Fig 1.
Image-processing flow from the optical coherence tomography (OCT) B-scan images to calculating the area of optic nerve head morphological changes.
The OCT B-scan images in central gaze (A) and horizontal gaze (B). (C) Superimposed OCT images with the image-movement functions from every direction and using image-tilting. (D) Quantitative measurement performed with manually-set pointers on optic nerve head tissues to form each measurement area. (For well-visualizing, original B-scan images were presented).
Fig 2.
Schema of optic nerve head (ONH) segmentation method.
A line connecting the two Bruch’s membrane openings (BMOs) was drawn at the primary position. Then vertical line dividing this line equally was drawn and the nasal and temporal sides were distinguished based on this vertical line. Each nasal or temporal-sided segment was classified into 2 groups based on BMO of ONH. (NP = nasal peripapillary segment, NC = nasal cup segment, TC = temporal cup segment, TP = temporal peripapillary segment).
Fig 3.
Overall and segmental optic nerve head (ONH) changes in abduction and adduction.
The distribution of ONH changes were provided. Bright yellow dotted line is configuration in horizontal eye movements, and faded yellow dotted line is configuration in primary position. (NP = nasal peripapillary segment, NC = nasal cup segment, TC = temporal cup segment, TP = temporal peripapillary segment, N = nasal, T = temporal).
Table 1.
Clinical demographics of enrolled subjects.
Fig 4.
Optical coherence tomography (OCT) images showing optic nerve head changes.
3-dimensional OCT images and B-scan OCT images in the primary position (A & D), abducted position (B & E), and adducted position (C & F). (For well-visualizing, original B-scan images were presented). White arrows indicated the morphological changes of optic nerve head according to the horizontal eye movements.
Table 2.
Mean areas of optic nerve changes from primary position.
Table 3.
Correlation coefficients of optic nerve changes on other parameters.
Fig 5.
Schematic drawing with MRI images to illustrate our hypothesis.
(Abduction) The ON becomes more redundant and sinusoidal during abduction. We hypothesized that the redundant ON in the abducted position would push the eyeball inward. In addition, it is presumed that the ON is moved to the medial side by abduction, and pressed by the narrow medial orbital space. As a result, the overall elevation of the ONH could occur in the abducted position. (Adduction) There is a stronger mechanical strain in adduction, especially for temporal peripapillary tissues. As a result, there could be elevation of the nasal side of the ONH and depression of the temporal side during adduction.