatomlc structures, such as the rods versus the cones, or fronl separate visual processes, such as the photoplc versus the scotoplc, workers in this field have so far failed to reach even general agreement upon the proper clinical procedm'es for their distinct ellcitation. "~ZetterstrSm failed to find an a-wave in her infant responses but this finding is difficult to interpret in view" of the fact that the typical adult E R G shown by ZetterstrSm for comparison also lacks an a-wave (s, v- -"~, Jrig. :). I n fach all of the records shown in this first paper lack the fine structure which newer techniques have since revealed. I t is not clear what the source of this m i g h t be, though such findings are common with low-intensity stimulation. The time constant is given for the low-{requency end of the spectrum ( t : l . 5 , thus F : 0 . 1 since f = ~ t) but not [or the upper end.
November 1964
Since this work 7 involved as many as 30 premature infants over the range of 1 to 10 weeks before term, with some tested on the first day of life, it stands as the major contribution in this field to date. Winkelman and Horsten 1, 10, 11, 12 began the next series of studies on this problem in their belief that normal fundi in blind infants might be more common than has hitherto been suspected. They reported, for example, that an electroretinographic response was absent in a blind infant with normal photoreceptor histology, 1~ and they sought to establish whether this lack of response could be used to diagnose this amaurosis congenita or whether, as was previously held, the response was in fact absent in m a n y normally sighted infants as well. Their technique differed from the earlier work in three important ways: The light intensity was slightly greater, the low-end frequency response of the amplifier was moved from about 1 c.p.s, up to about 5 c.p.s, because " . . . m a n y curves were disturbed by movements of the babies . . . . ,,,12 and selective amplification procedures were used in association with flicker stimulation. They studied several premature infants. We summarize their findings here in Table lB. These results, together with those of ZetterstrSm and her associates, constitute the present state of knowledge on the normal human neonatal ERG, and are thus lettered in sequence. PRESENT
STUDY
The particular problems to which we directed our attention were, first, a confirmation, as far as possible, of the previous findings, and, second, the development of a regular testing procedure that could be used routinely with neonates. Quantitative comparisons of electroretinograms from one clinic to another have so far not been possible even with adult eyes, and it must be admitted that such tech-
~This infant actually had ganglion cell disease--a finding not entirely consistent with the widespread hypothesis (If the absence of a ganglionic contribution to the ERG.
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Table IA A. The ERG of the newborn is of reduced amplitudes in comparison to the ERG of adults. B. It is somewhat more difficult to elicit than in adults. C. The more premature the infant, the longer the extrauterine period needed before the Y./a+b/ response reaches some arbitrary magnitude. D. The ERG of many premature infants can be recorded well before term. E. The ERG reaches adult form well within one year after birth. F. The response tends to be somewhat more sluggish than the adult ERG in terms of its rate of afterflash recovery, as revealed by slower following of a flickering light. G. A positive off-effect can occur in the newborn, as shown in a 14-hour-old infant s, p- sot, Fig. 3 with a flash duration of 60 roses. T a b l e IB H. N o definite histological [light microscopy] criterion could be f o u n d for t h e first a p p e a r a n c e of t h e e l e c t r o r e t i n o g r a m ' l ~ serves to reiterate Z e t t e r s t r S m ' s suggestion as and 14, p. s
that retinal immaturity may best be revealed I. J.
K.
L.
on u l t r a s t r u c t u r a l or e n z y m a t i c levels. A n E R G c a n be recorded f r o m all n o r m a l infants w i t h i n a few h o u r s after birth. By the use of selective amplification, it is possible to drive t h e n e o n a t a l E R G ( N z l 0 ) up to as h i g h as 72 c.p.s, at 6 footcandles [1 footcandle = 10 lux] a n d thus well u p into t h a t p a r t of t h e a d u l t r a n g e w h i c h is generally held to be m e d i a t e d by p h o t o p i c - c o n e vision. T h e i n f a n t E R G c a n be identical in s h a p e to t h e a d u l t response, w i t h b o t h a a n d b components. N o c o m p l e x a or b waves are yet reported, b u t in H o r s t e n a n d W i n k e l m a n ' s 12 Fig. 7, a double b-wave m a y possibly be seen in a 2 89 i n f a n t at 25 lux a n d 15 m i n u t e s d a r k a d a p t a t i o n ( t h o u g h this is by no m e a n s certain since electronic noise s o m e t i m e s behaves in j u s t this f a s h i o n ) . T h e i n f a n t E R G a m p l i t u d e s are definitely dim i n i s h e d under all arousal conditions; the age
at which they attain adult values is not yet known, but it could be as much as 4 to 6 months. NI. The infant ERG is responsive to intensity changes and exhibits darkness enhancement, albeit of a somewhat small amount. niques are especially difficult to s t a n d a r d i z e with i n f a n t s ? 1, 12 Nevertheless, with certain new instrum e n t a t i o n a n d as p a r t of a larger study on E R G n o r m a l i z a t i o n in adults, a5 we do feel t h a t some progress has been m a d e in this l a t t e r direction, a n d t h a t we are therefore
Electroretinogram in newborn
73 5
justified in presenting a p r e l i m i n a r y small sample r e p o r t a t this time. METHOD
T h e e q u i p m e n t which we have used is entirely p o r t a b l e a n d is p a r t i c u l a r l y convenient for use w i t h infants because it can be b r o u g h t directly into the nursery. ~ A c o n t a c t eye electrode was specially designed for this work, a n d is shown in Fig. 1. I t is elliptical in shape, a n d the small axis is 11 ram. long, the large axis 12 ram. T h e p u p i l l a r y a p e r t u r e is 6 ram. in d i a m e t e r a n d the vertical cylinder serving to hold the eyelids open is 7 ram. in height, T h e electrode itself consists in a ring of p l a t i n u m wire e m b e d d e d flush within the i n n e r surface of the plastic eye cup. This ring just encircles the cornea when p r o p e r l y inserted. T h e stimulus light is furnished b y three small q u a r t z X e n o n discharge l a m p s giving a p p r o x i m a t e l y a 650,000 p h o t o p i c footcandle (cnd) intensity m e a s u r e d at 6 inches f r o m the l a m p ; the flash d u r a t i o n is 13 ~sec. (too short, u n f o r t u n a t e l y , to elicit t h e E R G off-effect). Stimuli were single flashes presented at 30 second intervals. F l i c k e r stimuli were not presented, since we feel t h a t the i n t e r p r e t a t i o n of the simpler single flash E R G is still itself in question. T h e visual angle is 53 degrees. T h e r e c o r d i n g system functions well over the range of a b o u t 1 (t = 0.16) to 25 (t = 0.0064) cycles per second (6 decibel d o w n ) . This low high-freq u e n c y cutoff was chosen to eliminate the large a m o u n t of "noise" w h i c h was typical of most of our infant records. This p o i n t is i m p o r t a n t since p a r t of this noise seems to be physiologic because it a p p e a r s in quiet a n d even sleeping infants. Its a p p e a r a n c e is a p a r t i a l consequence of the use of relatively high gain in the electronics (Fig. 2). T h e gains used b o t h by H o r s t e n a n d W i n k e l m a n a n d by ourselves, e.g., 50 to 100 /sv. p e r c e n t i m e t e r were a b o u t twice the usual gain used with adults. T h e testing was done on one eye of each ~Addltional information will gladly be supplied by the senior author. The manufacturer is the Cordls Corporation, 241 N. E. 36th Street, Miami, Fla.
736
ShipIey and Anton
Fig. 1. The infant eye electrode larged).
November 1964
(greatly en-
INFAN T
ADULT
Fig. 2. Comparison of one of the best neonatal curves with a typical curve of an adult. Cal. ~- 100 #V; time z 250 msec. of 10 healthy babies in their first day of life. Six were female and four were male. One drop of mydriatic (1 per cent Mydriacyl) was first put in the eye to be tested. The baby was then dark adapted, both eyes being covered with opaque Elastoplast eye pads, for one hour before the test. When the baby was brought to the examination booth, the eye pads were taken off under deep red light and the size of the pupil was observed; with one exception it was found to be between 3 and 5 mm. before the beginning of the test. * 9 Taking 4 mm. as an average, we thus had 363.6 photopic troland seconds (pts) of illumination delivered to the eye (pts ~ photopic cnd./m-" X seconds X pupil area in square millimeters).
This small pupil size may be explained by a combination of several factors. The pupil of the newborn is well known to be quite sluggish, 16 though the reasons for this are still somewhat obscure. For example, Duke-Elder 17 states, but without reference, that "At birth the dilatator muscle is illformed and while it retains its embryonic nature throughout life the muscle does not assume its full proportions until about the 5th year; since this muscle is not functionally active until after birth, the pupil of the newborn is small." This fact, plus immature innervation, may be sufficient to account for the general finding. On the other hand, we used a mild mydriatic in weak dosage so as to avoid all possibility of poisoning. It should be emphasized that we are trying to develop a procedure applicable to all or almost all premature infants. Actually, one infant (No. 2 in Table I I ) , still had a pinpoint pupil and nevertheless gave a good response. Finally, 3 drops of 0.5 per cent Ophthaine anesthetic was applied to the eye to be tested, with 2 minute intervals between drops. No general anesthetic agent was given in any case, nor was it ever needed. The infants, as also reported by Horsten and Winkelman, a~ often fell asleep, or continued to sleep. With the head correctly supported, it was always possible to keep the pupil centered under the eye electrode. The reference electrode was on the midforehead, and the ground on the ear. The test was done first under the dark conditions just described, and then repeated after 2 minutes of light adaptation to ambient room illumination of 25 footcandles. RESULTS
The results shown in Table I I are means of at least three responses under each test condition. The data are presented in such a way as to give some idea of over-all displacement magnitudes. The mean zero to peak a-wave amplitude is 32 /~v., the mean a-trough to peak b-wave amplitude is 91 /~v. (thus, mean !a+b] = 123 ~v.). These values are somewhat larger than those reported by Horsten and Winkelman 15 (mean, Ia+b[ - -
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Electroretinogram in newborn
73 7
Table II Minutes [ a#er
birth when ERG Neonate 1 2 3 4 5 6 7 8 9 10
Sex M M F F M F M F F F
Weight (erams)
wtzs taken
3,976 2,851 3,480 2,578 2,721 3,060 3,400 3,684 2,834 3,451
398 495 600 780 824 858 1,005 1,094 1,230 t,380
Amplitudes DarkLightadapted adapted
(la+bl in (Ea+bl in #v.) 124 148 161 80 205 162 99 52 48 159
#v.) 40 --61 55 75 -30 ---
76 ~v. for seven eyes), probably both because our illumination was approximately 10 ~ times brighter than theirs (though m a n y times shorter) and because our period of dark adaptation was 1 hour while theirs was only 5 to 15 minutes. I n the light-adapted conditions, half of the cases also exhibited both a- and b-waves (mean, a = 16/zv., b = 35 /~v.; ]a+b[ = 51). A particularly good E R G on a dark-adapted infant (No. 4), is shown in Fig. 2, together with an E R G of a normal adult taken under similar test conditions. DISCUSSION Given the variables of birth weight, minutes post p a r t u m when the E R G was taken, and the mean a plus b amplitudes, a small sample statistical analysis reveals the following rank-difference correlation coefficients: grams-microvolts r =-0.030. microvolts-minutes r=0.273. grams-minutes r=0.067. O n l y the first two have physiologic relevance, and they are not statistically significant. Presumably, the first would have to be significant if the E R G were to serve as an index of maturity; but the very small
Birth Analgesia be[ore delivery Demerol-atropine Demerol-Phenergan Demerol-scopolamine Lorfan-atropine Dernerol-Phenergan Demerol-Phenergan Demerol-atropine Demerol Demerol-atropine None
history Anesthesia at delivery General (cyclopropane) Pudendal (Novocain) General (cyclopropane) None General (cyclopropane) None Pudendal (Novocain) Pudendal (Novocain) Pudendal (Novocain) Spinal for cesarean section (Novocain)
range of birth weights in our sample has probably masked whatever correlations might exist. T h e small positive correlation between minutes post p a r t u m and microvolts, though in a suggestive and reasonable direction, is not valid, for identical statistical reasons. I t is our intention to continue work along these lines, with particular attention to enlarging the range of birth weights within our sample. It is now clear that recording of the E R G in h u m a n full-term and premature infants can be a routine clinical procedure. T h e failures which we encountered resulted from using the normal adult high-frequency cutoff at 120 e.p.s. T h e y are not included in Table II. We also obtained several records so overlaid with physiologic noise that the E R G could not be distinguished; we have records where, with a reduction in frequency response, one can observe the E R G to emerge more clearly. ~ Further study might very profitably be directed toward "~Horsten and Winkelman :z used a low frequency cut-off at about 5 c.p.s. [t ~ 0.03], c o m p a r e d to ours at 1 c.p.s. T h e y do not state the upper frequency limit, t t is clear that their recordings could have been m a d e easier with the 5 cycle cutoff in view of the excess infant eye motions; their high-frequency cutoff could have been anywhere f r o m 25 to 80, j u d g i n g from the wave forms reported. L e t this note stand as a plea that workers in this field report both ends of the frequency range a n d not just the low e n d - - t h e y are equally important. Moreover, a frequency figure is m u c h m o r e meaningful than a time figure, f r o m both physiologic a n d electronic points of view.
7 3 8 Shipley and Anton
November 1964 Table IC
ascertaining the source(s) of this relatively high-frequency interference. We do not wish to give the impression that all the problems have been solved. This is by no means correct, since m a n y of the records we have are not as clear as one might wish. But we do feel that this work is no longer really experimental a n d that other E R G laboratories should be encouraged to enter this field. A n E R G , albeit of reduced m a g n i t u d e , can readily be recorded on all n o r m a l infants in the first day of life. A few of our specific findings ought to be noted. These are given in T a b l e IC, to be considered as an extension of Tables I A and IB. T w o cautions m u s t be raised concerning our i n t e r p r e t a t i o n of this type of work. M a n y workers consider that a constant-responseamplitude technique is superior to the constant-stimulus-amplitude technique which has so far been employed. T h u s the E R G response should be held constant at some a r b i t r a r y value (e.g., some just discernible threshold m a g n i t u d e of 10 to 15 ~v.), while the stimulus intensity should be varied from subject to subject a n d from condition to condition u n t i l this m a g n i t u d e is attained. Generally, this p a r t i c u l a r m a g n i t u d e is disclosed, in a given case, by extrapolation or interpolation. This m e t h o d is preferred primarily because of the greater reliability of the findings, though it is usually m u c h more difficult to employ. Now that the basic procedures for the elicitation of the n e o n a t a l E R G appear to have been worked out, future studies might well devote their a t t e n t i o n to such thresholds. I t is probable that individual differences a m o n g the n e w b o r n will be most sharply revealed by such measures. Finally, when studying the response in the light-adapted eye, it is i m p o r t a n t to realize that with the room i l l u m i n a t i o n (Io) present, the stimulus is really a AI/Io situation and is not exactly comparable to the situation for the d a r k - a d a p t e d eye, where Io is given only by the level of i n t e r n a l retinal noise. T h e control for this stimulation difference is clear, that is, one turns off the room lights at the m o m e n t of flash, and, strictly speak-
N. In some cases, e.g., Fig. 2, the neonatal ERG resembles the adult wave form almost exactly, both in terms of latencies and relative a/b ratios, as Hersten and Winkelman also found. O. But partly confirming Zetterstr6m's findings, this is not true in all cases; many infants do give slow-starting, slow-rising, and long-duration wave forms. Perhaps the maturity index for which we are searching lies hidden in this fact. P. Furthermore, one or two records (not included in Table II) exhibit what are apparently slow a-waves in the absence of any clear-cut b-wave component. Q. While we do not have sufficient evidence to suggest why these various wave-form changes may occur, we are confident that they are probably n o t due to intensity variations in the retinal light stimulation. The light energy was reasonably constant in all cases. Moreover, since it was extremely bright, albeit of short duration, small variations in pupil size from infant to infant could not have been very important. The light energy was well above the saturation point in all instances. R. This does raise the question that the optimum light time-intensity (pts.) could be somewhat different from that which we have used. It is known, for example, that adult amplitudes decrease under very bright stimulation. S. Mann~ has stressed the fact that the final histologic maturation of the rods and cones and the demarcation of the fovea in man takes place between the second and fourth postpartum months, though Horsten and Winkelman1~ have reported that the human macula does possess rudimentary cones at birth. In any case, they have observed, and we have confirmed, the existence of darkness enhancement of the ERG amplitudes in the first day of life. Considering our mean results, we find that the response amplitude after dark adaptation is about two and a half times the amplitude of the response after several minutes' exposure to light. This enhancement is quite comparable in magnitude to that which we have found in adults under similar test conditions (though with as little as 20 minutes' dark adaptation). T. Thus, marked darkness amplitude enhancement can and does take place long before the complete histologie differentiation of the human retina. U. Though duplex a and b peaks may have appeared in one of our records, and in one of Horsten and Winkelman's,12 no decisions are really possible on this point in view of the small samples involved. V. Drugs given to the mother during labor and at the moment of birth might still have been circulating in the infants when they were tested for the ERG, and so might have affected the results. As be~t we can tell. however, there is no relationship between either the analgesic or the anesthetic given to the mother and' the subsequent ERG responses of the babies (Table II, last two columns).
Volume 65 Number 5
ing, it m u s t be used when q u a n t i t a t i v e comparisons between light- a n d d a r k - a d a p t e d conditions a r e to be m a d e . I t is for this reason t h a t we have sometimes spoken of darkness e n h a n c e m e n t r a t h e r t h a n of d a r k a d a p t a t i o n p e r se ( t h o u g h the two are m u c h the same). M o r e i m p o r t a n t , this is possibly w h y we failed to o b t a i n a l i g h t - a d a p t e d response in half of our infants.
We wish to thank Dr. Lee Worley of the Department of Pediatrics, University of Miami School of Medicine, for his valuable assistance in this study.
REFERENCES
1. Winkelman, J. F., and Horsten, G. P. M.: Congenital blindness in the presence of a normal fundus, Ophthalmologica 137: 423, 1959. 2. Paufique, L., Ravault, M. P., and Picaud, C. : Eleetroretinography and ocular pathology of premature children, ISCERG Newsletter 5: 4, 1964. 3. Engel, R., and Butler, B. V.: Appraisal of conceptual age of newborn infants by electroencephalographic methods, J. PEDIAT. 63: 386, 1963. 4. Mann, I.: The develoldment of the human eye, New York, 1950, Grune & Stratton, Inc. 5. Gorman, J. J., Cogan, D. G., and Gellis, S. S.: An apparatus for grading the visual acuity of infants on the basis of optokinetie nystagmus, Pediatrics 19: 1088, 1957.
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739
6. Zetterstr6m, B.: The clinical electroretinogram. IV. The electroretinogram in children during the first year of life, Acta ophth. 29: 295, 1951. 7. ZetterstrSm, B,: The electroretinogram in prematurely born children, Acta ophth. 30: 405, 1952. 8. Zetterstr6m, B.: Flicker electroretinography in newborn infants, Acta ophth. 33: 158, 1955. 9. Heck, J. v., and Zetterstr6m, B.: Analyse des photopischen Flimmer-electroretinogramms bei Neugeborenen, Ophthalmologica 135: 205, 1958. 10. Horsten, G. P. M., and Winkelman, J. E.: Development of the ERG in relation to histological differentiation of the retina in man and animals, A. M. A. Arch. Ophth. 63: 232, 1960. 11. Winkelman, J. E., and Horsten, G. P. M;: The ERG of premature and full-term born infants in the first days of life, Ophthalmologica 143: 92, 1962. 12. Horsten, G. P. M., and Winkelman, J. E.: Electrical activity of the retina in relation to histological differentiation in infants born prematurely and at full-term, Vision Res. 2: 269, 1962. 13. Zetterstr~im, B.: The effect of light on the appearance and development of the electroretinogram in newborn kittens, Acta physiol. scandinav. 35: 272, 1955. 14. Zetterstr6m, B.: Studies on the postnatal development of the electroretinogram in newborn infants, Stockholm, Sweden, 1956, Tryekeri AB Thule. 15. Shipley, T.: Human electroretinography as a gauge of visual performance, Progress Report DA-49-193-MD-2344: 1, ASTIA. 16. Scharfetter, C.: Die Pupille des Neugeborenen, Monatsschr. Kinderh. l l h 94, 1963. 17. Duke-Elder, S.: System of Ophthalmology, Vol. III, Embryology, London, 1963, Henry Kimpton, p. 305.