Optical coherence tomography: clinical applications in medical practice

Abstract

Optical Coherence Tomography (OCT) is a success story of scientific and technological co-operation between a physicist and a clinician. The concept of cross-sectional imaging revolutionalized the applicability of OCT in the medical profession. OCT is a non-contact, topographic, biomicroscopic device that provides high resolution, cross-sectional digital images of live biological tissues in vivo and in real time. OCT is based on the property of tissues to reflect and backscatter light involving low-coherence interferometry. The spatial resolution of as little as 3 microns or even less has allowed us to study tissues almost at a cellular level. Overall, OCT is an invaluable adjunct in the diagnosis and follow up of many diseases of both anterior and posterior segments of the eye, primarily or secondary to systemic diseases. The digitalization and advanced software has made it possible to store and retrieve huge patient data for patient services, clinical applications and academic research. OCT has revolutionized the sensitivity and specificity of diagnosis, follow up and response to treatment in almost all fields of clinical practice involving primary ocular pathologies and secondary ocular manifestations in systemic diseases like diabetes mellitus, hypertension, vascular and neurological diseases, thus benefitting non-ophthalmologists as well. Systemically, OCT is proving to be a helpful tool in substantiating early diagnosis in diseases like multiple sclerosis and drug induced retinopathies by detecting early changes in morphology of the retinal nerve fiber layer.

Keywords: Biomicroscopy; Interferometry; Optical Coherence Tomography.

Figure 1

Color codes: Red - High reflectivity (white arrow); black– low reflectivity (blue arrow); green - intermediate reflectivity (magenta arrow). Normal retinal structures are labeled as: red for RNFL (arrowhead) and junction of inner and outer segments of photoreceptors (PR); green for plexiform layers (magenta arrow), and blue/black for nuclear layers (blue arrow). N: Nasal. T:Temporal.

Figure 2

Superior hemi-central retinal venous occlusion. Fundus photo shows classical superficial and deep retinal hemorrhages withcotton wool exudates. Middle: OCT image shows a large cystic swelling of the retina (blue arrow). White arrow indicates signal fromretinal hemorrhage. Right: OCT image of the same eye after intravitreal injections of bevacizumab, showing markedly resolved edema withresidual subfoveal scarring (white arrow head).

Figure 3

Central retinal venous occlusion- color fundus photo shows collateral blood vessels on the optic disc (white arrows), venous engorgement and diffuse retinal hemorrhages. OCT image shows cystic spaces in the retina (white arrows) indicating retinal edema. Lower arrow indicates serous retinal detachment.

Figure 4

Central serous chorioretinopathy with sub-retinal pigment epithelial fluid (between arrows) in a pregnant patient.

Figure 5

Diabetic retinopathy: Color fundus photo shows hemorrhages, exudates and retinal edema, (within square). FA shows leakage at the disc and superior retina (blue arrows). OCT (lower left) shows intraretinal edema (short arrow), subretinal fluid (long arrow) and hard exudates (arrowhead). Right side OCT image: Eight weeks after intravitreal triamcinolone: minimal residual edema (arrow). Hyperreflective exudates can be seen on right side of the scan (arrowhead).

Figure 6

Proliferative diabetic retinopathy: left: Fundus photo shows extensive hard exudates, hemorrhages, noevascularization and glialtissue proliferation. Middle: Fluoresceine angiography shows areas of retinal ischemia (non perfusion-white arrows). Right: OCT imageshows diffuse retinal edema (between arrows).

Figure 7

OCT in systemic disease (acute lymphoid leukemia): Fundus photo: ring shaped retinal opacification, with hemorrhages, attributed to leukemic cell infiltration and possible CMV retinitis. OCT shows marked retinal atrophy and a hyperreflective scar (between arrows).

Figure 8

OCT image in a patient with multiple sclerosis. Left image shows overall thinning of retina (depicted by yellow and red codes in upper nomogram). Right image is for comparison showing normal thickness of retina depicted by normal green code in the nomogram.