D. Yang

X-linked infantile periodic alternating nystagmus.

Objective: To describe the clinical and electrophysiological characterization of four family members from three generations who have X-linked infantile periodic alternating nystagmus (XIPAN). Methods: Complete clinical ophthalmological evaluation, pedigree analysis, electroretinograms (ERG), eye movement recordings (EMR), color vision, and fundus photography were performed on all subjects. Results: Three males in two generations and one female were examined. Clinical examinations showed a jerk/pendular nystagmus with a latent component, strabismus, and a significant refractive error in the three affected males, while the female had only myopic astigmatism. ERG, color contrast, and fundus examinations were normal in all four family members. All four family members showed EMR abnormalities with infantile jerk/dual jerk and pendular nystagmus waveforms. The female had nystagmus present on EMR only and all patients showed (a)periodicity to their nystagmus. Conclusions: In this family with no other congenital visual sensory system disease, affected males had obvious periodic alternating nystagmus, strabismus, and refractive errors, while the female had clinically ‘silent’ periodic nystagmus that is probably a marker for the carrier state.

Infantile Aperiodic Alternating Nystagmus

BACKGROUND This study identifies the clinical and ocular motility characteristics of the periodic and aperiodic forms of infantile alternating nystagmus (IAPAN) and establishes the range of electrophysiological and clinical characteristics while providing clues to its presence and pathophysiology. METHODS Seventy-eight patients with ocular oscillations consistent with IAPAN were reported. Outcome variables were: age, follow-up in months, vision, strabismus, other eye and systemic abnormalities, head position, periodicity, cycle and null period duration, foveation time, waveforms, and cycle symmetry. RESULTS Age range was 1 to 67 years, 50% had pure periodic and aperiodic forms, 46% had albinism, 26% had binocular acuity of 20/40 or greater, 72% had strabismus, 35% had amblyopia, 31% had other eye disease, 14% had systemic disease, 87% had an anomalous head posture, and 65% had binocular directional asymmetry. The periodic cycle averaged 224 seconds and the aperiodic cycle ranged from 2 to more than 300 seconds. One in three patients with strabismus and nystagmus periodicity had a static head posture. CONCLUSION Fifteen percent of the infantile nystagmus syndrome population had either the periodic or aperiodic form. A changing null period is often clinically missed because of long or irregular cycles, decreased acuity, associated strabismus, and either a nonexistent or inconsistent head posture. The changing null period is easier to recognize using eye movement recordings or if the non-preferred eye is occluded and the preferred eye is examined with the head straight and gaze in primary position for at least 5 to 7 minutes. The recognition of this variant has profound treatment implications.

Development and Validation of a Digital Head Posture Measuring System

PURPOSE To report the accuracy and repeatability of a new digital head posture measuring system. DESIGN Prospective study, clinical laboratory investigation. METHODS The digital head posture measuring system consists of a head-mounted motion tracker, a standard personal computer, and customized software to sample and display 3-dimensional (3D) head posture in real-time. Using a mechanical head posture measuring device as a reference, 3D head positions of an artificial head and 12 human subjects were recorded with the digital head posture device. Accuracy of the digital device outputs, relationship between digital outputs and actual head rotations, and repeatability of the tests were analyzed. RESULTS The digital head posture device showed consistent outcomes when compared to the mechanical one. The digital outputs of 3D rotations are very close to actual artificial head and human head rotations. The correlation coefficients of the linear relationship between the digital outputs and actual head movements were greater than 0.99. Repeatability tests for the artificial head and human subjects for all 3D rotations had 95% limits of agreement angles less than +/-6 degrees and +/-8 degrees, respectively. CONCLUSIONS The digital head posture device is an acceptable device with high accuracy, repeatability, and validity in measuring head posture in 3 dimensions.

Vergence nystagmus induced by motion in the ground plane: normal response characteristics.

We displayed backward/forward motion on a computer monitor in the ground plane. Subjects looked at the center of a moving pattern and eye movements of both eyes were recorded with a search coil system. Involuntary nystagmus including vertical version (VV) and horizontal vergence (HV) was recorded. Dynamics of the nystagmus showed that the slow and quick phase of VV and HV were always associated with each other while the monocular horizontal eye movements composed of HV were either symmetrical or asymmetrical. Peak velocity, amplitudes and frequency of the VV and HV responses were quantified. The results suggest that involuntary HV nystagmus can be induced by simple motion from simulated optic flow in the ground plane and the HV nystagmus helps moving subjects to stabilize their gazes on the object of interest.

A new algorithm for automated nystagmus acuity function analysis

Aims We developed a new data analysis algorithm called the automated nystagmus acuity function (ANAF) to automatically assess nystagmus acuity function. We compared results from the ANAF with those of the well-known expanded nystagmus acuity function (NAFX). Methods Using the ANAF and NAFX, we analysed 60 segments of nystagmus data collected with a video-based eye tracking system (EyeLink 1000) from 30 patients with infantile or mal-development fusional nystagmus. The ANAF algorithm used the best-foveation positions (not true foveation positions) and all data points in each nystagmus cycle to calculate a nystagmus acuity function. Results The ANAF automatically produced a nystagmus acuity function in a few seconds because manual identification of foveation eye positions is not required. A structural equation model was used to compare the ANAF and NAFX. Both ANAF and NAFX have similar measurement imprecision and relatively little bias. The estimated bias was not statistically significant for either methods or replicates. Conclusions We conclude that the ANAF is a valid and efficient algorithm for determining a nystagmus acuity function.

Relationships between versional and vergent quick phases of the involuntary version-vergence nystagmus.

We used ground-plane motion stimuli displayed on a computer monitor positioned below eye level to induce involuntary version-vergence nystagmus (VVN). The VVN was recorded with a search coil system. It was shown that the VVN had both vertical versional and horizontal vergence components. The VVN induced by backward motion (toward subjects) had upward versional and divergence quick phases, whereas those induced by forward motion (away from subjects) had downward and biphasic divergence-convergence quick phases. The versional and vergence components of the VVN quick phases were analyzed. A temporal dissociation of about 20 ms between version velocity peak and convergence velocity peak was revealed, which supported a modified saccade-related vergence burst neuron (SVBN) model. We suggest that the temporal dissociation may be partly because of a lower-level OKN control mechanism. Vergence peak time was dependent on version peak time. Linear relationships between vergence peak velocity and versional saccadic peak velocity were demonstrated, which was in line with the new multiplicative model. Our data support the hypothesis that the vergence system and the saccadic system can act separately but interact with each other whenever their movements occur simultaneously.

Application of a Digital Head-Posture Measuring System in Children

PURPOSE To report the repeatability of a digital head-posture measuring system when used to record anomalous head postures in children. DESIGN Prospective study and clinical laboratory investigation. METHODS Using a digital head-posture measuring system, we measured 36 different anomalous head postures in 27 children with infantile nystagmus syndrome. Repeatability values and 95% limits of repeatability of measurements were generated for anomalous head postures. RESULTS Among the 27 children, 3 had 2 head postures (right and left head turns) in 2 different directions; 6 had 2-dimensional head postures that were considered 2 different head postures; and 18 had a 1-dimensional head posture. There were 5 chin-up or chin-down postures, 23 head-turn postures, and 8 head-tilt postures in a total of 36 anomalous head postures. The repeatability value for all anomalous head postures was less than 10 degrees. Ninety-five percent limits of repeatability yielded ranges of less than 10 degrees for all anomalous head postures. CONCLUSIONS The digital head-posture measuring system is a valid and reliable device for measuring 3-dimensional head postures in children with nystagmus.

Effect of binocular rivalry suppression on initial ocular following responses.

To study the effect of binocular rivalry (BR) suppression on the ocular following response (OFR), we recorded the OFR in both the suppressed and the dominant phases of BR. The BR was established using stationary horizontal/vertical grating patterns presented on two PC monitors. Once a subjective image of a vertical or horizontal grating pattern was perceived, subjects pressed a button to trigger an onset of brief horizontal movement (750 ms) of the vertical grating pattern and an offset of the horizontal pattern. The OFRs were recorded using a scleral search coil system at 1 kHz. The OFRs from the suppressed phases were significantly reduced compared to those from the dominant phases. The OFRs were asymmetrical to temporalward and nasalward motion in most conditions. We suggest that asymmetry of OFRs under the incomplete BR conditions may be a reflection of imbalance binocular inputs and processing in the visual system similar to asymmetrical optokinetic nystagmus in strabismic subjects. The latency of the OFR in deeper suppressed conditions was prolonged, suggesting that the interaction of BR and OFR may occur at multiple stages including an early stage of the visual processing. The OFR may have the potential for objective measurement of BR suppression in clinical evaluation of binocular function.