Christopher M. Knapp

Horizontal and vertical look and stare optokinetic nystagmus symmetry in healthy adult volunteers.

PURPOSE Look optokinetic nystagmus (OKN) consists of voluntary tracking of details in a moving visual field, whereas stare OKN is reflexive and consists of shorter slow phases of lower gain. Horizontal OKN is symmetrical in healthy adults, whereas symmetry of vertical OKN is controversial. Horizontal and vertical look and stare OKN symmetry was measured, and the consistency of individual asymmetries and the effect of varying stimulus conditions were investigated. METHODS Horizontal and vertical look and stare OKN gains were recorded in 15 healthy volunteers (40 degrees /s) using new methods to delineate look and stare OKN. Responses with right and left eye viewing were compared to investigate consistency of individual OKN asymmetry. In a second experiment, the symmetry of stare OKN was measured in nine volunteers varying velocity (20 degrees /s and 40 degrees /s), contrast (50% and 100%), grating contrast profile (square or sine wave), and stimulus shape (full screen or circular vignetted). RESULTS There was no horizontal or vertical asymmetry in look or stare OKN gain for all volunteers grouped together. However, individual vertical asymmetries were strongly correlated for left and right eye viewing (look: r = 0.77, P = 0.0008; stare: r = 0.75, P = 0.001) and for look and stare OKN (r = 0.66, P = 7.3 x 10(-5)) because of a strong correlation for downward moving stimuli (r = 0.73, P = 0.002). Horizontal and vertical asymmetries were not significantly affected by variations in stimulus parameter. CONCLUSIONS Although no horizontal or vertical OKN asymmetries existed for volunteers grouped together, vertical OKN was characterized by idiosyncratic asymmetries that remained consistent for an individual. Look and stare OKN gain is strongly associated for downward moving stimuli.

OKN Asymmetry in Human Subjects: A Literature Review

Abstract Optokinetic nystagmus (OKN) is a reflex eye movement induced by motion of the whole or a large proportion of the visual field. It can be horizontal, vertical, and torsional in direction and consists of two basic components, a slow tracking movement and a rapid recovery saccade. Two forms of OKN exist: “look” and “stare” OKN. There is strong evidence that horizontal OKN is symmetrical in normal healthy adults and that the OKN gains can be influenced by a variety of different factors including target size, shape, contrast, and velocity. Vertical OKN on the other hand is less well understood, although there is a belief that vertical OKN is asymmetrical with an upward preference. Recent publications contradict this assertion. In this article a comprehensive literature review was carried out to determine whether a vertical OKN asymmetry exists in healthy subjects and to explain any anomalous findings.

Spasm of the near reflex associated with head injury

Spasm of the near reflex is characterized by intermittent miosis, convergence spasm and pseudomyopia with blurred vision at distance. Usually, it is a functional disorder in young patients with underlying emotional problems. Only rarely is it caused by organic disorder. We report a patient who developed convergent spasm associated with miosis after head trauma at the age of 84 years.

Effect of distance upon horizontal and vertical look and stare OKN.

Previous reports suggest that distance influences horizontal stare OKN gains; however, the effect of distance on vertical OKN and look OKN is unknown. Horizontal and vertical look and stare OKN gains were recorded in 16 healthy volunteers (velocity 38.4 degrees /s) at three distances (0.3 m, 1 m, and 2.5 m) and two different stimulus sizes. Asymmetry of responses and correlation of gains in different directions were compared. Measurements at near were compared with and without glasses. Distance did not significantly affect horizontal look and stare OKN or vertical look OKN, however, downward stare OKN gains were reduced at greater distances (p = 0.002). Mean downward stare OKN gains recorded in each individual were strongly correlated to leftward and rightward gains but not upward gains. In contrast, upward OKN gains were not correlated to gains in leftward, rightward, or downward directions. Downward stare OKN responses are significantly sensitive to the effects of distance, whereas stare OKN in other directions and look OKN responses in all directions are not. Individual mean downward stare OKN gains are more closely related to horizontal responses rather than upward responses. This suggests that the downward OKN system is more functionally related to the horizontal system rather than the upward OKN system.

Optic Nerve Sheath Fenestration: A Five Year Audit

Idiopathic intracranial hypertension (IIH), also known as benign intracranial hypertension (BIH) and pseudotumor cerebri, is a syndrome characterised by raised intracranial pressure (ICP) in the absence of an intracranial mass or ventricular abnormality and normal cerebrospinal fluid (CSF). Optic nerve sheath fenestration (ONSF) is advocated as a treatment for patients on maximal medical therapy with progressive visual field loss. We present the visual results of 13 patients undergoing ONSF on 27 eyes (primary, secondary and tertiary procedures) over a 5 year period. Overall 4 eyes (14.8%) had improved visual acuity after surgery, whilst 23 eyes (85.2%) were unchanged. Visual fields were improved in 18 eyes (66.7%), 2 (7.4%) were unchanged and 4 (14.8%) deteriorated despite surgery. Colour vision improved in 12 (44.4%), was unchanged in 3 (11.1%) and deteriorated in 7 (25.9%) eyes. 5 (18.5%) eyes had normal colour vision before and after surgery. 10 (77%) subjects were able to stop medical treatment after ONSF.

Cogan's syndrome associated with orbital inflammation.

Abstract Cogan’s syndrome is a relatively rare inflammatory disorder presenting with a combination of ocular and vestibuloauditory symptoms. The first cases were described by David Cogan in 1945. Typically the ocular signs involve the anterior segment; however there are no descriptions of orbital inflammation associated with Cogan’s syndrome. We describe such a case. A 66-year-old immunosuppressed male patient with known Cogan’s syndrome presented to the eye department with right-sided proptosis, chemosis and ocular injection. Ocular motility was reduced. Other than Cogan’s syndrome there were no other systemic disorders. Medical treatment included: Azathioprine 125 mg/day and low dose Tab Prednisolone 30 mg/day. A provisional diagnosis of orbital cellulitis was made and intravenous antibiotics started. Blood investigations showed raised CRP levels 475 mg/L and raised WCC (24 × 109/l). An urgent CT scan of the head and orbits ruled out orbital cellulititis. The diagnosis was revised and the patient was treated for orbital inflammatory disease. Pulsed intravenous methlyprednisolone was commenced and oral steroids were increased to 60 mg/day, the Azathioprine was continued. Over the following week, the proptosis had resolved, and oral steroids were reduced back to the maintenance dose. To our knowledge this is the first description of orbital inflammatory disease associated with Cogan’s syndrome.

Vertical optokinetic nystagmus in Parkinson's disease.

Parkinsons disease (PD) is associated with a number of oculomotor deficits; however, little is known about changes in vertical optokinetic nystagmus (OKN) associated with PD. We recorded eye movements in 14 PD patients and 14 age‐matched controls in response to large field OKN stimulation using stimulus velocities of 20°/second and 40°/second. We compared asymmetry of horizontal and vertical responses in the two groups. We found vertical OKN to be strongly asymmetric in PD with reduced gains for downward‐moving stimuli. This asymmetry was significantly greater than that recorded in control volunteers. We postulate that this could result from an abnormal pursuit/early OKN system in PD leading to greater influence of the delayed OKN system.

Neurofibromatosis type II presenting as vertical diplopia

Neurofibromatosis type II (NF II) is rare and most commonly presents with hearing loss, tinnitus and/or vestibular disturbance in the third decade of life. The authors describe a rare case presenting with NF II with vertical diplopia due to IVthnerve palsy. The patient was otherwise asymptomatic despite multiple extensive lesions on MRI.

Endogenous endophthalmitis treated with systemic ciprofloxacin and linezolid

Endogenous endophthalmitis is a serious sight-threatening condition. The role of intravitreal antibiotics is controversial. We present a case of endogenous endophthalmitis successfully treated with a combination of systemic ciprofloxacin and linezolid.