Glaucoma induces a number of morphologic changes in the optic nerve head (ONH), including loss of prelaminar neural tissue. A previous study recently described a phenomenon in glaucoma eyes in which ONH prelaminar tissue had schisis-like features on OCT. To better understand this finding, a recent study examined the clinical characteristics of ONH prelaminar schisis in eyes with advanced glaucoma. They found that in patients with this feature, macular measurements rather than peripapillary or ONH measurements were better predictors of functional status.
The cross-sectional study included 116 eyes with advanced glaucoma (30-2 MD < -12dB). Two independent evaluators identified ONH prelaminar schisis with SD-OCT, and only eyes with consensus evaluation were included in the study.
Additionally, the following measurements were also obtained: Bruch’s membrane opening-minimum rim width (BMO-MRW), lamina cribrosa (LC) thickness and depth, peripapillary retinal nerve fiber layer (RNFL) thickness, macular thickness (total, RNFL, ganglion cell layer, inner plexiform layer) and peripapillary and subfoveal choroidal thicknesses.
The evaluators identified 48 of 116 eyes as having ONH prelaminar schisis. Multivariate regression models showed that short axial length, thin and deep LC and a thick macula were associated with the presence of ONH prelaminar schisis in these eyes. The researchers noted that the structure-function relationships showed that “macular structural parameters tended to have a better relationship with functional parameters than the BMO-MRW and peripapillary RNFL thickness in eyes with ONH prelaminar schisis.”
The researchers noted in their paper that the structural changes of the LC and connective tissues in glaucomatous eyes are very complex and that their speculations regarding LC thinning, which they believe may be related to changing pressure gradients between IOP and cerebrospinal fluid compartments, may not completely explain the association between LC thinning and deepening and the development of ONH prelaminar schisis in eyes with advanced glaucoma. “Future studies with imaging of the laminar insertion and close inspection would help us elucidate the underlying biomechanical mechanisms behind the development of ONH prelaminar schisis,” they wrote.
Though the detailed mechanism behind ONH prelaminar schisis is still unclear, the researchers believe that glial cells may also play a role when the tissue is under stress. “Although we couldn’t provide evidence for glial cell involvement in the development of ONH prelaminar schisis, our results suggest that ONH prelaminar schisis was likely caused by a complex interaction between the backward displacement of LC and the vitreo-retinal tractional force during the development of glaucomatous cupping.
“Our findings have significant clinical implications for management of advanced glaucoma eyes with and without ONH prelaminar schisis,” the researchers concluded. “One of the most important clinical implications of ONH prelaminar schisis is its potential to influence several diagnostic OCT parameters.”
Sung M, Jin H, Park S. Clinical features of advanced glaucoma with optic nerve head prelaminar schisis Prelaminar schisis in advanced glaucoma. Am J Ophthalmol. June 18, 2021. [Epub ahead of print].