Josephine Shallo-Hoffmann

Recognizing periodic alternating nystagmus

Congenital or acquired periodic alternating nystagmus (PAN) is characterized by nystagmus occurring in a cycle. The cycle consists of a left-beating nystagmus, a transition phase, a right-beating nystagmus, and a further transition phase. The purpose of this review is to assist the clinician in the recognition of periodic alternating nystagmus (PAN), either as a type of congenital nystagmus or in its acquired form, and to highlight why such identification is important. Recent studies using eye movement recordings 1–3 are reviewed to point out the frequency of congenital PAN in samples of patients with congenital nystagmus, and to describe the characteristics of the waveforms and the influence of foveation time on the alternation of head turns. Classical and new surgical alternatives are reported. The identification of congenital PAN is essential when surgical treatment is being considered for the correction of anomalous head postures. Acquired PAN is usually due to cerebellar disease and causes oscillopsia. 4–10 Unlike other forms of acquired nystagmus, it responds well to drug treatment.

Vestibular perception in patients with acquired ophthalmoplegia

Using a perceptual technique it is shown that patients with chronic external ophthalmoplegia have shortened vestibular responses. It is postulated that this is secondary to the retinal image slip experienced by these patients during head movements and a useful compensatory mechanism to suppress motion-induced sickness and spatial disorientation.

Maximum Angle of Ocular Duction During Visual Fixation as a Function of Age

Purpose: To measure and compare the maximum angle of ocular duction in healthy individuals as a function of age. Methods: A calibrated arc perimeter was modified to display one of six randomly presented targets (high contrast Snellen equivalent letters), in both vertical (supra/infraduction) and horizontal (ab/adduction) gaze to the dominant eye of 204 healthy volunteers with best-corrected visual acuity. A bite-bar and headrest were employed to prevent head movement. Using a modified method of limits for discrimination threshold, a maximum mean angle of ocular duction was determined by stepping a target out in 5° steps until an error was reported and thereafter bracketing around the limits of the target identification in 1° steps. A mean threshold value was determined as the angle at which a subject obtained a correct response 75% of the time in two and as many as three trials in each of four randomly presented directions of gaze (abduction, adduction, supraduction and infraduction). Results: A decrease in mean maximum duction angle was found over all age groups in all four directions (p < 0.001), with a steep decline beginning in the sixth decade and almost doubling in the oldest age group tested (80–95 year-olds). The percent of change in mean maximum angle of duction due to age from the 14–19 to the 80–95 year-olds was: abduction 21%, adduction 24%, supraduction 35%, infraduction 26%. Conclusion: Baseline data are useful to differentiate normal changes occurring with age from early signs of disease. Additionally, disease progression and effects of treatment can be monitored.

The presumed influence of attention on accuracy in the developmental eye movement (DEM) test.

Background The developmental eye movement (DEM) test is a clinical test used widely to evaluate ocular motility function (accuracy and speed) in school-age children. Purpose The purpose of this study was to investigate, retrospectively, the change in accuracy over time while performing the DEM horizontal reading task in children. Methods The charts from children who had performed the DEM test during a routine eye examination in a pediatric optometry service were reviewed. The study included 22 patients (6 to 11 years old, 12 boys, 10 girls) who had a routine eye examination that was precepted by one of the authors (R.C.) during the period of 1995 to 1999. Patients were divided into two categories: 1) those with abnormal DEM test results and 2) a control group consisting of those with normal DEM test results. Chart review was done consecutively within each category. Collected data included patient age, gender, refractive error, and DEM test results. For analysis, the horizontal task of the DEM was divided into two halves (I and II), Part I always preceded part II, and data was sorted as the number of errors per part. Results More errors in accuracy occurred in part II than in part I (Wilcoxon signed rank test, p ≤ 0.01) of the horizontal DEM test in the group of subjects with an abnormal DEM test. No differences in the number of errors in parts I and II of the horizontal task of the DEM were found in the control group. Conclusions Findings showed that when excessive errors in accuracy occurred, the number of errors increased over time. If the errors were caused by an oculomotor dysfunction found in the DEM, errors should be equally distributed throughout the text. If errors were caused by fatigue, a difference in parts I and II should have occurred in both the test and the control group. These findings suggest that attention may influence accuracy over time in those patients that do poorly on the DEM test.

Reduced duration of a visual motion aftereffect in congenital nystagmus.

Congenital nystagmus (CN) is a primarily horizontal, involuntary, conjugate eye movement which can be observed soon after birth or during the first half-year of life. Individuals with CN rarely complain of oscillopsia. Using a motion aftereffect (MAE), we investigated if individuals with CN have abnormalities in motion perception and if any such abnormality could be due to nystagmus or to compensatory mechanisms to avoid oscillopsia.In task A, patients (n= 10) and control subjects (n= 10) indicated the direction, duration and relative velocity of MAEs. The subjects binocularly viewed a high contrast, grey scale grating (0.23 cyc/deg; visual angle: 18.3 deg) moving upward or downward at 1, 3, and 6 deg/sec for 60 sec. Vertical optokinetic nystagmus (OKN) was monitored. In task B, patients (n=8) and control subjects (n=8) viewed similar spatial frequency gratings (visual angle: 40.7 degs; 0.5, 0.2, 0.08 cyc/deg) which moved at 4, 10, and 16 deg/sec for 60 sec. In task C, five control subjects, with induced vestibular nystagmus, viewed a grating (0.2 cyc/deg; visual acuity: 28.5 deg), moving upward for 40 sec. In all three tasks, after adaptation with the moving grating, subjects viewed the then static grating and reported the duration and direction of the MAE. One CN patient and eight control subjects reported MABs at all three test velocities in task A. When patients exhibited OKN, the gain was close to one, as in the control group. In task B, seven of the eight patients and all of the control subjects had MABs at the faster adaptation velocities. CN patients had less MAEs at an adaptation velocity of 4 deg/sec and when MAEs were observed, the duration of the illusory motion was reduced by approximately 48%. Control subjects, with induced vestibular nystagmus, reported MAEs at 4 deg/sec (task C).These findings indicate that nystagmus cannot be the only factor accounting for the suppression of motion perception and suggest that compensatory mechanisms used to avoid oscillopsia contribute to the differences found between the groups.

Temporally directed deficits for the detection of visual motion in latent nystagmus: evidence for adaptive processing

The purpose of this study was to investigate if visual motion detection deficits are caused by exposure to latent nystagmus (LN). Four subjects with infantile esotropia (two with and two without LN) and six age-matched control subjects were required to detect the onset of motion and drift direction of a linearly increasing velocity spatial frequency grating, monocularly presented just above threshold for contrast in paracentral vision (either in the nasal or temporal retina). LN was damped during testing by ensuring that nystagmic subjects held their viewing eye in an adducted position. In a separate session after the initial testing, all strabismic subjects and two of the six age-matched control subjects repeated the motion detection task. Subjects were then monocularly occluded for three hours, thereby increasing the nystagmus intensity in the LN subjects. After this time, the motion detection task was repeated. The results from each session were consistent and showed motion detection asymmetries for ea...

A study of pre-school vision screening tests' testability, validity and duration: do group differences matter?

Vision screening was performed on 268 pre-school children: 170 from a private pre-school, 33 from a Caribbean-American parochial pre-school and 65 pre-school children from a clinic serving indigent Spanish farm-workers. Using a multi-station format, a stereoacuity test and two visual acuity tests were performed during a single screening session. The time it took to complete a test was recorded. To pass the screening, children were required to pass one visual acuity test and the stereoacuity test. Children who could not complete the protocol were retested at a later date. Children who failed the screening and every fourth child who passed the screening were referred for a full eye examination. The parents and teachers were masked to the results of the screening as well as the optometrists who performed the eye examination. Sensitivity, specificity and accuracy scores were 100%, 79% and 80%, respectively. Three-year-old children completed the Lea Symbol Chart more often than the HOTV. No differences in time required to complete a visual acuity test were found. The Lea Symbol chart is more likely to be completed by young children. Testability changes significantly with age rather than with the instrument when socio-ethnic factors are held constant. Differences among groups and the sensitivity of the screening are discussed.

Strategic design for users with diabetic retinopathy: factors influencing performance in a menu-selection task

This paper examines factors that affect performance of a basic menu selection task by users who are visually healthy and users with Diabetic Retinopathy (DR) in order to inform better interface design. Interface characteristics such as multimodal feedback, Windows® accessibility settings, and menu item location were investigated. Analyses of Variance (ANOVA) were employed to examine the effects of interface features on task performance. Linear regression was used to further examine and model various contextual factors that influenced task performance. Results indicated that Windows® accessibility settings significantly improved performance of participants with more progressed DR. Additionally, other factors, including age, computer experience, visual acuity, and menu location were significant predictors of the time required for subjects to complete the task.

The Influence of Adaptation on Visual Motion Detection in Chronic Sixth Nerve Palsy After Treatment with Botulinum Toxin

Purpose. To investigate changes in visual motion perception after treatment with botulinum toxin in patients with unilateral chronic lateral rectus muscle palsy. Methods. Five patients and control subjects were asked to report the perceived drift direction of a sinusoidal grating that was initially stationary and then began to accelerate at 0.09°/sec2 in a horizontal direction. The grating had a field size of 18.5° and was presented monocularly with a contrast just above threshold for visibility for central vision. Both the paretic and non-affected eyes were tested. Psychophysical testing was performed under the following conditions: 1) before treatment and testing, patients occluded their paretic eye for at least three days to avoid diplopia. 2) After treatment with botulinum toxin, alignment was corrected and patients stopped occluding their paretic eye for at least three days before testing. The control subjects occluded their non-dominant eye for three days before testing. Results. In condition 1, no differences in motion detection values between patients and control subjects were found. In condition 2, motion detection thresholds were raised approximately 0.15°/sec as compared to pre-treatment values and compared to the control group. Conclusions. After treatment, a raised threshold for motion detection is one mechanism used to avoid oscillopsia and visuo-vestibular disorientation during head movements in patients with chronic paralytic squint. This study lends evidence that perceptual-adaptive, compensatory mechanisms develop to reduce oscillopsia and disorientation rather than being caused by abnormal cortical motion processing or defective eye muscle action.

Topographical analysis of the optic nerve in migraine patients.

Purpose. Vascular dysfunction appears related to the development of migraines and has been associated with pressure-independent glaucoma. The purpose of this study is to investigate possible topographical differences in the optic nerve between migraine sufferers and normal age-matched control subjects. The identification of optic disc topographical differences between migraine and non-migraine sufferers may help clinicians determine if the presence of migraine influences the development and progression of glaucoma. Methods. Sixty consecutively seen patient-volunteers (30 subjects in migraine group: mean age 37.7 years, range from 19 to 66 years, 28 females and 2 males; 30 subjects in the control group: mean age 37.6 years, range from 19 to 61 years, 29 females and 1 male) were categorized as either migraine patients or control group subjects. All migraine subjects had been medically diagnosed with a migraine syndrome and were being treated with prophylactic medication. Optic nerve head topographical analysis was performed using a confocal scanning laser ophthalmoscope. The data was evaluated using generalized estimating equations, a priori and post hoc power analysis. Results. No significant differences were found in any of the optic nerve parameters examined between the two groups. Conclusions. This study indicates that the optic nerve parameters as measured by the Heidelberg retinal tomograph II do not differ between migraine sufferers and age-matched control subjects.