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A Study of Some Temporal Properties of the Human Visual Evoked Potential, and Their Relation to Binocular Function
Linköping University, Department of Clinical and Experimental Medicine, Ophthalmology . Linköping University, Faculty of Health Sciences.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As disturbed binocular functions in small children may lead to severe amblyopia it is of interest to detect it as early as possible. Most tests for binocular functions, however, demand active cooperation and may be unreliable in children up to 4-5 years of age. This study therefore aims to employ visual evoked potentials (VEP) to enable the examiner to evaluate the binocular function in a subject without need of active cooperation from the subject.

Initially we studied the relation of suprathreshold contrast to the latency of the transient pattern VEP (tpVEP). Although suprathreshold contrast independently influenced the tpVEP latency, interindividual variation was too large to suggest tpVEP as a possible method for objectively measuring contrast sensitivity in a subject.

The tpVEP latency in normal and microstrabismic adult subjects was examined. It was significantly shorter with binocular viewing in normals, but not in the microstrabismic group.

Contrast sensitivity and tpVEP latency was examined in adults, both with normal binocularity and with microstrabismus, using both luminance (black-and-white) contrast and colour contrast patterns. The tpVEP latency to colour contrast, like that to luminance contrast, is shorter in normal subjects who view the stimulus binocularly. Interindividual variation or overlap between the normal and microstrabismic groups did not improve with colour contrast.

The most significant features of the tpVEP are amplitude and latency. Depending on stimulus conditions, the response may show variations in configuration, amplitude and, to a lesser degree, latency. To decrease the influence of such variations steady-state VEP (ssVEP) can be used. The stimulus is presented in a fast repetitive manner, yielding a VEP response shaped as a continuous curve. The frequency components of this curve can be analysed using Fast Fourier Analysis.

Fast Fourier analysis of ssVEP in children aged 8-15 years with normal binocularity and with microstrabismus showed that the power of the second harmonic (the double frequency of stimulus frequency) of the response with binocular viewing was larger than with monocular viewing, both in normals and microstrabismic subjects. For higher stimulus frequencies, microstrabismic subjects showed a significantly lower power of the second harmonic compared with subjects with normal binocularity, when the stimulus was presented binocularly.

Finally, Fast Fourier analysed ssVEP in pre-school children aged 4-5 years was studied. A normal group was compared with a group with microstrabismus and a group with significant amblyopia. Amblyopic subjects had significant interocular differences in the first harmonic. We confirmed the significant difference found between microstrabismic subjects and subjects with normal binocularity regarding the second harmonic’s power with higher temporal frequency binocular stimulation, although at a slightly lower frequency than for older children. A low power of the second harmonic in the ssVEP to a binocular stimulus with high temporal frequency is a strong indicator of disturbed binocular function.

Abstract [sv]

För att förhindra amblyopi (ensidig synsvaghet) hos barn är det viktigt att upptäcka störningar i samsynsfunktionerna så tidigt som möjligt. Samsynstester kräver dock aktiv medverkan och kan ge osäkra resultat hos barn upp till 4-5 års ålder. Den här avhandlingen studerar möjligheterna att utifrån tidsmässiga (temporala) egenskaper hos visual evoked potentials (VEP) undersöka samsynsfunktioner objektivt, utan att den undersökte behöver medverka aktivt.

Första delstudien visar att ett synstimulus kontrastnivå i relation till kontrastkänslighetströskeln oberoende påverkar latensen i VEP, men variationer mellan individer gör metoden olämplig som objektiv kontrastkänslighetstest.

Andra delstudien jämför latensen i VEP hos individer med normal samsyn med den hos personer med mikroskelning. Stimulering av båda ögonen gav signifikant kortare latens än stimulering av ett öga hos normala, men inte hos mikroskelare.

I den tredje delstudien jämfördes känslighet för luminanskontrast och färgkontrast hos individer med normal samsyn och personer med mikroskelning. Både luminansmönster (svart-vita) och färgkontrastmönster upptäcktes vid lägre kontrast om båda ögonen stimulerades istället för ett i taget hos normalseende. Mikroskelare uppfattade mönstren sämre med båda ögonen än med ett öga (det dominanta). Latensen i VEP mättes i båda grupperna för både luminans- och färgkontrastmönster. Båda typerna av kontrast gav förkortning av latensen när båda ögonen stimulerades vid normal samsyn, men denna förkortning uteblev hos mikroskelare. Både luminans- och färgkontrast gav för varierande resultat för att utnyttja metoden för objektiv undersökning av samsynen.

Fourier-analys innebär att en kurvform delas upp i sinuskurvor med olika frekvens, amplitud och fas. Om ett stimulus växlar hastigt får man ett steady-state VEP (ssVEP), dvs en kontinuerligt vågformad VEP-kurva, som kan delas upp i delsinuskurvor med Fourieranalys. Detta gör att man särskilt kan studera frekvenser som är relaterade till stimuleringsfrekvensen, till exempel grundton och övertoner (multipler av grundtonsfrekvensen).

Barn 8-15 år gamla, med normal samsyn och med mikroskelning undersöktes med ssVEP i det fjärde delarbetet. Den första övertonen (= ”second harmonic”) var statistiskt signifikant svagare hos mikroskelare jämfört med normala individer, när stimuleringsfrekvensen var hög.

Det femte och sista delarbetet undersökte ssVEP hos 4-5 år gamla förskolebarn på motsvarande sätt. I denna studie deltog också en grupp barn med amblyopi (synsvaghet) på ena ögat. På en något lägre stimuleringsfrekvens bekräftades den svagare första övertonen hos barnen med mikroskelning jämfört med barnen med normal samsyn. De amblyopa barnen visade tydligast förändringar vid lägre stimuleringsfrekvenser och i ssVEP:s grundtonsfrekvens (= ”first harmonic” eller ”fundamental harmonic”). Resultaten i de olika grupperna är så pass åtskilda att metoden verkar lämpa sig för objektiv undersökning av samsynsfunktioner, i det att en svag första överton i binokulärt ssVEP utlöst av hög stimuleringsfrekvens inger en stark misstanke om störd samsyn, medan en stor skillnad i grundtonens styrka i höger respektive vänster ögas ssVEP tyder på amblyopi.

Place, publisher, year, edition, pages
Institutionen för nervsystem och rörelseorgan , 2006.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 964
Keyword [en]
VEP (Visual Evoked Potential), contrast sensitivity, binocularity, latency, Fourier analysis, strabismus, amblyopia
National Category
Ophthalmology
Identifiers
URN: urn:nbn:se:liu:diva-7584ISBN: 91-85523-08-9 (print)OAI: oai:DiVA.org:liu-7584DiVA: diva2:22612
Public defence
2006-11-21, Berzeliussalen, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2009-08-22
List of papers
1. The effect of spatial frequency and contrast on the latency in the visual evoked potential
Open this publication in new window or tab >>The effect of spatial frequency and contrast on the latency in the visual evoked potential
1992 (English)In: Documenta Ophthalmologica, ISSN 0012-4486, Vol. 79, no 2, 187-194 p.Article in journal (Refereed) Published
Abstract [en]

The latency in the visual evoked potential was measured at spatial frequencies of 2–12 c/deg in 10 subjects. The contrast levels of the sinuosoidal grating patterns were set at 1.5, 1.75, 2.0, 2.25, 2.5, 2.75 and 3.0 log units above each subject's contrast sensitivity threshold. Two factors were shown to influence the latency: suprathreshold contrast and, to a lesser extent, spatial frequency. The visual evoked potential latencies at contrast sensitivity threshold were extrapolated. These threshold latencies showed considerable variation with spatial frequency and between subjects. Therefore, the visual evoked potential latency cannot be considered a useful tool for estimating the contrast sensitivity function.

Keyword
Latency, spatial frequency, suprathreshold contrast, visual evoked potential
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14094 (URN)10.1007/BF00156577 (DOI)
Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2009-08-19
2. VEP latency: a comparison between normal and defective binocularity.
Open this publication in new window or tab >>VEP latency: a comparison between normal and defective binocularity.
1993 (English)In: Clinical Vision Sciences, Vol. 8, 245-251 p.Article in journal (Refereed) Published
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14095 (URN)
Available from: 2006-10-23 Created: 2006-10-23
3. Luminance and color contrast sensitivity and VEP latency in subjects with normal and defective binocularity
Open this publication in new window or tab >>Luminance and color contrast sensitivity and VEP latency in subjects with normal and defective binocularity
1997 (English)In: European Journal of Ophthalmology, ISSN 1724-6016, Vol. 7, 82-90 p.Article in journal (Refereed) Published
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14096 (URN)
Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2009-08-19
4. Fourier analysis of steady-state visual evoked potentials in subjects with normal and defective stereo vision
Open this publication in new window or tab >>Fourier analysis of steady-state visual evoked potentials in subjects with normal and defective stereo vision
2000 (English)In: Documenta Ophthalmologica, ISSN 0012-4486, Vol. 101, no 3, 233-246 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this work was to study the second harmonic in the steady state pattern visual evoked potential (ssVEP) to various stimulus frequencies in subjects with normal and defective binocularity. ssVEPs were elicited by 4 c/deg sinusoidal gratings, with temporal frequencies ranging from 5 to 20 Hz (exp. 1) and 15 to 27.5 Hz (exp. 2). Responses were Fourier analysed and power and phase of the second harmonic to stimulus frequency were measured. For power, binocular enhancement in a bimodal fashion was found both in normals and in subjects with defective binocularity. The power with binocular stimulation was significantly higher in the normal group in the high frequency domain. Latency, estimated from the phase-frequency function, was longer in the group with defective binocularity, but this was statistically significant only for the high frequency domain. The results suggest that a visual system with normal binocular function can follow a stimulus with high temporal frequency more accurately than a system with disturbed binocularity.

Keyword
binocular vision, Fourier analysis, strabismus, temporal frequency, visual evoked potential (VEP)
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14097 (URN)10.1023/A:1002876804178 (DOI)
Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2009-08-19
5. Fourier-analysed steadystate VEPs in pre-school children with and without normal binocularity
Open this publication in new window or tab >>Fourier-analysed steadystate VEPs in pre-school children with and without normal binocularity
2006 (English)In: Documenta Ophthalmologica, ISSN 0012-4486, Vol. 112, no 1, 13-22 p.Article in journal (Refereed) Published
Abstract [en]

Pre-school children aged 4–5 were examined with steady-state VEP in response to a sinusoidal grating pattern with a spatial frequency of 4 c/deg, reversing at rates 5, 10, and 15 Hz. Normal children (n = 10) were compared with subjects lacking stereo perception (n = 6) and with subjects showing significant unilateral amblyopia with visual acuity in the worse eye <0.5 (n = 7). Fast Fourier Transform was used for analysis of the crude steady-state VEP responses. Compared to normals, the subjects lacking stereo perception showed a significantly lower power of the second harmonic in the response evoked by binocular stimulation with gratings reversed at 15 Hz. The amblyopic group showed a significant difference between the dominant and the non-dominant eye regarding the first harmonic power in the responses evoked by gratings reversed at 5 and 10 Hz. These findings are discussed in relation to the magnocellular and parvocellular visual pathways and suggested models for linear and non-linear processing of visual signals.

Keyword
amblyopia, binocularity, Fourier analysis, strabismus, visual evoked potential
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14098 (URN)10.1007/s10633-005-5889-4 (DOI)
Available from: 2006-10-23 Created: 2006-10-23

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