En-face OCT the newest technology in glaucoma management
Of the many technological innovations in terms of glaucoma detection and management, one of the latest advancements that has come up is the en-face OCT (Optical coherence tomography) imaging. This technology allows the clinician to visualize three-dimensional data in a fundus projection. Using this technique, particular retinal and/or choroidal layers at a given depth are projected onto an en-face view.
The OCT’S, ever since its launch has been known for its non-contact, non-invasive imaging technique which can reveal layers of the retina by looking at the interference patterns of reflected laser light. Automated software segmentation algorithms are able to outline the retinal nerve fiber layer with much precision, which is relevant in glaucoma since this layer is thinned as ganglion cells are lost.
En-face OCT scans, available on most OCT systems, are a modality that create frontal images that are compatible with conventional fundus images. By scanning the retina and choroid on a coronal plane at 90 degrees from cross section, en-face OCT scans helps detect retinal and choroid diseases under a new different angle, facilitating new clinical possibilities and providing a useful complement to the conventional cross sectional B-scans. Some OCT technology produces frontal scans adapted to the concavity of the cup-shaped retina and parallel to ideal pigment epithelium at a constant depth in the retina.
Although cross-sectional images have helped delineate pathological features in retinal diseases, as such, microstructural changes and morphology of the retinal and choroidal vasculature are hard to evaluate. In this regard the en-face imaging provides further improved detail about the subtle pathological features in the retina and choroid in diseased states. “The en-face OCT takes one down to in-vivo microscopic level and helps to see the nerve cells in detail”, said Dr Rajesh S Kumar, Deputy Director of Research, Consultant Glaucoma Services, Narayana Nethralaya, Bengaluru.
En face images enables visualization of the porous structure of the lamina cribrosa, nerve fiber layer, choroid, photoreceptors, RPE, and capillaries of the inner retina. The technology is yet to come in India, however this newer en-face OCT technology is going to go a long way, he further added.
The en-face OCT imaging seems more suitable to perform topography than the longitudinal OCT imaging. If the object is a surface oriented perpendicular to the optic axis, the en-face OCT can provide the topography in one single frame, while longitudinal OCT requires interpolation of many scans. The en-face OCT imaging may allow a quicker inference of the approximate topography profile. The approximate topography may be visible in the very process of frame which is not possible to grasp when performing longitudinal OCT.