ORIGINAL PAPER

VEP asymmetry with ophthalmological and MRI findingsin two achiasmatic children

Jelka Brecelj Æ Branka Stirn-Kranjc ÆNuska Pecaric-Meglic Æ Miha Skrbec

Received: 5 July 2006 / Accepted: 6 December 2006 / Published online: 13 January 2007� Springer Science+Business Media B.V. 2007

Abstract Achiasmia is a rarely diagnosed visual

pathway maldevelopment where all or the major-

ity of nasal retinal fibres fail to decussate at the

optic chiasm. It has been identified by neuroi-

maging and also by visual evoked potential

(VEP) asymmetry. VEP asymmetry has not been

defined consistently in previous studies. The aim

was to study VEP asymmetry to flash stimulation

in two children with maldevelopment of the optic

chiasm in comparison to control children. Both

children had congenital nystagmus, optic nerve

hypoplasia with a bilateral small double ring,

bitemporal visual field defect and normal colour

vision. In child 1 visual acuity in both eyes was

0.1, in child 2 it was 0.2. MRI showed reduced

chiasmal size in child 1, while in child 2 it was

combined with other midline abnormalities. VEP

to monocular flash stimulation showed in both

children distinctive occipital distribution, which

was not observed in control children. The N2

wave was distributed asymmetrically over the

ipsilateral hemisphere to the stimulated eye,

while the P2 wave was distributed over both

hemispheres. The P2 wave was however better

defined over the ipsilateral hemisphere. Flash

VEP occipital distribution remained similar in

child 1, who was followed from 10 months to

9 years. These cases of achiasmia demonstrate a

distinctive VEP asymmetry in the distribution of

the flash VEP N2 wave, as well as the expected

structural defect determined by neuroimaging.

Keywords Achiasmia � Bitemporal visual field

defect � Nystagmus � Optic nerve hypoplasia �Optic chiasm � Septo-optic dysplasia � Visual

evoked potentials

Introduction

In the visual pathway optic nerve fibres from the

nasal part of each retina decussate at the optic

chiasm and project to the contralateral hemi-

sphere. A congenital visual pathway maldevelop-

ment, in which optic nerve fibres from the nasal

half of each retina fail to decussate, was first

detected by visual evoked potentials (VEP).

Apkarian et al. [1] demonstrated in two children

that optic nerve fibres from the nasal retina did

not cross at the chiasm, but projected to the

ipsilateral instead of the contralateral visual

cortex. This achiasmatic condition was confirmed

by MRI and reported as the non-decussating

retinal-fugal fibre syndrome. In further studies, a

J. Brecelj (&) � B. Stirn-KranjcUnit for Visual Electrophysiology, Eye Clinic,University Medical Centre, 1525 Ljubljana, Sloveniae-mail: jelka.brecelj@kclj.si

N. Pecaric-Meglic � M. SkrbecClinical Institute for Radiology, University MedicalCentre, Ljubljana, Slovenia

123

Doc Ophthalmol (2007) 114:53–65

DOI 10.1007/s10633-006-9037-6

small number of children with absence or defi-

ciency of optic nerve fibres that cross over at the

optic chiasm, have also been presented [2–9].

Ophthalmological findings in achiasmia and

chiasmal hypoplasia were shown to be associated

with congenital nystagmus. See-saw, rotatory or

purely horizontal nystagmus were noted. Visual

fields were normal or abnormal, but bitemporal

hemianopia was not reported. Optic discs ap-

peared normal or hypoplastic. MRI findings

showed complete achiasmia as an isolated devel-

opmental abnormality, or were found together

with other midline abnormalities (a review in [7]).

Electrophysiological features that distin-

guished absent or reduced chiasmal decussation

had not been reported consistently in previous

studies. Apkarian et al. [1, 2] found ipsilateral

asymmetric occipital distribution to onset stimu-

lation in two achiasmatic children and to flash

stimulation in one of them. It was demonstrated

that the peak of the potential distribution was

lateralized over the left hemisphere following left

eye stimulation and shifted to the right hemi-

sphere following right eye stimulation. Leitch

et al. [3] reported that the main positivity was

recorded over the contralateral visual cortex to

flash stimulation in a child with no chiasm.

Thompson et al. [4] described a crossed asymme-

try occipital distribution to flash stimulation in

five children with achiasmia or chiasmal hypopla-

sia. A waveform, which was shown from one

child, was described as a negative peak at 80–

100 ms at the channel ipsilateral to the stimulated

eye and a positive peak at the channel contralat-

eral to the stimulated eye. Jansonius et al. [5]

showed that a positive wave around 150–200 ms

was lateralised over the hemisphere on the side of

the stimulated eye to flash stimulation in one

achiasmatic child. Korff et al. [6] reported ipsi-

lateral asymmetry to flash and pattern onset

stimulation in one achiasmatic child. Sami et al.

[7] reported crossed contralateral positvity to

flash stimulation in a review of nine achiasmatic

children, while they presented waveforms in only

two of them. In a recent study, VEP crossed

asymmetry was reported to the left eye flash

stimulation, while to the right eye stimulation was

VEP attenuated and prolonged in a child

with achiasmia and optic nerve hypoplasia [8].

A number of these studies showed that recording

differential potentials between hemispheric chan-

nels was helpful in demonstrating abnormal optic

pathway decussation in achiasmia and chiasmal

hypoplasia [1, 2, 4, 6–8]. Some studies did not

define components or their polarities within VEP

asymmetries [6–9].

So far in literature, a small number of VEP

waveforms in children with achiasmia or chiasmal

hypoplasia have been reported, unfortunately

there is no consistency in the reporting of asym-

metrical occipital distributions. This gives us a

good reason to present two more children with

achiasmia in which VEP asymmetry was studied

to flash stimulation and compared to control

children. Ophthalmological and electrophysiolog-

ical follow-up and MRI findings were also stud-

ied. Both children were defined as achiasmatic

according to Sami et al. [7], who described

achiasmia as an absence or relative lack of

crossing fibres at the optic chiasm.

Subjects and methods

The study was approved by the Slovene Research

and Medical Ethics Committee. Two boys were

referred in infancy because of congenital nystag-

mus, both of whom had a normal neurological

and psychomotor development and attend regular

school. Electrophysiological features were also

studied in 16 control children (mean 5 years;

range 4–7.6 years).

Ophthalmological examination

Child 1 was presented for ophthalmological eval-

uation at 9 months and child 2 at 2 months of age.

Both had complete eye examinations and had

been followed-up for over 7 years. Visual acuity

tests for near and distance (Jaeger, L. Hyvarinnen

system, Teller Acuity Cards, Cambridge Acuity

cards, standard optotypes), refractive error

(retinoscopy, ultrasound biometric measure-

ments, Retinomax and Humphrey automated

refractometers), contrast sensitivity testing

(Vision Optotech), colour vision (Ishihara tables,

Farnsworth 15 hue) and visual fields (Goldmann

perimetry, automated Octopus G2 top) were

54 Doc Ophthalmol (2007) 114:53–65

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evaluated. Ocular fundus morphology was vali-

dated by fundus digital image analysis.

Electrophysiological examination

Both were followed, child 1 from 10 months till

9 years and child 2 from 2 months till 7 years.

Child 1 was recorded at 10 months, 5, 6 and

9 years to binocular and monocular flash stimu-

lation, while child 2 was recorded at 2 and

9 months only to binocular flash stimulation and

at 6 and 7 years to binocular and monocular flash

stimulation. Flash VEP, which was tested from

child 2 at 2 and 9 months only to binocular

stimulation, was found abnormal for age and

reported as suspected for visual pathway dysfunc-

tion. In both children were simultaneously re-

corded also electroretinograms (ERG) to flash

stimulation with skin electrodes and without pupil

dilatation. Flash ERG were normal for age at all

recordings from both children [10].

VEP were recorded from three electrodes

applied to the posterior scalp according to Kriss

and co-workers [11], who introduced this montage

in paediatric electrophysiology: the midline elec-

trode was placed at Oz (International 10–20

system, 10% of the nasion-to-inion separation),

while the electrode over the right hemisphere

(O2’) and the electrode over the left hemisphere

(O1’) were placed to either side of the midline

electrode (halfway between Oz and the mastoid,

approximately 4 cm). VEP electrodes were refer-

red to Fz. ERG were recorded by skin electrodes

(disposable Nicolet electrodes) attached to the

lower eyelid and referred to Fz [10, 11].

ERG and VEP activity (Espion Diagnosys

LLC, Littleton, MA) was recorded to white

flashes elicited with a Grass PS33 plus (Astro-

Med Inc, West Wanwick, Rhode Island, USA)

flash stimulator (intensity setting 4) which was

hand held at a distance of 20 cm. The flash

intensity was 455 cd s/m2 (calibrated with inte-

grating photometer International Light IL1700,

Newburyport, Massachusetts, USA). The stimu-

lation rate of flash was 3 Hz. The analysis time

was 300 ms (with a 10 ms pre-stimulus interval).

The band pass was 0.3–300 Hz. Each time 100

responses were averaged and repeated at least

twice.

VEP recordings were analysed to monocular

stimulation. Amplitudes (peak to peak) and laten-

cies were measured at channels O2’ (right hemi-

sphere), O1’ (left hemisphere) and O1’-O2’

(channel which showed the difference in potentials

between the left and right hemisphere). A negative

wave (N2) and a positive wave (P2) were analysed

in control children and in children with achiasmia.

The nomenclature used was according to ISCEV

standards [12] and for evaluation of peak latencies

and polarities of waves in children was considered

a review [13] and our normative data.

MRI examination

Magnetic resonance images were obtained with a

1.5 T system (General Electric, Signa Horizon) in

both children. In child 1 Spin Echo (SE) T1-

weighted images (TR/TE 460/15 ms, 5.0 mm slice

thkickness (thk), 1.5 mm interslice space (sp)) and

Fast Spin Echo (FSE) T2-weighted images (TR/

TE 3000/82.5 ms, 5.0 mm thk, 1.5 mm sp) in the

axial plane, FSE T2-weighted coronal images

through the anterior visual pathways (TR/TE

4800/88.6 ms, 3.0 mm thk, 1.5 mm sp) and SE

T1-weighted images (TR/TE 420/18 ms, 3.0 mm

thk, 0.3 mm sp) in the oblique axial, coronal and

sagittal planes through the anterior visual path-

ways were performed. In child 2 3-D spoiled

gradient echo sequences (3DSPGR: TR/TE 30/6

ms) with reconstructions (1.4 mm thk, 0.0 mm sp)

in the sagittal, coronal and oblique axial planes

through the anterior visual pathways, FSE T2

weighted images (TR/TE 4000/98.2 ms, 3.0 mm

thk, 0.1 mm sp) in the axial and coronal planes and

Fluid-Attenuated Inversion Recovery (FLAIR:

TR/TE/TI 8777/133/2193 ms, 5.0 mm thk, 0.5 mm

sp) in the axial plane were performed.

Results

Ophthalmological findings

Both children studied and followed up had

horizontal nystagmus of low frequency and

amplitude with a vertical component, but no

signs of a see-saw nystagmus, and also both had a

very mild convergent concomitant alternate stra-

bismus. Their anterior eye segments and optic

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media were normal and there was no evident

abnormality of the pupils. Their fundi showed

bilateral moderate optic nerve hypoplasia with a

small double ring, slightly tortuous retinal vessels

and normal chorioretina and fovea (Fig. 1). At

their last examination, low myopic astigmatism

was found in child 1 aged 9 years, and low

hypermetropic astigmatism in child 2 aged

7 years. The best corrected monocular and bin-

ocular visual acuity for distance was 0.1 in the

child 1 and 0.2 in the child 2. Near vision was

practically normal in both - Jaeger 3 tables (text

1–2 extra small text size, 3 normal text size, 4–9

larger text size). Colour vision was within normal

limits for age, while contrast sensitivity was

reduced for all spatial frequencies. A bitemporal

visual field defect was revealed to kinetic Gold-

mann and static Octopus perimetry (Figs. 2, 3),

when both children were cooperative to perform

reliable visual field examination (child 1 at 9 and

child 2 at 7 years).

Flash VEP asymmetry in two achiasmatic

children

In both children VEP distribution indicated

deficit of the crossed optic nerve fibres at the

chiasm, as occipital distribution was opposite to

that found in albinism where there is an excess of

decussation of optic nerve fibres at the chiasm.

Reduced decussation of the optic nerve fibres at

the chiasm was subsequently anatomically con-

firmed by MRI. To monocular flash stimulation,

occipital distribution was asymmetrical in all the

recordings from both achiasmatic children. Child

1 was recorded at 10 months, 5, 6 and 9 years, and

child 2 at 6 and 7 years.

Figures 4–6 present flash VEP asymmetry

found in both achiasmatic children. The N2 wave

was clearly defined over the ipsilateral hemi-

sphere to the stimulated eye; to the right eye

stimulation over the right hemisphere and to the

left eye stimulation over the left hemisphere. On

the other hand, the P2 wave was found over both

hemispheres in responses from both eyes. There

was, however, a tendency that the P2 wave was

better defined over the ipsilateral hemisphere. In

child 1 the P2 amplitude was higher over the

ipsilateral hemisphere to the stimulated eye

(Fig. 5), while in child 2 the difference between

the P2 amplitude over the hemispheres was less

distinct (Fig. 6).

VEP asymmetry in both achiasmatic children

was opposite to that seen in albinism. Figure 7

presents waveform from a child with albinism

showing contralateral asymmetry according to the

N2 and P2 wave distribution over the hemisphere

contralateral to the stimulated eye. In both

Fig. 1 Fundi showbilateral moderate opticnerve hypoplasia in child1 and child 2

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achiasmatic children ipsilateral asymmetry was

seen according to the lateralization of the N2

wave over the ipsilateral hemisphere to the

stimulated eye. In addition the P2 wave was

better defined over the ipsilateral hemisphere. On

the other hand, the asymmetry could be also

Fig. 2 Bitemporal visualfield defect is shown byGoldmann and Octopusperimetry in child 1 at9 years of age

Fig. 3 Bitemporal visualfield defect is shown byGoldmann and Octopusperimetry in child 2 at7 years of age

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described as crossed asymmetry, according to the

N2 wave, which switched distribution in responses

to the right and left eye stimulation.

The bottom traces in Figs, 5 and 6 show

differential potentials derived from traces re-

corded over the left hemisphere and from traces

recorded over the right hemisphere. Channel

O1’-O2’ showed interocular inverse polarity.

From the right eye a positive peak and from left

eye stimulation a negative peak was noted. This

interocular difference in potentials between the

left and right hemispheres was in both achias-

matic children opposite to that found in albinism

(Fig. 7).

Fig. 4 Flash VEPasymmetry in child 1 at10 months (negative waveN2 and positive P2 waveare marked by arrows)

Fig. 5 Follow-up in child 1 at 5 and 9 years shows flashVEP asymmetry (negative wave N2 and positive P2 waveare marked by arrows) and interocular inverse polarity at a

channel O1’-O2’ (from the right eye a positivity and fromthe left eye a negativity are marked by arrows)

58 Doc Ophthalmol (2007) 114:53–65

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A long-term follow-up from 10 months to

9 years showed no major variation in flash VEP

asymmetry in child 1 (Figs. 4, 5). Note that

latencies of the N2 and P2 wave were longer at

10 months than at 5 and 9 years, which is

normally expected for that age group.

Comparison of flash VEP in the control group

to achiasmatic children

In none of the control children was the occipital

distribution similar to that found in both achias-

matic children. Figure 8 presents the symmetrical

Fig. 6 Flash VEP asymmetry in child 2 at 6 and 7 years(negative wave N2 and positive P2 wave are marked byarrows) and interocular inverse polarity at a channel

O1’-O2’ (from the right eye a positivity and from the lefteye a negativity are marked by arrows)

Fig. 7 Flash VEPasymmetry in child withalbinism (negative waveN2 and positive P2 waveare marked by arrows)and interocular inversepolarity at a channel O1’-O2’ (from the right eye anegativity and from theleft eye a positvity aremarked by arrows)

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occipital distribution of the N2 and P2 wave to the

right and left eye stimulation in a control child.

Such symmetrical occipital distribution appeared

in some control children. In others, asymmetrical

occipital distribution was also seen as attenuation

of the N2 and P2 wave over the same hemisphere

to the right and left eye stimulation. The bottom

trace in Fig. 8 shows differential potentials

derived from traces recorded over the left hemi-

sphere and from traces recorded over the right

hemisphere in a control child. In none of the

control children a positive peak was found to the

right eye stimulation and a negative peak to the

left eye stimulation as was evident in both

achiasmatic children.

Figure 9 compares the N2 and P2 wave ampli-

tude and latency data for both achiasmatic

children from 5 recordings (for child 1 at 5, 6

and 9 years for child 2 at 6 and 7 years) and for

age-matched controls. Latency and amplitude

values of the P2 wave were similar over both

hemispheres to right and left eye stimulation in

both the control and achiasmatic children. There

was a difference in the N2 amplitude, but not in

the N2 latency, between the two groups. The N2

amplitude was similar over both hemispheres to

stimulation of both eyes in controls, while the N2

amplitude was obtained over the right hemi-

sphere to the right eye stimulation and over the

left hemisphere to the left eye stimulation in both

achiasmatic children.

MRI findings

In child 1 MRI examination was performed at age

seven years. Images showed absence of the optic

chiasm. Both posterior parts of the optic nerves

were hypoplastic, the right more than the left, and

they continued posteriorly into the hypoplastic

optic tracts. Pituitary gland, septum pellucidum,

and other brain structures were normal (Fig. 10).

In child 2 MRI was performed at age six years.

Images showed hypoplasia in optic nerves, chiasm

and tracts, especially the chiasm. The infundibu-

lum and pituitary gland were very small, hypo-

plastic. The septum pellucidum was absent and

corpus callosum was thinner. Both lateral ventri-

cles were enlarged and periventricular white

matter was diminished with high signal changes

on FLAIR images, indicating possible mild peri-

ventricular leucomalacia after intrauterine or

perinatal hypoxic injury (Fig. 11).

Fig. 8 Flash VEPdistribution of the N2 andP2 wave in a control child

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Figure 12 compares images of optic nerves,

chiasm and optic tractus from a control child to

both achiasmatic children.

Discussion

The assessment of congenitally reduced chiasmal

decussation is dependent on ophthalmological,

MRI and also VEP findings. In both children with

congenital nystagmus, optic disc hypoplasia and

reduced visual acuity was found VEP asymmetry

that indicated a reduced decussation of optic

nerve fibres at the chiasm. This was confirmed by

MRI, which showed achiasmia in one child and

chiasmal hypoplasia plus midline central nervous

system abnormalities in the other child. It was

proposed recently that diagnosis of achiasmia can

be associated with absence and also with relative

lack of crossing fibres at the optic chiasm. MRI

examination would require extremely thin sec-

tions to determine if there was a complete

absence of decussation [7]. Therefore, both chil-

dren in this study were defined as achiasmatic.

In this VEP study to flash stimulation the

negative N2 and positive P2 wave were defined in

children with achiasmia and compared with data

from controls. The nomenclature was according

to ISCEV standards [12]. However, in paediatrics

the nomenclature of flash VEP is not standard-

ized. Most authors have reported P2 latency

reaching around 95–105 ms at about 3 months [a

review 13] and that the mean value of the

preceding negative wave was reaching 67.9 ms

at 24 weeks [14]. Our own laboratory normative

data were comparable with these values. The

monocular N2 and P2 latencies and amplitudes

recorded from both achiasmatic children were

Fig. 9 The N2 and P2 wave latencies and amplitudes incontrols and achiasmatic children. There is no difference inamplitude and latency values of the P2 wave to the righteye (open circles) and left eye (closed circle) betweencontrol and achiasmatic children. Between both there is adifference in the N2 wave amplitude, and not N2 latency.Over the right hemisphere (channel O2’) the N2 wave isrecorded in control children to the right eye (open

rectangular) and left eye (closed rectangular) stimulation,while in achiasmatic children only to the right eyestimulation (open rectangular). Over the left hemisphere(channel O1’) the N2 wave is recorded in control childrento the right eye (open rectangular) and left eye (closedrectangular) stimulation, while in achiasmatic childrenonly to the left eye stimulation (closed rectangular)

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similar to those recorded in controls, although the

distribution was different. Latencies of the N2

and P2 wave were also longer at 10 months than

at 5 years, which is predictable according to VEP

maturation. Results from this case study can be

compared to Apkarian et al. [2] who analysed a

positive wave at 100 ms and to Thompson et al.

[4] who analysed a negative wave that appeared

around 80 ms, unlike Jansonius et al. [5] who

analysed a later positive wave that appeared from

150 to 200 ms.

Results from the cases presented here agree

with those previous studies, which showed that in

achiasmia and chiasmal hypoplasia the VEP

asymmetry was distinctive and opposite to that

found in albinism [2–4, 6, 9]. In previous studies of

achiasmia the occipital distribution to flash stim-

ulation was described as ipsilateral asymmetry [1,

2, 6], crossed asymmetry [4, 8] and crossed

contralateral asymmetry [7] whereas in our study

the asymmetry could be defined as either ipsilat-

eral or as crossed asymmetry. Also, not studied

previously, this study showed that VEP asymme-

try remained unchanged from 10 months to

9 years in one achiasmatic child. Using a pat-

tern-reversal stimulus VEP crossed asymmetry

was also shown to be present in chiasmal com-

pressive lesions when crossed fibres were affected

[15–20]. In the current report it would be

expected that pattern-reversal stimulation might

reveal crossed asymmetry in the two achiasmatic

children. However, due to their nystagmus, which

suppress VEP responses to pattern-reversal stim-

ulation [21], as well as their low visual acuity,

pattern-reversal stimulation has not been re-

corded. It is possible that methodological differ-

ences in electrode placement are factors that

could account for the discrepancies between

achiasmia studies. We believe that further re-

search is needed to define VEP waveforms and

peaks upon which VEP aymmetry will be defined

in achiasmia.

As demonstrated by others [1, 2, 4, 6–8], the

channel which recorded differential potentials

Fig. 10 MRI of child 1recorded at 7 years ofage, which shows theachiasmia. (a, b, c)Coronal T1- weightedimages show the absenceoptic chiasm. The septumpellucidum is normallydeveloped. (d, e)Continuous axial T1-weighted images showthat there is no opticchiasm betweenhypoplastic optic nerves(arrows)

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between left to right hemispheric activity, showed

interocular inverse polarity. It was opposite to

that recorded in albinism and was not found in

congenital idiopathic nystagmus [2] or in this

study in control children.

Ophthalmologically both achiasmatic children

have been followed-up from infancy until school

age. Their ophthalmological findings and function

were stable and in correlation with moderate

optic nerve hypoplasia [22, 23]. Both children in

this study have useful vision especially for read-

ing. Colour vision was relatively preserved in

both, despite congenitally anomalous optic discs

[24]. The small optic discs with a spectrum of

appearances, found in the current case report,

could be associated with a variety of malforma-

tions involving central nervous system [22, 23, 25].

In both children there was no evidence of see-saw

nystagmus previously believed to be characteristic

in achiasmia [1, 2], or associated with other

midline abnormalities. Purely horizontal nystag-

mus or combined horizontal and torsional nys-

tagmus, or other descriptions of nystagmus were

reported in achiasmia [4, 5, 7–9].

Bitemporal visual field defect was revealed in

both children when they were old enough to

Fig. 11 MRI of child 2 recorded at 6 years of age showingchiasmal hypoplasia. (a) Axial T1-weighted image showshypoplastic optic nerves and optic tracts and there is novisible optic chiasm (arrow). (b) Coronal T2 weightedimage shows a tiny chiasm (lower arrow), absence of theseptum pellucidum with mild enlargement and mildsquaring of the frontal horns of the lateral ventricles(upper arrow). (c) Axial FLAIR image shows enlarged

lateral ventricles (upper arrow) with absence of the septumpellucidum. In the posterior periventricular white matterthere is a high signal (lower arrow), indicating intrauterineor perinatal hypoxic injury. (d) Sagittal T1-weighted imageshows thinning of the corpus callosum (upper arrow) andhypoplasia of the chiasm and the pituitary gland (lowerarrow)

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cooperate well. The field defect was less

complete, particularly from child 1, possibly due

to nystagmus and fixation instability. To our

knowledge no bitemporal visual field defects

had been found in children with maldevelopment

of the optic chiasm [for review 7, 26].

MRI findings confirmed that achiasmia or

chiasmal hypoplasia may not be the only central

nervous abnormality, as shown in previous stud-

ies. Achiasmia can appear as an isolated abnor-

mality [1, 2, 5, 6, 8, 9] or as a part of septooptic

dysplasia with a constellation of small anterior

visual pathways, absence of the septum peluci-

dum, thinning of the corpus callosum and possible

other abnormalities of pituitary gland, hemi-

spheric migration anomalies and perinatal hemi-

spheric injury [3, 4, 7]. In child 1 the MRI results

confirmed lack of connection between both

hypoplastic optic nerves and tracts as an isolated

abnormality. In child 2 MRI showed hypoplastic

anterior visual pathways with associated abnor-

malities of absent septum pelucidum, hypoplastic

pituitary gland, hypoplastic corpus callosum and

signs of perinatal hemispheric injury.

So far, VEP has proven indispensable in

detecting misrouted visual pathway in albinism

[27–29]. In our previous study we showed that

visual electrophysiological screening of infants

with congenital nystagmus can establish or

exclude retinal and postretinal pathway dysfunc-

tion [30]. Children with maldeveloped optic

chiasm in this and other studies were electro-

physiologically assessed due to their congenital

nystagmus [4, 6, 8, 9, 31] or were suspected of

having albinism [2]. Therefore, from previous

studies and ours, we may assume that already in

early infancy the distinctive VEP will help in the

diagnosis of achiasmia. We believe that in the

future congenitally reduced chiasmal decussation

might be a more often recognised visual pathway

anomaly and that further studies are needed to

define VEP characteristics in achiasmia to flash

and pattern stimulation.

This study concludes that absent or reduced

visual pathway decussation at the chiasm is

associated with a distinctive flash VEP asymmetry

and by bitemporal visual field defect. Ipsilateral

N2 wave distribution can define achiasmia.

Acknowledgements We thank to Mrs Tatjana Vidmar,Mrs Nevenka Zlatnar, Mrs Marija Jesensek for assistancein recording the children, and to Mrs Polonca Baloh-Brown, Mrs Maja Sustar, Mrs Barbara Klemenc, Mr IgnacZidar and Mr Tone Zakelj for their valuable assistance inthis paper. This study was supported by the SlovenianResearch Agency, Grant No. J3–6167.

References

1. Apkarian P, Bour L, Barth PG (1993) A uniqueachiasmatic anomaly detected in non-albinos withmisrouted retinal-fugal projections. Eur J Neurosci6(3):501–507

Fig. 12 MRI structures of optic nerves, chiasm and optictracts are presented in a control 7 years old child and inboth achiasmatic children. Axial T1-weighted images showwell formed optic nerves, chiasm, optic tracts in a control

child while in both achiasmatic children images showhypoplastic optic nerves, hypoplastic optic tracts andmaldeveloped optic chiasm

64 Doc Ophthalmol (2007) 114:53–65

123

2. Apkarian P, Bour LJ, Barth PG, Wenninger-Prick L,Verbeeten B (1995) Non-decussating retinal-fugal fibresyndrome. An inborn achiasmatic malformationassociated with visuotopic misrouting, visual evokedpotential ipsilateral asymmetry and nystagmus. Brain118:1195–1216

3. Leitch RJ, Thompson D, Harris CM, Chong K,Russell-Eggitt I, Kriss A (1996) Achiasmia in a caseof midline craniofacial cleft with seesaw nystagmus. BrJ Ophthalmol 80:1023–1024

4. Thompson DA, Kriss A, Chong K, Harris C, Russell-Eggitt I, Shawkat F, Neville BGR, Aclimandos W,Taylor DSI (1999) Visual evoked potential evidence ofchiasmal hypoplasia. Ophthalmology 106:2354–2361

5. Jansonius NM, van der Vliet TAM, Cornelissen FW,Pott JWR, Kooijman AC (2001) A girl without achiasm: electrophysiologic and MRI evidence for theabsence of crossing optic nerve fibers in a girl with acongential nystagmus. J Neuroophthalmol 21(1):26–29

6. Korff CM, Apkarian P, Bour LJ, Meuli R, Verrey JD,Roulet Perez E (2003) Isolated absence of optic chiasmrevealed by congenital nystagmus, MRI and VEPs.Neuropediatrics 34:219–223

7. Sami DA, Saunders D, Thompson DA, Russell-EggittIM, Nischal KK, Jeffery G, Dattani M, Clement RA,Liassis A, Taylor DS (2005) The achiasmia spectrum:congenitally reduced chiasmal decussation. Br JOphthalmol 89:1311–1317

8. Pomeranz HD, Agadzi AK, Ekesten B (2006)Achiasmia and unilateral nerve hypoplasia in anotherwise healthy subject. Acta Ophthalmol Scand84:140–144

9. Brown MC, Southern CL, Anbarasu A, Kaye SB,Fisher AC, Hagan RP, Newman WD (2006)Congenital absence of optic chiasm: demonstration ofan uncrossed visual pathway using monocular flashvisual evoked potentials. Doc Ophthalmol 113(1):1–4

10. Brecelj J, Stirn-Kranjc B, Lenassi E, Likar K (2006)Recording ERG and VEP in infants and children.Ophthalmol Croat, in press

11. Kriss T, Jeffrey B, Taylor D (1992) Theelectroretinogram in infants and young children. JClin Neurophysiol 9:373–393

12. Odom JV, Bach M, Barber C, Brigell M, Marmor MF,Tormene AP, Holder GE, Vaegan (2004) Visualevoked potentials standard. Doc Ophthalmol108:115–123

13. Harden A (1982) Maturation of the visual evokedpotentials. In: Chiarenza GA, Papakostopoulos (eds)Clinical application of cerebral evoked potentials inpediatric medicine. Amsterdam: Excerpta Medica pp.41–59

14. Benavente I, Tamargo P, Tajada N, Yuste V, OlivanMJ (2005) Flash visually evoked potentials in thenewborn and their maturation during the first sixmonths of life. Doc Ophthalmol 110:255–263

15. Halliday AM, Halliday E, Kriss A, McDonald WI,Mushin J (1976) The pattern-evoked potential incompression of the anterior visual pathways. Brain99(2):357–374

16. Brecelj J, Denislic M, Skrbec M (1989) Visual evokedpotential abnormalities in chiasmal lesions. DocOphthalmol 73:139–148

17. Brecelj J, Strucl M, Skrbec M (1992) Visual evokedpotentials in compressive lesions of the optic chiasm.Neuro-ophthamol 12(4):207–214

18. Brecelj J (1992) A VEP study of the visual pathwayfunction in compressive lesions of the optic chiasm.Full-field versus half-field stimulation.Electroencephalogr Clin Neurophysiol 84(3):209–218

19. Halliday AM (1993) Evoked potentials in clinicaltesting, 2nd edition. Edinburgh: Churchill Livingstone

20. Brecelj J (1994) Electrodiagnostics of chiasmalcompressive lesions. Int J Psychophysiol 16:263–272

21. Hoffmann MB, Seufert PS, Bach M (2004) Simulatednystagmus suppresses pattern-reversal but not pattern-onset visual evoked potentials. Clin Neurophysiol115(11):2659–2665

22. Brodsky MC, Glasier CM (1993) Optic nervehypoplasia. Arch Ophthalmol 111:66–74

23. Hellstrom A, Wiklund LM, Svensson E (1999) Theclinical and morphologic spectrum of optic nervehypoplasia. J AAPOS 3(4):212–220

24. Brodsky MC (1994) Major review. Congenital opticdisk anomalies. Surv Ophthalmol 39(2):89–112

25. Fahnenhjelm TK, Wide K, Flodmark O, Ek U,Hellstrom A (2003) Posterior ocular malformationsin children: somatic, neuroradiologic and cognitiveaspects. Acta Paediatr 92(3):301–308

26. Victor JD, Apkarian P, Hirsch J, Conte MM, PackardM, Relkin NR, Kim KHS, Shapley RM (2000) Visualfunction and brain organization in non-decussatingretinal-fugal fibre syndrome. Cereb Cortex 10(1):2–22

27. Apkarian P, Reits D, Spekreijse H, Dorp van D (1983)A decisive electrophysiological test for humanalbinism. Electroencephalogr Clin Neurophysiol55(5):513–531

28. Kriss A, Russell-Eggitt I, Taylor D (1990) Childhoodalbinism. Visual electrophysiological features.Ophthalmol Paediatr Genet 11(3):185–192

29. Dorey SE, Neveu MM, Burton LC, Sloper JJ, HolderGE (2003) The clinical features of albinism and theircorrelation with visual evoked potentials. Br JOphthalmol 87:767–772

30. Brecelj J, Stirn-Kranjc B (2004) Visualelectrophysiological screening in diagnosing infantswith congenital nystagmus. Clin Neurophysiol115(2):461–470

31. Kriss A (1996) Nystagmus and pediatric visualelectrophysiology . In: Kimura J, Shibasaki H (eds)Recent advances in clinical neurophysiology.Amsterdam: Elsevier, pp. 480–487

Doc Ophthalmol (2007) 114:53–65 65

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