Implications of Central Corneal Thickness-corrected Intraocular Pressure in Normal-tension Glaucoma with Reduced Central Corneal Thickness

Purpose: Reduced central corneal thickness (CCT) is a risk factor for glaucoma progression and can impact intraocular pressure (IOP) measurement. Therefore, we investigated the glaucoma progression pattern and associated risk factors among individuals with normal-tension glaucoma (NTG) and reduced CCT.Methods: This retrospective study enrolled 187 eyes of 187 NTG patients with an open angle and a baseline IOP < 20 mmHg, adjusted for CCT. Reduced CCT was defined as < 500 µm thickness in both eyes. Patients with a history of corneal disease or surgery affecting CCT were excluded. We used Goldmann tonometry to measure baseline and CCT-corrected IOP (ccIOP; [IOP - [CCT - 545]/50 × 2.5]). The participants were divided into progressing and stable subgroups.Results: The mean CCT was 481.2 ± 17.5 µm and the mean follow-up period was 6.3 ± 2.5 years. The baseline IOP and ccIOP were 13.7 ± 2.4 and 16.6 ± 2.5 mmHg, respectively. The average visual field progression rate was -0.79 ± 1.26 dB/yr. Of the participants, 47 (26.6%) and 140 (73.4%) were in the progressing and stable group, respectively. Participants in the progressing group were older, had a higher baseline ccIOP, and had a higher proportion of pseudophakia than those in the stable group. Multivariate analysis showed that baseline ccIOP was a significant risk factor.Conclusions: Individuals presenting with NTG and reduced CCT had a relatively stable glaucoma progression rate. However, glaucoma progression was associated with old age, pseudophakia, and high baseline IOP in individuals with reduced CCT. In particular, the only significant factor associated with glaucoma progression was ccIOP. Therefore, ccIOP is a clinically significant factor in individuals with NTG and reduced CCT.