Measurement of retinal nerve fibre layer by scanning laser polarimetry andhigh pass resolution perimetry in normal tension glaucoma with relatively high or low intraocular pressure

Aims-To determine whether any differences may exist in the relation between the neural capacity as determined by high pass resolution perimetry and th e thickness of the retinal nerve fibre layer (RNFL) in patients having norm al tension glaucoma (NTG) with a relatively high intraocular pressure (IOP) between 16 and 21 mm Hg (HNTG) v those with a lower IOP below 15 mm Hg (LN TG). Methods-Scanning laser polarimetry and high pass resolution perimetry were performed in 20 eyes of 20 patients with HNTG and 21 eyes of 21 patients wi th LNTG. The correlation between total and regional thickness of the peripa pillary RNFL and the corresponding total and regional neural capacity with linear regression analysis were evaluated. Results-Overall, although the total RNFL thickness was not significantly co rrelated with the total neural capacity, the RNFL thickness in each of the superior and inferior quadrants was significantly correlated with the corre sponding regional neural capacity (r=0.44, p=0.0045; r=0.39, p=0.0126 for e ach). The RNFL thickness in each of the superior and inferior quadrants in the HNTG group was significantly correlated with the corresponding regional neural capacity (r=0.52, p=0.0196; r=0.49, p=0.0286 for each). No signific ant correlation between neural capacity and the RNFL thickness was observed either globally or regionally in the LNTG group. Conclusion-The degree of the correlation between neural capacity as determi ned by high pass resolution perimetry and thickness of the RNFL as measured by scanning laser polarimetry appeared to differ in NTG patients with an I OP higher than 15 mm Jig v those with a lower IOP.