Permanent transduction of retinal ganglion cells by rAAV2-retro

Adeno-associated virus (AAV) is widely used as a vector for delivery of gene therapy. Long term therapeutic benefit depends on perpetual expression of the wild-type gene after transduction of host cells by AAV. To address this issue in a mass population of identified single cells, 4 rats received an injection of a 1:1 mixture of rAAV2-retro-hSyn-EGFP and rAAV2-retro-hSyn-mCherry into each superior colliculus. After the virus was transported retrogradely to both retinas, serial fundus imaging was performed at days 14, 45, 211, and 375 to visualize individual fluorescent ganglion cells. The location of each cell was plotted to compare labeling at each time point. In 12/16 comparisons, 97% or more of the cells identified in the initial baseline fundus image were still labeled at day 375. In 4 cases the percentage was lower, but in these cases the apparent reduction in the number of labeled cells at day 375 was attributable to the lower quality of follow-up fundus images, rather than true loss of transgene expression. These data indicate that retinal ganglion cells transduced by rAAV2-retro are transduced permanently.

Postoperative magnetic resonance imaging of the inferior oblique muscle

No previous imaging study has described the appearance of the inferior oblique muscle after surgery. It is unknown whether findings signifying prior myectomy or recession are recognizable on magnetic resonance (MR) imaging and how they might differ for the two procedures. After myectomy via a temporal approach, the cauterized muscle stump retracts into the medial orbit. How far it retracts and whether it reattaches to the globe remains unclear. To address these issues, orbital MR images were reviewed in 5 patients who had previously undergone inferior oblique myectomy or recession. In each case, the operated muscle exhibited subtle but telltale features, when compared with the normal, fellow inferior oblique. After myectomy, the inferior oblique still terminated lateral to the inferior rectus muscle and appeared closely apposed to the globe, although not necessarily attached to the sclera.

Decussating axons segregate within the anterior core of the primate optic chiasm

BACKGROUND

The axons of ganglion cells in the nasal retina decussate at the optic chiasm. It is unclear why tumours cause more injury to crossing nasal fibres, thereby giving rise to temporal visual field loss in each eye. To address this issue, the course of fibres through the optic chiasm was examined following injection of a different fluorescent tracer into each eye of a monkey.

METHODS

Under general anaesthesia, cholera toxin subunit B-Alexa Fluor 488 was injected into the right eye and cholera toxin subunit B-Alexa Fluor 594 was injected into the left eye of a single normal adult male rhesus monkey. After a week's survival for anterograde transport, serial coronal sections through the primary optic pathway were examined.

RESULTS

A zone within the core of the anterior and mid portions of the optic chiasm was comprised entirely of crossing fibres. This zone of decussation was delineated by segregated, interwoven sheets of green (right eye) and red (left eye) fibres. It expanded steadily to fill more of the optic chiasm as fibres coursed posteriorly towards the optic tracts. Eventually, crossed fibres became completely intermingled with uncrossed fibres, so that ocular separation was lost.

CONCLUSIONS

A distinct, central compartment located within the anterior two-thirds of the optic chiasm contains only crossing fibres. Sellar tumours focus their compressive force on this portion of the structure, explaining why they so often produce visual field loss in the temporal fields.

Quotidian Profile of Vergence Angle in Ambulatory Subjects Monitored With Wearable Eye Tracking Glasses

Purpose

Wearable eye trackers record gaze position as ambulatory subjects navigate their environment. Tobii Pro Glasses 3 were tested to assess their accuracy and precision in the measurement of vergence angle.

Methods

Four subjects wore the eye tracking glasses, with their head stabilized, while fixating at a series of distances corresponding to vergence demands of: 0.25, 0.50, 1, 2, 4, 8, 16, and 32°. After these laboratory trials were completed, 10 subjects wore the glasses for a prolonged period while carrying out their customary daily pursuits. A vergence profile was compiled for each subject and compared with interpupillary distance.

Results

In the laboratory, the eye tracking glasses were comparable in accuracy to remote video eye trackers, outputting a mean vergence value within 1° of demand at all angles except 32°. In ambulatory subjects, the glasses were less accurate, due to tracking interruptions and measurement errors, partly mitigated by the application of data filters. Nonetheless, a useful record of vergence behavior was obtained in every subject. Vergence profiles often had a bimodal distribution, reflecting a preponderance of activities at near (mobile phone and computer) or far (driving and walking). As expected, vergence angle correlated with interpupillary distance.

Conclusions

Wearable eye tracking glasses make it possible to compile a nearly continuous record of vergence angle over hours, which can be correlated with the corresponding visual scene viewed by ambulatory subjects.

Translational Relevance

This technology provides new insight into the diversity of human ocular motor behavior and may become useful for the diagnosis of disorders that affect vergence function such as: convergence insufficiency, Parkinson disease, and strabismus.

Ambulatory Monitoring With Eye Tracking Glasses to Assess the Severity of Intermittent Exotropia

PURPOSE

To explore the utility of eye tracking glasses in patients with intermittent exotropia as a means for quantifying the occurrence of exotropia, defined as the percentage of time that the eyes are misaligned.

DESIGN

Prospective observational study.

METHODS

Eye tracking glasses were used to obtain 68 recordings in 44 ambulatory patients with a history of intermittent exotropia. Vergence angle was monitored for up to 12 hours to document the occurrence of exotropia.

RESULTS

Intermittent exotropia was present in 31 of 44 patients. They had a mean exotropia of 19.3 ± 5.3° and a mean occurrence of 40% (range 3-99%). There was a moderate correlation between the magnitude of exotropia and its occurrence (r = 0.59). In 13 patients the occurrence of exotropia was <1%; they were deemed to have an exophoria only. In 35 of 44 cases, families reported an occurrence of intermittent exotropia greater than that measured by the eye tracking glasses.

CONCLUSIONS

Eye tracking glasses may be a useful tool for quantifying the severity of intermittent exotropia and for defining more precisely its clinical features.

Retinal Input to the Primate Lateral Geniculate Nucleus Revealed by Injection of a Different Label Into Each Eye

ABSTRACT

The primate lateral geniculate nucleus has long been a favorite structure among anatomists because of its striking lamination. It has been shown that each lamina receives input from a different eye using various single label techniques but never by double labeling. Here, we illustrate the organization of retinal inputs to the lateral geniculate nucleus by injection of cholera toxin-B conjugated to Alexa Fluor-488 into the right eye and cholera toxin-B conjugated to Alexa Fluor-594 into the left eye.

TRAF7 somatic mosaicism in a patient with bilateral optic nerve sheath meningiomas: illustrative case

BACKGROUND

In the past decade, next-generation sequencing has spurred significant progress in the understanding of cytogenetic alterations that occur in meningiomas. Eighty percent of adult meningiomas harbor pathogenic somatic variants involving NF2, TRAF7, SMARCB1, KLF4, PI3K, or POLR2A. Somatic variants in TRAF7 associated with meningiomas usually localize to the gene’s WD40 domains but are mutually exclusive to germline mutations, which cause a distinctive autosomal dominant syndrome.

OBSERVATIONS

This case involved a 15-year-old girl with bilateral optic nerve sheath meningiomas, diffuse meningiomatosis, and syndromic features, including craniosynostosis, brain anomalies, syndactyly, brachydactyly, epicanthus, and patent ductus arteriosus. Genetic testing of the meningioma specimen 7 years after biopsy showed a pathogenic p.R641C variant within the WD40 domain of the TRAF7 gene. Additional testing of unaffected tissues identified the same variant at lower allele frequencies, consistent with postzygotic somatic mosaicism.

LESSONS

The authors report postzygotic somatic mosaicism for a p.R641C variant in the TRAF7 gene in a patient with bilateral optic nerve sheath meningiomas, diffuse meningiomatosis and a constellation of systemic findings previously recognized in patients with germline mutations of this gene. This is the first report of optic nerve sheath meningioma in a patient with mutation in the TRAF7 gene.

Massive periorbital edema following hematopoietic stem cell transplantation

Purpose

To describe a case of severe, bilateral periorbital edema after hematopoietic stem cell transplantation.

Observations

A three-year old girl with metastatic neuroblastoma underwent the second of two tandem autologous peripheral blood stem cell transplants, complicated by engraftment syndrome. On post-engraftment day 11, she developed acute onset of severe periorbital edema. She was soon thereafter diagnosed with transplant-associated thrombotic microangiopathy with significant volume overload requiring treatment with eculizumab and etanercept. Periorbital edema resolved after four days with concurrent treatment of her underlying condition.

Conclusions and Importance

We report an ocular manifestation related to complications of hematopoietic stem cell transplantation. This highlights a non-infectious etiology of eyelid swelling in the post-transplant, immunocompromised population.

Fundus imaging of retinal ganglion cells transduced by retrograde transport of rAAV2-retro

Access of adeno-associated virus (AAV) to ganglion cells following intravitreal injection for gene therapy is impeded by the internal limiting membrane of the retina. As an alternative, one could transduce ganglion cells via retrograde transport after virus injection into a retinal target nucleus. It is unknown if recombinant AAV2-retro (rAAV2-retro), a variant of AAV2 developed specifically for retrograde transport, is capable of transducing retinal ganglion cells. To address this issue, equal volumes of rAAV2-retro-hSyn-EGFP and rAAV2-retro-hSyn-mCherry were mixed in a micropipette and injected into the rat superior colliculus. The time-course of viral transduction was tracked by performing serial in vivo fundus imaging. Cells that were labeled by the fluorophores within the first week remained consistent in distribution and relative signal strength on follow-up imaging. Most transduced cells were double-labeled, but some were labeled by only EGFP or mCherry. Fundus images were later aligned with retinal wholemounts. Ganglion cells in the wholemounts matched precisely the cells imaged by fundus photography. As seen in the fundus images, ganglion cells in wholemounts were sometimes labeled by only EGFP or mCherry. Overall, there was detectable label in 32-41% of ganglion cells. Analysis of the number of cells labeled by 0, 1, or 2 fluorophores, based on Poisson statistics, yielded an average of 0.66 virions transducing each ganglion cell. Although this represents a low number relative to the quantity of virus injected into the superior colliculus, the ganglion cells showed sustained and robust fluorescent labeling. In the primate, injection of rAAV2-retro into the lateral geniculate nucleus might provide a viable approach for the transduction of ganglion cells, bypassing the obstacles that have prevented effective gene delivery via intravitreal injection.

Columnar and Laminar Segregation of Retinal Input to the Primate Superior Colliculus Revealed by Anterograde Tracer Injection Into Each Eye

Purpose

After the lateral geniculate nucleus, the superior colliculus is the richest target of retinal projections in primates. Hubel et al. used tritium autoradiography to show that axon terminals emanating from one eye form irregular columns in the stratum griseum superficiale. Unlabeled gaps were thought to be filled by the other eye, but this assumption was never tested directly.

Methods

Experiments were performed in two normal macaques. In monkey 1, [³H]proline was injected into the left eye and the pattern of radiolabeling was examined in serial cross-sections through the entire superior colliculus. In monkey 2, cholera toxin subunit B conjugated to Alexa 488 was injected into the right eye and cholera toxin subunit B - Alexa 594 was injected into the left eye. The two fluorescent labels were compared in a reconstruction of the superior colliculus prepared from serial sections.

Results

In monkey 1, irregular columns of axon terminals were present in the superficial grey. The projection from the peripheral retina was stronger than the projection from the macula. In monkey 2, the two fluorescent Alexa tracers mainly interdigitated: a conspicuous gap in one label was usually filled by a clump of the other label. There was also partial laminar segregation of ocular inputs. In the far peripheral field representation, the contralateral eye's input generally terminated closer to the tectal surface. In the midperiphery the eyes switched, bringing the ipsilateral input nearer the surface.

Conclusions

Direct retinal input to the macaque superior colliculus is segregated into alternating columns and strata, despite the fact that tectal cells respond robustly to stimulation of either eye.

Interocular suppression in primary visual cortex in strabismus: impact of staggering the presentation of stimuli to the eyes

Diplopia (double vision) in strabismus is prevented by suppression of the image emanating from one eye. In a recent study conducted in two macaques raised with exotropia (an outward ocular deviation) but having normal acuity in each eye, simultaneous display of stimuli to each eye did not induce suppression in V1 neurons. Puzzled by this negative result, we have modified our protocol to display stimuli in a staggered sequence, rather than simultaneously. Additional recordings were made in the same two macaques, following two paradigms. In trial type 1, the receptive field in one eye was stimulated with a sine-wave grating while the other eye was occluded. After 5 s, the occluder was removed and the neuron was stimulated for another 5 s. The effect of uncovering the eye, which potentially exposed the animal to diplopia, was quantified by the peripheral retinal interaction index (PRII). In trial type 2, the receptive field in the fixating eye was stimulated with a grating during binocular viewing. After 5 s, a second grating appeared in the receptive field of the nonfixating eye. The impact of the second grating, which had the potential to generate visual confusion, was quantified by the receptive field interaction index (RFII). For 82 units, the mean PRII was 0.48 ± 0.05 (0.50 = no suppression) and the mean RFII was 0.46 ± 0.08 (0.50 = no suppression). These values suggest mild suppression, but the modest decline in spike rate registered during the second epoch of visual stimulation might have been due to neuronal adaptation, rather than interocular suppression. In a few instances neurons showed unequivocal suppression, but overall, these recordings did not support the contention that staggered stimulus presentation is more effective than simultaneous stimulus presentation at evoking interocular suppression in V1 neurons.NEW & NOTEWORTHY In strabismus, double vision is prevented by interocular suppression. It has been reported that inhibition of neuronal firing in the primary visual cortex occurs only when stimuli are presented sequentially, rather than simultaneously. However, these recordings in alert macaques raised with exotropia showed, with rare exceptions, little evidence to support the concept that staggered stimulus presentation is more effective at inducing interocular suppression of V1 neurons.

Congenital Visual Field Loss from a Schizencephalic Cleft Damaging Meyer's Loop

A healthy, asymptomatic woman was referred after incidental discovery of a right superior incongruous hemianopia. Magnetic resonance imaging disclosed a schizencephalic cleft passing through Meyer's loop of the left optic radiation. The lesion may have resulted from a focal vascular accident or disruption of cortical neurogenesis during gestation.

Interocular Suppression in Primary Visual Cortex in Strabismus

People with strabismus acquired during childhood do not experience diplopia (double vision). To investigate how perception of the duplicate image is suppressed, we raised two male monkeys with alternating exotropia by disinserting the medial rectus muscle in each eye at age four weeks. Once the animals were mature, they were brought to the laboratory and trained to fixate a small spot while recordings were made in primary visual cortex (V1). Drifting gratings were presented to the receptive fields of 500 single neurons for eight interleaved conditions: (1) right eye monocular; (2) left eye monocular; (3) right eye's field, right eye fixating; (4) right eye's field, left eye fixating; (5) left eye's field, right eye fixating; (6) left eye's field, left eye fixating; (7) both eyes' fields, right eye fixating; (8) both eyes' fields, left eye fixating. As expected, ocular dominance histograms showed a monocular bias compared with normal animals, but many cells could still be driven via both eyes. Overall, neuronal responses were not affected by switches in ocular fixation. Individual neurons exhibited binocular interactions, but mean population indices indicated no net interocular suppression or facilitation. Even neurons located in cortex with reduced cytochrome oxidase (CO) activity, representing portions of the nasal visual field where perception is suppressed during binocular viewing, showed no net inhibition. These data indicate that V1 neurons do not appear to reflect strabismic suppression and therefore the elimination of diplopia is likely to be mediated at a higher cortical level.SIGNIFICANCE STATEMENT In patients with strabismus, images fall on non-corresponding points in the two retinas. Only one image is perceived, because signals emanating from the other eye that convey the duplicate image are suppressed. The benefit is that diplopia is prevented, but the penalty is that the visual feedback required to adjust eye muscle tone to realign the globes is eliminated. Here, we report the first electrophysiological recordings from the primary visual cortex (V1) in awake monkeys raised with strabismus. The experiments were designed to reveal how perception of double images is avoided.

The Mechanism of Macular Sparing

Patients with homonymous hemianopia sometimes show preservation of the central visual fields, ranging up to 10°. This phenomenon, known as macular sparing, has sparked perpetual controversy. Two main theories have been offered to explain it. The first theory proposes a dual representation of the macula in each hemisphere. After loss of one occipital lobe, the back-up representation in the remaining occipital lobe is postulated to sustain ipsilateral central vision in the blind hemifield. This theory is supported by studies showing that some midline retinal ganglion cells project to the wrong hemisphere, presumably driving neurons in striate cortex that have ipsilateral receptive fields. However, more recent electrophysiological recordings and neuroimaging studies have cast doubt on this theory by showing only a minuscule ipsilateral field representation in early visual cortical areas. The second theory holds that macular sparing arises because the occipital pole, where the macula is represented, remains perfused after occlusion of the posterior cerebral artery because it receives collateral flow from the middle cerebral artery. An objection to this theory is that it cannot account for reports of macular sparing in patients after loss of an entire occipital lobe. On close scrutiny, such reports turn out to be erroneous, arising from inadequate control of fixation during visual field testing. Patients seem able to detect test stimuli on their blind side within the macula or along the vertical meridian because they make surveillance saccades. A purported treatment for hemianopia, called vision restoration therapy, is based on this error. The dual perfusion theory is supported by anatomical studies showing that the middle cerebral artery perfuses the occipital pole in many individuals. In patients with hemianopia from stroke, neuroimaging shows preservation of the occipital pole when macular sparing is present. The frontier dividing the infarcted territory of the posterior cerebral artery and the preserved territory of the middle cerebral artery is variable, but always falls within the representation of the macula, because the macula is so highly magnified. For physicians, macular sparing was an important neurological sign in acute hemianopia because it signified a posterior cerebral artery occlusion. Modern neuroimaging has supplanted the importance of that clinical sign but at the same time confirmed its validity. For patients, macular sparing remains important because it mitigates the impact of hemianopia and preserves the ability to read fluently. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Purpose

The most common form of strabismus, intermittent exotropia, is thought to become manifest when the drive to fuse is overcome by excessive divergent muscle tone. This principle is tested by examining the alignment of the eyes in the absence of vision. We compare the ocular deviation in patients with intermittent exotropia under conditions of monocular versus binocular occlusion.

Methods

This prospective study of a patient cohort referred to our laboratory enrolled 18 patients with typical findings of well-controlled intermittent exotropia. Eye positions were recorded with video eye trackers while patients looked at a fixation spot at a distance of 57 cm. One eye was occluded, and the resulting ocular deviation was measured. Both eyes were then occluded, and the ocular deviation was re-measured.

Results

The majority of patients (11/18) had a smaller deviation when both eyes were covered. Occlusion of one eye resulted in a mean exotropia of 13.5° ± 4.7°. Occlusion of both eyes reduced the mean exotropia to 6.0° ± 6.5° (paired t-test, P < 0.001), corresponding to a 56% reduction in the ocular deviation. This reduction persisted during prolonged bilateral occlusion but reversed as soon as vision was restored.

Conclusions

Bilateral occlusion reveals a fixation-free state of alignment that is different from orthotropia and usually less than the exotropia that occurs spontaneously during binocular viewing. This finding demonstrates that the deviation angle in patients with intermittent exotropia is actively mediated by visual feedback, which the fixating eye is capable of providing alone.

Long-term labeling of microelectrode tracks with fluorescent latex microspheres

BACKGROUND

After physiological recordings are performed in behaving animals, it is valuable to identify microelectrode tracks in histological sections so that neuronal responses can be correlated with brain anatomy. However, no good method currently exists for long-term labeling, so that microelectrode tracks can be recovered months or even years after recording sessions.

NEW METHOD

Penetrations were made into the brains of mice with microelectrodes coated with fluorescent dyes packaged into 0.2 μm polystyrene microspheres, followed by survival periods of 3 days, 2, 4, or 6 months. Sections were examined by fluorescence microscopy before and after cytochrome oxidase histochemistry to identify microelectrode tracks.

RESULTS

After all 4 survival periods, 0.2 μm fluorescent microspheres clearly marked the tracks of microelectrode penetrations.

COMPARISON WITH EXISTING METHODS

Fluorescent microspheres label microelectrode penetrations for longer than do fluorescent lipophilic dyes, such as FM 1-43FX. The label appears punctate, and resistant to degradation, because it is protected by the barrier of the polystyrene micro-container.

CONCLUSIONS

Coating of microelectrodes with fluorescent microspheres allows one to identify the penetration track in histological sections half a year later. This technique may be useful when electrophysiological recording sessions are being carried out in behaving animals, with plans to identify electrode tracks in histological sections many months later.

Saccade Strategy in Alternating Exotropia

Patient with exotropia frequently alternate fixation, looking at something with one eye and then switching their attention to acquire a new target with the other eye. Which eye informs the brain about the location of the new target? To address this issue, we presented targets dichoptically to 16 exotropes that were visible to the fixating eye, the deviated eye, or to both eyes. We then compared the subjects' choice of eye for target acquisition with the organization of their suppression scotomas. There was a correspondence between suppression scotoma maps and the eye used to acquire peripheral targets. In other words, a target perceived via an eye was also fixated by it. These studies reveal how patients with alternating strabismus, despite eye misalignment, manage to localize and fixate efficiently visual targets in their environment.

Vertical Optokinetic Stimulation Induces Diagonal Eye Movements in Patients with Idiopathic Infantile Nystagmus

Purpose

In patients with early ocular misalignment and nystagmus, vertical optokinetic stimulation reportedly increases the horizontal component of the nystagmus present during fixation, resulting in diagonal eye movements. We tested patients with infantile nystagmus syndrome but normal ocular alignment to determine if this crosstalk depends on strabismus.

Methods

Eye movements were recorded in seven patients with infantile nystagmus. All but one patient had normal ocular alignment with high-grade stereopsis. Nystagmus during interleaved trials of right, left, up, and down optokinetic stimulation was compared with waveforms recorded during fixation. Six patients with strabismus but no nystagmus were also tested.

Results

In infantile nystagmus syndrome, horizontal motion evoked a mostly jerk nystagmus with virtually no vertical component. A vertical optokinetic pattern produced nystagmus with a diagonal trajectory. It was not simply a combination of a vertical component from optokinetic stimulation and a horizontal component from the subject's congenital nystagmus, rather in six of seven patients, the slow-phase velocity of the horizontal component during vertical optokinetic stimulation differed from that recorded during fixation. In the six strabismus patients without nystagmus, responses to vertical optokinetic stimulation were normal.

Conclusions

In patients with congenital motor nystagmus, a vertical noise pattern drives a diagonal nystagmus. This appears to arise because of crosstalk between the vertical and horizontal components of the optokinetic system. This abnormal response to vertical stimulation is not caused by strabismus because it occurs in patients with infantile nystagmus without strabismus. Moreover, it is absent in patients with strabismus and no spontaneous nystagmus.

Papilledema from gain-of-function mutations in the STAT3 gene

BACKGROUND

Signal Transducer and Activator of Transcription 3 (STAT3) gain-of-function germline mutations are associated with diverse clinical manifestations, including autoimmune cytopenia, lymphadenopathy, immunodeficiency, endocrinopathy, and enteropathy. We describe a new feature: raised intracranial pressure with papilledema.

MATERIALS AND METHODS

Report of two cases.

RESULTS

The first patient had a de novo heterozygous c.2144C>T (p.Pro715Leu) mutation in the STAT3 gene. At age 1 she had papilledema with marked sheathing of the proximal vessels on the optic discs. Follow-up 8 years later showed chronic papilledema, cystoid macular edema, and vision loss. The second patient had a de novo heterozygous c.2147C>T (p.Thr716Met) mutation. At age 12 he developed papilledema, which recurred despite treatment. In both patients, repeated sampling of the cerebrospinal fluid demonstrated a lymphocytic pleocytosis.

CONCLUSIONS

Papilledema can occur as a manifestation of STAT3 gain-of-function mutation, sometimes accompanied by prominent vascular sheathing and cystoid macular edema. The mechanism may be chronic meningeal infiltration by white blood cells, impairing cerebrospinal fluid absorption.

Experimental upper bound and theoretical expectations for parity-violating neutron spin rotation in 4He

Neutron spin rotation is expected from quark-quark weak interactions in the standard model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid 4He medium. The value for the neutron spin rotation angle per unit length in 4He, d ϕ / d z = [ + 2.1 ± 8.3 (stat.) - 0.2 + 2.9 (sys.) ] × 10 - 7 rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in then → + 4He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.

Recurrent Superior Oblique Myokymia Treated by Distal Tendon Extirpation

BACKGROUND

We describe successful surgical treatment of superior oblique myokymia, which had recurred after superior oblique tenectomy.

METHODS

Single case report.

RESULTS

The distal stump of the superior oblique tendon was extirpated by stripping it from the globe. The ipsilateral superior rectus muscle also was recessed, to correct a hypertropia that had resulted from the original superior oblique tenectomy.

CONCLUSIONS

Complete removal of the distal superior oblique muscle tendon provided definitive relief of superior oblique myokymia. Superior rectus muscle recession, combined with previous inferior oblique myectomy, compensated effectively for loss of superior oblique function.

Spontaneous Reattachment of the Medial Rectus After Free Tenotomy

PURPOSE

To assess the outcome of free tenotomy of the medial rectus muscle in post-natal monkeys.

METHODS

The medial rectus muscle was disinserted in both eyes of 6 macaques at age 4 weeks to induce an alternating exotropia. After the impact on the visual cortex and superior colliculus was investigated, the animals were examined post-mortem to assess the anatomy of the medial rectus muscles.

RESULTS

After tenotomy, the monkeys eventually recovered partial adduction. Necropsy revealed that all 12 medial rectus muscles had reattached to the globe. They were firmly connected via an abnormally long tendon, but at the native insertion site.

CONCLUSIONS

Medial rectus muscles are able to reattach spontaneously to the eye following free tenotomy in post-natal macaques. The early timing of surgery and the large size of the globe relative to the orbit may explain why reinsertion occurs more readily in monkeys than in children with a lost muscle after strabismus surgery. [J Pediatr Ophthalmol Strabismus. 2018;55(5):335-338.].

Incomitance and Eye Dominance in Intermittent Exotropia

Purpose

To determine if the deviation angle changes in subjects with intermittent exotropia as they alternate fixation between the right and left eye in primary gaze.

Methods

In this prospective observational cohort study, 37 subjects with intermittent exotropia were tested for evidence of incomitance. The position of each eye was recorded with a video tracker during fixation on a small central target. A cover-uncover test was performed by occluding one eye with a shutter that passed infrared light, allowing continuous tracking of both eyes. The deviation angle was measured during periods of right eye and left eye fixation. Incomitance was assessed as a function of eye preference, fixation stability, and exotropia variability.

Results

The mean exotropia was 18.2° ± 8.1°. A difference between right exotropia and left exotropia was detectable in 16/37 subjects. Allowing for potential tracking error, the incomitance had a mean amplitude of 1.7°. It was not related to a difference in accommodative effort, eye preference, fixation stability, or variability in deviation.

Conclusions

Comitance is regarded as a feature that distinguishes strabismus from paralytic or restrictive processes. Unexpectedly, eye tracking during the cover-uncover test showed that incomitance is present in approximately 40% of subjects with intermittent exotropia. It averages 10% of the exotropia, and can equal up to 5°. When substantial, it may be worth considering when planning surgical correction.

Capturing the Moment of Fusion Loss in Intermittent Exotropia

PURPOSE

To characterize eye movements made by patients with intermittent exotropia when fusion loss occurs spontaneously and to compare them with those induced by covering 1 eye and with strategies used to recover fusion.

DESIGN

Prospective study of a patient cohort referred to our laboratory.

PARTICIPANTS

Thirteen patients with typical findings of intermittent exotropia who experienced frequent spontaneous loss of fusion.

METHODS

The position of each eye was recorded with a video eye tracker under infrared illumination while fixating on a small central near target.

MAIN OUTCOME MEASURES

Eye position and peak velocity measured during spontaneous loss of fusion, shutter-induced loss of fusion, and recovery of fusion.

RESULTS

In 10 of 13 subjects, the eye movement made after spontaneous loss of fusion was indistinguishable from that induced by covering 1 eye. It reached 90% of full amplitude in a mean of 1.75 seconds. Peak velocity of the deviating eye's movement was highly correlated for spontaneous and shutter-induced events. Peak velocity was also proportional to exotropia amplitude. Recovery of fusion was more rapid than loss of fusion, and often was accompanied by interjection of a disconjugate saccade.

CONCLUSIONS

Loss of fusion in intermittent exotropia is not influenced by visual feedback. Excessive divergence tone may be responsible, but breakdown of alignment occurs via a unique, pathological type of eye movement that differs from a normal, physiological divergence eye movement.

Normal correspondence of tectal maps for saccadic eye movements in strabismus

The superior colliculus is a major brain stem structure for the production of saccadic eye movements. Electrical stimulation at any given point in the motor map generates saccades of defined amplitude and direction. It is unknown how this saccade map is affected by strabismus. Three macaques were raised with exotropia, an outwards ocular deviation, by detaching the medial rectus tendon in each eye at age 1 mo. The animals were able to make saccades to targets with either eye and appeared to alternate fixation freely. To probe the organization of the superior colliculus, microstimulation was applied at multiple sites, with the animals either free-viewing or fixating a target. On average, microstimulation drove nearly conjugate saccades, similar in both amplitude and direction but separated by the ocular deviation. Two monkeys showed a pattern deviation, characterized by a systematic change in the relative position of the two eyes with certain changes in gaze angle. These animals' saccades were slightly different for the right eye and left eye in their amplitude or direction. The differences were consistent with the animals' underlying pattern deviation, measured during static fixation and smooth pursuit. The tectal map for saccade generation appears to be normal in strabismus, but saccades may be affected by changes in the strabismic deviation that occur with different gaze angles.

Variability of Ocular Deviation in Strabismus

IMPORTANCE

In strabismus, the fixating eye conveys the direction of gaze while the fellow eye points at a peripheral location in space. The stability of the eyes may be reduced by the absence of a common target.

OBJECTIVE

To quantify the stability of eye position in strabismus and to measure variability in the ocular deviation.

DESIGN, SETTING, AND PARTICIPANTS

From 2010 to 2014, a prospective comparative case study of 25 patients with alternating exotropia with normal visual acuity in each eye and 25 control individuals was conducted in a laboratory at a tertiary eye center. A video eye tracker was used to measure the position of each eye while participants alternated fixation on the center of a cross under dichoptic conditions or scanned pictures of natural scenes.

MAIN OUTCOMES AND MEASURES

Spatial and temporal variability in the position of the fixating eye and the nonfixating eye in patients with strabismus and control individuals, quantified by the log area of ellipses containing 95% of eye positions or mean SDs of eye position.

RESULTS

In the 25 patients with strabismus, the mean (SD) age was 28 (14) years (range, 8-55 years) and the mean (SD) ocular deviation was 14.2° (5.9°) (range, 4.4°-22.4°). In the patients with strabismus, the mean position variability (1.80 log units; 95% CI, 1.66-1.93) for the deviating eye was greater than for the fixating eye (1.26 log units; 95% CI, 1.17-1.35) (P < .001). The fixating eye of patients with strabismus was more variable in position than the fixating eye of individuals without strabismus (0.98 log units; 95% CI, 0.88-1.08) (P < .005).

CONCLUSIONS AND RELEVANCE

In patients with strabismus, even without amblyopia, the deviated eye is more variable in position than the fixating eye. Both eyes are less stable in position than the eyes of control individuals, which indicates that strabismus impairs the ability to fixate targets steadily. Saccades contribute to variability of the deviation angle because they are less conjugate in patients with strabismus.

Cortical Representation of a Myopic Peripapillary Crescent

PURPOSE

To determine how formation of an acquired myopic crescent adjacent to the optic disc affects metabolic activity in the primary visual cortex.

DESIGN

Laboratory animal study.

PARTICIPANTS

Three macaque monkeys.

METHODS

The blind spot region in the primary visual cortex was labeled by cytochrome oxidase (CO) histochemistry analysis or [(3)H]proline autoradiography.

MAIN OUTCOME MEASURES

Visualization of the representation of the blind spot and myopic peripapillary crescent in the visual cortex.

RESULTS

In high myopia, a region resembling the myopic peripapillary crescent was visible in cortical sections processed for CO. In this region, metabolic activity was reduced in ocular dominance columns that normally would be driven by input from retina corresponding to the myopic peripapillary crescent.

CONCLUSIONS

The formation of a myopic crescent is accompanied by loss of metabolic activity in the cortex supplied by the affected retina. This observation confirms that retinal tissue is damaged by the development of a myopic crescent, rather than simply translocated in a temporal direction. The cortical defect matches the myopic peripapillary crescent in size and shape, indicating that fill-in of the retinotopic map by healthy, surrounding retina does not occur.

Direct visualization of improved optic nerve pial vascular supply following tuberculum meningioma resection: case report

Tuberculum sellae meningiomas frequently produce visual loss by direct compression from tumor, constriction of the optic nerve (ON) under the falciform ligament, and/or ON ischemia. The authors hypothesized that changes in visual function after tumor removal may be related to changes in blood supply to the ON that might be seen in the pial circulation at surgery. Indocyanine green (ICG) angiography was used to attempt to document these changes at surgery. The first patient in whom the technique was used had a left-sided, 1.4-cm, tuberculum meningioma. Time-lapse comparison of images was done postsurgery, and the comparison of video images revealed both faster initial filling and earlier complete filling of the ON pial circulation, suggesting improved pial blood flow after surgical decompression. In follow-up the patient had significant improvements in both visual acuity and visual fields function. Intraoperative ICG angiography of the ON can demonstrate measurable changes in pial vascular flow that may be predictive of postoperative visual outcome. The predictive value of this technique during neurosurgical procedures around the optic apparatus warrants further investigation in a larger cohort.

Spontaneous Regeneration of Human Photoreceptor Outer Segments

Photoreceptors are damaged in many common eye diseases, such as macular degeneration, retinal detachment, and retinitis pigmentosa. The development of methods to promote the repair or replacement of affected photoreceptors is a major goal of vision research. In this context, it would be useful to know whether photoreceptors are capable of undergoing some degree of spontaneous regeneration after injury. We report a subject who lost retinal function in a wide zone around the optic disc, giving rise to massive enlargement of the physiological blind spot. Imaging with an adaptive optics scanning laser ophthalmoscope (AOSLO) showed depletion of cone outer segments in the affected retina. A year later visual function had improved, with shrinkage of the enlarged blind spot. AOSLO imaging showed repopulation of cone outer segments, although their density remained below normal. There was a one-to-one match between sites of formerly missing outer segments and new outer segments that had appeared over the course of the year's recovery. This correspondence provided direct morphological evidence that damaged cones are capable, under some circumstances, of generating new outer segments.

A slow neutron polarimeter for the measurement of parity-odd neutron rotary power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10(-7) rad/m.

Contrasting effects of strabismic amblyopia on metabolic activity in superficial and deep layers of striate cortex

To probe the mechanism of visual suppression, we have raised macaques with strabismus by disinserting the medial rectus muscle in each eye at 1 mo of age. Typically, this operation produces a comitant, alternating exotropia with normal acuity in each eye. Here we describe an unusual occurrence: the development of severe amblyopia in one eye of a monkey after induction of exotropia. Shortly after surgery, the animal demonstrated a strong fixation preference for the left eye, with apparent suppression of the right eye. Later, behavioral testing showed inability to track or to saccade to targets with the right eye. With the left eye occluded, the animal demonstrated no visually guided behavior. Optokinetic nystagmus was absent in the right eye. Metabolic activity in striate cortex was assessed by processing the tissue for cytochrome oxidase (CO). Amblyopia caused loss of CO in one eye's rows of patches, presumably those serving the blind eye. Layers 4A and 4B showed columns of reduced CO, in register with pale rows of patches in layer 2/3. Layers 4C, 5, and 6 also showed columns of CO activity, but remarkably, comparison with more superficial layers showed a reversal in contrast. In other words, pale CO staining in layers 2/3, 4A, and 4B was aligned with dark CO staining in layers 4C, 5, and 6. No experimental intervention or deprivation paradigm has been reported previously to produce opposite effects on metabolic activity in layers 2/3, 4A, and 4B vs. layers 4C, 5, and 6 within a given eye's columns.

Vertical diplopia and ptosis from removal of the orbital roof in pterional craniotomy

PURPOSE

To describe a newly recognized clinical syndrome consisting of ptosis, diplopia, vertical gaze limitation, and abduction weakness that can occur after orbital roof removal during orbito-zygomatic-pterional craniotomy.

DESIGN

Case series.

PARTICIPANTS

Eight study patients (7 women), 44 to 80 years of age, with neuro-ophthalmic symptoms after pterional craniotomy.

METHODS

Case description of 8 study patients.

MAIN OUTCOME MEASURES

Presence of ptosis, diplopia, and gaze limitation.

RESULTS

Eight patients had neuro-ophthalmic findings after pterional craniotomy for meningioma removal or aneurysm clipping. The cardinal features were ptosis, limited elevation, and hypotropia. Three patients also had limitation of downgaze and 2 patients had limitation of abduction. Imaging showed loss of the fat layers that normally envelop the superior rectus and levator palpebrae superioris. The muscles appeared attached to the defect in the orbital roof. Ptosis and diplopia developed in 2 patients despite Medpor titanium mesh implants. Deficits in all patients showed spontaneous improvement. In 2 patients, a levator advancement was required to repair ptosis. In 3 patients, an inferior rectus recession using an adjustable suture was performed to treat vertical diplopia. Follow-up a mean of 6.5 years later revealed that all patients had a slight residual upgaze deficit, but alignment was orthotropic in primary gaze.

CONCLUSIONS

After pterional craniotomy, ptosis, diplopia, and vertical gaze limitation can result from tethering of the superior rectus-levator palpebrae superioris complex to the surgical defect in the orbital roof. Lateral rectus function sometimes is compromised by muscle attachment to the lateral orbital osteotomy. This syndrome occurs in approximately 1% of patients after removal of the orbital roof and can be treated, if necessary, by prism glasses or surgery.

Prodromal posterior cortical atrophy: clinical, neuropsychological, and radiological correlation

We present longitudinal clinical, cognitive, and neuroimaging data from a 63-year-old woman who enrolled in research as a normal control and evolved posterior cortical atrophy (PCA) over 5 year follow-up. At baseline she reported only subtle difficulty driving and performed normally on cognitive tests, but already demonstrated atrophy in left visual association cortex. With follow-up she developed insidiously progressive visuospatial and visuoperceptual deficits, correlating with progressive atrophy in bilateral visual areas. Amyloid PET was positive. This case tracks the evolution of PCA from the prodromal stage, and illustrates challenges to early diagnosis as well as the utility of imaging biomarkers.

Vascular Supply of the Cerebral Cortex is Specialized for Cell Layers but Not Columns

The vascular supply to layers and columns was compared in macaque primary visual cortex (V1) by labeling red blood cells via their endogenous peroxidase activity. Alternate sections were processed for cytochrome oxidase to reveal "patches" or "blobs," which anchor the interdigitated column systems of striate cortex. More densely populated cell layers received the most profuse blood supply. In the superficial layers the blood supply was organized into microvascular lobules, consisting of a central venule surrounded by arterioles. Each vessel was identified as an arteriole or venule by matching it with the penetration site where it entered the cortex from a parent arteriole or venule in the pial circulation. Although microvascular lobules and cytochrome oxidase patches had a similar periodicity, they bore no mutual relationship. The size and density of penetrating arterioles and venules did not differ between patches and interpatches. The red blood cell labeling in patches and interpatches was equal. Moreover, patches and interpatches were supplied by an anastomotic pial arteriole system, with no segregation of blood supply to the two compartments. Often a focal constriction was present at the origin of pial arterial branches, indicating that local control of cortical perfusion may be accomplished by vascular sphincters.

Enlargement of the sella turcica in pseudotumor cerebri

OBJECT

The sella turcica usually appears partially empty in MR images obtained from patients with chronic elevation of intracranial pressure. The authors measured the size of the sella turcica to determine if enlargement of the pituitary fossa explains the partially empty sella associated with pseudotumor cerebri.

METHODS

The medical records from 2005 to 2011 of a single neuro-ophthalmologist were searched to identify consecutive patients with pseudotumor cerebri. Age-matched control patients were selected from the same practice. The sella turcica and pituitary gland were measured on sagittal T1-weighted MR images.

RESULTS

Measurements were obtained for 48 patients with pseudotumor cerebri and 48 controls. The cross-sectional area of the sella was 38% greater in the patients with pseudotumor cerebri, with only a slight reduction in mean pituitary gland size.

CONCLUSIONS

Chronic elevation of intracranial pressure is associated with bony enlargement of the sella turcica. Enlargement of the sella turcica contributes to its partially empty appearance.

Skull thickening, paranasal sinus expansion, and sella turcica shrinkage from chronic intracranial hypotension

In children or young adults, the morphology of the skull can be altered by excessive drainage of CSF following placement of a ventriculoperitoneal (VP) shunt. In Sunken Eyes, Sagging Brain Syndrome, gradual enlargement of the orbital cavity occurs from low or negative intracranial pressure (ICP), leading to progressive bilateral enophthalmos. The authors report several heretofore unrecognized manifestations of this syndrome, which developed in a 29-year-old man with a history of VP shunt placement following a traumatic brain injury at the age of 9 years. Magnetic resonance imaging showed typical features of chronic intracranial hypotension, and lumbar puncture yielded an unrecordable subarachnoid opening pressure. The calvaria was twice its normal thickness, owing to contraction of the inner table. The paranasal sinuses were expanded, with aeration of the anterior clinoid processes, greater sphenoid wings, and temporal bones. The sella turcica showed a 50% reduction in cross-sectional area as compared with that in control subjects, resulting in partial extrusion of the pituitary gland. These new features broaden the spectrum of clinical findings associated with low ICP. Secondary installation of a valve to restore normal ICP is recommended to halt progression of these rare complications of VP shunt placement.

Facial nerve injury: a complication of superficial temporal artery biopsy

PURPOSE

To describe 4 patients who sustained facial nerve injury during temporal artery biopsy.

DESIGN

Retrospective, observational case series.

METHODS

The medical records were reviewed of 4 patients (2 men, 2 women; mean age 72.8 years, range 60 to 87), referred for evaluation of palsy of the frontal branch of the facial nerve following temporal artery biopsy. Main outcomes measured were site of incision, length of follow-up, and degree of recovery.

RESULTS

In all cases, incisions were made in the preauricular region or on the pretrichial temple within 3 cm of the lateral canthal angle. Follow-up ranged from 1 month to over 5 years. No patient recovered completely; 2 had partial return of function, and 2 reported no improvement.

CONCLUSIONS

Branch facial nerve palsy can occur with temporal artery biopsy and is likely to result in permanent disability. In all cases the incision was placed within the known course of the frontal branch of the facial nerve. To prevent this rare complication, we advocate biopsy of the parietal, rather than the frontal, branch of the superficial temporal artery.

A watertight acrylic-free titanium recording chamber for electrophysiology in behaving monkeys

Neurophysiological recording in alert monkeys requires the creation of a permanent aperture in the skull for repeated insertion of microelectrodes. Most laboratories use polymethyl methacrylate to attach a recording chamber over the skull opening. Here, we describe a titanium chamber that fastens to the skull with screws, using no polymethyl methacrylate. The gap between the base of the chamber and the skull is filled with hydroxyapatite, forming a watertight gasket. As the chamber base osseointegates with the skull, the hydroxyapatite is replaced with bone. Rather than having a finite lifetime, the recording chamber becomes more firmly anchored the longer it is in place. It has a small footprint, low profile, and needs little maintenance to control infection. Toilette consists of occasional application of betadine to clean the scalp margin, followed by application of neomycin, polymyxin, and bacitracin ointment. Antibiotic is also placed inside the chamber to suppress bacterial proliferation. Thickening of the dura within the chamber can be prevented by regular application of mitocycin C and/or bevacizumab, an antibody against vascular endothelial growth factor. By conducting an e-mail survey, this protocol for chamber maintenance was compared with procedures used in 37 other vision research laboratories. Refinement of appliances and techniques used for recordings in awake monkeys promises to increase the pace of scientific discovery and to benefit animal welfare.

Ocular dominance columns: enigmas and challenges

In some mammalian species, geniculocortical afferents serving each eye are segregated in layer 4C of striate cortex into stripes called ocular dominance columns. Having described the complete pattern of ocular dominance columns in the human brain, the authors enumerate here the principal enigmas that confront future investigators. Probably the overarching challenge is to explain the function, if any, of ocular dominance columns and why they are present in some species and not others. A satisfactory solution must account for the enormous natural variation, even within the same species, among individuals in column expression, pattern, periodicity, and alignment with other components of the functional architecture. Another major priority is to explain the development of ocular dominance columns. It has been established clearly that they form without visual experience, but the innate signals that guide their segregation and maturation are unknown. Experiments addressing the role of spontaneous retinal activity have yielded contradictory data. These studies must be reconciled, to pave the way for new insights into how columnar structure is generated in the cerebral cortex.