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Editors Selection IGR 17-4

Basic Research - Sclera: Histomorphometry of parapapillary region

Comment by Jeffrey Liebmann & Sung-Chul Park on:

46455 Histology of the Parapapillary Region in High Myopia, Jonas JB; Jonas SB; Jonas RA et al., American Journal of Ophthalmology, 2011;

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Jonas et al. (1162) investigated the histomorphometry of parapapillary region of enucleated human eyes and demonstrated that the scleral flange (sclera between optic nerve border and optic nerve dura mater) elongates and its thickness decreases with increasing axial myopia. They also described the parapapillary retinal anatomy in the area with elongated scleral flange in highly myopic eyes: retinal nerve fiber layer without other retinal layers or choroid. These results are helpful to researchers of the optic nerve head investigating its biomechanics, peripapillary subarachnoid space, beta-zone parapapillary atrophy, and surrounding structures. More importantly, these results enhance clinicians' understanding of optic nerve complex (optic nerve head + parapapillary structure) anatomy leading to more sophisticated clinical assessment especially in highly myopic eyes. In that sense, readers might have benefited by more histology figures of various degree of myopia. One of the limitations is that they examined only one histology section, which had previously been prepared for other purposes. Therefore, as the authors mentioned, it was not possible to determine whether the histology section was located in the very center of the optic disc or not. More importantly, one should examine different parts of the subarachnoid space to characterize its structure, because the subarachnoid space exists 360 degrees around the optic nerve and because its structure may vary considerably depending on the location (temporal, nasal, superior and inferior) and the direction of optic nerve head insertion (optic disc tilting). This variation of subarachnoid structure at different locations is likely greater in highly myopic eyes. The histology figures in this article were taken after the cerebrospinal fluid had been lost. Therefore, the morphology of subarachnoid space might be different from what could be observed in vivo: the extension of subarachnoid space into the retroparapapillary region might look more columnar or straighter. These factors would not have affected the authors' results significantly, but researchers should keep these in mind for future investigations. Lastly, retinal nerve fiber layer on the scleral bed without other retinal layers or choroid is also found in non-highly myopic eyes (mainly in the temporal area), although the segment is shorter than in highly myopic eyes. Clinicians assess and get much information from the optic disc and parapapillary retina, which are only the superficial parts of the optic nerve complex. Our clinical assessment would be better if could image the structure behind the optic nerve surface, creating a 3-dimensional image of the whole optic nerve complex.

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