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Optic disc tilt measurement valuable for glaucoma damage identification
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Measuring vertical disc tilt can provide useful information regarding the location of glaucomatous visual field defects, according to study findings.
Researchers retrospectively reviewed medical records to select 136 patients with primary open-angle glaucoma with isolated superior or inferior hemifield loss and 99 normal control participants examined at a clinic between August 2010 and September 2011.
The researchers obtained optic disc imaging using Heidelberg retinal tomography (HRT) III and Cirrus spectral-domain optical coherence tomography (Carl Zeiss Meditec). Using retinal imaging, the researcher measured patients’ disc ovality index and degree of torsion. They also assessed the degree of temporal and vertical disc tilt using horizontal and vertical topographic imaging.
Disc ovality was shown to have a significant association with HRT and OCT-measured temporal disc tilt and axial length, whereas the degree of disc torsion was associated with HRT and OCT-measured vertical disc tilt and axial length, according to the researchers.
In comparing data from patients with glaucoma with isolated superior or inferior hemifield, vertical disc tilt and the degree of disc torsion were significantly different. Multivariate analysis showed that HRT-measured vertical disc tilt was an independent factor determining the initial location of visual field defects.
Disclosure: The authors have no relevant financial disclosures.
Perspective
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Blair Lonsberry, MS, OD, MEd, FAAO
There are unique challenges in glaucoma diagnosis and management of myopic patients. For example, morphologic changes common in myopia make optic nerve head assessment difficult, and the optical coherence tomography “normative database” may not be an appropriate comparison point for the highly myopic patient.
Of particular interest is distinguishing between visual field defects secondary to myopia vs. glaucomatous visual field defects.
In this study, investigators examined differences in optic disc tilt and torsion between normal and glaucoma subjects and determined whether the direction of optic disc tilt was consistent with the location of initial glaucomatous field defects. The optic disc tilt direction was divided into horizontal and vertical tilt. Disc tilt is thought to be secondary to changes in the posterior sclera that may also result in a predisposition to develop glaucoma.
The authors found that disc tilt and torsion differed between glaucomatous and normal control eyes and that vertical disc tilt was associated with the initial location of field defects in glaucomatous eyes. This study lends credence to the hypothesis that tilted/myopic discs are more susceptible to glaucoma and potentially gives the clinician another sign to watch out for in myopic patients and their potential development of glaucoma.
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