Lamina cribrosa depth according to the level of axial length in normal and glaucomatous eyes.

Abstract

To compare the lamina cribrosa (LC) depth of the optic nerve head in normal and glaucomatous eyes over a wide range of axial length (AXL). A total of 402 eyes, including 210 normal and 192 glaucomatous eyes, were imaged by spectral domain optical coherence tomography. Normal and glaucomatous eyes were each divided into three subgroups according to the level of AXL; long (> 26mm), mid-level (23-26mm), and short (< 23mm). Visual field mean deviation (VF MD), LC thickness, and LC depth were compared between normal and glaucomatous eyes in each of the AXL subgroups. These parameters were also compared between normal and glaucomatous eyes in the three AXL subgroups. Factors associated with LC depth in each AXL subgroup were evaluated by univariate and multivariate regression analyses. A comparison of the three AXL subgroups in normal eyes showed that the LC was thinnest in the long AXL subgroup (short; 189.7 ± 24.1μm, mid-level; 179.9 ± 34.3μm, long; 149.2 ± 36.2μm, p < 0.001), but LC depth did not differ significantly in the three subgroups (short; 527.1 ± 144.4μm, mid-level; 578.2 ± 163.5μm, long; 594.4 ± 187.5μm, p = 0.144). In glaucomatous eyes, glaucoma severity assessed by VF MD did not differ significantly among the three AXL subgroups (short; -6.99 ± 8.50dB, mid-level; -6.40 ± 7.64dB, long; -4.61 ± 5.22dB, p = 0.168). However, LC depth was greater in the long than in the short AXL subgroup (679.5 ± 192.7μm and 555.9 ± 134.1μm, respectively, p = 0.004), although neither subgroup differed significantly in LC depth from the mid-level AXL subgroup (611.8 ± 162.3μm, p = 0.385, p = 0.090). LC thickness was significantly different between normal and glaucomatous eyes (p < 0.001). LC depth was not different between normal and glaucomatous eyes in both short and mid-level AXL subgroups (p = 0.297, 0.222), but differed in the long AXL subgroup (p = 0.022). The presence of glaucoma was associated with greater LC depth only in the long AXL subgroup (p = 0.012). LC depth may vary according to the level of AXL in glaucomatous eyes with a similar level of glaucoma severity, with the greatest LC depth found in eyes with long AXL. Those findings suggest that glaucomatous optic disc cupping would manifest differently according to the level of AXL.