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Normal IOP found in high percentage of eyes with angle closure glaucoma
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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.
PACG eyes with normal IOP also had significantly longer axial length, deeper “true” anterior chamber depth (ACD), a flatter cornea and more hyperopic refractive error than eyes with high IOP of more than 21 mm Hg. Multiple logistic regression analysis showed that deeper true ACD and more hyperopic refractive error could be considered as independent predictors of normal IOP in PACG eyes at their first visit.
This study confirms the value of performing gonioscopy when screening patients for glaucoma, the authors said. In real-world practice, gonioscopy is often avoided because it is time-consuming, difficult to perform and uncomfortable for the patient. However, based on IOP alone, many cases of PACG could be overlooked.
Biometry was also shown to be a valuable additional method of supporting the diagnosis of PACG in eyes with normal IOP.
“We hypothesize that PACG eyes with initially normal IOP likely evolved from normal tension glaucoma because of progressive shallowing of ACD with age. It means that glaucomatous damage might start in an open-angle status,” the authors wrote.
Laser peripheral iridectomy or cataract surgery may be beneficial at this point to widen the drainage angle to prevent trabecular damage, peripheral anterior synechiae and IOP rise, they said.
“Otherwise, they will eventually evolve to PACG eyes with high IOP,” the authors wrote. – by Michela Cimberle
Disclosure: The authors reported on relevant financial disclosures.
Perspective
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Daniel Roberts, OD, PhD, FAAO
The primary message of this study, although not new, is worth repeating: Gonioscopy is underutilized in clinical practice and glaucoma care. Van Herick angle estimation is insufficient, and the outflow apparatus must be visualized to determine if there is any degree of obstruction or potential for it.
Angle closure can have a complex natural history. IOP may be normal in patients with impending or partial angle closure, and gonioscopy is necessary to accurately diagnose these cases and appropriately manage them.
This study underscores the fact that different glaucoma types overlap. For example, a patient can have overt or impending angle closure even when they have normal tension or high tension primary open-angle glaucoma.
The research is clear on this. Impending and varying degree of angle closure are frequently missed because gonioscopy isn’t performed.
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