Optical coherence tomography (OCT) of the rim and peripapillary retina can aid in the diagnosis of glaucoma and its progression.
Different machines: different capabilities
The Spectralis gathers information about the fovea and the ONH and uses the axis between the foveal centroid and the Bruch’s membrane opening (BMO) centroid to acquire and parameterize regionalized data on all subsequent images of a particular eye, he explained.
The current scan patterns of the Spectralis include a combination of radial B-scans and peripapillary circular scans, a posterior pole grid scan, and high-resolution vertical and macular scans.
“The strength of acquiring radial B-scans allows each to be repeated up to 100 times, which improves the signal:noise ratio and image quality,” Dr. Burgoyne said.
This is in contrast to acquiring a grid, which the Spectralis can do, and as most other instruments do, which provide higher density but the scans cannot be repeated as many times and so the demonstrate lower signal to noise ratios.
Acquisition and parameterization relative to the foveal-to-BMO (FoBMO) axis facilitates reduction of the cyclotorsional effects.
The Spectralis uses BMO as the measurement for estimating minimum rim width, defined as the minimal distance to the internal limiting membrane in all B-scans. The measurements are done within 24 radial B-scans and the data are displayed either in six Garway-Heath sectors, 12 clock-hour sectors or in a TSNIT graph. The Spectralis also shows the actual anatomy.
“We believe this is important for clinicians to improve their clinical examinations by viewing the anatomy in that way,” Dr. Burgoyne said.
The progression analysis of the minimum rim width and the peripapillary RNFL using the Spectralis is plotted over time relative to the effects of aging in the cross-sectional database.
Angiography is currently available in this instrument, but does not yet include data analysis.
Related: Angiography boosts OCT in glaucoma
The Cirrus acquires a grid of A-scans of the ONH within which BMO is segmented and used as the orientation for peripapillary retinal circle scans that are extracted from the grid, Dr. Burgoyne explained.
Dr. Burgoyne showed that the minimal rim measurement, when evaluated three-dimensionally, can provide an estimate of the minimal rim area.
This instrument shows the data obtained for the optic disc parameters, cup-to-disc ratio, and the peripapillary RNFL thickness for individual eyes in tables, Garway-Heath sectors, and graphs; the peripapillary RNFL thicknesses also can be shown in deviation plots. The instrument also provides glaucoma progression analysis for the ONH and peripapillary RNFL. Angiography of the ONH is available and FDA approval of the indices is pending.
Related: Managing glaucoma with OCTA