A study performed in Korea found that 60% of patients with primary angle closure glaucoma had normal IOP. Without gonioscopy, these cases could be misdiagnosed as normal tension glaucoma, the authors noted.

The study included a retrospective series of 160 eyes of 160 patients with primary angle closure glaucoma (PACG). Of these, 128 (80%) did not present symptoms, and 97 (60.6%) had normal IOP of less than 21 mm Hg at the first visit.