OCT for beginners

Glasgow Caledonian University’s Dr Alice McTrusty guided delegates through an overview of how to interpret an ocular coherence tomography (OCT) scan in the lead up to the Topcon National OCT Conference (19-20 November, Hilton London Paddington).

During her presentation, Dr McTrusty stressed the importance of looking beyond the OCT scan.

“As far as I’m concerned, OCT is the best thing since sliced bread, but you can’t just rely on the OCT scan alone,” she highlighted.

“An OCT scan should never be interpreted in isolation,” Dr McTrusty added.

The emerging use of OCT meant that understanding retinal anatomy was increasingly important, she observed.

“When I was an undergraduate we didn’t have all of the information that we do now about the retina,” Dr McTrusty elaborated.

While patients tended to prefer to look at OCT scans in colour, Dr McTrusty highlighted that more detail can often be observed in grey scale scans.

This is particularly important when using swept-source OCT because of the amount of information provided by this technology.

Dr McTrusty clarified that OCT scans are not a picture of the layers of the retina.

“It does marry up well with the retinal anatomy but it is really a reflectivity map rather than an actual picture,” she said

Red areas of a colour scan correspond with areas of high reflectivity, while blue areas are regions with low reflectivity.

Dr McTrusty detailed a process that practitioners can use when analysing a scan, beginning with the inner layers of the retina and working their way down.

She recommended first looking at the vitreous and observing if the foveal contour is normal, before moving on to the inner retina.

The practitioner can then assess the retinal nerve fibre layer and ganglion cell layer before checking the outer retina and retinal pigment epithelium.

Dr McTrusty encouraged practitioners to look out for areas of hyper and hypo reflectivity, as well as paying attention to which layers of the retina are involved in any potential pathology.

This information could be helpful when referring a case on, she emphasised.

“You don’t necessarily always need to diagnose it but it’s helpful if you can give an accurate description of what you’re seeing,” Dr McTrusty added.