Department of Ophthalmology, University of California, Los Angeles, USA.
Stein Eye Institute, University of California, Los Angeles, USA.
Curr Eye Res. 2021 Apr;46(4):568-578. doi: 10.1080/02713683.2020.1817491. Epub 2020 Sep 11.
PURPOSE/AIM: The optic nerve (ON) becomes taut during adduction beyond ~26° in healthy people and patients with primary open angle glaucoma (POAG), but only retracts the globe in POAG. We used magnetic resonance imaging (MRI) to investigate this difference.
MRI was obtained in 2-mm quasi-coronal planes in central gaze, and smaller (23-25°) and larger (30-31°) adduction and abduction in 21 controls and 12 POAG subjects whose intraocular pressure never exceeded 21 mmHg. ON cross-sections were analyzed from the globe to 10 mm posteriorly. Area centroids were used to calculate ON path lengths and changes in cross-sections to calculate elongation assuming volume conservation.
For both groups, ON path was nearly straight (<102.5% of minimum path) in smaller adduction, with minimal further straightening in larger adduction. ON length was redundant in abduction, exceeding 103% of minimum path for both groups. For normals, the ON elongated 0.4 ± 0.5 mm from central gaze to smaller adduction, and 0.4 ± 0.5 mm further from smaller to larger adduction. For POAG subjects, the ON did not elongate on average from central gaze to smaller adduction and only 0.2 ± 0.4 mm from smaller to larger adduction ( = .045 vs normals). Both groups demonstrated minimal ON elongation not exceeding 0.25 mm from central gaze to smaller and larger abduction. The globe retracted significantly more during large adduction in POAG subjects than normals (0.6 ± 0.7 mm vs 0.2 ± 0.5 mm, = .027), without appreciable retraction in abduction. For each mm increase in globe axial length, ON elongation in large adduction similarly increased by 0.2 mm in each group.
The normal ON stretches to absorb force and avert globe retraction in adduction. In POAG with mild to severe visual field loss, the relatively inelastic ON tethers and retracts the globe during adduction beyond ~26°, transfering stress to the optic disc that could contribute to progressive neuropathy during repeated eye movements.
在健康人和原发性开角型青光眼（POAG）患者中，眼球内收超过 26°时视神经（ON）会变紧，但只有 POAG 会使眼球回缩。我们使用磁共振成像（MRI）来研究这种差异。
在中央注视时，获得 2 毫米准冠状平面的 MRI，并在 21 名对照者和 12 名 POAG 患者中获得较小（23-25°）和较大（30-31°）内收和外展的 MRI。从眼球到 10 毫米后分析 ON 横截面。使用面积质心计算 ON 路径长度，并假设体积守恒，通过横截面变化计算伸长率。
对于两组患者，ON 路径在较小的内收时几乎是直的（<102.5%的最短路径），在内收更大时仅稍有伸直。ON 在外展时冗余，超过两组的最小路径的 103%。对于正常人，ON 从中央注视到较小的内收时伸长 0.4±0.5 毫米，从较小的内收到更大的内收时进一步伸长 0.4±0.5 毫米。对于 POAG 患者，ON 从中央注视到较小的内收时平均没有伸长，仅从较小的内收到较大的内收时伸长 0.2±0.4 毫米（=0.045 与正常人相比）。两组患者从中央注视到较小和较大的外展，ON 伸长均不超过 0.25 毫米。POAG 患者眼球在较大的内收时明显回缩多于正常人（0.6±0.7 毫米与 0.2±0.5 毫米，=0.027），在外展时无明显回缩。对于眼球轴向长度每增加 1 毫米，每组患者在较大的内收时 ON 伸长也同样增加 0.2 毫米。
正常的 ON 伸展以吸收力并避免眼球在眼球内收时回缩。在有轻度至重度视野丧失的 POAG 中，相对无弹性的 ON 在眼球内收超过 26°时会束缚和回缩眼球，将压力转移到视盘，这可能导致在反复眼球运动期间进行性神经病变。
