Electro-Oculography as a Test of Retinal Function

ELECTRO-OCULOGRAPHY AS A T E S T O F R E T I N A L F U N C T I O N T H E NORMAL AND SUPERNORMAL FREDERICK REESER, M.D.,

GEORGE W.

W E I N S T E I N , M.D.,

AND RONALD S. OSER,

EOG KATHARINE B. FEIOCK,

M.D.

Baltimore, Maryland The electrical potential generated across the eye was noted first by Du Bois-Reymond.1 This resting or standing potential with the cornea positive relative to the poste­ rior pole was recorded from the human eye in 1877 by Dewar. Miles2 observed that the standing potential increased over a period of several minutes with an increase in back­ ground illumination. The orientation of this electrical potential corresponds approximately to the visual axis, and it is possible to record eye move­ ments with skin electrodes placed at the me­ dial and lateral canthi. The electrode closer to the cornea produces a positive deflection on the galvanometer. The magnitude of this deflection depends in part on the degree of rotation of the eye from the midline. This technique is the basis of the electro-oculogram and electro-oculography, both of which are abbreviated EOG. François 3 studied the relation of the ampli­ tude of the EOG to the state of the subject's visual adaptation. He noted that the standing potential falls to a minimum during dark adaptation, and on exposure to light it reaches a maximum and then decreases to the pre-adaptation state. The magnitude of this "modification" of amplitude was utilized to assess ocular disease states. François rec­ ommended the use of the EOG as a clinical test of retinal function and that it be carried out in moderate brightness without previous light or dark adaptation. Arden and his associates4"6 extended the

use of the EOG as a clinical tool by first dark-adapting the subject to obtain a mea­ surement of the minimal electrical potential (the dark trough), and then exposing the subject to bright illumination to obtain a peak level of electrical potential (the light peak). These two values were then ex­ pressed as a ratio : Light peak Dark trough

EOG ratio

The representation of the changes in the EOG during various states of adaptation as an absolute numerical, ratio has several ad­ vantages. The most important of these is that it allows the comparison of one eye to the fellow eye or to that of another subject, without regard to the magnitude of the standing potential, which is influenced by many variables, including electrode place­ ment and changes in skin resistance. Fur­ thermore, the diurnal changes in the stand­ ing potential, which have been studied ex­ haustively by Kolder,7 have a negligible effect, since the test takes no more than 30 minutes. The significance of the changes in the standing potential produced by adaptation, as well as the exact source of the generator of the dark trough and light peak, are still not well understood. For this reason, alterations of the EOG ratio which have been noted in retinal disease must be regarded as empirical observations. It is known, though, that the standing potential's existence and its altera­ tions depend upon the structural and func­ tional integrity of the choroid, the pigment From The Wilmer Ophthalmological Institute of 89 the Johns Hopkins Hospital and School of Medi­ epithelium, and the photoreceptors. ' Fur­ cine, Baltimore, Maryland. This study was sup­ thermore, the maintenance of such an elec­ ported in part by USPHS Grant NB 07647-02. Reprint requests to George W. Weinstein, M.D., trical potential difference requires the exis­ The Wilmer Institute, Room 117, Johns Hopkins tence of a barrier which functions to impede Hospital, Baltimore, Maryland 21205. the flow of electrons from a "source" to a SOS

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AMERICAN JOURNAL OF OPHTHALMOLOGY

"sink" ; and this barrier would be character­ ized by high resistance, high capacitance, or both. Brindley10 encountered such a barrier in his microelectrode studies on the frog eyecup and proposed the concept of the "R membrane." Brown and Wiesel11 and Tomita and colleagues12 suggested that Bruch's membrane is the R membrane, as a result of their microelectrode experiments in mam­ malian eyes. Byzov13 believes that the R membrane has at least two components, the major one being the internal layer of the pig­ ment epithelium ; whereas Brindley and Hamasaki14'15 favor the photoreceptor layer. Byzov's work is strongly supported by a marking technique which has recently added much to an understanding of intracellular retinal recordings.16'17 This paper presents a summary of the re­ sults obtained in our EOG laboratory on 50 normal subjects (100 eyes). The similari­ ties to, and the differences between, previous studies and the present study on normals will be discussed. Another purpose of this paper is to report an unusual EOG finding in two presumably unrelated pathologic conditions.

OCTOBER, 1970

E

LIGHT SOURCE

METHODS

Test apparatus—The selection and design, of the test equipment used in this study was similar to that described by Arden, Barrada and Kelsey,6 and Imaizumi2 and is shown schematically in Figure 1. The apparatus consists of a large white plastic panel, illumi­ nated uniformly from its rear surface by four fluorescent bulbs. The luminance of the panel was 800 foot-candles. Two small red fixation lights were incorporated into this panel to produce a horizontal eye movement of 30 degrees. A headrest was located 18 inches in front of the illumination panel. Re­ cordings were obtained with 5 mm silver skin electrodes, one at each canthus of each eye. A fifth electrode was secured to the pa­ tient's ear and connected to ground. The electrodes were fixed in position with tape after the skin was cleansed with alcohol and

Fig. 1 (Reeser, Weinstein, Feiock, and Oser). Schematic diagram of EOG test equipment, with ink writer shown at bottom.

the conduction was enhanced by electrode paste. Most testing was performed with a Schwarzer 6-channel recorder, which incor­ porates DC amplifiers. Some EOG tests were made using two Brush single-channel recorders with AC amplification (time con­ stant of one second). The resultant tracings were quite similar with either recording ap­ paratus. The room lights were on while the subject was prepared. Then all lights were extinguished and dark adaptation was begun. During the next 15 minutes, the subject was requested to look back and forth from one red fixation light to the other, at a rate of one sweep per second, until satisfactory re-

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cordings were obtained. This was repeated every minute. The adapting panel was then turned on and the same routine was followed for an additional 15 minutes. The subject was encouraged to keep his eyes open despite the initial discomfort of the bright light. Normal subjects—EOG's were obtained from responses of 100 eyes in 50 normal subjects. These subjects, both male and female, were selected to represent a broad age span. The subjects all had corrected vi­ sion of 20/20 or better in each eye, with a refractive error no greater than 4 diopters. In addition, each subject had a normal ocular examination with no history of ocular inflam­ mation or injury. Also, five normal sub­ jects were studied with bilateral EOGs be­ fore and after the dilation of the left pupil, in order to ascertain the effect of retinal illu­ mination on the EOG ratio. Abnormal subjects—In attempting to as­ sess the role of melanin pigment contained in the normal retinal pigment epithelium upon the EOG changes with adaptation, Gouras and Gunkel18 studied a subject with complete albinism. They found a normal EOG ratio. However, Imaizumi2 found a "supernormal" ratio in albinos. The latter report includes a study of four albinos and seven apparently unaffected family members. Five subjects with aniridia were studied as representing another clinical entity char­ acterized by exceptionally high levels of reti­ nal illumination. RESULTS

Normal subjects—The subjects in this group ranged in age from 20 to 62 years, with an average age of 33.8 years. There were 10 men and 40 women. Of the 50 sub­ jects, 15 were Negro and the remainder were Caucasian. The details of the results in these normal subjects are given in Table 1. The average ratio of the light peak to the dark trough was 2.48, with a range from 1.75 to 3.62. Figure 2 is a frequency distri­ bution histogram of these values for the nor-

507 TABLE 1

RESULTS OF EOG RECORDINGS IN NORMAL SUBJECTS

Case No.

Age and Sex

1 2 3 4 S 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

30-M 35-M 24-F 20-F 21-M 24-F 33-M 25-F 20-F 20-F 21-F 30-M 32-F 25-M 26-F 44-F 20-F 21-F 30-F 20-F 33-M 22-M 27-F 30-F 20-F 24-F 23-F 51-F 22-F 51-F 39-F 59-F 62-F 48-F 21-F 50-F 25-F 44-F 21-F 22-F 29-M 58-F 59-F 22-F 26-F 56-F 26-F 55-F 45-F 22-M

EOG Ratio Right Eye

Left Eye

3.07 1.75 1.84 2.66 2.29 2.66 3.00 2.77 3.62 2.45 1.88 1.85 1.75 3.00 2.66 3.27 1.94 2.37 2.89 2.75 3.60 2.11 1.85 2.55 2.54 2.74 2.36 1.88 2.87 2.00 3.12 2.60 2.50 2.94 1.83 2.99 2.08 2.54 2.64 2.08 1.92 2.00 2.33 2.60 3.35 2.05 2.60 2.60 2.00 2.00

2.22 1.85 1.84 3.62 2.66 3.20 3.00 3.10 2.58 3.53 2.46 1.92 1.85 2.72 2.46 2.81 2.40 2.53 3.20 2.72 2.17 1.89 2.00 2.83 2.30 2.61 2.90 1.88 2.30 1.92 3.33 2.90 2.00 3.20 2.23 2.46 2.70 2.25 2.12 1.88 1.85 1.82 1.94 2.66 3.50 2.50 2.15 2.50 1.95 1.90

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OCTOBER, 1970

though there were some variations from one subject to another, the dark trough usually was obtained seven to nine minutes after be­ ginning dark adaptation. Upon initiating Mean: 3.47 1 σ : ίθ.» light adaptation, the light peak usually was produced after six to eight minutes. The subjects over 35 years of age showed a slightly lower average ratio than those sub­ jects under age 35. The former ratio was 2.40, while the latter averaged 2.51. How­ ever, the negative correlation between age and EOG ratio was not statistically signifi­ 1.7 I.« 9.1 fcl cant in this series. There was a close correla­ tion between the ratios for the right and left Fig. 2 (Reeser, Weinstein, Feiock, and Oser). Frequency distribution histogram of EOG ratios eyes of a subject. of SO normal subjects, with ratio of light peak/dark The five normal subjects who were tested trough shown on bottom. both before and after dilation of one pupil are summarized in Table 2. There was no significant change in the ratio as compared to the predilation value. Abnormal subjects—Four patients with Maar» 0 . 7 0 M albinism and seven nonalbinic family mem­ i n «o.o·» bers were evaluated, as well as five patients with aniridia. The results revealed a super­ normal EOG ratio (>4.00) in two of the al­ binos and in seven of the 10 eyes with ani­ ridia (Figs. 5 and 6). All family members of patients with albinism had normal EOG's. These results are shown in Table 3. -O.M

-t.lt

13

2Λ

-4M

-*JU

17

It

U

*t.w

XS

*aia

*7

*fcH

Fig. 3 (Reeser, Weinstein, Feiock, and Oser). Frequency distribution histogram of logarithmic transformation of EOG ratio of SO normal subjects.

mal subjects. The distribution was not Gaus­ sian, and therefore not subject to the statisti­ cal methods usually employed to describe normal populations. Arden and Barrada 5 suggested using the logarithm of the EOG ra­ tio in order to produce more nearly a normal distribution. This was done with our data and the resultant histogram is given in Fig­ ure 3. It is obvious that this histogram pro­ vides no real advantage for statistical treat­ ment of our data. Figure 4 represents a typical result of an EOG recording in a normal subject. Al­

DISCUSSION

In order to enhance the usefulness of EOG as a clinical test of retinal function, it is important to develop more fully an under­ standing of the generation of the standing potential of the eye, as well as a wider ex­ perience with the test in normal and abnor­ mal subjects. Clinical electroretinography (ERG) has been undergoing such a process over the past three decades and this is not yet complete. Although many of the disease states which alter the EOG also affect the ERG in a par­ allel fashion, the EOG appears to be pro­ duced in a different part of the retina, and at least in part results from different influ­ ences.19"21 The standing potential is constituted by

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ELECTRO-OCULOGRAPHY

509

NORMAL

2.0-

TIME (MIN.)

Fig. 4 (Reeser, Weinstein, Feiock, and Oser). Normal EOG: Plot of EOG amplitude with changes in adaptation. The graph begins as room illumination is extinguished. Minimum amplitudes are recorded after eight minutes of dark adaptation. When the adapting panel is turned on, maximum amplitudes are reached in another eight to 10 minutes. The ratios indicated are derived from the maximum and minimum ampli­ tudes for each eye. two separate potentials, one light-sensitive and the other light insensitive. The light in­ sensitive DC potential, which decreases tran­ siently as the dark trough during dark adap­ tation, appears to depend on both a combina­ tion of and the orderly arrangement of the pigment epithelium and various extraretinal sources.22 The exact localization of this mass response, and the brief diminution of the po­ tential during dark adaptation, are not yet understood, but they involve to some degree the choroid, the pigment epithelium and the photoreceptors.8'9 Noell23 has proposed that a large portion of this standing potential is caused by membrane polarization of the pig­ ment epithelium in close approximation with the retinal neural cells, which are maintained by an active ion transport system. Bortoff

and Norton, 24 on the other hand, as a result of studies on the isolated frog retina, con­ cluded that this DC standing potential origi­ nated from structures on the receptor side of the retina, perhaps from Müller cells in the region of the inner segments and the recep­ tor bipolar synapses. The light-sensitive po­ tential has been shown by Gouras and Carr 25 to originate in the bipolar cell region. These authors, and others,26 believe that it origi­ nates in an area between the sites responsible for the a- and b-waves of the ERG. Although the retinal pigment epithelium generates the c-wave of the ERG, it is dif­ ficult to record this under clinical condi­ tions. Furthermore, the EOG, in addition to testing areas of the retina and pigment ep­ ithelium which are not easily studied by any

510

AMERICAN JOURNAL OF OPHTHALMOLOGY TABLE 2 EFFECT OF PUPILLARY DILATION ON RATIO IN NORMAL SUBJECTS

Case No.

—

EOG

EOG Ratio Predilation

Postdilation

18. Control eye Test eye

2.91 2.66

2.33 2.73

26. Control eye Test eye

2.12 1.80

2.00 2.00

34. Control eye Test eye

1.74 1.50

1.77 1.80

29. Control eye Test eye

2.00 2.00

2.22 2.00

46. Control eye Test eye

2.20 3.00

2.10 2.00

TABLE 3 E O G RESULTS IN PATIENTS WITH ALBINISM AND ANIRIDIA

Age and Sex 37-M 16-F 18-M 8-M 34-F 20-F 13-F 12-F 14-M 1S-F 10-F 13-M* 28-M 16-F 36-F* 24-F

EOG Ratio Condition

Right Eye

11.67 Generalized albinism 3.17 Generalized albinism 3.50 Ocular albinism 6.15 Ocular albinism 3.09 Carrier of ocular albinism 3.00 Carrier of ocular albinism 3.00 Carrier of ocular albinism Sibling had ocular albinism 2.78 Sibling had ocular albinism 2.70 Sibling had ocular albinism 2.64 Sibling had ocularjalbinism 2.70 5.20 Aniridia 5.68 Aniridia 3.58 Aniridia 5.00 Aniridia 3.33 Aniridia

Left Eye 8.50 2.66 3.40 6.45 2.88 2.02 2.62 3.09 3.62 2.54 3.00 6.20 10.00 5.00 4.33 3.30

* Negro. The other 14 patients were Caucasian.

other method, has the advantage of being somewhat more acceptable to the subject, since skin electrodes are used without direct contact made to the eyes. Arden and Kolb27 believe that "by record­ ing both the EOG and ERG, more informa­

OCTOBER, 1970

tion about the disease process is obtained than by employing either test alone." In a study of 74 patients with retinitis pigmentosa, Arden and Fojas 28 concluded that "the EOG is the most sensitive of the electrical tests." In addition, they found the EOG to be abnormal in early or atypical retinitis pigmentosa when the ERG was occasionally normal. Kolb and Galloway29 found a re­ duced EOG in the unaffected eye of a pa­ tient with unilateral retinitis pigmentosa when dark adaptation and ERG were nor­ mal. Arden, Barrada and Kelsey6 tested a se­ ries of patients with high myopia and con­ cluded that the "EOG is a much more cer­ tain detector of myopic changes than the ERG." In the same series of studies, they found a reduced EOG in mild vascular insuf­ ficiencies and abnormalities when the ERG was not altered until a large portion of the retina was disturbed. Arden and Kolb27-30 also have suggested that the EOG shows a mild alteration in patients receiving chloroquine, and that this is reversible with the dis­ continuance of the drug before either ERG or fundus changes take place. Imaizumi and his co-workers31 concluded that the EOG is affected earlier and to a greater degree in certain types of uveitis such as choroiditis and Behçet's disease than is the SRG. Krill,32 in an extensive examination of the ERG and EOG in patients with various macular lesions, noted that the EOG was abnormal in three patients with vitelliruptive macular de­ generation in spite of normal ERG and nor­ mal peripheral dark adaptation. Not all of these initially enthusiastic eval­ uations of the EOG have been confirmed by other investigators. Gouras and Carr 33 stud­ ied eight cases of relatively early retinitis pigmentosa in an attempt to determine which of these two responses, the ERG or the EOG, is affected first. They concluded that the scotopic component of the ERG and the EOG was affected early in retinitis pigmen­ tosa and in a parallel manner. Carr and Siegels* tested a variety of ocular disorders in­ volving the retina in an effort to evaluate the

Sll

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ALBINISM T. M . 37 W.M. 20AMP (CMS

L5-

RIGHT EYE β 11.67 LEFT EYE · A 8 . 5 0

U>-

LIGHTS TIME

(MIN)

Γ

ID-

ON 20

25

Fig. 5 (Reeser, Weinstein, Feiock, and Oser). EOG in a patient with albinism. The EOG ratio in each eye is markedly supernormal.

relative merits of the ERG and the EOG. They found no clear-cut advantage of the EOG over the ERG, but suggested the use of the EOG "in conjunction with psychophysical and electrophysical tests of visual function." Gouras and Gunkel18 reported the comparative findings of the EOG and the ERG in eight patients with early and with late chloroquine retinopathy. The conclusion of those workers was that the changes in the EOG parallel those seen with the ERG in this condition, and that these tests are not sensi­ tive indices of chloroquine retinopathy in pa­ tients who are no longer on chloroquine ther­ apy. They believe that the marked EOG changes noted by Arden, which were often reversible on discontinuance of the drug, must have been transient phenomena. The major drawback of both the EOG and the ERG is that both are relatively in­

sensitive tests, requiring relatively large ar­ eas of retinal dysfunction before abnormali­ ties can be recorded. The EOG findings in normal subjects reported here are essentially similar to those previously reported by oth­ ers. Arden, Barrada and Kelsey6 examined the EOG in 91 normal eyes and concluded that any ratio of less than 2.00 is "suspi­ cious" and any value less than 1.85 is "frankly pathologic." In the present nor­ mal series, a ratio of 1.75 was found in two eyes. Of the 100 eyes evaluated in this re­ port, 8% showed a ratio between 1.75 and 1.85. The highest normal ratio in Arden's se­ ries was 3.82, about the same as the corre­ sponding value in this report. We also share their opinion that, because of the skewed dis­ tribution of the ratios, the series was not amenable to statistical evaluation as a normal population of values. Kelsey4 performed

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ANIRIDA P.W. W.M.

28

2.0AMP. (CMS)

RIGHT EYE Θ 5.68 LEFT EYE

A 10.00

TIME (MIN)

Fig. 6 (Reeser, Weinstein, Feiock, and Oser). EOG ratio in a patient with aniridia. The EOG ratio is markedly supernormal. EOGs in eight normal subjects at weekly intervals for 10 or 11 weeks and found a ra­ tio of less than or equal to 1.85 in eight re­ cordings out of 166 measurements. Kelsey also pointed out the considerable variations in ratios occasionally obtained when retesting subjects on multiple occasions. Krill32 stud­ ied 26 normal subjects whose average age was 27 years. He states that a ratio of 2.00 is two standard deviations below the mean and this was interpreted as abnormal. He points out that data on the normal EOG in subjects over 50 years of age are lacking in the litera­ ture. Henkes 35 studied the EOG in 15 nor­ mal subjects and found that the lower limit of normal was a ratio of 1.65. The series reported in this investigation is weighted towards subjects in the second and third decades of life. However, 16% of the subjects were over 50 years of age, while 32% were over 35 years of age. There was a

small negative correlation between age and the EOG ratio, but unlike Arden's series, this correlation was not significant. There was, likewise, no significant difference be­ tween right and left eyes. It is interesting to speculate on findings of clearly supernormal ratios obtained in two of four patients with ocular albinism and in four patients (seven out of eight eyes) stud­ ied with aniridia. Gouras and Gunkel18 stud­ ied one patient with ocular albinism and ob­ tained a normal EOG ratio. Imaizumi2 showed that the EOG in traumatic aniridia was supernormal. He explained this phe­ nomenon as being the result of an increased quantity of light entering the fundus. How­ ever, the present study includes an experi­ ment on the effect of wide pupillary dilation upon the EOG ratio, and this effect was found to be minimal in normal subjects. Thus, it would appear possible that the

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markedly abnormal E O G ratio in aniridia and albinism is related to the effects of chronic overexposure to light in both of these conditions. T h e r e has been great inter­ est in this subject since Dowling 3 6 first noted the protective effect of darkness on retinal degeneration in dystrophic rats, and Noell and colleagues 37 studied the destructive effects of even relatively brief exposure to excessive light on the photoreceptors. Both albinism and aniridia are frequently accom­ panied by pendular nystagmus, a sign of poor visual function. This condition usually is acquired, whereas both albinism and aniri­ dia are congenital. It is conceivable that the latent period before the development of nys­ tagmus in these conditions is characterized by progressive damage resulting from the ab­ normally high levels of retinal illumination. T h e question of why such damage might produce supernormal E O G values is even more perplexing. I t must suffice for the present to note that in these cases this finding apparently characterized conditions that are associated with light-induced retinal damage. SUMMARY

A study of SO normal subjects using the E O G as a test of retinal function gave re­ sults essentially in agreement with earlier re­ ports by other workers. Both albinism and aniridia were character­ ized by supernormal E O G ratios. This effect cannot be produced in normal subjects by short-term pupillary dilation. T h e elevated E O G ratio might be the result of chronic light-induced retinal damage. ACKNO WLEDGM ENT

We thank Mr. Robert Hobson for his technical assistance. REFERENCES

1. Kris, C. : Corneo-fundal potential variations during light and dark adaptation. Nature 182:1027, 1958. 2. Imaizumi, K. : The clinical application of electro-oculography (EOG). In Burian, H. M., and Ja-

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cobson, J. H. (eds.) : Clinical Electroretinography. Oxford, England, Pergamon Press, 1966, p. 311. 3. François, J., Verriest, G., and De Rouck, A.: Modification of the amplitude of the human electro-oculogram by light and dark adaptation. Brit. J. Ophth. 39:398, 19SS. 4. Kelsey, J.H. : Variations in the normal electrooculogram. Brit. J. Ophth. 51:44, 1967. 5. Arden, G. B., and Barrada, A. : Analysis of the electro-oculogram. Brit. J. Ophth. 46:468, 1962. 6. Arden, G. B., Barrada, A., and Kelsey, J. H. : New clinical test of retinal function based upon the standing potential of the eye. Brit J. Ophth. 46: 449, 1962. 7. Kolder, H. : Spontane und experimentelle Än­ derungen des Bestandpotentials des menschlichen Auges. Pflüger's Arch. ges. Physiol. 268:2S8, 1959. 8. Lasansky, A., and De Fisch, F. W. : Potential, current, and ionic fluxes across the isolated retinal pigment epithelium and choroid. J. Gen. Physiol. 49 : 913, 1966. 9. Arden, G. B., and Kelsey, J. H. : Some obser­ vations on the relationship between the standing po­ tential of the human eye and the bleaching and re­ generation of visual purple. J. Physiol. 161:205, 1962. 10. Brindley, G. S. : The passive electrical proper­ ties of the retina and the sources of the electroretinogram. Bibl. Ophth. 48:(Suppl.) :24, 1957. 11. Brown, K. T., and Wiesel, T. N. : Intraretinal recording in the unopened cat eye. Am. J. Ophth. 46:91, 1958. 12. Tomita, T., Murakami, M., and Hashimoto, Y. : On the R membrane in the frog's eye. J. Gen. Physiol. 43 :81, 1960. 13. Byzov, A. L. : Localization of the R mem­ brane in the frog eye by means of an electrode mar­ king method. Vision Res. 8:697, 1968. 14. Brindley, G. S. : The passive electrical proper­ ties of the frog's retina, choroid and sciera for ra­ dial fields and currents. J. Physiol. 134:339, 1956. 15. Brindley, G. S., and Hamasaki, D. I.: The properties and nature of the R membrane of the frog's eye. J. Physiol. 167:599, 1963. 16. Werblin, F. S., and Dowling, J. E. : Organi­ zation of the retina of the mudpuppy, Necturus maculosus. II. Intracellular recording J. Neurophysiol. 32:339, 1969. 17. Kaneko, A. : Electrophysiological and ana­ tomical studies of single neurons in the carp retina. Presented at the Association for Research in Oph­ thalmology meeting, Sarasota, Florida, April 20, 1969. 18. Gouras, P., and Gunkel, R. D. : The EOG in chloroquine and other retinopathies. Arch. Ophth. 70:629, 1963. 19. Brown, K. T. : Analysis of the electroretinogram and the origins of its components. Jap. J. Ophth. 10(suppl.) :130, 1966. 20. Duke-Elder, S. : System of Ophthalmology, vol. 10. St. Louis, Mosby, 1967, p. 496. 21. Carr, R. E. : Optics and visual physiology. Arch. Ophth. 80:280, 1968. 22. Gouras, P. : Relationships of the electro-ocu-

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logram to the electroretinogram. In François, J. (ed.) : The Clinical Value of Electroretinography. Basel, Karger, 1968, p. 66. 23. Noell, W. K. : Cellular physiology of the ret­ ina. J. Opt. Soc. Am. 53:36, 1963. . 24. Bortoff, A., and Norton, A. L. : An electrical model of the vertebrate photoreceptor cell. Vision Res. 7 :253, 1967. 25. Gouras, P., and Carr, R. E. : Light-induced DC responses of monkey retina before and after central retinal artery interruption. Invest. Ophth. 4 : 310, 1965. 26. Carr, R. E., Ripps, H., Siegel, I. M., and Weale, R. A. : Rhodopsin and the electrical activity of the retina in congenital night blindness. Invest. Ophth. 5:497, 1966. 27. Arden, G. B., and Kolb, H. : Electrophysiological investigations in retinal metabolic disease: Their range and application. Exp. Eye Res. 3 :334, 1964. 28. Arden, G. B., and Fojas, M. R. : Electrophysiological abnormalities in pigmentary degenerations of the retina. Arch. Ophth. 68:369, 1962. 29. Kolb, H., and Galloway, N. R. : Three cases of unilateral pigmentary degeneration. Brit. J.

OCTOBER, 1970

Ophth. 48:471, 1964. 30. Kolb, H. : Electro-oculogram findings in pa­ tients treated with antimalarial drugs. Brit. J. Ophth. 49:573, 1965. 31. Imaizumi, K., Toyama, T., and Horie, E. : The electro-oculography (EOG) of various eye dis­ eases. Jap. J. Ophth. 8 :204, 1964. 32. Krill, A. E. : The electroretinographic and electro-oculographic findings in patients with macular lesions. Tr. Am. Acad. Ophth. Otol. 70:1063, 1966. 33. Gouras, P., and Carr, R. E. : Electrophysiological studies in early retinitis pigmentosa. Arch. Ophth. 72:104, 1964. 34. Carr, R. E., and Siegel, I. M. : Electrophysiologic aspects of several retinal diseases. Am. J. Ophth. 58 :95, 1964. 35. Henkes, H. E. : Electro-oculography as a di­ agnostic aid in phenothiazin retinopathy. Tr. Ophth. Soc. U.K. 87 :285, 1967. 36. Dowling, J. E. : Nutritional and inherited blindness in the rat. Exp. Eye Res. 3 :348, 1964. 37. Noell, W. K., Walker, V. S., Kang, B. S., and Berman, S. : Retinal damage by light in rats. Invest. Ophth. 5:450, 1966.

OPHTHALMIC MINIATURE

. . . The author is frequently asked in giving a talk to make it "practical" and not too "theoretical." By "practical" is usually meant "therapeutic" ; by "theoretical" is usually meant "fundamental." The author has no patience with such a philosophy. One cannot possibly practice good medi­ cine and not understand the fundamentals underlying therapy. Few if any rules for therapy are more than 90% correct. If one does not under­ stand the fundamentals, one does more harm in the 10% of instances to which the rules do not apply than one does good in the 90% to which they do apply. The same policy carries over to medical education. There are those who advocate medical schools which will turn out practical physicians rather than "theorists." But they end by turning out a poorer grade of doctors. As with eggs, there is no such thing as a poor doctor ; doctors are either good or bad. Fuller Albright In Cecil-Loeb Textbook of Medicine, 11th ed. Philadelphia, W. B. Saunders, 1963, p. 1341.