The emergence of multimodal imaging in ophthalmology

Today, retina specialists have access to a broad range of imaging devices with different image-acquiring technologies. There has been rapid development in the field, from colour fundus photography, fluorescein angiography (FA), near-infrared (NIR) reflectance, fundus autofluorescence (FAF) and indocyanine green angiography (ICG) to high-resolution and swept-source optical coherence tomography (OCT), OCT-angiography (OCT-A) and adaptive optics.

The term ‘multimodal imaging’ is becoming increasingly used in the scientific literature to describe the approach to diagnose a single retinal disease by combining different imaging modalities. It can be defined as the use of more than one complementary technological system that is used to acquire images, concurrently or in a short period of time, for the purpose of diagnosis, prognostication, management and monitoring of disease.

Whilst the availability of today’s great number of imaging instruments is certainly impressive, it has the potential to cause the benefits of new diagnostic tests to be exaggerated, leading to premature adoption, unnecessary testing and increased health care costs. Thus, the question arises: which technologies are really necessary in clinical practice and which still need to be further evaluated?

Comparing techniques

Of the different imaging technologies, FA remains, at present, the gold standard technique for the evaluation, management and follow-up of patients affected by retinal vascular disease such as diabetic retinopathy and vein occlusions. And with its capability to identify choroidal vascular blood flow, ICG is helpful in detecting lesions underneath the retinal pigment epithelium, such as occult choroidal neovascularisations or polypoidal lesions. In addition, ICG plays a crucial role in the diagnosis of central serous chorioretinopahy.

Meanwhile, OCT is able to image retinal morphology and, specifically, retinal thickness, producing cross-sectional and three-dimensional images of the central retina. This technique is now well established in the diagnosis, management and treatment of almost all retinal diseases, mainly to quantify macular oedema and to highlight the signs of choroidal neovascularisation.

However, the scientific evaluation of additional parameters delivered by high-resolution OCT technology and a structure/function correlation is still needed. This is also true for adaptive optics, a technology that also provides a higher resolution by eliminating disruptive elements.

OCT-A represents the newest development in the field of retinal imaging. In combination with OCT, this non-invasive technique may show to be superior to conventional methods in the future. Numerous studies have been published surrounding its benefits in recent years, although no study has yet demonstrated the superiority of OCT-A over FA in both detecting and managing vascular diseases of the retina.

In real-world clinical practice, the use of OCT-A is challenging and we still need prospective data to show whether it can lead to better outcomes before we can use it in clinical practice. Until then, OCT-A will likely remain a scientific tool rather than become routinely used.

Another technique, FAF, can be used to observe both central and peripheral retinal health by evaluating the fluorescence of lipofuscin produced by photoreceptors. FAF also seems to be helpful in the diagnosis of hereditary diseases. However, its role in the diagnosis and follow up of dry age-related macular degeneration remains to be clarified, and a correlation between FAF and function is yet to be seen.

In summary, the spectrum of imaging technologies is rapidly evolving, providing fresh hope to ophthalmologists and their patients. However, all new technologies need to be critically evaluated before they transition from the bench to clinical routine practice, and we should be mindful of this as we look to embrace multimodal imaging.

Dr Emiliano Di Carlo
E-mail: emi.dicarlo@hotmail.it
Dr Di Carlo is an ophthalmology resident at University of Rome Tor Vergata, Rome, Italy.

Professor Albert J. Augustin
E-mail: albertjaugustin@googlemail.com
Prof. Augustin is professor and chairman of the Department of Ophthalmology, Klinikum Karlsruhe, Karlsruhe, Germany. He is a member of the Ophthalmology Times Europe Editorial Advisory Board.