Muscimol inactivation caudal to the interstitial nucleus of Cajal induces hemi-seesaw nystagmus

Hemi-seesaw nystagmus (hemi-SSN) is a jerk-waveform nystagmus with conjugate torsional and disjunctive vertical components. Halmagyi et al. in Brain 117(Pt 4):789–803 (1994), reported hemi-SSN in patients with unilateral lesions in the vicinity of the Interstitial Nucleus of Cajal (INC) and suggested that an imbalance in projections from the vestibular nuclei to the INC was the source of the nystagmus. However, this hypothesis was called into question by Helmchen et al. in Exp Brain Res 119(4):436–452 (1998), who inactivated INC in monkeys with muscimol (a GABAA agonist) and induced failure of vertical gaze-holding (neural integrator) function but not hemi-SSN. We injected 0.1–0.2 ?l of 2% muscimol into the supraoculomotor area, 1–2 mm dorso-lateral to the right oculomotor nucleus and caudal to the right INC. A total of seven injections in two juvenile rhesus monkeys were performed. Hemi-SSN was noted within 5–10 min after injection for six of the injections. Around the time the hemi-SSN began, a small skew deviation also developed. However, there was no limitation of horizontal or vertical eye movements, suggesting that the nearby oculomotor nucleus was not initially compromised. Limitations in eye movement range developed about ½–1 h following the injections. Clinical signs that were observed after the animal was released to his cage included a moderate to marked head tilt toward the left (contralesional) side, consistent with an ocular tilt reaction. We conclude that hemi-SSN can be caused by lesions just caudal to the INC, whereas lesions of the INC itself cause down-beat nystagmus and vertical gaze-holding failure, as demonstrated by Helmchen et al. Combined deficits may be encountered with lesions that involve several midbrain structures

Pharmacotherapy of vestibular and ocular motor disorders, including nystagmus

We review current pharmacological treatments for peripheral and central vestibular disorders, and ocular motor disorders that impair vision, especially pathological nystagmus. The prerequisites for successful pharmacotherapy of vertigo, dizziness, and abnormal eye movements are the “4 D’s”: correct diagnosis, correct drug, appropriate dosage, and sufficient duration. There are seven groups of drugs (the “7 A’s”) that can be used: antiemetics; anti-inflammatory, anti-Ménière’s, and anti-migrainous medications; anti-depressants, anti-convulsants, and aminopyridines. A recovery from acute vestibular neuritis can be promoted by treatment with oral corticosteroids. Betahistine may reduce the frequency of attacks of Ménière’s disease. The aminopyridines constitute a novel treatment approach for downbeat and upbeat nystagmus, as well as episodic ataxia type 2 (EA 2); these drugs may restore normal “pacemaker” activity to the Purkinje cells that govern vestibular and cerebellar nuclei. A limited number of trials indicate that baclofen improves periodic alternating nystagmus, and that gabapentin and memantine improve acquired pendular and infantile (congenital) nystagmus. Preliminary reports suggest suppression of square-wave saccadic intrusions by memantine, and ocular flutter by beta-blockers. Thus, although progress has been made in the treatment of vestibular neuritis, some forms of pathological nystagmus, and EA 2, controlled, masked trials are still needed to evaluate treatments for many vestibular and ocular motor disorders, including betahistine for Ménière’s disease, oxcarbazepine for vestibular paroxysmia, or metoprolol for vestibular migraine

Management of nystagmus in children: A review of the literature and current practice in UK specialist services

Nystagmus is an eye movement disorder characterised by abnormal, involuntary rhythmic oscillations of one or both eyes, initiated by a slow phase. It is not uncommon in the UK and regularly seen in paediatric ophthalmology and adult general/strabismus clinics. In some cases, it occurs in isolation, and in others, it occurs as part of a multisystem disorder, severe visual impairment or neurological disorder. Similarly, in some cases, visual acuity can be normal and in others can be severely degraded. Furthermore, the impact on vision goes well beyond static acuity alone, is rarely measured and may vary on a minute-to-minute, day-to-day or month-to-month basis. For these reasons, management of children with nystagmus in the UK is varied, and patients report hugely different experiences and investigations. In this review, we hope to shine a light on the current management of children with nystagmus across five specialist centres in the UK in order to present, for the first time, a consensus on investigation and clinical management

Optic Nerve Head Drusen (ONHD) in Black Patients

Several studies have suggested racial differences in the prevalence of ONHD. 2% of autopsied American patients (of unknown race) had ONHD, whereas 0.2% of the Chinese general population had ONHD on fundus photography

Journal Club Update: Nystagmus and Saccadic Intrusions

Nystagmus is common, with a prevalence of approximately 24 per 10,000 in the general population. Because of the associated visual symptoms and negative impact on quality of life, many patients with nystagmus request treatment. Unlike physiologic nystagmus (e.g., during head movements), where slow phase drifts minimize retinal image slip, the slow phase drifts of pathologic nystagmus cause retinal image slip. When retinal image slip from pathologic slow phase drifts is greater than about 5 degrees per second, it can produce blurred vision, because the image of the object of interest no longer lies on the fovea, and illusory motion of the visual environment (oscillopsia).3 Saccadic intrusions also cause visual symptoms, such as difficulty reading, as they consist of inappropriate saccadic eye movements that take the image of the object of interest off the fovea

Eye Movement Perimetry: Evaluation of Saccadic Latency, Saccadic Amplitude, and Visual Threshold to Peripheral Visual Stimuli in Young Compared With Older Adults

Previous studies have evaluated for age-related differences in saccadic latency and amplitude to peripheral visual stimuli, but have not evaluated for differences using stimuli close to visual threshold. Several studies have suggested that eye movements could be used to evaluate for visual field loss, but have not evaluated the relationship between saccadic latency, amplitude, and visual threshold.We aimed to determine saccadic latency and amplitude, as well as visual threshold, to peripheral visual stimuli in young adults compared with older adults using a novel automated perimetry technique

Binocular Summation of High- And Low-Contrast Visual Acuities in Multiple Sclerosis Patients Compared with Normal Humans

High- and low-contrast visual acuities (VA) are higher with binocular than with monocular viewing in normal humans due to binocular summation. Low-contrast vision is often abnormal in multiple sclerosis (MS) patients, even when high-contrast VA is normal

Building conceptual knowledge of fraction operations among pre-service teachers: Effect of a representation-based teaching approach within a teacher education program

A deep understanding of fraction concepts and operations is necessary if pre-service teachers (PSTs) are to present the concepts in multiple forms to learners. Such an understanding needs to be grounded in rich conceptual knowledge. In the present study, we explore the development of this understanding by supporting a cohort of 103 PSTs, who had previously demonstrated poor conceptual understanding of fraction concepts and operations, with a Representational Reasoning in Teaching and Learning (RRTL) approach aimed at strengthening their conceptual knowledge. A comparison of pre- and post-test results indicated that participants showed a significant improvement in shifting the balance of their fraction knowledge to the conceptual end of the procedural-conceptual spectrum. Insights into how this approach assisted in developing PSTs\u27 conceptual understanding were explored through interviews with four participants and an analysis of their pre- and post-test responses. We suggest that the use of teaching strategies such as RRTL are necessary in order to assist PSTs develop strong conceptual knowledge of fractions

Acute Monocular Blindness Due to Mucocele of the Anterior Clinoid Process

Sphenoid mucoceles are benign cystic lesions that are well known to cause a variety of neuro-ophthalmic complications, including visual loss due to compression of the anterior visual pathways (1). In contrast, anterior clinoid mucoceles, which arise from a pneumatized anterior clinoid process, are rarely reported as a cause of isolated monocular visual loss (2-4)

Eye movement perimetry for evaluation of visual field loss in patients with glaucoma versus recovered optic neuritis

We have developed an eye-movement based perimetry technique that evaluates two novel response measures, saccadic eye movement latency and accuracy, in addition to visual threshold.1 We aimed to determine if this technique demonstrates abnormalities in the latency or accuracy of saccadic eye movements made to peripheral visual stimuli, or visual threshold, in patients with optic neuropathy due to glaucoma or prior optic neuritis