Supernormal scotopic ERG in cone dystrophy · In response to a white flash ofmoderate intensity the scotopic b-wave amplitude wasconsiderably larger than normal. Onepatient had elevated

British Journal ofOphthalmology, 1984, 68, 69-78

Supernormal scotopic ERG in cone dystrophyKENNETH R. ALEXANDER AND GERALD A. FISHMANFrom the Department of Ophthalmology, University of Illinois Eye and Ear Infirmary, Chicago, USA

SUMMARY Three patients with a bull's-eye macular lesion and other signs characteristic of conedystrophy gave an unusual ERG finding. In response to a white flash of moderate intensity thescotopic b-wave amplitude was considerably larger than normal. One patient had elevated rodthresholds and nyctalopia, while the other 2 had normal rod sensitivity associated with thesupernormal scotopic b-wave amplitude. In the latter 2 patients the abnormal ERG pattern wasunchanged for 4 years and 7 years respectively. This atypical finding, of a supernormal scotopicb-wave amplitude in response to light of moderate intensity, appears to characterise a subgroup ofpatients with cone dystrophy, probably of autosomal recessive inheritance. The pathogenesis of theabnormal ERG remains uncertain.

Cone dystrophy is a group of disorders often char-acterised by an atrophic macular lesion, typicallybull's-eye-like in appearance, associated with reducedvisual acuity, poor colour vision, light sensitivity, andin some instances nystagmus. ' The dystrophy maybe diffuse, with a reduced or nondetectable photopicERG, or localised in the macula, with a normalphotopic electroretinogram (ERG).4 Abnormalitiesof rod function are sometimes also apparent, includ-ing a scotopic ERG which is reduced in amplitude(cone-rod dystrophy).7" Recently an unusual type of.cone dystrophy has been reported in which the rodERG is subnormal at low flash intensities but issupernormal with brighter flashes. 10 In the 2 patientsdescribed the cone dystrophy occurred in associationwith nyctalopia.The purpose of this report is to describe 3 cases of a

supernormal scotopic ERG associated with anatrophic macular lesion. One case is similar to thoseofcone dystrophywith nyctalopia reported by Gouraset al. 0 The other 2 cases seem to represent apreviously unreported clinical entity of conedystrophy with a supernormal scotopic ERG withoutnyctalopia. The latter patients demonstrate that asupernormal scotopic ERG can occur withoutimpaired rod function.

Materials and methods

The procedures for recording the ERG have beendescribed elsewhere." Briefly, the patients' pupilsCorrespondence to Dr Gerald A. Fishman, University of Illinois Eyeand Ear Infirmary, 1855 W. Taylor Street, Chicago, IL 60612, USA.

were dilated with 10% phenylephrine and 1% cyclo-pentolate drops, following the application of 5%proparacaine hydrochloride as a topical anaesthetic.The ERGs were recorded with a Burian-Allen mono-polar electrode wetted with methylcellulose.Responses were elicited by a Grass PS-22 photo-stimulator that illuminated a diffusing sphere toprovide Ganzfeld stimulation. Signals were amplifiedby a Grass preamplifier and by a Tektronix dual traceamplifier. Results were displayed on an oscilloscopeand photographed with an oscilloscope camera.

Subjects were adapted for 5 minutes to a Ganzfeldillumination of 1-7 log cd m2, and then a single-flashphotopic response was recorded against a backgroundof 1-4 log cd m2, using the unattenuated I-16 setting,which had nominal intensity of 1 5 x 101 candle powerand a duration at half-amplitude of 10 ,us. The back-ground was extinguished, and single-flash recordingswere obtained after 5, 10, 15, 20, and 30 minutes ofdark adaptation, again with the use of the un-attenuated 1-16 setting. A single-flash response todim blue light (produced by Wratten 47 and 0 5 logunit neutral density filters and anI-4 setting) was alsoobtained after 30 minutes of dark adaptation tostimulate the rod system preferentially. Anamplitude-intensity function was then obtained. The1-16 flash intensity was attenuated by 3.5 log units ofneutral density filtering, and a single-flash white-lightERG response was recorded. The flash intensity wasthen systematically increased in 0-5 log unit steps, andthe ERG was recorded at each intensity. A briefperiod of dark adaptation of approximately 2minutes' duration followed each flash presentation.

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Kenneth R. Alexander and Gerald A. Fishman

Static profile perimetry was performed with aTubinger perimeter. The patients' pupils were dilatedas above, and then patients were dark-adapted for atleast 40 minutes. Absolute thresholds were obtainedacross the visual field for a test stimulus (TS) that was104' in diameter, 500 ms in duration, and either of along wavelength (Oculus glass filter, bandpass >620nm) or a middle wavelength (Oculus interferencefilter, Xmax=5OO nm). The relative threshold valuesfor the 2 chromatic stimuli at each retinal locationindicate whether rods or cones determine theabsolute threshold.'2 The sensitivity of the conesystem was further assessed by light-adapted flickerperimetry."3 The threshold luminance for detectingflicker across the visual field was measured with a 25Hz white TS, 104' in diameter and 3 seconds induration, presented against a Ganzfeld backgroundof 0 5 log cd m-2 to suppress the rod system.

Case reports and results

CASE 1: CONE-ROD DYSTROPHYA 19-year-old black woman was referred for poorvisual acuity of approximately 2 years' duration. Thepatient's only other complaint was that she seemed totake longer than usual to adjust to darkness. She gaveno specific history of poor colour vision or photo-sensitivity. The patient had noted no furtherreduction in central acuity, or increased difficulty inadjusting to darkness over the past 2 years. Thepatient was in good health and had no knownsystemic disorders. She was taking Ortho-Novum(tablets containing norethisterone) for birth control.A review of the family pedigree indicated that thepatient has a brother, age 26, who also has reducedvisual acuity that is uncorrectable with glasses. Hewas unavailable for examination. Two other brothersand two sisters were, by history, normal.

Vision was correctable to 20/100+1 OD with a-1-75 and 20/100+1 OS with a -3 50. The patientcould read J-2 at 6 inches without correction.External examination showed 20 prism dioptres ofleft exotropia for near and distance, but was other-wise normal. Slit-lamp examination of the cornea,anterior chamber, iris, and lens was similarly normal.The vitreous was moderately fibrillar but otherwiseunremarkable. Fundus examination showed normaloptic discs. The retinal arterioles were mildlyattenuated. Both maculas showed bilateral atrophic-looking lesions that had a bull's-eye appearance (theright fundus is shown in Fig. 1). Examination of theperipheral retina showed no evidence of pigmentaryabnormalities.

Visual field testing, with the 4-e-II and 2-e-II testtargets on a Goldmann perimeter, showed noperipheral depression or central scotomas. Colour

Fig. 1 Fundus photograph ofthe right eye ofpatient 1,showing a bull's-eye-like macular lesion.

vision was abnormal, with a large increase in thenumber of errors on the FM 100-hue test (with nospecific axis), and a shift toward the red setting on theNagel anomaloscope.

Absolute thresholds across the horizontal meridianof the visual field are shown in Fig. 2. Data areplotted in photopic units; coincident data points forthe middle and long wavelength test stimuli represent

0

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O -30

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-5

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80Nasal

80 40 20 0 20 40 60 80Retinal Temporal

Eccentricity (Deg)Fig. 2 Absolute thresholds across the horizontal meridianofthe righteye ofpatient Ifor long wavelength (filled circles)and middle wavelength (open circles) test stimuli. Shadedregions represent the range ofthresholds for 5 normalobservers.

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_3-E

1

(0

80 60 40 2.0 0 20 40 60 80Nasal Retinal Temporal

Eccentricity (Deg)Fig. 3 Light-adaptedflicker thresholds across thehorizontal meridian ofthe right eye ofpatient I for a 25 Hzwhite test stimulus (open circles). Shaded region representsthe range offlicker thresholds forfour normal observers.

cone-mediated absolute thresholds, whereas avertical separation of 2-6 log units indicatesrod-mediated thresholds for both test stimuli.Intermediate vertical separations indicate that conesdetect the long wavelength TS, while rods detect themiddle wavelength TS. 11 Dotted regions in Fig. 2represent the range of absolute threshold settings for5 normal subjects. For this patient absolute

thresholds are mediated by rods throughout thehorizontal meridian. (The absence of a central regionof cone-mediated thresholds is due to the patient'suse of a nonfoveal region for fixation.) Rodthresholds are elevated by at least 2 log unitsthroughout the retina, supporting the patient'scomplaint of nyctalopia.Cone sensitivity across the horizontal meridian of

the visual field, as measured by light-adapted flickerperimetry, is shown in Fig. 3, with the dotted regionrepresenting the range of flicker thresholds for 4normal observers. The patient had a loss of conesensitivity at all tested locations, indicating thediffuse nature of the dystrophy.The patient's ERG responses in comparison with

those of a normal subject are shown in Fig. 4. Verticalbars on the normal tracings represent90% confidencelimits for the mean of 21 (photopic white flash), 18(scotopic white flash), or 23 (blue flash) normalresponses. The top tracing shows the light-adaptedphotopic ERG. The a-wave is normal in amplitudebut prolonged in implicit time, while the b-waveamplitude is reduced to approximately 50% ofnormal, and the implicit time is prolonged (see Table1). The next 3 tracings show the single-flash ERGresponse after 5, 15, and 30 minutes of dark adapta-tion. The a-wave amplitude and implicit time are

Table 1 Summary ofERG responses

Photopicflash (white)

Patient no. a-wave b-wave

Amplitude* Implicit timet Amplitude: Implicit time§

1 Normal Prolonged (24 ms) Reduced (50 ,uV) Prolonged (42 ms)2 Normal Normal Normal Normal3 Normal Normal Normal Normal

Scotopicflash

Patient no. White flash Blueflash

a-wave b-wave b-wave

Amplitude Implicit time Amplitude** Implicit time Amplitudett Implicit timett

1 Normal Normal Supernormal Normal Reduced Prolonged(750 AV) (80,uV) (108 ms)

2 Normal Normal Supernormal Normal Supernormal Normal(800 AV) (460 MV)

3 Normal Normal Supernormal Normal Normal Normal(820 AV)

*'Normal' indicates that the value was within 90% confidence limits for the mean.t90% confidence limits= 14 to 20 ms, n=30.1:90% confidence limits= 100 to 180 ,uV, n=21.§90% confidence limits=26 to 34 ms, n=21.**90% confidence limits=400 to 610 AV, n= 18.tt9O% confidence limits= 190 to 300 ,uV, n=29.#490% confidence limits=80 to 92 ms, n=21.

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CONE - ROD DYSTROPHY

100 Pv L20 ms

NORMAL

Fig. 4 ERG responses for theright eye ofpatient 1 (left column)andfor a typical normal observer b

(right column) under the conditionsindicated. Vertical bars represent90% confidence limits for the mean b

of the normal responses.Calibration bars are shown at the \top.

a

within normal limits, but the b-wave amplitude isclearly supernormal, although normal in implicit time(Table 1). The bottom tracing represents the ERGresponse to a dim blue flash after 30 minutes of darkadaptation. While the b-wave amplitude to a brightflash is supernormal, the b-wave response to the dimblue flash is subnormal in amplitude and prolonged inimplicit time. The b-wave amplitude-intensityfunctions for this patient and for 2 normal subjectsare shown in Fig. 5. At low flash intensities the b-wave amplitude for the cone-rod dystrophy patient issubnormal, but the amplitude rapidly overtakes thenormal response and becomes supernormal at highflash intensities.

CASE 2: CONE DYSTROPHY

A 30-year-old white woman first noted blurred visionin each eye at approximately age 23. The blurredvision slowly increased in severity over the ensuing 3years. When first seen by the authors at age 26 shegave no history of photosensitivity, poor colourvision, or nyctalopia. The patient was otherwise ingood health and was not taking any medication. A

Scotopic White

Scotopic White

Scotopic White

in. Scotopic Blue

b

a

b

ASa

a

b

a

a

review of the family history was pertinent in that hermaternal grandparents were first cousins. There wereno other known family members with ocular disease.When the patient was initially seen, visual acuity

was correctable to 20/40+2 OD with a + 1 -00 and20/40-2 OS with a + 1 -00. External examinationshowed no abnormalities of ocular motility. Slit-lampexamination of the cornea, anterior chamber, lens,and vitreous were normal. Fundus examination dis-closed normal optic discs and retinal vessels. Therewas no evidence of any peripheral pigmentaryabnormalities. However, the patient had bilateralbull's-eye macular lesions (Fig. 6). The bull's-eyeappearance was accentuated on fluorescein angi-ography (Fig. 7).The patient was seen subsequently at age 30, 4

years after her initial examination. Visual acuity haddecreased to 20/200 OD but was still 20/40-2 OS.Grossly, the bull's-eye lesions were somewhat more

extensive than on her initial examination. The opticdiscs, retinal vessels, and peripheral retina remainednormal. At this time visual field testing with the 2-e-IItarget on a Goldmann perimeter showed normal

20 Y/O BF

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73Supernormal scotopic ERG in cone dystrophy

2

I-

0.E

0-3.5 -3.0 -2.5 -2.0 - 1.5 -1.0 -0.5 0.0

Log Relative Intensity

Fig. 5 A b-wave amplitude-intensity function for the lefteye ofpatient I (filled circles) andfor 2 normal observers(open symbols). Dashed line connects the mean ofthe 2normal values.

peripheral boundaries but bilateral central scotomas.Colour vision testing with the FM 100-hue and D-15tests showed normal findings. On the Nagel anomalo-scope the patient showed a shift toward red in theRayleigh equation.

Fig. 7 Fluorescein angiogram of the right eye ofpatient 2,in which a hyperfluorescent window defect accentuates thebull's-eye macular lesion shown in Fig. 6.

Absolute thresholds across the horizontal meridianof the visual field are shown in Fig. 8. The fovealthreshold for the long wavelength (cone-detected) TSis somewhat elevated. In the parafoveal andperipheral retina absolute thresholds are rod-mediated and within normal limits. Cone thresholdsobtained by flicker perimetry are shown in Fig. 9. Inthe fovea the flicker threshold is elevated, but coneflicker thresholds are within normal limits outside the

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coI--4-

0-J

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80 60 40 20 0 20Nasal Retinal

Eccentricity (Deg)

Fig. 6 Fundus photograph ofthe right eye ofpatient 2,showing a bull's-eye-like macular lesion.

Fig. 8 Absolute thresholds across the horizontal meridianofthe right eye ofpatient2for long wavelength (filled circles)and middle wavelength (open circles) test stimuli. Shadedregions represent the range ofthresholds for 5 normalobservers.

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Eccentricity (Deg)Fig. 9 Light-adaptedflicker thresholds across thehorizontal meridian ofthe right eye ofpatient2for a 25 Hzwhite test stimulus (open circles). Shaded region representsthe range offlicker thresholds for 4 normal observers.

fovea. In contrast to patient 1 this patient has adystrophy that is localised in the macula and affectsprimarily cone photoreceptors.The patient's ERG was tested on the initial visit

and then was retested 4 years later, with the findings

unchanged. The most recent results are shown in Fig.10. The photopic a- and b-waves (top tracing) arewithin normal limits, both in amplitude and inimplicit time, consistent with the localised nature ofthe dystrophy. Under dark-adapted conditions (next3 tracings), the a-wave amplitude and implicit timeare normal, as is the b-wave implicit time, but theb-wave amplitude is supernormal, even with the low-intensity blue flash (Table 1). The b-wave amplitude-intensity function (Fig. 11) confirms these findings.At low flash intensities the b-wave is somewhat largerthan normal and becomes considerably larger thannormal with higher flash intensities.

CASE 3: CONE DYSTROPHYA 31-year-old white woman's chief complaint waspoor central acuity, which she had experienced since5 years of age. The patient did not complain of photo-sensitivity, poor colour vision, or nyctalopia, andspecifically mentioned that her acuity was better atnight. The patient was otherwise in good health andwas not taking any medication. A review of the familypedigree was noninformative, since the patient wasadopted.

CONE DYSTROPHY

100 JvAL20 ms

30 Y/O WF

Fig. 10 ERG responses for theright eye ofpatient2 (left column)andfor a typical normal observer(right column) underthe conditionsindicated. Vertical bars represent90% confidence limits for the meanofthe normal responses.Calibration bars are shown at thetop. 5 mi. Scotopic White

\20 min Scotopic White

min Scotopic Blue

NORMAL

b

b

b

a

b

a

0

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Supernormal scotopic ERG in cone dystrophy

.9

.1

,

0

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/ ,,I._

-3.5 -3.0 -2.5 -2.0 -1.5 -1.o -0.5 0.0Log Relative Intensity

Fig. 11 A b-wave amplitude-intensity function for the righteye ofpatient 2 (filled circles) andfor 2 normal observers(open symbols). Dashed line connects the mean ofthe 2nornal values.

Visual acuity was correctable to 10/60(+1 OD with a

+4-75+-50x100, and 10/50+1 OS with a+5 25+ -25 x70 using a Feinbloom chart. The patientread J-7 at 12 inches (30 cm). External examinationshowed no abnormalities of ocular motility. Slit-lamp

Fig. 13 Fluorescein angiogram ofthe left eye ofpatient 3,showing window defects within the macula.

examination of the cornea, anterior chamber, lens,and vitreous was normal. Fundus examinationshowed normal optic discs and retinal vessels. Therewas no evidence of any peripheral pigmentary abnor-malities. The foveas exhibited bilateral, somewhatsubtle atrophic changes that had the appearance of abull's-eye pattern (Fig. 12). Fluorescein angiographyshowed bilateral window defects within the fovea,which somewhat highlighted the bull's-eye appear-ance of her atrophic changes (Fig. 13).

Visual field testing with the 4-e-II and 2-e-II test

0-

o -1-

E

0 2

'a0

0)

p0

/:j Reo

BGo

80 60 40 20 0 20 40Nasal Retinal

Eccentricity (Deg)

Fig. 12 Fundus photograph ofthe left eye ofpatient 3,depicting an atrophic macular lesion.

60 80Temporal

Fig. 14 Absolute thresholds across the horizontal meridianofthe right eye ofpatient3for long wavelength (filled circles)and middle wavelength (open circles) test stimuli. Shadedregions represent the range ofthresholds forS normalobservers.

9007

800

700-

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SI.co0-J

3-

2-

1-

0-

-1-

80 60 40 20 0 20 40 60 80Nasal Retinal Temporal

Eccentricity (Deg)

Fig. 15 Light-adaptedflicker thresholds across thehorizontal meridian ofthe right eye ofpatient3for a 25Hzwhite test stimulus (open circles). Shaded region representsthe range offlicker thresholds for4 normal observers.

targets on a Goldmann perimeter showed no evidenceof peripheral depression but did show bilateralcentral scotomas. Colour vision testing with the FM100-hue test demonstrated a bilateral tritan(blue-yellow) defect. The patient was technicallyunable to perform on the Nagel anomaloscope.

Absolute thresholds across the horizontal meridianare rod-mediated (Fig. 14). As with patient 1, theprofile missed the anatomical fovea due to a non-foveal fixation pattern. Within the central 40°absolute thresholds were elevated compared withnormal, but returned to normal values at the greatereccentricities. Cone flicker thresholds are presentedin Fig. 15. There was a slight loss of cone sensitivity inregions near the fovea but normal cone sensitivity atgreater eccentricities. As with the previous patient,the dystrophy was confined to the macular region.The ERG pattern for this patient has been

unchanged for 7 years. The most recent results areshown in Fig. 16. The photopic ERG showsamplitudes and implicit times that are within normallimits, consistent with the localised nature of thedystrophy. The dark-adapted a-wave amplitudes andimplicit times, as well as the b-wave implicit times,are normal (Table 1). The b-wave response to thedim blue flash is within normal limits. However, theb-wave elicited by the white flash is of supernormalamplitude. An amplitude-intensity function (Fig. 17)shows that the dark-adapted b-wave is normal at lowflash intensities, but becomes supernormal withbright flashes.

CONE DYSTROPHY

00 AvL20 ms

31 Y/O WF NORMAL

Fig. 16 ERG responsesfor theright eye ofpatient3 (left column)andfor a typical normal observer(right column) underthe conditionsindicated. Vertical bars represent90o% confidence limitsfor the meanofthe normal responses.Calibration bars are shown at thetop.

While

min. Scotopic White

White

min. Scotopic Blue

b

a

b

0 b

a

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Supernormal scotopic ERG in cone dystrophy 7

900

800-

700-

2 600E

500-

E 400-

300o

200

10010 -

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

Log Relative Intensity

Fig. 17 A b-wave amplitude-intensity function for the righteye ofpatient 3 (filled circles) andfor 2 normal observers(open symbols). Dashed line connects the mean of t-he 2normnal values.

Discussion

The 3 patients with cone dystrophy described in thisreport have a supernormnal dark-adapted b-waveresponse to a moderately intense light flash. Aconsideration of inheritance patterns suggests thatthe dystrophy may be an autosomal recessive trait. Inseveral respects patient 1 resembles the 2 patientsreported by Gouras et al.'10 Patient 1 has reducedacuity, decreased colour vision, nyctalopia, adiminished photopic ERG, and a dark-adapted b-wave amplitude that is subnormal with dim flashesand superonoral with brighter flashes. Unlike the 2patients reported previously'0 patient 1 has a bull's-eye macular lesion (rather than a nonspecific maculargranularity), with an absence of sensitivity to light.Patients 2 and 3 also have a supernormal dark-adapted b-wave, but they appear to represent adifferent type, or perhaps stage, of cone dystrophy.For both patients the dystrophy is restricted to themacular region rather than being a diffuse cone-rodloss. The scotopic b-wave is normnal or larger thannormal at low flash intensities, rather than subnormalas with patient 1.

T'he pathogenesis of the supernormal scotopic b-wave is uncertain. The ERG b-wave is thought toarise predominantly from the Mueller cells in

response to changes in the concentration of extra-cellular potassium that result from the activity ofretinal neurons.'4 The supernormal scotopic b-waveobserved in these patients with cone dystrophy maybe due to an abnormnality in this process. Alternatively'Gouras et al.'0 have suggested that the abnormalERG may result from an increase in the level of cyclicguanosine monophosphate (cGMP) in the rod photo-receptors, which in turn leads to an abnormal photo-receptor response.Other conditions besides cone dystrophy have been

reported in association with a supernormal ERG inhumans, including albinism,'" hyperthyroidism,'6corticosteroid administration,"7 optic atrophy,'8 andretinal vascular disorders.'91We have not been able toimplicate any of these factors in the abnormal ERGresponse in our patients. A supernormal b-wave hasalso been reported to accompany an increase in Po, inthe isolated perfused cat eye."0 However, therelationship between this finding and the results fromour patients is uncertain. Although the pathogenesisof the supernormal scotopic b-wave in these patientswith cone dystrophy is unclear, the abnormal b-waverepresents a diagnostic device that may prove usefulin the clinical delineation of cone dystrophy geno-copies, which currently appear to be a heterogeneousgroup of conditions under the same diagnostic label.

Supported by NIH Training Grant EY07038, NIH Core GrantEY01792, and a grant from the National Retinitis PigmentosaFoundation.We thank Dr M. F. Goldberg and Ms M. Gere for helpful

comments on the manuscript.

Refeirences

1ISorsby A, Davey HE. Dominant macular dystrophy. Br JOphthalmol 1955; 39:385-97.

2 Goodman 0, Ripps H, Siegel IM. Cone dysfunction syndromes.Arch Ophthalmol 1963; 70:214-31.

3 Berson EL, Gouras P, Gunkel RD. Progressive cone degenera-tion, dominantly inherited. Arch Ophthalmol 1968; S0: 77-83.

4 Krill AE, Deutman AF. Dominant macular degenerations; thecone dystrophies. AmiJ Ophthalmol 1972; 73:352-69.

5 Krill AE, Deutman AF, Fishman M. The cone degenerations.Doc Ophthalmol 1973; 35: 1-80.

6 Franeois J, DeRouck A, Verriest G, etal. Progressive generalizedcone dysfunction. Ophthalmologica 1974; 169: 255-84.

7 Berson EL, Gouras P, Gunkel RD. Progressive cone-roddystrophy. Arch Ophthalmol 1968; 80:68-76.

8 Hittner HM, Murphree AL, Garcia CA, et aL. Dominant cone-rod dystrophy. Doc Ophthalmol 1975; 39: 29-52.

9 Fishman GA. Progressive human cone-rod dysfunction(dystrophy). Trans Am Acad Ophthalmol Otolaryngol 1976; 81:716-24.

10 Gouras P, Eggers HM, MacKay CJ. Cone dystrophy. nyctalopiaand supernormal rod responses: a new retinal degeneration. ArchOphthalmol 1983; 101: 718-24.

11Fishman GA, Buckman G, Van Every T. Fundus flavimaculatus:a clinical classification. Doc Ophthalmol Proc Ser 1977; 13:213-20.

12 Massof RW, Finkelstein D. Two forms of autosomal dominantprimary retinitis pigmentosa. Doc Ophthalmol 1981; 51:289-346.

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13 King-Smith PE, Carden D. Luminance and opponent-colorcontributions to visual detection and adaptation and to temporaland spatial integration. J Opt SocAm 1976; 66: 709-17.

14 Kline R, Ripps H, Dowling JE, Generation of b-wave currents inthe skate retina. Proc Nad Acad Sci USA 1978; 75: 5727-31.

15 Krill AE, Lee GB. The electroretinogram in albinos and carriersof the ocular albino trait. Arch Ophthalmol 1963; 69: 32-8.

16 Pearlman JT, Burian HM. Electroretinographic findings inthyroid dysfunction. Am J Ophthalmol 1964; 58: 216-25.

17 Zimmerman TJ, Dawson WW, Fitzergald CR. Electroretino-

graphic changes in normal eyes during administration ofprednisone. Ann Ophthalmol 1973; 5: 757-65.

18 Feinsod M, Rowe H, Auerbach E. Changes in the electroretino-gram in patients with optic nerve lesions. Doc Ophthalmol 1971;29: 169-200.

19 Henkes HE. Electroretinography. An evaluation of the influenceof the retinal and general metabolic condition on the electricalresponse of the retina. Am J Ophthalmol 1957; 43: 67-81.

20 Niemeyer G. ERG dependence on flow rate in the isolated andperfused mammalian eye. Brain Res 1973; 57: 203-7.

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Documents

Supernormal scotopic ERG in cone dystrophy · In response to a white flash ofmoderate intensity the scotopic b-wave amplitude wasconsiderably larger than normal. Onepatient had elevated