Optical Coherence Tomography (OCT) has become an indispensable imaging tool in ophthalmology, offering high-resolution, non-invasive, real-time cross-sectional visualization of ocular tissues. Since its introduction in the early 1990s, OCT has rapidly evolved and expanded its clinical applications from retinal diagnostics to surgical guidance and therapeutic monitoring.
In ophthalmology, OCT has become a standard diagnostic tool, enabling detailed visualization of retinal layers, optic nerve structures, and anterior segment anatomy. The technology has evolved from time-domain OCT (TD-OCT) to Fourier-domain OCT (FD-OCT), including spectral-domain OCT (SD-OCT) and swept-source OCT (SS-OCT), leading to higher scanning speeds, deeper tissue penetration, and improved image resolution.
The clinical value of OCT lies in its ability to non-invasively assess tissue microarchitecture, quantify pathological changes, and monitor therapeutic outcomes. Its applications range from early detection of retinal and optic nerve disorders to intraoperative guidance and assessment of treatment efficacy. This review focuses on ophthalmic OCT applications, highlighting advances in microscope integration and ocular injection guidance, which collectively represent a significant portion of current clinical practice.
Evolution of OCT Technology
OCT technology has undergone substantial evolution over the past three decades. Time-domain OCT, the earliest form, relied on mechanical scanning of the reference arm to capture depth-resolved reflectivity profiles, achieving axial resolution of approximately 10 micrometers but limited scanning speed. This technology enabled early visualization of retinal layers and detection of macular pathologies, laying the foundation for clinical OCT applications.
The introduction of Fourier-domain OCT revolutionized the field by replacing mechanical depth scanning with spectral analysis. SD-OCT, a widely adopted FD-OCT variant, allowed rapid acquisition of high-resolution cross-sectional images, while SS-OCT further improved penetration depth and imaging speed, enabling full-eye visualization and volumetric reconstructions. The advancement of OCT angiography (OCTA) provided functional imaging of retinal and choroidal vasculature without dye injection, further expanding its clinical utility.
Domestic and international development of OCT has diverged in pace and scope. Western companies, particularly in the United States, Japan, and Europe, pioneered clinical adoption, including early applications in retinal disease assessment, glaucoma monitoring, and surgical guidance. In contrast, domestic (e.g., Chinese) OCT technology has advanced rapidly in recent years, achieving competitive imaging resolution, scan speed, and software capabilities. The expanding availability of OCT in domestic hospitals has facilitated widespread clinical application, particularly in ophthalmology.
Clinical Applications in Retinal and Optic Nerve Diseases
OCT has become essential for diagnosing and managing retinal and optic nerve disorders. In retinal disease, OCT enables quantitative assessment of macular thickness, cystoid macular edema, subretinal fluid, and structural changes associated with age-related macular degeneration (AMD) and diabetic retinopathy. For example, serial OCT imaging allows clinicians to monitor response to anti-VEGF therapy, guiding treatment frequency and dosage adjustments based on objective measurements of fluid resolution and retinal morphology.
In glaucoma management, OCT provides precise measurement of retinal nerve fiber layer thickness and optic disc morphology. Early glaucomatous changes, often undetectable by conventional perimetry, can be identified using OCT, enabling timely intervention. OCT also facilitates longitudinal monitoring of disease progression, offering quantitative endpoints for clinical decision-making.
Anterior segment OCT has proven valuable in assessing corneal thickness, anterior chamber depth, angle configuration, and lens morphology. These measurements are critical for planning refractive surgery, glaucoma interventions, and cataract surgery, as well as evaluating postoperative outcomes.
Microscope-Integrated OCT in Ophthalmic Surgery
Microscope-integrated OCT (MIOCT) combines high-resolution OCT imaging with surgical microscopy, providing real-time cross-sectional visualization of ocular tissues during surgery. Traditional surgical microscopes offer only two-dimensional magnification, limiting depth perception and the ability to evaluate tissue microstructure intraoperatively. MIOCT addresses this limitation by overlaying OCT imaging within the surgical view, enabling the surgeon to visualize retinal layers, membranes, and fluid dynamics during delicate procedures.
In vitreoretinal surgery, MIOCT has proven particularly beneficial. For instance, during vitrectomy for macular hole repair or epiretinal membrane peeling, real-time OCT imaging allows the surgeon to monitor membrane separation, retinal contour, and fluid accumulation. This guidance reduces the risk of incomplete membrane removal and inadvertent retinal injury. Studies have shown that MIOCT-assisted surgeries improve anatomical outcomes and reduce intraoperative complications, particularly in complex cases involving diabetic retinopathy or macular pathology.
Anterior segment surgeries also benefit from MIOCT integration. In procedures such as lamellar keratoplasty, Descemet’s membrane endothelial keratoplasty (DMEK), and glaucoma surgery, MIOCT enables accurate assessment of graft thickness, angle positioning, and intraocular device placement. The ability to visualize fine structures in real time enhances surgical precision, reduces operative time, and improves patient safety.
MIOCT provides several advantages, including real-time visualization, high axial and lateral resolution, and non-invasive intraoperative guidance. Future developments are likely to include higher-speed scanning, automated tissue recognition, and integration with robotic-assisted surgery. As artificial intelligence algorithms advance, real-time analysis of OCT images may facilitate automated identification of surgical landmarks, risk prediction, and optimized instrument guidance.