LAUSR

Dear Editor, We read with great interest the paper by Esfandiari et al. [1] investigating the relationship of lamina cribrosa (LC) displacement to corneal biomechanical properties and visual function after mitomycin C-augmented trabeculectomy. They found that a larger intraocular pressure (IOP) reduction and younger age were correlated with a larger negative LC displacement and improving Humphrey visual field test. Moreover, they stated that corneal biomechanics did not predict LC displacement, even though only the corneal hysteresis (CH) had been taken into account in their study. However, it is well known that corneal biomechanics is characterized not only by CH but also by other factors, such as the corneal resistance factor (CRF) [2]. On the other hand, in addition to the LC displacement, a wide range of structural modifications have been described in the peripapillary region as a response to IOP changes, concerning the LC and the prelaminar tissue (PT) thickness and the anterior scleral canal width [3–6]. These morphological changes might influence their mechanical responses to pressure fluctuations [7]. We recently published a longitudinal prospective study [8] to assess corneal biomechanical properties and optic nerve head (ONH) changes following deep sclerectomy (DS) and the relation to each other. We found that eyes having a greater preoperative CRF had a greater cupping reversal (p = 0.002) and prelaminar tissue thickening (p = 0.003) after DS. Furthermore, CRF was the single largest preoperative factor influencing these morphological changes. Therefore, we hypothesized that a higher CRF might reflect a greater resistance of the prelaminar tissue allowing greater tissue decompression after IOP reduction. In contrast, patients with lower CRF might have larger destruction in the supporting tissue, resulting in a negative impact in the cupping compliance and reversibility after IOP reduction. Besides that, a higher central corneal thickness (CCT) was also significantly associated with a greater LC thickening after glaucoma surgery, supporting that elastic properties of the cornea might reflect the elasticity of other ocular structures such as the sclera and the LC. For all the abovementioned reasons, we consider that amore extensive analysis by the authors, including correlations among the CRF, CCT, prelaminar tissue thickness, and cup and LC depth, would be desirable to a better understanding of the relationship between the corneal and the optic nerve head biomechanics and their implications in glaucoma pathophysiology.