The association of corneal thickness with ocular structures from corneal epithelium to optic nerve sheath diameter

To determine the association of central corneal thickness with corneal epithelium, ocular A-scan parameters, anterior chamber angle, and optic nerve sheath diameter.

A total of 161 individuals with thick, thin or normal corneas, with average ages of 53.3, 56.8 and 52.9 years, respectively, were included in this study. During routine eye examination, the right and left eyes of those with corneas thicker than 600 µm or thinner than 500 µm were assessed by comparing them separately with the eyes of those with normal corneas and with each other. After the participants' corneal thicknesses were measured by a non-contact tonometry/pachymetry, anatomical structures such as anterior chamber depth, lens thickness, and axial length were calculated with the A-Scan mode of an ultrasound device, and optic nerve sheath diameter was measured by the B-Scan mode of the same analyzer. Measurements of anterior segment structures, including corneal epithelium, corneal pachymetry and anterior chamber angle were recorded with a spectral domain optical coherence tomography. The optic disc area was automatically measured with the same device and compared with the optic nerve sheath diameter and central corneal thickness.

Central corneal thickness was inversely correlated with age. Thicker central cornea was associated with smaller anterior chamber angle (for normal vs. thick 34.7 ± 5.7° and 29.4 ± 6.9°, P = 0.00, for normal vs. thin 34.7 ± 5.7° and 30.7 ± 7.3°, P = 0.00), whereas ocular A-scan parameters, including anterior chamber depth, lens thickness, and axial length did not show significant differences. Intraocular pressure measurements lower than 17.9 mmHg were significantly different between the groups, with the highest measurements obtained from the thick group (17.9 ± 3.2 mmHg, 15.3 ± 2.3 mmHg, and 16.7 ± 2.1 mmHg for thick, thin and normal corneas, respectively). Despite within normal limits in all groups, the optic nerve sheath diameter in the control group was significantly smaller than that in the thick and thin groups (4.23 ± 0.71 mm vs. 4.66 ± 0.54 mm for normal and thick, P = 0.00, 4.23 ± 0.71 mm vs. 4.58 ± 0.55 mm for normal and thin, P = 0.02). The epithelium at nine points in the thick corneas, was significantly thicker than the corresponding points of the other two groups (the central thickness of epithelium for the thick and thin 58.4 ± 3.9 µm vs. 52.8 ± 2.9 µm, P = 0.00, for the thick and normal 58.4 ± 3.9 µm vs. 53.4 ± 2.4 µm, P = 0.00). For the thick cornea group, optic nerve sheath diameter was significantly correlated with optic disc area (r = 0.86, P = 0.000) and central corneal thickness (P = 0.003, regression coefficients).

Thicker central cornea was associated with thicker corneal epithelium, smaller anterior chamber angle, greater optic nerve sheath diameter, and higher intraocular pressure readings.