Increased frequency of optic disc drusen encountered among patients with normal tension glaucoma

A new study found that the prevalence of optic disc drusen (ODD) in patients diagnosed with normal tension glaucoma (NTG) is substantially higher than in the background population. A low cup/disc ratio lower than 0.5 indicates the presence of ODD. The study results were published in the journal Acta Ophthalmologica.  

Glaucoma is a heterogeneous group of optic nerve diseases with a global prevalence and is the leading cause of irreversible blindness. Normal tension glaucoma (NTG) is a subtype of primary open-angle glaucoma. Optic disc drusen (ODD) are calcified deposits consisting of extruded axonal material located in the prelaminar region of the optic nerve head (ONH). As many ODDs are buried in the ONH and may have a chance of misdiagnosis, researchers conducted a study to investigate the prevalence of optic disc drusen (ODD) and optic nerve head (ONH) morphology in patients diagnosed with normal tension glaucoma (NTG). 

Eligible patients diagnosed with NTG from two glaucoma units participated in this prospective cross-sectional study. Dense enhanced depth imaging optical coherence tomography volume scans of the ONH were performed in both eyes using standardized scanning guidelines to examine for the presence of ODD. Radial ONH scans were used for investigating parameters such as scleral canal diameter, cup/disc ratio, and cup depth. 

Results

• ODD was found in 7 (3.6%) of 195 eyes, and 6 (6.1%) out of 98 patients diagnosed with NTG.
• In five out of six patients, ODD was not ophthalmoscopically visible.
• Eyes with ODD had a lower cup/disc ratio, 0.44 ± 0.4 (p = 0.040), and less-prominent cup depth, 236.6 ± 204.4 μm (p = 0.041) compared to eyes without ODD, 0.81 ± 0.2 and 437.8 ± 139.1 μm, respectively.
• There was no significant difference in scleral canal diameter between the eyes without (1602.8 ± 193 μm) and those with ODD (1492 ± 123.4 μm, p = 0.057). 

Thus, this was the first study that investigated the prevalence of ODD in patients diagnosed with NTG. Due to challenges associated with NTG diagnosis, researchers recommended examining the deep layers of the ONH in NTG patients with a cup/disc ratio lower than 0.5 to avoid misdiagnosing ODD as NTG. 

Further study: Ahmadi H, Fotesko K, Ba-Ali S, Hamann S, Kolko M. Optic disc drusen in patients diagnosed with normal tension glaucoma [published online ahead of print, 2022 Nov 14]. Acta Ophthalmol. 2022;10.1111/aos.15286. doi:10.1111/aos.15286