Congenital Absence of the Optic Chiasm

Congenital absence of the optic chiasm or achiasma is a rare condition. Only a few cases have been reported in the literature. We report on a child with early onset nystagmus. Magnetic resonance imaging demonstrated absence of the optic chiasm with normal optic nerves and optic tracts. There were no other midline abnormalities, migration anomalies, space-occupying lesions, nor destructive processes. The child had an associated partial growth hormone deficiency. Early onset nystagmus may have many causes and congenital absence of the optic chiasm is very rare, but it should be included in the differential diagnosis of early onset nystagmus. Brain imaging is indicated when an abnormality of the visual pathways is suspected.     

Congenital absence of optic chiasm: demonstration of an uncrossed visual pathway using monocular flash visual evoked potentials

A 35 month old child was referred for electrophysiology testing with pendular nystagmus, corresponding head oscillations and reduced vision. Flash visual evoked potential (VEP) revealed large responses at the right occiput (but not the left occiput) from the right eye and similar large responses at only the left occiput from the left eye, indicating absent/deficient crossover at the chiasm. A magnetic resonance imaging (MRI) scan subsequently confirmed absence of the optic chiasm. There was no other evidence of midline brain defects. Her subsequent development to age 11 has been followed. The nystagmus has remained mainly horizontal but a torsional component was noted from age 5 years and described as see-saw at age 6 years. A small right esotropia was noted at 6 years and spectacles prescribed for low hypermetropic refractive error. Bilateral superior rectus recessions at age 7 years produced an improved head posture. Her visual acuity has remained stable at around 6/24 from age 4 years. No binocularity nor stereopsis has been demonstrated over subsequent visits.     

Achiasmia and unilateral optic nerve hypoplasia in an otherwise healthy infant

An 18-month-old white boy, observed by his parents at 1-2 months age to have poor visual attentiveness and nystagmus, underwent an ophthalmological evaluation. The patient also underwent unsedated 5-channel flash visual evoked potentials (VEP) and sedated electroretinogram (ERG) testing as well as magnetic resonance imaging (MRI) of the brain and orbits. The VEP in response to monocular stimulation demonstrated occipital asymmetry and was clearly suggestive of crossed asymmetry and also showed right optic nerve hypoplasia. The MRI and fundoscopic examinations supported the findings of achiasmia and probable optic nerve hypoplasia. The patient also had decreased Teller card visual acuity, nystagmus and a variable right esotropia. Neurological examination was normal. The ophthalmological and MRI findings in this 18-month-old male patient support the diagnosis of isolated non-decussating retinal-fugal fibre syndrome as well as hypoplasia of the optic nerve.     

Alfred Bielschowsky (1871-1940) A life for strabismology

Purpose The purpose of the present study was to accurately document the oculomotor misalignments and instabilities associated with the non-decussating retinal-fugal fiber syndrome, a rare inborn, isolated, achiasmatic condition. 1–3 To date, the achiasmatic syndrome described has thus far been identified in three unrelated females. 1–4 A comparable achiasmatic condition has also been identified in a canine breed. 5,6 Materials and Methods The unique, inborn visual pathway malformation in the form of an isolated absence of the optic chiasm was confirmed by metabolic assay, the visual evoked potential (VEP) misrouting paradigm and neuroradiological evaluation, including magnetic resonance imaging (MRI). Horizontal and vertical, left and right eye, oculomotor scleral search coil recordings were measured, in one of the achiasmats, at 15 years of age. Comparable oculomotor recordings were implemented in three controls, including a normal age-matched control, an adult control and an adult with idiopathic congenital nystagmus (CN). In addition to central and eccentric target fixation with binocular and monocular viewing, binocular and monocular pursuit and optokinetic nystagmus (OKN) also were recorded. Results Following a binocular and monocular fixation paradigm, classic congenital nystagmus (CN) profiles were recorded in the achiasmat in the horizontal planes together with see-saw nystagmus (SSN) in the vertical planes; an alternating esotropia and vertical tropias also were documented. The CN showed interocular conjugacy and waveforms typically exhibited well-defined foveation periods. In general, both achiasmatic horizontal and vertical eye movements as well as corresponding interocular misalignments varied with stimu-lus and recording conditions. Moreover, horizontal eye movements showed sustained interocular conjugacy while vertical eye movements typically showed disconjugacy. Previous oculomotor studies in the achiasmatic canine breed revealed comparable oculomotor instabilities, albeit the latter were reported to present primarily with unyoked eye movements and uniocular saccades. In the present study, in addition to target fixation with binocular and monocular viewing, binocular and monocular pursuit and OKN responses also were recorded. For the achiasmat, high-gain pursuit results, as with eccentric fixation, emphasized a preference for fixation with the adducting eye. Also at eccentric gaze with monocular viewing, the eye under cover showed, relative to the fixating eye, a hypodeviation concomitant with adduction and a hyperdeviation concomitant with abduction. OKN profiles in the achiasmat with stimuli presented under both normal viewing and open-loop, retinal-field locked conditions proved rather complex; however, when an OKN response was identified, reversed OKN tracking was not apparent. Conclusions In general, the oculomotor results reported herein demonstrate that the non-decussating retinal-fugal fiber syndrome is an afferent visual pathway disorder associated with vertical and horizontal misalignments concurrent with congenital nystagmus and also with the rarer see-saw nystagmus.     

See-saw nystagmus and brainstem infarction MRI finclings

A patient with see-saw nystagmus had a lesion localized by Magnetic Resonance Imaging (MRI) to the paramedian ventral midbrain with involvement of the right interstitial nucleus of Cajal. This is the first MRI study of see-saw nystagmus associated with a presumed brainstem vascular event. Our finclings support animal and human studies suggesting that dysfunction of the interstitial nucleus of Cajal or its connections is central in this disorder.     

Nystagmus in periventricular leucomalacia

BACKGROUND/AIMS—Periventricular leucomalacia (PVL) is a lesion in the immature brain involving the optic radiation. Children with PVL have visual problems including crowding, visual field defects, strabismus, and visual perceptual/cognitive deficits, together with nystagmus. They often have optic nerve hypoplasia seen either as small discs or as large cupping of normal sized optic discs. This study aimed to perform eye movement recordings in a group of children with PVL in order to characterise and classify the nystagmus.METHODS—19 children with PVL on cerebral imaging underwent eye movement recordings with the Ober-2 infrared reflection technique.RESULTS—16 of the 19 subjects had horizontal nystagmus.CONCLUSION—The present study shows that nystagmus is commonly seen in children with PVL.     

See-saw nystagmus due to unilateral mesodiencephalic lesion.

See-saw nystagmus is a unique torsional-vertical eye movement disorder with a characteristic appearance. It is a pendular nystagmus with two distinct components: a conjugate torsional component and a disjunctive vertical component. In those cases of see-saw nystagmus in which a focal lesion has been identified, the lesion is usually a bilateral, symmetric lesion located at the mesodiencephalic junction. We report an unusual case of see-saw nystagmus which was due to a strictly unilateral mesodiencephalic lesion. Furthermore, the see-saw nystagmus had, in this case, a jerk wave-form rather than the usual pendular wave-form, with the torsional component of the jerk see-saw nystagmus beating toward the side of the lesion. These observations have an impact upon the localizing and lateralizing significance of torsional nystagmus in general and of see-saw nystagmus in particular.     

Congenital see-saw nystagmus associated with retinitis pigmentosa

Two sibling patients with see-saw nystagmus associated with advanced retinitis pigmentosa are presented. The see-saw nystagmus was most likely congenital but demonstrated a torsional pattern different from that previously reported for congenital see-saw nystagmus. Anatomic and etiologic factors associated with see-saw nystagmus are discussed.     

VEP asymmetry with ophthalmological and MRI findings in two achiasmatic children

Achiasmia is a rarely diagnosed visual pathway maldevelopment where all or the majority of nasal retinal fibres fail to decussate at the optic chiasm. It has been identified by neuroimaging 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.     

The prevalence of strabismus in congenital nystagmus: the influence of anterior visual pathway disease.

PURPOSE: To determine the influence of underlying visual system disorders on the risk of developing strabismus in children with congenital nystagmus. METHODS: We retrospectively reviewed 82 cases of congenital nystagmus from a pediatric ophthalmology referral practice. RESULTS: Strabismus was found in 50% of children with congenital nystagmus. The prevalence of strabismus was 82% in children with bilateral optic nerve hypoplasia, 53% in patients with albinism, 36% in children with congenital retinal dystrophies, and 17% in children with idiopathic congenital nystagmus. CONCLUSION: The risk that a child with congenital nystagmus will have strabismus develop can be predicted from the nature of the underlying visual disorder.     

Monocular nystagmus with sectoral optic nerve hypoplasia in a patient with septo‐optic dysplasia

This case depicts an unusual presentation of septo‐optic dysplasia. A four‐year‐old female presented with monocular nystagmus and temporal optic disc pallor in her left eye. Despite a normal sized optic nerve head, magnetic resonance imaging (MRI) showed a hypoplastic intraorbital and intracranial left optic nerve in the absence of a septum pellucidum. She was subsequently diagnosed with septo‐optic dysplasia with sectoral optic nerve head hypoplasia.     

Abnormal Retinal Vessel Architecture in Albinism and Idiopathic Infantile Nystagmus

PurposeInfantile nystagmus syndrome (INS) causes altered visual development and can be associated with abnormal retinal structure, to which vascular development of the retina is closely related. Abnormal retinal vasculature has previously been noted in albinism but not idiopathic infantile nystagmus. We compared the number and diameter of retinal vessels in participants with albinism (PWA) and idiopathic infantile nystagmus (PWIIN) with controls.MethodsFundus photography data from 24 PWA, 10 PWIIN, and 34 controls was analyzed using Automated Retinal Image Analyzer (ARIA) software on a field of analysis centered on the optic disc, the annulus of which extended between 4.2 mm and 8.4 mm in diameter.ResultsCompared with controls, the mean number of arterial branches was reduced by 24% in PWA (15.5 vs. 20.3, P < 0.001), and venous branches were reduced in both PWA (29%; 12.9 vs. 18.2, P < 0.001) and PWIIN (17%; 15.1 vs. 18.2, P = 0.024). PWA demonstrated 7% thinner “primary” (before branching) arteries (mean diameter: 75.39 µm vs. 80.88 µm, P = 0.043), and 13% thicker (after branching) “secondary” veins (66.72 µm vs. 59.01 µm in controls, P = 0.009).ConclusionsPWA and PWIIN demonstrated reduced retinal vessel counts and arterial diameters compared with controls. These changes in the superficial retinal vascular network may be secondary to underdevelopment of the neuronal network, which guides vascular development and is also known to be disrupted in INS.     

Acuity development in infantile nystagmus

PURPOSE: To compare development of acuity in patients with isolated infantile nystagmus and infantile nystagmus associated with a visual sensory defect. METHODS: Visual acuities in 57 children (1 month to 4 years of age) with infantile nystagmus were assessed by using Teller acuity cards oriented vertically during binocular viewing. Twenty-two had isolated infantile nystagmus, 21 had albinism, 7 had aniridia, and 7 had mild or moderate bilateral optic nerve hypoplasia (BONH). Longitudinal acuity was measured in 40 of these patients (mean 1.8, 2.3, 3.1, and 3.3, measurements per patient group, respectively). The rate of acuity development across the study groups was quantified by linear regression of log acuity versus log age and compared to published normative data. RESULTS: The rate of acuity development was similar across all groups and paralleled the normative data. The slope of log grating acuity versus log age (+/-SEM) was normal, 0.73; isolated infantile nystagmus, 0.80 +/- 0.11; albinism, 0.80 +/- 0.11; aniridia, 0.87 +/- 0.16; and BONH, 0.79 +/- 0.18. The slopes were not significantly different (ANCOVA, F(4,142) = 0.21, P = 0.93). Compared with published binocular normative data, mean acuity adjusted for age was reduced by 1.2 octaves in isolated infantile nystagmus and by 1.7 to 2.5 octaves in nystagmus with associated sensory defect. CONCLUSIONS: The rate of acuity development in infantile nystagmus is largely independent of the gaze-holding instability or an associated visual sensory defect. Reduction of mean acuity in albinism, aniridia, and BONH is due to the visual sensory defect and exceeds the acuity reduction observed in isolated infantile nystagmus.     

The sub-clinical see-saw nystagmus embedded in infantile nystagmus

A transient, decompensated vertical phoria in an individual with infantile nystagmus syndrome (INS) resulted in two images that oscillated vertically-a diplopic oscillopsia. Ocular motor studies during the vertical oscillopsia recreated by vertical prisms, led to the identification of a sub-clinical see-saw nystagmus (SSN), present under the prism-induced diplopic condition. Retrospective analysis of ocular motor recordings made prior to the above episode of vertical diplopia revealed the presence of that same sub-clinical SSN. The SSN had not been detected previously despite extensive observations and recordings of this subject's pendular IN over a period of forty years. Three- dimensional search-coil data from fourteen additional INS subjects (with pendular and jerk waveforms) confirmed the existence of sub-clinical SSN embedded within the clinically detectable horizontal-torsional IN in seven of the fifteen and a sub-clinical, conjugate, vertical component in the remaining eight. Unlike the clinically visible SSN found in achiasma, the cause of this sub-clinical SSN is hypothesized to be due to a failure of the forces of the oblique muscles (responsible for the torsional component of the IN) to balance out the associated forces of the vertical recti; the net result is a small, sub-clinical SSN. Thus, so-called "horizontal" IN is actually a horizontal-torsional oscillation with a secondary, sub-clinical SSN or conjugate vertical component. The suppression of oscillopsia by efference copy in INS appears to be accomplished for each eye individually, even in a binocular individual. However, failure to fuse the two images results in oscillopsia of one of them.     

A new surgery for congenital nystagmus: effects of tenotomy on an achiasmatic canine and the role of extraocular proprioception.

PURPOSE: Human eye-movement recordings have documented that surgical treatment of congenital nystagmus (CN) also produces a broadening of the null zone and changes in foveation that allow increased acuity. We used the achiasmatic Belgian sheepdog, a spontaneously occurring animal model of human CN and see-saw nystagmus (SSN), to test the hypothesis that changes induced by surgical interruption of the extraocular muscle afference without a change in muscle-length tension could damp both oscillations. METHODS: An achiasmatic dog with CN and SSN underwent videotaping and infrared oculography in a sling apparatus and head restraints before and after all extraocular muscles (stage 1: 4 horizontal rectus muscles and stage 2 [4 months later]: 4 vertical rectus muscles and 4 oblique muscles) were surgically tenotomized and immediately reattached at their original insertions. RESULTS: The dog had immediate and persistent visible, behavioral, and oculographic changes after each stage of this new procedure. These included damped CN and SSN, increased ability to maintain fixation, and increased periods of maintaining the target image on the area centralis over a broad range of gaze angles. CONCLUSIONS: Severing and reattaching the tendons of the extraocular muscles affect some as-yet-unknown combination of central nervous system processes producing the above results. This new procedure may prove effective in patients with CN with either no null, a null at primary position, or a time-varying null (due to asymmetric, (a)periodic, alternating nystagmus). We infer from our results in an achiasmatic dog that tenotomy is the probable cause of the damping documented in human CN after Anderson-Kestenbaum procedures and should also damp CN and SSN in achiasma in humans. It may also prove useful in acquired nystagmus to reduce oscillopsia. The success of tenotomy in damping nystagmus in this animal suggests that the proprioceptive feedback loop has a more important role in ocular-motor control than has been appreciated. Finally, we propose a modified bimedial recession procedure, on the basis of the damping effects of tenotomy.     

Nystagmus in suprasellar tumors: Recent advances in diagnosis and therapy

Congenital and acquired nystagmus, particularly pendular and jerk nystagmus, see-saw nystagmus and spasmus nutans, may be the presenting sign of a suprasellar mass lesion.¹ The large variety of different suprasellar mass lesions requiring quite different therapeutic measures necessitates exact histological diagnosis for optimal therapeutic strategy planning.² Stereotactic tumor biopsy has become a well-established diagnostic approach, combining minimal surgical trauma with a high degree of diagnostic safety. Particularly in the two most frequent suprasellar mass lesions – craniopharyngiomas and pilocytic astrocytomas – accurately planned stereotactic drainage of tumor cysts combined with radiotherapy and/or stereotactic radiosurgery allows successful decompression and tumor control as well as maximum preservation of visual and endocrinological functions when compared with conventional surgical procedures. 2–11     

Neuro-Ophthalmological Findings in Children and Adolescents with Chronic Ataxia

Chronic ataxia is a challenging problem in paediatric neurology. It is caused by a multitude of disorders that at least initially have similar or non-specific phenotype. Some of these disorders have associated neuro-ophthalmological signs (N-OS). The aims of this study are to describe the N-OS and their frequencies in general and by disease aetiology in paediatric patients with chronic ataxia. The authors identified 184 patients under age 17 years with chronic ataxia (>2 months duration or recurrent) during 1991–2008 from multiple sources. Diagnoses and N-OS were ascertained following charts review. Mean age (SD) was 15 (7.7) years. Median duration of follow-up was 6.4 years. There were 214 N-OS in 115 patients (median = 2, range = 1–5 N-OS/patient). Strabismus was present in 29.3% of patients, nystagmus 27.7%, impaired smooth pursuit 23.4%, hypometric saccades 10.3%, decreased visual acuity 9.2%, abnormal optic discs 8.7%, abnormal pupillary examination 2.7%, hypermetric saccades 2.2%, impaired ductions 1.6%, and abnormal visual fields in 1.1% of patients. N-OS were reported most commonly among patients with the following disorders (commonest N-OS): hypoxic-ischaemic encephalopathy following birth (strabismus), episodic ataxia (nystagmus), neuronal ceroid lipofuscinosis (abnormal optic discs), neuronal migration disorder (strabismus), ischaemic stroke (nystagmus), Joubert syndrome–related disorders (strabismus), leukodystrophy (nystagmus), Friedreich ataxia (hypometric saccades, impaired smooth pursuit, nystagmus), mitochondrial disease (strabismus, nystagmus), ataxia telangiectasia (impaired smooth pursuit), and Angelman syndrome (strabismus). N-OS occur commonly in children with chronic ataxia. Although non-specific, they vary with disease aetiology, potentially aiding in the assessment of these patients.     

Social and visual function in nystagmus

AIM: To investigate the influence of nystagmus on visual and social function and determine if parents are able to assess visual and social function in children with nystagmus. METHOD: A postal questionnaire comprising 14 questions related to visual function (VF-14) and questions pertaining to social function were sent to all 1013 members of the Nystagmus Network-a UK based organisation for nystagmus sufferers and their families. Visual and social function scores were compared by regression analysis. RESULTS: 180 adult, 233 parent, and 124 child questionnaires were returned. Idiopathic nystagmus was the most common cause. In adults the mean VF-14 score indicated very low visual function, in the same range as patients assessed in low vision services. Children's visual function scored better than adults, between scores of patients with age related macular disease and corneal grafts. There was a strong correlation between perceived visual and social function for adults (p<0.001) and parental assessment of their children (p<0.001), but not between child self assessment of visual and social function. There was strong correlation between parental and child assessment of visual and social function (p<0.001, p<0.001) CONCLUSION: Questionnaires indicated that nystagmus is associated with very low visual function. There is a strong correlation between visual and social impairment. The authors have shown for the first time in an ophthalmic disease that parents are able to estimate the impact of nystagmus on their child both in terms of visual and social functioning, although they underestimate the impact of nystagmus on emotional aspects of wellbeing.     

Evidence for Non-Opponent Coding of Colour Information in Human Visual Cortex: Selective Loss of “Green” Sensitivity in a Subject with Damaged Ventral Occipito-Temporal Cortex

Damage to ventral occipito-temporal extrastriate visual cortex leads to the syndrome of prosopagnosia often with coexisting cerebral achromatopsia. A patient with this syndrome resulting in a left upper homonymous quadrantanopia, prosopagnosia, and incomplete achromatopsia is described. Chromatic sensitivity was assessed at a number of locations in the intact visual field using a dynamic luminance contrast masking technique that isolates the use of colour signals. In normal subjects chromatic detection thresholds form an elliptical contour when plotted in the Commission Internationale d’Eclairage, (x-y), chromaticity diagram. Because the extraction of colour signals in early visual processing involves opponent mechanisms, subjects with Daltonism (congenital red/green loss of sensitivity) show symmetric increase in thresholds towards the long wavelength (“red”) and middle wavelength (“green”) regions of the spectrum locus. This is also the case with acquired loss of chromatic sensitivity as a result of retinal or optic nerve disease. Our patient’s results were an exception to this rule. Whilst his chromatic sensitivity in the central region of the visual field was reduced symmetrically for both “red/green” and “yellow/blue” directions in colour space, the subject’s lower left quadrant showed a marked asymmetry in “red/green” thresholds with the greatest loss of sensitivity towards the “green” region of the spectrum locus. This spatially localized asymmetric loss of “green” but not “red” sensitivity has not been reported previously in human vision. Such loss is consistent with selective damage of neural substrates in the visual cortex that process colour information, but are spectrally non-opponent.KEYWORDS: cerebral achromatopsia, chromatic sensitivity, colour opponency, colour vision, prosopagnosia     

Nystagmus in suprasellar tumors: recent advances in diagnosis and therapy

Congenital and acquired nystagmus, particularly pendular and jerk nystagmus, see-saw nystagmus and spasmus nutans, may be the presenting sign of a suprasellar mass lesion.(1) The large variety of different suprasellar mass lesions requiring quite different therapeutic measures necessitates exact histological diagnosis for optimal therapeutic strategy planning.(2) Stereotactic tumor biopsy has become a well-established diagnostic approach, combining minimal surgical trauma with a high degree of diagnostic safety. Particularly in the two most frequent suprasellar mass lesions - craniopharyngiomas and pilocytic astrocytomas - accurately planned stereotactic drainage of tumor cysts combined with radiotherapy and/or stereotactic radiosurgery allows successful decompression and tumor control as well as maximum preservation of visual and endocrinological functions when compared with conventional surgical procedures.(2-11)