Quantitative Analysis of Translatory Movements in Patients With Horizontal Strabismus.

Purpose: To investigate translatory movement during the lateral gaze in patients with horizontal strabismus using magnetic resonance imaging. Methods: Patients with esotropia or exotropia and normal controls underwent orbital magnetic resonance imaging during the central gaze and lateral gaze at 40°. The position of the static tissues was superimposed three-dimensionally for all gazes using a self-developed software, allowing the analysis of the net eyeball movement. Then, the eyeball centroid coordinates were extracted for each gaze, and the distance and direction of centroid movement from the central to lateral gaze were calculated. Results: The mean distance ± standard deviation of the centroid movement was 1.0 ± 0.5 mm during abduction in the exotropia group, which was significantly longer than that in the esotropia (0.6 ± 0.3 mm; P = 0.003) and control (0.7 ± 0.2 mm; P = 0.002) groups. Conversely, the centroid moved farther in the esotropia group (0.9 ± 0.3 mm) than the exotropia (0.6 ± 0.3 mm; P = 0.005) and control (0.7 ± 0.2 mm; P = 0.023) groups during adduction. Posterior translation during abduction was longer in the exotropia group (-0.8 ± 0.3 mm) compared with the esotropia (-0.5 ± 0.3 mm; P = 0.017) and control (-0.4 ± 0.3 mm; P = 0.001) groups, whereas that during adduction was longer in the esotropia group (-0.4 ± 0.4 mm) than the exotropia (-0.1 ± 0.2 mm; P = 0.033) and control (-0.1 ± 0.2 mm; P = 0.026) groups. Conclusions: During abduction, more translatory movement occurred in the exotropia group, whereas the centroid moved farther in the esotropia group during adduction. The translatory movement difference between both strabismus groups implies that there is a difference in biomechanics among the types of strabismus.

Quantitative Analysis of Eyeball Rotation During Lateral Gaze in Intermittent Exotropia: A Magnetic Resonance Imaging Study.

Purpose: To evaluate the eyeball rotation during lateral gaze in patients with intermittent exotropia (IXT) using three-dimensional magnetic resonance imaging (MRI). Methods: In this prospective observational study, patients with IXT (n = 29) underwent orbital MRI during central, right, and left gazes. Fixation targets were placed at a 40° angle for lateral gaze. After acquisition of MR images, the position of the static tissues other than the eyeball in the MR images were matched three-dimensionally. The optical axis was defined as the perpendicular line to its lens passing through the corneal vertex. The rotation angle was measured as the angle between optical axes in central gaze and lateral gaze using ImageJ. A difference of 3° or more in the rotational angle between both eyes was considered a significant difference. Results: Eight patients (26.7%) had a larger adduction angle than the abduction angle of the fellow eye and six patients (20.0%) showed a smaller adduction angle during lateral gaze on at least one side. There was no significant factor associated with the pattern of rotation. Conclusions: Almost one-half of the patients with IXT had significant difference in the rotation angle between both eyes during lateral gaze. Measurement of the rotation angle during lateral gaze using MRI showed that IXT is not a perfectly comitant disturbance of gaze in some subjects. Translational Relevance: Quantitative analysis for eye movements using MRI can provide useful information for physiologic mechanism and proper surgical planning in patients with IXT.

Positional Change of the Eyeball During Eye Movements: Evidence of Translatory Movement.

Purpose: To investigate the positional change of the eyeball induced by horizontal and vertical gazing to deduce translatory movement, using three-dimensional (3D) magnetic resonance imaging (MRI). Methods: In this prospective observational study participants underwent orbital MRI during central, right, left, up, and down gazing. MRI scans were processed using self-developed software; this software enabled 3D MR image reconstruction and the superimposition of reconstructed image sets between different gazes. After acquiring the coordinates of the eyeball centroid in each gaze, the changes in centroid coordinates from central gaze to the other gazes were estimated, and correlations with associated factors were evaluated. Results: The mean distance of centroid movement was 0.69 ± 0.27 mm in abduction, 0.68 ± 0.27 mm in adduction, 0.43 ± 0.23 mm in elevation, and 0.44 ± 0.19 mm in depression. The mean angle of centroid movement in horizontal gaze, measured in terms of the movement of the left eye centroid in the axial plane, was 228.7° in abduction and -4.2° in adduction. In vertical gaze, the mean angle of centroid movement was -96.8° in elevation and 101.8° in depression. Axial length and ocular volume were negatively correlated with the distance of centroid movement in horizontal gaze. Conclusions: The position of the eyeball moved in the same direction as the gaze during horizontal gaze, but in the opposite direction during vertical gaze. For accurate eye movement analyses, such as the measurement of the deviation angle in strabismus, translation should be considered in addition to rotation.

Correction: Changes in the optic nerve head induced by horizontal eye movements.

[This corrects the article DOI: 10.1371/journal.pone.0204069.].

Changes in the optic nerve head induced by horizontal eye movements.

PURPOSE: To investigate the effect of eye movement on the optic nerve head (ONH) using swept-source optical coherence tomography (SS-OCT), and to measure the degree of ONH changes. METHODS: We enrolled 52 healthy subjects, 20 to 40 years of age, and performed a prospective observational study. Both ONH and macula were imaged simultaneously using wide volume scan of the SS-OCT in the primary and different gaze positions. Horizontal eye movements were used to obtain OCT images in abducted and adducted eyeball positions. Multilateral 3-dimensional registration was used to process and analyze the images to measure the degree of ONH changes. RESULTS: The mean axial length (AXL) was 25.73 ± 1.42mm and the mean spherical equivalents was -4.49 ± 2.94 D (The proportion of high myopia was 39.4%). Significant morphologic changes were observed in the ONH during both abduction and adduction. In abduction, the overall ONH tissues were elevated, and the mean area of elevation was 115,134 ± 9,424 µm2 (p<0.001). In adduction, the mean areas from two perspectives, which were nasal or temporal, and peripapillary tissues or optic nerve cupping were 95,277 ± 73,846 µm2, 34,450 ± 44,948 µm2, -108,652 ± 91,246 µm2, and -30,581 ± 46,249 µm2, respectively. Elevation in abduction (overall, nasal cup segment, and temporal cup segment; R = 0.204, 0.195 and 0.225, p = 0.038, 0.047 and 0.021, respectively) and elevation of nasal peripapillary segments in adduction were positively correlated with AXL (R = 0.346, p<0.001). CONCLUSION: We found significant morphologic changes in the ONH in both abduction and adduction and these changes were associated with AXL. Considering these morphologic changes as physical properties, it allows a better understanding of the biomechanical characteristics of the ONH.