Since the glaucoma involves deformation of the lamina cribrosa (LC), evaluation of the LC may provide additional information for diagnose and managing glaucoma. Degree of LC deformation has been assessed by measuring the LC depth, which was defined as the distance between the Bruch's membrane opening (BMO) level and the anterior laminar surface. Vianna et al. demonstrated that the LC depth measurement was influenced by choroidal thickness. It is of note that the significant choroidal thinning occurred in 89% of the included patients. It indicates that the influence choroidal thinning on the measurement of LC depth is not an issue that is limited to some patients but relevant to almost all patients.
The magnitude of deformation of any material is defined as the difference between its original and current status. Lamina cribrosa is contiguous with peripapillary anterior sclera not choroid. Therefore, it is reasonable to assess the LC deformation from the anterior scleral plane level. BMO has been used as the reference plane probably because it is easily identified even in moderate quality image. LC depth measured from BMO is the sum of actual deformation and choroidal thickness. As long as the choroidal thickness is a constant value, such measurement would be acceptable. However, the choroidal thickness is not a constant value. Vianna et al. nicely pointed out this important issue. Since the choroidal thickness is varying among subjects, this idea is applied not only into the serial measurement in the same individual but also relevant with the interindividual comparison.