A contact lens for routine electroretinography which contains a Ganzfeld light source is described. The light source consists of six light-emitting diodes and serves both as a stimulus source and a background illumination. The response characteristics with this source are comparable with those of an integrating sphere stimulator

Damhof, A

Kooijman, AC

English

University of Groningen

   University of GroningenErg lens with built-in ganzfeld light-source for stimulation and adaptationKooijman, AC; Damhof, APublished in:Investigative ophthalmology & visual scienceIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1980Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Kooijman, AC., & Damhof, A. (1980). Erg lens with built-in ganzfeld light-source for stimulation andadaptation. Investigative ophthalmology & visual science, 19(3), 315-318.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019Volume 19Number 3 Reports 315The results of the study on the efficacy of CP-45,634 in delaying cataract development in dia-betic rats are depicted in Fig. 1. Within 3 weeksafter the onset of diabetes, small vacuoles in theequatorial region appeared in the lens of a diabeticrat. This change was followed by a diffuse but un-even cloudiness in the anterior subcapsular re-gion. In some cases the posterior subcapsular re-gion was involved, but the anterior region wasmuch more severely affected. As the cataractprogressed, there was considerable disruption ofthe cortical fibers, leading to diffuse but markedclouding of this region. In 6 to 9 weeks a densenuclear opacity appeared. However, the strikingfact was that in diabetic rats treated with CP-45,634, none of these lens changes occurred. Evenafter 5 months, the early lens changes were notdetected by slit-lamp examination in any of the 36diabetic rats treated with CP-45,634.Discussion. The AR inhibitor CP-45,634 ishighly potent and effective in animals. Previously,Peterson et al.2 found that CP-45,634 adminis-tered orally at a dose of 5 to 10 mg/kg/day togalactose-fed rats delayed lens changes so thatonly 10% of treated rats developed any lensopacities after 29 days on the galactose diet. At thesame time untreated galactose-fed rats all devel-oped lens opacities after 15 days on the diet. Inour study with diabetic rats where we used ahigher daily dose of 60 mg/kg, cataract formationappeared to be prevented. During the 5-monthperiod no discernible lens changes were observedby slit-lamp examination of the diabetic ratstreated with the AR inhibitor, whereas lenschanges in the untreated diabetic rats were de-tected within 3 weeks after onset of diabetes. Inaddition, the sorbitol level in the lenses of treateddiabetic rats was not significantly elevated.In contrast to the low dose of the Pfizer inhibitornecessary to alter the course of cataract formationin diabetic rats, a much higher dose of quercitrinwas used in delaying cataracts in diabetic degus.4In those studies quercitrin at a level of approxi-mately 700 mg/kg was administered orally to re-tard the development of the nuclear opacity.4In the quercitrin-treated diabetic degus, lenschanges in the form of vacuoles did appear, indi-cating that the cataractous process was not com-pletely abolished.The effectiveness of CP-45,634 in retarding thecataractous process in diabetic rats and the delay-ing of cataract formation in diabetic degus byquercitrin treatment strongly indicate that AR isinvolved in the initiation of diabetes cataracts. Thestudy also suggests the possibility that AR inhibi-tors may be useful clinically in altering the courseof human diabetes cataracts.From the Laboratory of Vision Research, NationalEye Institute, National Institutes of Health, Bethesda,Md. Submitted for publication Sept. 14, 1979. Reprintrequests: Jin H. Kinoshita, Laboratory of Vision Re-search, NEI, 9000 Rockville Pike, Bldg. 6, rm. 222,Bethesda, Md. 20205.Key words: diabetes cataracts, aldose reductase, sorbitolREFERENCES1. Kinoshita JH: Mechanisms initiating cataract forma-tion (Proctor Lecture). INVEST OPHTHALMOL 13:713,1974.2. Peterson MT, Sarges R, Aldinger CE, and Mac-Donald DP: CP-45,634: a novel aldose reductase in-hibitor that inhibits polyol pathway activity in dia-betic and galactosemic rats. Metabolism 28:456,1979.3. Hayman S, Lou MF, Merola LO, and Kinoshita JH:Aldose reductase activity in the lens and other tis-sues. Biochim Biophys Acta 128:474, 1966.4. Varma SD, Mikuni I, and Kinoshita JH: Flavonoids asinhibitors of lens aldose reductase. Science 182:1146,1973.ERG lens with built-in Ganzfeld light sourcefor stimulation and adaptation. AART C.KOOIJMAN AND ALBERT D A M H O F .A contact lens for routine electroretinography which con-tains a Ganzfeld light source is described. The lightsource consists of six light-emitting diodes and servesboth as a stimulus source and a background illumination.The response characteristics with this source are compa-rable with those of an integrating sphere stimulator.For clinical electroretinography generally aGanzfeld stimulus is required. This is done toavoid indirect stimulation of a part of the retinathrough stray light and to obtain maximal re-sponses.Usually an integrating sphere is used with axenon flash tube attached to it, and, if an adaptingbackground is required, a second light source isalso incorporated. In this report we describean electroretinogram (ERG) contact lens with abuilt-in Ganzfeld light source which serves bothfor stimulation and for adaptation.It proved possible to obtain identical ERGs withthis light-emitting diode (LED) stimulator and anintegrating sphere stimulator.Methods. The design of our contact lens with0146-0404/80/030315+04$00.40/0 © 1980 Assoc. for Res. in Vis. and Ophthal., Inc.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018316 Reports invest- Ophthahnol. Vis, Set,March 1980Fig. 1. Diffuse ERG lens with Ganzfeld light source. A, Corneal part of the scleral lens is madeof diffusely translucent plastic to scatter the light emitted by the six LEDs. B, Six LEDs areground off to fit them in a compact unit which can be placed on the corneal part of the contactlens. The convex frontal surfaces of the LEDs are polished concave to increase the distributionangle of the emitted light. The combination of the diffusing cornea! lens with the flat LEDsgives a light distribution on the cornea which is comparable to the light distribution of lightrays arising from an integrating sphere stimulator, The ERG lens contains a corneal ringelectrode.Fig. 2, Contact lens with LED unit placed on theeye.built-in sitmulator is a modified Henkes type con-tact lens (Figs. 1 and 2). On the outer surface ahollow Perspex cylinder was made with a diameterof about 12 mm and a height of 15 mm. Into thishollow cylinder fits an array of six yellow-green(peak 570 mn, half-width 25 nm) LEDs (SiemensLD57C). The convex frontal surfaces are polishedto a concave shape to increase the distributionangle of the emitting light and to fit closely thefrontal surface of the contact lens. The corneal partof the scleral lens is made of diffusely translucentplastic and covers the whole cornea.The combination of the LED array and theopaline corneal lens makes the distribution of thelight rays which reach the cornea equal to the dis-tribution of a Ganzfeld. The illumination energy atthe cornea can be selected in steps of 0.5 log unitbetween 10~3 to 10 lux • sec by changing thestimulus flash duration (minimal 3 ftsec and maxi-mal 30 msec). This compares well with the stimu-lus energy range of our Ganzfeld sphere stimulatorwith the white xenon flash (General ElectricStrobotac). In this apparatus the maximum energyis 3 lux • sec and can be reduced by neutral den-sity filters (Agfa-Gevaert gelatin filters).The LED stimulator can also serve as an adapt-ing background. In that case a direct current iscontinuously passed through the LEDs, and theflashes are given as additional short-lasting currentpulses. The maximum corneal illumination is 10lux. With the integrating sphere the adaptingbackground is given by incandescent lamps, andthe corneal illumination is 5 lux.The responses to both types of stimulus weremeasured in the same eye. The subject dark-adapted during 30 min before the start of the mea-surements. The pupil was dilated by 2 drops oftropicamide (0.5%). Measurements were taken inone session in the following order; (1) white flashstimulation in the dark, (2) LED flash stimulationDownloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018Volume 19Number 3 Reports 317in the dark, (3) light adaptation by the LED lightsource, (4) LED flash stimulation on the adaptingbackground, (5) light adaptation in the spherestimulator, and (6) white flash stimulation on theadaptinq background. Nine subjects participatedin these measurements.Results. Typical examples of responses withboth the LED and the sphere stimulator areshown in Fig. 3. None of the sets of responses toboth stimulators of the subjects showed differ-ences greater than those presented in this figure.The amplitudes of a and b wave and the implicittime of the b wave of the responses with the LEDstimulus of nine subjects are plotted in Fig. 4.Several subjects preferred the LED stimulatorabove the sphere stimulator because they werefrightened by the loud click with the discharge ofthe flash tube whereas the LED stimulator wassilent.Discussion. The LED stimulator in a light-diffusing contact lens can replace the integratingsphere stimulator for routine ERG measurementswith Ganzfeld stimulation. The LEDs can produceflash stimuli in a large energy range and simulta-neously can provide an adapting background.These stimulus conditions are required for thestandardized ERG-measuring procedure of theNetherlands Group Physical Methods in Oph-thalmology. 1 A single LED in a clear contact lens2seems less suitable for routine ERG measure-ments because the response characteristics areinfluenced by the pupil diameter and it is not pos-sible to make a Ganzfeld adapting background.With an incandescent lamp as light source3 it is notpossible to stimulate with short flashes, and itsintensity range is rather short. The yellow-greencolor of the LEDs is no disadvantage vs. the whitexenon flash. The sensitivity of the rod system forthis color is much larger than that of the conesystem. Therefore it is possible (1) to measure theisolated rod response in a large stimulus energyrange and (2) to use the LEDs as a very effectiveadapting light for rod response suppression tomeasure isolated cone responses. In normal aswell as in protanomalous and deuteranomaloussubjects the yellow-green color is able to stimulatethe cone system.4The control of stimulus energy and backgroundillumination can be done electronically with theuse of LEDs. This is much simpler than the hybridcontrol with filters and electronics in an integrat-ing sphere stimulator. Furthermore, the con-struction of the contact lens with the LEDstimulator is much cheaper than that of an inte-grating sphere-flash arrangement.100 msFig, 3. Scotopic condition; dark adapted subject.A, ERG responses to a white flash stimulus. B,ERG responses to a yellow-green LED stimulus.Traces are averages of 10 responses (1 stimulusflash/sec).-200 -2 1 0 1 0 0.5log stimulus energy (lux s)Fig. 4. Characteristics of the responses of ninesubjects measured with the Ganzfeld contact lensstimulator. Left, scotopic condition; right, pho-topic condition.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018318 Reports Invest. Ophthalmol. Vis. Sci.March 1980We are indebted to Dr. G. van Lith, Oogziekenhuis,Rotterdam, and to Dr. D. van Norren, Ooglijdersgast-huis, Utrecht, for testing our lens design and for sug-gestions for improvement in the manuscript.From the Kliniek voor Oogheelkunde, Rijks-Universi-teit Groningen, Groningen, The Netherlands. Submit-ted for publication July 2, 1979. Reprint requests: AartC. Kooijman, Kliniek voor Oogheelkunde, Rijks-Uni-versiteit Groningen, Oostersingel 59, 9713 EZ Gronin-gen, The Netherlands.Key words: ERG, Ganzfeld stimulator, LED lightREFERENCES1. Thijssen JM, Braakhuis W, Pinckers A, and van LithG: Standardized electro-ophthalmography. In Pro-ceedings of the 170th meeting of the NetherlandsOphthalmological Society. Junk, The Hague, 1976,p. 185.2. Krakau CET, Nordenfelt L, and Ohmen R: RoutineERG recording with LED light stimulus. Ophthal-mologica 175:199, 1977.3. Brodner H: ERG-Test fur die Praxis. Klin MonatsblAugenheilkd 167:909, 1975.4. Kooijman AC, Bos LPM, and te Strake, L: Differ-entiation of cone and rod responses in the humanERG by means of colour frequency characteristics. InProceedings of the Xlth ISCERG Symposium. DocOphthalmol Proc Ser 4:59, 1974.The scalp topography of the human visuallyevoked subcortical potential. G. F. A.HARDING AND M. P. RUBINSTEIN.Stimulus and analysis parameters have been adjusted toprovide optimum conditions for producing and recordingthe early components of flash visual evoked potentials. Avisual evoked subcortical potential (VESP) of mean la-tency f>23"^ 28"^ >34 has been recorded in 86% of subjects.The triphasic wave was maximal at an electrode positionslightly posterior to the RolandicISylvian fissure and to-pographically separate from the lid electroretinogramand the visual evoked cortical potential. Monocularstimulation shows bilateral reduction of the amplitude ofthe VESP, indicating that the wave is independent of theretina and optic nerve and must be arising from apostchiasmal site.The early components, i.e., components before50 msec latency, of the visually evoked potential inman are poorly documented because of theirminute amplitude, intersubject variability, andpoor repeatability under the standard experimen-tal conditions used for eliciting the visual evokedcortical potential (VECP).1Van Hasselt2 reported an "ear-mastoid" poten-tial of 10 msec latency which could only be re-corded in a small percentage of subjects and sug-gested the optic nerve as its origin. Cracco andCracco3 described early oscillatory potentials at100 cy/sec recorded from a wide scalp distributionof electrodes, referred to earlobe electrodes. Earlyin 1979 we identified a triphasic positive-negative-positive component (msec) in some sub-jects at latencies of positive 22 (P22)> negative 27(N27), and positive 35 (Pas).4 Since it appeared im-portant to delineate this component from both thescalp-recorded ERG and the VECP, we have car-ried out a topographic study of the scalp dis-tribution.Materials and method. Observations were madeon 14 normal volunteer subjects (eight male andsix female) ages between 19 and 38 years (mean 26years). All had visual acuities of 6/6 or better. Forthis topographical study, electrodes were placedaccording to the International 10/20 system.5 Inthe first study, an anterior-posterior series of elec-trodes at FPZ, F8, T4, T6, and Oz and half-distanceelectrodes at F8V4 and T4% were used (Fig. 1). Forthe study of the transverse distribution, electrodeswere placed at C4, C6, T4, and T8 and at CP4, CP6,T4&, and T8V!, (Fig. 2). All recordings were madewith common reference, but the choice of a rela-tively inactive reference site was confounded byboth the ERG and VECP. Investigation of com-monly used reference sites shows that the mid-frontal (Fz) was affected by the ERG and both theearlobe and mastoid were highly active for theP22-N2rP35 component. Indeed it is likely that theactive nature of this site6 is probably responsiblefor some so-called early components of the visuallyevoked potential. It was found that the vertex site(Cz) was relatively inactive at the latency of theearly components and had the added advantage ofbeing equidistant from all the electrodes in theanterior-posterior chain.This site was also used for the transverse topo-graphic study, but since the rules of equal in-terelectrode distance are negated, a further refer-ence on the anterior neck was used for compari-son. The subjects were seated in a dimly lit room,and flash stimulation was delivered by a GrassPS22 photostimulator 25 cm from the eyes.Silver-silver chloride electrodes were affixed withcollodion, and the resistance was maintainedbelow 5 Kohm. A PDP8E computer was used toaverage the response from each of the eight chan-nels of the electroencephalogram recorded on anElema Schonander machine. The analysis timewas 100 msec, and the bandpass of the equipmentwas from 66 to 700 Hz.To maximize the signal, it was found necessaryto average the response to 500 stimuli delivered at0146-0404/80/030318+04$00.40/0 © 1980 Assoc. for Res. in Vis. and Ophthal., Inc.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018

Erg lens with built-in ganzfeld light-source for stimulation and adaptation

ARTS repository - University of Groningen

   University of GroningenErg lens with built-in ganzfeld light-source for stimulation and adaptationKooijman, AC; Damhof, APublished in:Investigative ophthalmology & visual scienceIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1980Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Kooijman, AC., & Damhof, A. (1980). Erg lens with built-in ganzfeld light-source for stimulation andadaptation. Investigative ophthalmology & visual science, 19(3), 315-318.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 07-06-2022Volume 19Number 3 Reports 315The results of the study on the efficacy of CP-45,634 in delaying cataract development in dia-betic rats are depicted in Fig. 1. Within 3 weeksafter the onset of diabetes, small vacuoles in theequatorial region appeared in the lens of a diabeticrat. This change was followed by a diffuse but un-even cloudiness in the anterior subcapsular re-gion. In some cases the posterior subcapsular re-gion was involved, but the anterior region wasmuch more severely affected. As the cataractprogressed, there was considerable disruption ofthe cortical fibers, leading to diffuse but markedclouding of this region. In 6 to 9 weeks a densenuclear opacity appeared. However, the strikingfact was that in diabetic rats treated with CP-45,634, none of these lens changes occurred. Evenafter 5 months, the early lens changes were notdetected by slit-lamp examination in any of the 36diabetic rats treated with CP-45,634.Discussion. The AR inhibitor CP-45,634 ishighly potent and effective in animals. Previously,Peterson et al.2 found that CP-45,634 adminis-tered orally at a dose of 5 to 10 mg/kg/day togalactose-fed rats delayed lens changes so thatonly 10% of treated rats developed any lensopacities after 29 days on the galactose diet. At thesame time untreated galactose-fed rats all devel-oped lens opacities after 15 days on the diet. Inour study with diabetic rats where we used ahigher daily dose of 60 mg/kg, cataract formationappeared to be prevented. During the 5-monthperiod no discernible lens changes were observedby slit-lamp examination of the diabetic ratstreated with the AR inhibitor, whereas lenschanges in the untreated diabetic rats were de-tected within 3 weeks after onset of diabetes. Inaddition, the sorbitol level in the lenses of treateddiabetic rats was not significantly elevated.In contrast to the low dose of the Pfizer inhibitornecessary to alter the course of cataract formationin diabetic rats, a much higher dose of quercitrinwas used in delaying cataracts in diabetic degus.4In those studies quercitrin at a level of approxi-mately 700 mg/kg was administered orally to re-tard the development of the nuclear opacity.4In the quercitrin-treated diabetic degus, lenschanges in the form of vacuoles did appear, indi-cating that the cataractous process was not com-pletely abolished.The effectiveness of CP-45,634 in retarding thecataractous process in diabetic rats and the delay-ing of cataract formation in diabetic degus byquercitrin treatment strongly indicate that AR isinvolved in the initiation of diabetes cataracts. Thestudy also suggests the possibility that AR inhibi-tors may be useful clinically in altering the courseof human diabetes cataracts.From the Laboratory of Vision Research, NationalEye Institute, National Institutes of Health, Bethesda,Md. Submitted for publication Sept. 14, 1979. Reprintrequests: Jin H. Kinoshita, Laboratory of Vision Re-search, NEI, 9000 Rockville Pike, Bldg. 6, rm. 222,Bethesda, Md. 20205.Key words: diabetes cataracts, aldose reductase, sorbitolREFERENCES1. Kinoshita JH: Mechanisms initiating cataract forma-tion (Proctor Lecture). INVEST OPHTHALMOL 13:713,1974.2. Peterson MT, Sarges R, Aldinger CE, and Mac-Donald DP: CP-45,634: a novel aldose reductase in-hibitor that inhibits polyol pathway activity in dia-betic and galactosemic rats. Metabolism 28:456,1979.3. Hayman S, Lou MF, Merola LO, and Kinoshita JH:Aldose reductase activity in the lens and other tis-sues. Biochim Biophys Acta 128:474, 1966.4. Varma SD, Mikuni I, and Kinoshita JH: Flavonoids asinhibitors of lens aldose reductase. Science 182:1146,1973.ERG lens with built-in Ganzfeld light sourcefor stimulation and adaptation. AART C.KOOIJMAN AND ALBERT D A M H O F .A contact lens for routine electroretinography which con-tains a Ganzfeld light source is described. The lightsource consists of six light-emitting diodes and servesboth as a stimulus source and a background illumination.The response characteristics with this source are compa-rable with those of an integrating sphere stimulator.For clinical electroretinography generally aGanzfeld stimulus is required. This is done toavoid indirect stimulation of a part of the retinathrough stray light and to obtain maximal re-sponses.Usually an integrating sphere is used with axenon flash tube attached to it, and, if an adaptingbackground is required, a second light source isalso incorporated. In this report we describean electroretinogram (ERG) contact lens with abuilt-in Ganzfeld light source which serves bothfor stimulation and for adaptation.It proved possible to obtain identical ERGs withthis light-emitting diode (LED) stimulator and anintegrating sphere stimulator.Methods. The design of our contact lens with0146-0404/80/030315+04$00.40/0 © 1980 Assoc. for Res. in Vis. and Ophthal., Inc.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018316 Reports invest- Ophthahnol. Vis, Set,March 1980Fig. 1. Diffuse ERG lens with Ganzfeld light source. A, Corneal part of the scleral lens is madeof diffusely translucent plastic to scatter the light emitted by the six LEDs. B, Six LEDs areground off to fit them in a compact unit which can be placed on the corneal part of the contactlens. The convex frontal surfaces of the LEDs are polished concave to increase the distributionangle of the emitted light. The combination of the diffusing cornea! lens with the flat LEDsgives a light distribution on the cornea which is comparable to the light distribution of lightrays arising from an integrating sphere stimulator, The ERG lens contains a corneal ringelectrode.Fig. 2, Contact lens with LED unit placed on theeye.built-in sitmulator is a modified Henkes type con-tact lens (Figs. 1 and 2). On the outer surface ahollow Perspex cylinder was made with a diameterof about 12 mm and a height of 15 mm. Into thishollow cylinder fits an array of six yellow-green(peak 570 mn, half-width 25 nm) LEDs (SiemensLD57C). The convex frontal surfaces are polishedto a concave shape to increase the distributionangle of the emitting light and to fit closely thefrontal surface of the contact lens. The corneal partof the scleral lens is made of diffusely translucentplastic and covers the whole cornea.The combination of the LED array and theopaline corneal lens makes the distribution of thelight rays which reach the cornea equal to the dis-tribution of a Ganzfeld. The illumination energy atthe cornea can be selected in steps of 0.5 log unitbetween 10~3 to 10 lux • sec by changing thestimulus flash duration (minimal 3 ftsec and maxi-mal 30 msec). This compares well with the stimu-lus energy range of our Ganzfeld sphere stimulatorwith the white xenon flash (General ElectricStrobotac). In this apparatus the maximum energyis 3 lux • sec and can be reduced by neutral den-sity filters (Agfa-Gevaert gelatin filters).The LED stimulator can also serve as an adapt-ing background. In that case a direct current iscontinuously passed through the LEDs, and theflashes are given as additional short-lasting currentpulses. The maximum corneal illumination is 10lux. With the integrating sphere the adaptingbackground is given by incandescent lamps, andthe corneal illumination is 5 lux.The responses to both types of stimulus weremeasured in the same eye. The subject dark-adapted during 30 min before the start of the mea-surements. The pupil was dilated by 2 drops oftropicamide (0.5%). Measurements were taken inone session in the following order; (1) white flashstimulation in the dark, (2) LED flash stimulationDownloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018Volume 19Number 3 Reports 317in the dark, (3) light adaptation by the LED lightsource, (4) LED flash stimulation on the adaptingbackground, (5) light adaptation in the spherestimulator, and (6) white flash stimulation on theadaptinq background. Nine subjects participatedin these measurements.Results. Typical examples of responses withboth the LED and the sphere stimulator areshown in Fig. 3. None of the sets of responses toboth stimulators of the subjects showed differ-ences greater than those presented in this figure.The amplitudes of a and b wave and the implicittime of the b wave of the responses with the LEDstimulus of nine subjects are plotted in Fig. 4.Several subjects preferred the LED stimulatorabove the sphere stimulator because they werefrightened by the loud click with the discharge ofthe flash tube whereas the LED stimulator wassilent.Discussion. The LED stimulator in a light-diffusing contact lens can replace the integratingsphere stimulator for routine ERG measurementswith Ganzfeld stimulation. The LEDs can produceflash stimuli in a large energy range and simulta-neously can provide an adapting background.These stimulus conditions are required for thestandardized ERG-measuring procedure of theNetherlands Group Physical Methods in Oph-thalmology. 1 A single LED in a clear contact lens2seems less suitable for routine ERG measure-ments because the response characteristics areinfluenced by the pupil diameter and it is not pos-sible to make a Ganzfeld adapting background.With an incandescent lamp as light source3 it is notpossible to stimulate with short flashes, and itsintensity range is rather short. The yellow-greencolor of the LEDs is no disadvantage vs. the whitexenon flash. The sensitivity of the rod system forthis color is much larger than that of the conesystem. Therefore it is possible (1) to measure theisolated rod response in a large stimulus energyrange and (2) to use the LEDs as a very effectiveadapting light for rod response suppression tomeasure isolated cone responses. In normal aswell as in protanomalous and deuteranomaloussubjects the yellow-green color is able to stimulatethe cone system.4The control of stimulus energy and backgroundillumination can be done electronically with theuse of LEDs. This is much simpler than the hybridcontrol with filters and electronics in an integrat-ing sphere stimulator. Furthermore, the con-struction of the contact lens with the LEDstimulator is much cheaper than that of an inte-grating sphere-flash arrangement.100 msFig, 3. Scotopic condition; dark adapted subject.A, ERG responses to a white flash stimulus. B,ERG responses to a yellow-green LED stimulus.Traces are averages of 10 responses (1 stimulusflash/sec).-200 -2 1 0 1 0 0.5log stimulus energy (lux s)Fig. 4. Characteristics of the responses of ninesubjects measured with the Ganzfeld contact lensstimulator. Left, scotopic condition; right, pho-topic condition.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018318 ReportsInvest. Ophthalmol. Vis. Sci.March 1980We are indebted to Dr. G. van Lith, Oogziekenhuis,Rotterdam, and to Dr. D. van Norren, Ooglijdersgast-huis, Utrecht, for testing our lens design and for sug-gestions for improvement in the manuscript.From the Kliniek voor Oogheelkunde, Rijks-Universi-teit Groningen, Groningen, The Netherlands. Submit-ted for publication July 2, 1979. Reprint requests: AartC. Kooijman, Kliniek voor Oogheelkunde, Rijks-Uni-versiteit Groningen, Oostersingel 59, 9713 EZ Gronin-gen, The Netherlands.Key words: ERG, Ganzfeld stimulator, LED lightREFERENCES1. Thijssen JM, Braakhuis W, Pinckers A, and van LithG: Standardized electro-ophthalmography. In Pro-ceedings of the 170th meeting of the NetherlandsOphthalmological Society. Junk, The Hague, 1976,p. 185.2. Krakau CET, Nordenfelt L, and Ohmen R: RoutineERG recording with LED light stimulus. Ophthal-mologica 175:199, 1977.3. Brodner H: ERG-Test fur die Praxis. Klin MonatsblAugenheilkd 167:909, 1975.4. Kooijman AC, Bos LPM, and te Strake, L: Differ-entiation of cone and rod responses in the humanERG by means of colour frequency characteristics. InProceedings of the Xlth ISCERG Symposium. DocOphthalmol Proc Ser 4:59, 1974.The scalp topography of the human visuallyevoked subcortical potential. G. F. A.HARDING AND M. P. RUBINSTEIN.Stimulus and analysis parameters have been adjusted toprovide optimum conditions for producing and recordingthe early components of flash visual evoked potentials. Avisual evoked subcortical potential (VESP) of mean la-tency f>23"̂ 28"̂ >34 has been recorded in 86% of subjects.The triphasic wave was maximal at an electrode positionslightly posterior to the RolandicISylvian fissure and to-pographically separate from the lid electroretinogramand the visual evoked cortical potential. Monocularstimulation shows bilateral reduction of the amplitude ofthe VESP, indicating that the wave is independent of theretina and optic nerve and must be arising from apostchiasmal site.The early components, i.e., components before50 msec latency, of the visually evoked potential inman are poorly documented because of theirminute amplitude, intersubject variability, andpoor repeatability under the standard experimen-tal conditions used for eliciting the visual evokedcortical potential (VECP).1Van Hasselt2 reported an "ear-mastoid" poten-tial of 10 msec latency which could only be re-corded in a small percentage of subjects and sug-gested the optic nerve as its origin. Cracco andCracco3 described early oscillatory potentials at100 cy/sec recorded from a wide scalp distributionof electrodes, referred to earlobe electrodes. Earlyin 1979 we identified a triphasic positive-negative-positive component (msec) in some sub-jects at latencies of positive 22 (P22)> negative 27(N27), and positive 35 (Pas).4 Since it appeared im-portant to delineate this component from both thescalp-recorded ERG and the VECP, we have car-ried out a topographic study of the scalp dis-tribution.Materials and method. Observations were madeon 14 normal volunteer subjects (eight male andsix female) ages between 19 and 38 years (mean 26years). All had visual acuities of 6/6 or better. Forthis topographical study, electrodes were placedaccording to the International 10/20 system.5 Inthe first study, an anterior-posterior series of elec-trodes at FPZ, F8, T4, T6, and Oz and half-distanceelectrodes at F8V4 and T4% were used (Fig. 1). Forthe study of the transverse distribution, electrodeswere placed at C4, C6, T4, and T8 and at CP4, CP6,T4&, and T8V!, (Fig. 2). All recordings were madewith common reference, but the choice of a rela-tively inactive reference site was confounded byboth the ERG and VECP. Investigation of com-monly used reference sites shows that the mid-frontal (Fz) was affected by the ERG and both theearlobe and mastoid were highly active for theP22-N2rP35 component. Indeed it is likely that theactive nature of this site6 is probably responsiblefor some so-called early components of the visuallyevoked potential. It was found that the vertex site(Cz) was relatively inactive at the latency of theearly components and had the added advantage ofbeing equidistant from all the electrodes in theanterior-posterior chain.This site was also used for the transverse topo-graphic study, but since the rules of equal in-terelectrode distance are negated, a further refer-ence on the anterior neck was used for compari-son. The subjects were seated in a dimly lit room,and flash stimulation was delivered by a GrassPS22 photostimulator 25 cm from the eyes.Silver-silver chloride electrodes were affixed withcollodion, and the resistance was maintainedbelow 5 Kohm. A PDP8E computer was used toaverage the response from each of the eight chan-nels of the electroencephalogram recorded on anElema Schonander machine. The analysis timewas 100 msec, and the bandpass of the equipmentwas from 66 to 700 Hz.To maximize the signal, it was found necessaryto average the response to 500 stimuli delivered at0146-0404/80/030318+04$00.40/0 © 1980 Assoc. for Res. in Vis. and Ophthal., Inc.Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933090/ on 05/03/2018

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