What is the role of imaging studies in the workup of primary open-angle glaucoma (POAG)?

Updated: Mar 16, 2020
  • Author: Kristin Schmid Biggerstaff, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Fundus photography provides a permanent record of the appearance of the optic disc. Photographs taken over a period of time may be compared to track the progression of glaucoma.

The retinal nerve fiber layer sometimes can be imaged on high-contrast black and white film using red-free techniques. This can allow identification of nerve fiber layer defects that are characteristic of glaucomatous damage.

New techniques that use optical analysis of different physical properties of light can document the status of the optic nerve and the thickness of the nerve fiber layer, and they can be used to detect changes over time. The value of these technologies for diagnosing and following glaucoma over time continues to be an active topic of discussion and investigation. Modalities of the various technologies continue to be upgraded and enhanced, hopefully increasing the accuracy and likelihood of detecting glaucomatous damage.

Confocal scanning laser ophthalmoscopy (eg, HRT III) can examine the optic disc and peripapillary retina in 3 dimensions and provides quantitative information about the cup, neuroretinal rim, and contour of the nerve fiber layer. Increased resolution and software enhancements continue to improve this technology.

Scanning laser polarimetry (eg, GDX) measures the change in the polarization state of an incident laser light passing through the naturally birefringent nerve fiber layer to provide indirect estimates of peripapillary nerve fiber layer thickness. Improvements in neutralizing corneal light polarization (as opposed to that of the nerve fiber layer) have helped to decrease artifact in data obtained by this methodology.

Optical coherence tomography (eg, Stratus OCT) uses reflected light in a manner analogous to the use of sound waves in ultrasonography to create computerized cross-sectional images of the retina and optic disc, and it also gives quantitative information about the peripapillary retinal nerve fiber layer thickness. Newer increased resolution and three-dimensional spectral analysis hardware and software are also helping to propel this technology. Retinal nerve fiber layer (RNFL) thickness maps generated by spectral-domain OCT can help detect the progression of RNFL in glaucoma patients. [12]

For these technologies, continuing studies show good reproducibility over time for the same instrument. However, significant variability and fluctuating correlation between instruments is still noted, especially when compared with visual field testing results and other clinical examination findings. Therefore, testing results for each modality should be clinically confirmed by examination findings and other testing and not just singly used for clinical decision-making. [13]

The combination of structural and functional measurements with standard automated perimetry and optical coherence tomography performs better in estimating the rate of retinal ganglion cell loss in glaucoma patients than either measure alone. [14]

Fluorescein angiography, ocular blood flow analysis via laser Doppler flowmetry, color vision measurements, contrast sensitivity testing, and electrophysiological tests (eg, pattern electroretinograms) are used currently as research tools in the evaluation and management of patients with POAG. Routine clinical use is not advocated at this time.

Ultrasound biomicroscopy (UBM) may prove to be helpful in the future for obtaining a better view of the angle, iris, and ciliary body structures to rule out anatomical pathology and secondary causes of elevated IOP.

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