What does Oct refer to in a medical context?

OCT in Medical Context

OCT stands for Optical Coherence Tomography, a non-invasive imaging technology that generates high-resolution cross-sectional and en face images of retinal and anterior segment structures in ophthalmology. 1

Primary Clinical Applications

Retinal Imaging

• OCT provides in vivo quantitative and qualitative measures of retinal structure, allowing visualization of distinct retinal and choroidal layers through boundary-specific segmentation 2, 3
• Spectral-domain OCT (SD-OCT) is the current standard, offering superior resolution (10 μm axial resolution) compared to older time-domain systems 1
• The technology enables visualization of individual retinal layers, including photoreceptor integrity, retinal pigment epithelium, and inner retinal structures 1, 4

Macular Disease Assessment

• SD-OCT is highly sensitive for diagnosing epiretinal membranes (ERM), vitreomacular traction (VMT), and macular edema, appearing as hyperreflective layers on the inner retinal surface 1
• For diabetic macular edema, OCT central subfield thickness ≥250 μm (on Stratus OCT) indicates clinically significant edema requiring treatment 1, 5
• OCT detects cystoid spaces, lamellar holes, and posterior cystoid retinal degeneration that may not be visible on clinical examination 1

Drug Toxicity Screening

• SD-OCT is recommended for hydroxychloroquine/chloroquine retinopathy screening, detecting localized thinning of photoreceptor layers in the parafoveal region before visual symptoms develop 1
• Outer retinal damage from systemic drug toxicity (hydroxychloroquine, chloroquine, ethambutol, tamoxifen) appears as focal interruption of photoreceptor outer segment structural lines 1, 6
• Time-domain OCT is NOT recommended for screening—only spectral-domain systems provide adequate resolution 1

Anterior Segment Applications

Angle-Closure Assessment

• Anterior segment OCT (AS-OCT) evaluates iridocorneal angle anatomy when gonioscopy is difficult, showing good agreement with ultrasound biomicroscopy 1
• AS-OCT is limited to evaluating the iridocorneal angle and cannot assess structures posterior to the iris like ultrasound biomicroscopy can 1

Accommodating Intraocular Lens Studies

• OCT measures biometric changes including anterior chamber depth, IOL thickness, and surface curvatures to document accommodation in clinical trials 1
• Physical accommodative changes measured by OCT can be converted to optical power changes through Gaussian optics calculations 1

Advanced OCT Modalities

OCT Angiography (OCT-A)

• OCT-A visualizes retinal and choroidal vasculature without dye injection, detecting macular neovascularization and vascular changes in diabetic retinopathy 1, 7
• For type 3 macular neovascularization, OCT-A shows flow deepening from the deep vascular complex to the RPE/sub-RPE space at baseline and recurrence 7

Enhanced Imaging Techniques

• Swept-source OCT and enhanced depth imaging (EDI) provide improved visualization of deeper structures including choroid and optic nerve 1, 3
• En face OCT generates coronal images of specific retinal layers, revealing pathoanatomical details previously only visible through histology 2, 4

Key Clinical Pitfalls

• OCT cannot detect early hydroxychloroquine toxicity if resolution is insufficient—always use spectral-domain systems, not time-domain 1
• Corneal edema impairs OCT image quality—in acute angle-closure, topical glycerin may be needed to clear the cornea before imaging 1
• OCT findings must be correlated with clinical examination and other tests—isolated findings without supporting evidence should prompt repeat testing 1
• Vascular plexus appearance varies by retinal location—four plexuses near the fovea, fewer peripherally—which affects interpretation of OCT-A in different diseases 4