Jain Neeranjali S, Jain Swaranjali V, Wang Xiaofei, Neely Andrew J, Tahtali Murat, Jain Sanjiv, Lueck Christian J
Department of Neurology, The Canberra Hospital, Canberra, Australian Capital Territory, Australia 2Faculty of Medicine, University of New South Wales, Kensington, Sydney, New South Wales, Australia.
School of Engineering and Information Technology, University of New South Wales, Canberra, Australian Capital Territory, Australia.
Invest Ophthalmol Vis Sci. 2015 Oct;56(11):6734-9. doi: 10.1167/iovs.15-17443.
Hemidecussation of fibers entering the optic chiasm from the optic nerves is well recognized. The reason why bitemporal hemianopia results from chiasmal compression has not been fully explained. There is still a paucity of data relating to the precise details of the routes that the nerve fibers take through the chiasm and, in particular, where and how nerve fibers cross each other. This information is important to understanding why crossing fibers are selectively damaged as a result of chiasmal compression.
An optic chiasm obtained at postmortem was fixed, stained, and sectioned to allow high-resolution photomicrographs to be taken. The photomicrographs were integrated to allow regions of interest across entire sections to be analyzed for fiber direction and crossing.
The results confirmed that fibers from the temporal retina pass directly backward in the lateral chiasm to the optic tract, whereas fibers from the nasal retina cross to the contralateral optic tract. Crossings take place in the paracentral regions of the chiasm rather than in the center of the chiasm (where the nerve fibers are traveling mostly in parallel). The paracentral crossing regions are distributed in a largely postero-superior to antero-inferior arrangement.
These findings clarify the precise locations and crossing angles of crossing nerve fibers in the chiasm. This information may help explain the clinical observation of junctional scotoma and will provide a much better basis for structural modeling of chiasmal compression which, in turn, will improve our understanding of how and why bitemporal hemianopia occurs.
视神经进入视交叉的纤维发生半交叉已得到充分认识。视交叉受压导致双颞侧偏盲的原因尚未完全阐明。关于神经纤维穿过视交叉的精确路径细节，尤其是神经纤维相互交叉的位置和方式的数据仍然匮乏。这些信息对于理解视交叉受压时交叉纤维为何会被选择性损伤很重要。
对一具尸体解剖后获得的视交叉进行固定、染色和切片，以拍摄高分辨率显微照片。整合显微照片，以便对整个切片的感兴趣区域进行纤维方向和交叉分析。
结果证实，来自颞侧视网膜的纤维在视交叉外侧直接向后进入视束，而来自鼻侧视网膜的纤维交叉至对侧视束。交叉发生在视交叉的中央旁区域，而非视交叉中心（此处神经纤维大多平行走行）。中央旁交叉区域大致呈后上至前下分布。
这些发现阐明了视交叉中交叉神经纤维的精确位置和交叉角度。这些信息可能有助于解释交界性暗点的临床观察结果，并将为视交叉受压的结构建模提供更好的基础，进而增进我们对双颞侧偏盲如何以及为何发生的理解。
