Reduced Variability in the Electro-Oculogram
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VOL. 97, NO. 3 LETTERS TO THE JOURNAL 395 procedure, I do find that most ophthal- mologists do not seem to be aware of it, and I frequently have to allay patients' fears regarding subconjunctival injections because of the pain they have experi- enced elsewhere. I believe that this tech- nique might be worth trying by those who have not used it. REDUCED VARIABll.JTY IN THE ELECTRO-OCULOGRAM WILLIAM M. DAWSON, PH.D., AND tOM M. MAIDA, M.S. Department of Ophthalmology, College of Medicine, University of Florida. This study was supported in part by National Eye Institute grant 1 ROI EY 04460 and by an unrestricted grant from Research to Prevent Blindness, Inc. Inquiries to W. M. Dawson, Ph. D. , Department of Ophthalmology, University of Florida, College of Medicine, BoxJ-284, J. Hillis Miller Health Center, Gainesville, FL 32.610. The standing potential of the eyes may be measured indirectly in human electro- oculograms, and has numerous diagnostic appllcations.P Variations in the electro- oculogram during dark and subsequent light adaptation have been converted to a ratio of peak amplitudes (light/dark, UD). Light- and dark-phase ratios have been adopted widely as relatively repeat- able, but they require a choice of the "representative" peaks. Variations as great as UD = 0.5 have been reported in normal subjects" when light and dark were based on amplitude measures of the electro-oculograms. We used a simple integration tech- nique for objective measurement in 38 male and female patients. The subjects, aged between 20 and 60 years, had nor- mal ocular examinations. Stimulation and recording methods have been described elsewhere.! The amplified electrical sig- nals (electro-oculograms) were digitally converted and stored in the core memory of a general purpose computer. Electro- oculograms were plotted as amplitude variations (Fig. 1, left). The minimum amplitude, "dark trough" (D) for each eye during last minutes of dark adaptation was identified by inspection (the usual method) and its peak-peak amplitude measured. A similar measure was made at the "light peak" (L), which was found approximately eight minutes after the onset of light adaptation (Fig. 1, left). 00 DARK DARK LIGHT I I I I 11111111111 liliJllllIIllllllIIll1 AMPLITUDE INTEGRAL Fig. 1. (Dawson and Maida). Electro-oculogram analog records (left) and their cumulative integrals (right) recorded during ten-second periods before 16 minutes of darkness (arrow) and subsequently after light adaptation. Calculation of light- and dark-phase ratios (1.87, right eye; 1.20, left eye) was made from ("representative") peak-peak points selected from regions marked D and L on the analog records. Similar calculations were made for the integral values (Li/bD (1.90. right eye; 0.99, left eye). The right eye was normal; the left eye had a small choroidal melanoma. This patient's data were not included in the statistical analysis.
Transcript of Reduced Variability in the Electro-Oculogram
VOL. 97, NO. 3 LETTERS TO THE JOURNAL 395
procedure, I do find that most ophthalmologists do not seem to be aware of it,and I frequently have to allay patients'fears regarding subconjunctival injectionsbecause of the pain they have experienced elsewhere. I believe that this technique might be worth trying by thosewho have not used it.
REDUCED VARIABll.JTY IN THEELECTRO-OCULOGRAM
WILLIAM M. DAWSON, PH.D.,AND tOM M. MAIDA, M.S.
Department of Ophthalmology, College ofMedicine, University of Florida.
This study was supported in part by National EyeInstitute grant 1 ROI EY 04460 and by anunrestricted grant from Research to PreventBlindness, Inc.
Inquiries to W. M. Dawson, Ph. D. , Department ofOphthalmology, University ofFlorida, College ofMedicine, BoxJ-284, J. Hillis Miller Health Center,Gainesville, FL 32.610.
The standing potential of the eyes maybe measured indirectly in human electrooculograms, and has numerous diagnosticappllcations.P Variations in the electrooculogram during dark and subsequentlight adaptation have been converted to aratio of peak amplitudes (light/dark,UD). Light- and dark-phase ratios havebeen adopted widely as relatively repeatable, but they require a choice of the"representative" peaks. Variations asgreat as UD = 0.5 have been reported innormal subjects" when light and darkwere based on amplitude measures of theelectro-oculograms.
We used a simple integration technique for objective measurement in 38
male and female patients. The subjects,aged between 20 and 60 years, had normal ocular examinations. Stimulation andrecording methods have been describedelsewhere.! The amplified electrical signals (electro-oculograms) were digitallyconverted and stored in the core memoryof a general purpose computer. Electrooculograms were plotted as amplitudevariations (Fig. 1, left). The minimumamplitude, "dark trough" (D) for each eyeduring last minutes of dark adaptationwas identified by inspection (the usualmethod) and its peak-peak amplitudemeasured. A similar measure was made atthe "light peak" (L), which was foundapproximately eight minutes after theonset of light adaptation (Fig. 1, left).
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DARK DARK LIGHTI I I I
11111111111 liliJllllIIllllllIIll1
AMPLITUDE INTEGRALFig. 1. (Dawson and Maida). Electro-oculogram
analog records (left) and their cumulative integrals(right) recorded during ten-second periods before 16minutes of darkness (arrow) and subsequently afterlight adaptation. Calculation of light- and dark-phaseratios (1.87, right eye; 1.20, left eye) was made from("representative") peak-peak points selected fromregions marked D and L on the analog records.Similar calculations were made for the integral values(Li/bD (1.90. right eye; 0.99, left eye). The right eyewas normal; the left eye had a small choroidalmelanoma. This patient's data were not included inthe statistical analysis.
396 AMERICAN JOURNAL OF OPHTHALMOLOGY MARCH, 1984
Light- and dark-phase ratios were calculated for the amplitude measures. Integrals (sums of the serial digital values) ofthe signals in the ten-second sample periods containing the Land D values wereused to generate a second set of ratios,L/D j (Fig. 1, right). Difference scores (A)were generated by subtracting the two(OD, OS) amplitude values [LID (OD) LID (OS) = Aa] and the two (OD, OS)integral end [L/D j (OD) - L/D i (OS) = Ai)values which were generated from thesame eye movements of each subject.Our integral algorithm (a) refers theelectro-oculogram signals contained inthe selected ten-second sample epoch too voltage with positive peaks and (b)converts them into a cumulative distribution which appears as an increasing,sloped, ramp-like waveform (D, or L,Fig. 1) with only positive components.
For the 38 normal subjects evaluationof the Aa values (Fig. 2) disclosed a mean
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AMPLITUDE INTEGRAL
Fig. 2 (Dawson and Maida). Mean and S.E. interocular dllference values (OD - OS) for the electrooculogram amplitude ratio (UD) and the derivedintegral ratio (L;/Di). All data are from the samenormal paired eyes of 38 subjects.
of 0.27 (S.E. = 0.033). For the same eyethe mean Ai was 0.15 (S.E. = 0.024). Bythe chi-square test (X2) , we tested thehypothesis that the distribution of signsof the subtracted difference scores (Aa Ai) would be distributed by chance. TheX2 is 7.41 (P < .01) and indicates that thefrequency of small Ai values is muchgreater than chance. Inspection ofFigure 1 suggests that the stability of Aiarises from the nonsubjective nature ofintegrals used in calculation of L/D j •
Choice of the voltage peaks for amplitudemeasures may be arbitrary.
Since Steinberg, Griff, and Linsenmeier! have recently provided cellulardata that establish the pigment epithelium cells as the source of the lightmodulated ion currents that produce theelectro-oculogram, more clinical use willfollow shortly. It has already been shownthat the light- and dark-phase ratio isexquisitely sensitive to the presence ofsmall choroidal melanomas.! We believethat integral or other objective electrooculogram transforms will be valuable inthe more reliable detection of early disease of the pigment epithelium.
REFERENCES
1. Marmor, M., and Lurie, M.: Light-inducedelectrical responses in the retinal pigment epithelium. In Zen, K., and Marmor, M. (eds.): The RetinalPigment Epithelium. Cambridge, Harvard University Press, 1972, pp. 226-244.
2. Krill, A.: Hereditary Retinal and ChoroidalDisease. Vol. I. Evaluation. New York, Harper andRow, 1972, p. 277.
3. Van Lith, G. H. M., and Balik, J.: Variability ofthe electrooculogram. (EOG). Acta Ophthalmol.48:1091, 1970.
4. Staman, J. A., Fitzgerald, C. R., Dawson,W. W., and Barris, M. C.: The EOG and choroidalmalignant melanomas. Doc. Ophthalmol. 49:201,1980.
5. Steinberg, R. H., GriH', E. R., andLinsenmeier, R. A.: The cellular origin of the lightpeak. In Kolder, H. E. J. W. (ed.): Slow Potentialsand Microprocessor Applications. Doc. Ophthalmol.Proc. Ser. 37:1, 1983.
