Understanding Optical Coherence Tomography Technology in One Article.

I. What is OCT? A Core Metaphor

Let’s understand OCT through a vivid analogy:

Imagine a fresh sandwich. A regular camera can only capture its top view (a two-dimensional photo). OCT, however, acts like a precise “optical scalpel.” It can slice the sandwich layer by layer without damage, capturing ultra-high-resolution images of each component (bread, vegetables, meat slices). These cross-sectional images are then reconstructed into a three-dimensional model.

In the eye, this “sandwich” is your retina—the light-sensitive tissue at the back of the eyeball. OCT generates cross-sectional images of the retina’s microscopic structure without any incisions or contact, achieving micrometer-level precision (1 micrometer = 0.001 millimeters)—far finer than a strand of hair!



II. How Does OCT Work?

OCT operates on a principle similar to ultrasound, but instead of sound waves, it uses near-infrared light.

1. Emission: The device emits a safe, low-energy near-infrared light beam toward your eye.
   
2. Reflection: This light passes through the eyeball and reflects back from different layers of the retina. Each tissue layer reflects light signals with distinct intensities and time delays.
   
3. Analysis: The device’s core interferometer precisely measures the differences between these reflected signals and the reference light (“interference” phenomenon).
   
4. Imaging: A computer analyzes and processes the countless captured light signal points, instantly constructing detailed 2D or 3D images.
   
   III. What Can OCT Detect? Which Eye Conditions Does It Diagnose?
   OCT is a powerful tool for examining the macula (the central part of the retina responsible for sharpest vision). With it, doctors can:
   
5. Precisely measure thickness: Determine whether the retina has thickened (edema, hemorrhage) or thinned (atrophy).
   
6. Identify minute lesions: Detect fluid accumulation, abnormal membranes, and microbleeds invisible to the naked eye.
   
7. Monitor disease progression dynamically: Evaluate treatment efficacy and guide subsequent therapeutic decisions.
   
   It is primarily applied in the diagnosis and management of these major blinding eye diseases:
   
8. Age-related macular degeneration (AMD)
   
   Wet AMD: OCT clearly visualizes abnormal subretinal vessels and fluid accumulation, serving as the gold standard for diagnosis and determining the need for intravitreal injections.
   
   Dry AMD: OCT monitors for macular thinning (geographic atrophy) and the deposition of drusen.
   
9. Diabetic Retinopathy & Diabetic Macular Edema (DME)
   
   OCT is the most sensitive tool for detecting DME (intraretinal fluid accumulation), precisely guiding laser or anti-VEGF drug injection treatments while objectively evaluating their efficacy.
   
10. Glaucoma
    
    OCT accurately measures the thickness of the retinal nerve fiber layer (RNFL). Glaucoma causes the RNFL to gradually thin like the growth rings of a tree. OCT can detect these changes early, before visual field defects occur, enabling early diagnosis, timely treatment, and lifelong follow-up for glaucoma.
    
11. Vitreoretinal Interface Diseases
    
    Such as epiretinal membrane (a membrane growing over the retina’s surface, causing distorted vision) and macular hole (a “hole” forming in the center of the macula). OCT clearly displays the morphology and staging of lesions, serving as a key basis for determining surgical necessity.
    
    IV. What is the OCT examination experience like?
    
12. Preparation: Typically requires no special preparation. Sometimes dilating eye drops are administered to enlarge the pupil for clearer imaging, resulting in light sensitivity and blurred near vision for several hours afterward.
    
13. Procedure: Simply rest your chin and forehead on the instrument’s support to keep your head steady. Focus on the fixation point inside the device (possibly a flashing cursor). The device does not touch your eyes.
    
14. Duration: Scanning each eye usually takes only a few minutes.
    
15. Safety: OCT uses near-infrared light. It is radiation-free, non-invasive, and has no known side effects. It is very safe and can be repeated frequently.
    
    V. Cutting-Edge Technology: Enhanced OCT
    OCT technology continues to evolve:
    
16. OCT Angiography (OCTA): This is a revolutionary advancement. Without requiring contrast agent injections, it non-invasively reveals the intricate retinal vascular network, greatly facilitating the diagnosis of vascular diseases.
    
17. Wider, Deeper, Faster: Scanning coverage is broader, penetration is deeper, speed is faster, and image quality is higher.
    

    3. Artificial Intelligence (AI): AI algorithms are being applied to automatically analyze OCT images, assisting physicians in rapid disease screening and diagnosis. This holds immense potential for future application in large-scale health screenings.

    
    

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