We read with interest the recent article by Kim et al., and we think this is an impressive article. It reveals a new factor that leads to pathological IOP increase and gives us a new thinking of the pathology of NTG. In this prospective study, Kim et al. investigated the effect of the lateral decubitus position (LDP) on intraocular pressure (IOP) in glaucoma patients with asymmetric visual field loss and found that IOP elevation asymmetry in LDP is associated with asymmetric visual field loss. The LDP, habitually preferred by glaucoma patients, also may be associated with asymmetric visual field damage. Although several studies1,2 have reported that IOP in the LDP was consistently higher in the dependent eye than that in the sitting or supine position. To our knowledge, it is the first study to investigate the relationship between LDP IOP and visual field defect in glaucoma patients. The author pointed out that most of the previous studies had obtained measurements in a fixed sequence, which may have worked as a confounding factor. In this study neither repeated measurements nor the measurement sequence had much effect on the IOP by the rebound tonometer, which did not increase aqueous outflow or fluid shift with a tiny plastic probe. However, except for the effect caused by applanation of the cornea, the time effect should be evaluated. In the current study, IOP was always measured in supine first, and then LDP. We do not know whether the higher IOP of the dependent eye in the LDP than that in the supine position was a result of the time accumulation or just caused by different position. For this reason, the random measurement sequence should be designed to strengthen this study.
Kiuchi et al.3 found that the progression of visual field damage in NTG patients correlated with the magnitude of IOP elevation from sitting to supine. A longitudinal and follow-up study would be better to study this question on the progression of asymmetric visual field loss and IDP IOP.
The diagnosis of NTG was not adequate in this study. The author showed that the IOP was checked at least at three visits, and the measurements were obtained at different times during the daylight hours. But the variability of diurnal-nocturnal IOP could not be ignored and the peak IOP may happen nocturnally. It is necessary to measure the IOP in twenty-four hours during at least at two visits. Last but not least, postural changes in intraocular pressure with a marked elevation when lying flat during during the night must be excluded before diagnosis.4