Among the three most popular optical coherence tomography and angiography devices, there are important differences in hardware, resolution and the manner in which the data are analyzed and displayed.
Other reported data are the minimum rim width along the Bruch’s membrane opening (BMO-MRW) and numerical and color-coded graphical comparisons of sectors in the RNFL and BMO-MRW with the normative database.
Regarding changes in serial scans obtained over time, the machine highlights the changes and the amount of thinning compared with the baseline scan, but the clinician must determine the statistical relevance of that change.
For all the instruments, the clinical relevance of any detected change must be determined by the ophthalmologist. There are different ways of generating reports when using the Avanti instrument.
An effective approach is to include a heatmap of the RNFL and a deviation map of the macular compared to the normative database along with color-coded graphical comparisons of the 3.4 mm circumpapillary RNFL profile and sectors with the normative database.
The analytics for change over time provide various displays including, for example, heatmaps of the GCC and RNFL thickness and linear regression analyses of the rates of change over time.
The instrument is also capable of providing a change analysis compared to the normative database for the macular GCC, Dr. Tanna pointed out.
OCTA All of the previously mentioned devices have OCTA capability; however, regarding pricing, for each instrument OCTA is an add-on feature. The big difference among the devices, Dr. Tanna noted, is that analytics relevant to glaucoma are only available with the Avanti device.
“All devices have strong evidence-based support for the concept that the changes seen in structure particularly that of the RNFL, are predictive of future visual field changes,” he said. Dr. Tanna noted that the Cirrus analytics, particularly for progression, are very strong.
“For Avanti, the OCTA analytics are very powerful and we do not have meaningful glaucoma-relevant analytics for the others,” Dr. Tanna concluded. For the Spectralis, the scan speeds are very high, resulting in superior effective resolution.”
Angelo P. Tanna, MD
E: [email protected]
This article is based on Dr. Tanna’s presentation at the American Glaucoma Society 2019 annual meeting in San Francisco. Dr. Tanna is a consultant to Carl Zeiss Meditec