Imaging retrobulbar subarachnoid space around optic nerve by swept-source optical coherence tomography in eyes with pathologic myopia.

PURPOSE

To examine the subarachnoid space (SAS) of eyes with pathologic myopia and analyze the characteristics of the SAS and the surrounding tissues by swept-source optical coherence tomography (OCT).

METHODS

One hundred thirty-three eyes of 76 patients with pathologic myopia (spherical equivalent refractive error of >-8.00 diopters (D) or an axial length >26.5 mm) and 32 eyes of 32 subjects with emmetropia were enrolled. The eyes in both groups were not tested to determine whether glaucoma was present. The papillary and peripapillary areas were examined with a swept-source OCT prototype system that uses a wavelength sweeping laser operated at 100,000 Hz A-scan repetition rate in 1-μm wavelength.

RESULTS

In the B-scan images, the arachnoid trabeculae inside the SAS were clearly observed as a pattern of reticular lines and dots interspersed with hyporeflective zones consistent with fluid, whereas orbital fat had more uniform features with gray intervening spaces. The SAS was triangular, with the base toward the eye surrounding the optic nerve in the region of the scleral flange. An SAS was found in 124 highly myopic eyes (93.2%) but not in the emmetropic eyes. The shortest distance between the inner surface of lamina cribrosa and SAS was 252.4 ± 110.9 μm, and the thinnest region of peripapillary sclera above SAS (scleral flange thickness) was 190.6 ± 51.2 μm. In one myopic patient, there appeared to be direct communication between the intraocular cavity and SAS through pitlike pores.

CONCLUSIONS

Optic SAS is seen in 93% of highly myopic eyes, and the SAS appears to be dilated in highly myopic eyes. The expanded area of exposure to CSF pressure along with thinning of the posterior eye wall may influence staphyloma formation and the way in which certain diseases, such as glaucoma, are manifested.