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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1.Improvements at the hardware level

(1) Increase the scanning speed

Frequency domain OCT (FD-OCT) : Compared with time domain OCT (TD-OCT), FD-OCT has A faster scanning speed (up to tens of thousands to hundreds of thousands of A-scans per second), significantly reducing artifacts caused by patients’ minor movements (such as eye tremors and breathing).

Swept-frequency OCT (SS-OCT) : By rapidly tuning the laser light source to achieve high-speed scanning, it further shortens the single imaging time.

(2) Eye-tracking system

Real-time active tracking: In ophthalmic OCT, infrared cameras or pupil tracking technology (such as Zeiss’s Follow-Up Mode) are integrated to dynamically adjust the scanning position to compensate for eye movement.

Adaptive scanning: Adjust the scanning path based on real-time tracking data to avoid image shift caused by sudden movement of the patient.

(3) Probe stability design

Handheld OCT: For non-cooperative patients (such as children and Parkinson’s disease patients), lightweight probes or head fixation devices (such as jaw supports) are used.

Contact OCT: In intravascular OCT (IVOCT), the movement caused by heartbeats or breathing is reduced by touching the vessel wall through a catheter.



2. Correction of software algorithms

(1) Image Registration

Feature point matching: Align B-scan images from multiple scans using stable anatomical structures in the image (such as retinal vascular bifurcations).

Registration based on mutual information: Motion compensation is achieved by maximizing the similarity index between images (such as normalized mutual information).

(2) Motion detection and rejection

Abnormal frame detection: Identify invalid frames caused by intense movement (such as signal loss and distortion) and eliminate them during reconstruction.

Dynamic weighted average: Weights are assigned to images scanned multiple times (frames with smaller motion have higher weights), and the influence of random motion is reduced after fusion.

(3) Deep learning for artifact removal

Generative Adversarial networks (Gans) : Train models to restore clear structures from motion-degraded images (such as Artifact-Net).

Time series prediction model: Utilizing networks such as LSTM to predict eye movement trajectories and correct scanning positions in advance.



3. Optimization of operation processes

(1) Patient preparation

Fixed position: During ophthalmic examinations, use a head support and a forehead support, and remind the patient to avoid speaking or swallowing.

Shorten the time of a single scan: Prioritize small-area high-definition scanning (such as 5× 5mm instead of 12× 12mm) and complete large-area imaging in different regions.

Anesthesia or sedation: In animal experiments or pediatric examinations, surface anesthesia (such as in ophthalmology) or mild sedation may be used when necessary.

(2) Scanning strategy

Repeated scanning: Collect multiple sets of data from the same area and improve the signal-to-noise ratio through software fusion.

Orthogonal scanning: Scan the same area from a vertical direction (such as horizontal + vertical) to cross-verify the influence of motion.

(3) Real-time feedback

Operator monitoring: Observe real-time images during the scanning process. If motion artifacts are detected, immediately pause and re-scan.

Patient cooperation prompt: Guide the patient to remain stable through the gaze light or voice prompt (such as “Please gaze at the green light flashing”).



4. Solutions for special scenarios

Cardiovascular OCT (IVOCT)

Trigger the scan synchronously with the electrocardiogram (ECG), avoiding the cardiac pulsation period (collection during the diastolic period).

Use rapid withdrawal catheters (such as 20 mm/s) to reduce the impact of vascular displacement.

Intraoperative OCT

Combine the navigation system (such as neurosurgical robots) to update the scanning position in real time.

Non-contact probes are adopted to avoid interference from instruments.

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Exudative Retinal Detachment (ERD) is a lesion in which the neuroepithelial layer of the retina separates from the pigment epithelial layer without holes. The core mechanism is the destruction of the blood-retinal barrier or the imbalance of choroidal osmotic pressure, resulting in abnormal accumulation of plasma, lipids or blood in the subretinal space. Unlike rhegmatogenous or tractional detachment, ERD does not have retinal holes. ERD is often an "ocular crisis signal" of systemic or local diseases.

ERD is essentially the fundus manifestation of multi-system diseases, and its causes can be divided into two major categories:
(1) Systemic diseases and pregnancy-related diseases: Severe preeclampsia (S-PE) and HELLP syndrome are high-risk factors for ERD; Hypertensive nephropathy: Malignant hypertension can cause choroidal circulation disorders, and fibrinoid necrosis of choroidal arteriole leads to a large amount of plasma exudation. (2) Ocular diseases such as uveitis and retinal vasculitis: Uveitis ranks first among the causes of ERD, especially posterior uveitis like VOGT-Koyanagi-Harada syndrome (VKH) and sympathetic ophthalmia. Inflammation leads to increased permeability of choroidal vessels, causing exudation. Tuberculous uveitis can form subretinal abscesses or granulomas, directly damaging the blood-retinal barrier. Vascular diseases: Coats' disease - Highly prevalent in children and adolescents. Retinal capillary dilation accompanied by a large amount of lipid exudation can lead to total detachment. Retinal vein occlusion (BRVO) - Ischemic vein occlusion induces the release of inflammatory factors, leading to vascular leakage; Tumors and congenital abnormalities: Choroidal melanoma or hemangioma disrupts the blood-retinal barrier, leading to the accumulation of exudate. Metastatic breast cancer and lung cancer are the most common primary foci. According to the latest study of EURETINA 2024, exudative detachment is the main manifestation of invasive retinopathy of prematurity (ROP), accompanied by edema in the anvascular area and subretinal exudation.

The symptoms of ERD patients are diverse, but there are usually four key warning signs:
Painless vision loss: When the macular area is involved, vision can drop sharply to below 0.1. Unlike rhegmatogenous detachment, vision loss in ERD usually progresses more slowly, but patients in the acute phase of hypertensive crisis or VKH syndrome may lose central vision within a few hours. Visual distortion: Due to the displacement of photoreceptor cells caused by subretinal fluid, wavy distortion occurs when looking at straight lines. Amsler grid examination reveals typical grid distortion. Central dark spot: When the macular area is affected, a fixed black shadow appears in the center of the visual field, but the peripheral visual field remains relatively intact. Abnormal color vision and flashes: Inflammatory ERD (such as VOGT-Koyanagi-Harada disease) is prone to blue-yellow color vision shift.

Multimodal imaging combined application of optical coherence tomography (OCT) : The gold standard for ERD diagnosis, which can directly display low-reflection dark areas of subretinal fluid and RPE detachment. EDI-OCT technology - enhanced penetration depth, can quantify choroidal thickness, and help distinguish VKH from CSC; Fluorescein angiography (FFA) : Active leakage foci show "ink-stained" or "chimney-like" hyperfluorescence (such as CNV); The bleeding area shows fluorescence occlusion, and the non-perfusion area suggests ischemic etiology. Indocyanine green angiography (ICGA) : Evaluation of choroidal vessels - Diagnosis of polypoid choroidal vasculopathy (PCV) or VKH complex; OCT angiography (OCTA) : Non-invasive detection of retinal/choroidal neovascularization and quantification of blood flow density; B-type ultrasound: When the refractive media is turbid, it shows subretinal fluid dark areas, differentiating choroidal tumors or hemorrhage. Multifocal electroretinography (mfERG) : Objectively assess retinal functional impairment, especially suitable for children or uncooperative patients;

The treatment of ERD should focus on etiological therapy, supplemented by surgical intervention.

Drug therapy: Glucocorticoids - systemic or topical application (such as intrauterine injection) to suppress inflammation (such as uveitis, Eales' disease); Anti-vegf drugs - reduce vascular leakage (such as BRVO, Coats' disease); Laser and photocoagulation therapy: Retinal laser photocoagulation - sealing abnormal blood vessels (Coats' disease, ischemic BRVO); Micro-pulse laser - Treating macular edema and reducing thermal damage; Surgical intervention: It is only used for complex cases, such as vitrectomy when Coats' disease is secondary to traction detachment. Spontaneous absorption is possible. After blood pressure is controlled in hypertensive choroidal lesions, the detachment can spontaneously return to its original position. The prognosis is highly dependent on the control of the primary disease: inflammatory ERD - early hormone therapy can completely reset it, and the visual recovery is relatively good; Tumors or Coats' disease - Delayed diagnosis and treatment can cause permanent photoreceptor damage. Amblyopia should be vigilant in children. Follow-up requirements - OCT and FFA should be reexamined every 3 to 6 months to monitor recurrence.

Example 1: The retinal neuroepithelial layer in the macular area protrudes, with dark reflex cavities inside

Exudative retinal detachment is a "crisis signal" of systemic diseases within the eye, and its diagnosis and treatment require collaboration between ophthalmology and multiple disciplines. Early identification of the primary disease, combined multimodal imaging assessment, and targeted control of inflammation/vascular leakage are the core strategies to avoid permanent vision loss. Especially for premature infants and patients with chronic inflammation, regular fundus screening is a key line of defense for saving visual function!

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When OCT meets artificial intelligence, a diagnostic revolution quietly arrives:

Automatic lesion identification: The algorithm based on convolutional neural network (CNN) can complete the pathological analysis of ophthalmic OCT images within 0.3 seconds, identifying dozens of lesions such as macular holes and retinal detachment, with an accuracy rate exceeding 95%

Real-time surgical navigation: During tumor surgery, the AI-enhanced OCT system can dynamically mark the tumor boundary. Experimental data show that this reduces the residual rate of malignant tissues by 40%

Elastography breakthrough: The Bayesian neural network strain reconstruction technology developed by the team from Guangdong University of Technology has successfully solved the problem of measuring signals related to chromatographic regression, enabling OCT to map the mechanical properties of tissues and providing a new dimension for the diagnosis of cancer hardness

Knowledge Corner: The Mystery of “Coherence” in OCT

Low-coherence interferometry (LCI) is the core technology of OCT. When the light beam reflected from the tissue meets the reference light beam, only the light with an optical path difference less than the coherence length of the light source will interfere. By measuring interference signals, OCT can precisely locate the depth position of scatterers - just like measuring the microscopic world of life with a “ruler” of light.



Full-field OCT (FF-OCT) : Breaking through the traditional resolution limit and achieving cell-level dynamic imaging. In breast cancer surgery, the experimental system has been able to determine within 20 seconds whether there are residual cancer cells at the resection margin

Chip-level light source: Columbia University has developed a millimeter-level supercontinuum light source chip, replacing traditional bulky lasers and paving the way for handheld OCT devices

Multimodal fusion: Combining OCT with photoacoustic imaging, fluorescence microscopy and other technologies to simultaneously obtain the triple information of structure, function and molecule. For example, in brain science research, such systems can observe hemodynamics and neuronal activities in parallel



Despite the bright prospects, OCT still faces practical constraints:

Penetration depth limitation: The strong scattering characteristics of light in biological tissues limit the effective detection depth to 2-3mm (skin) to 2-3cm (eye).

Data Ocean Challenge: A single OCT scan of the entire body skin generates data at the GB level, and more intelligent compression analysis algorithms need to be developed

Standardization dilemma: The differences in equipment parameters among different manufacturers lead to a decline in data comparability, and it is urgent to establish a cross-platform quality control system

While the latest published papers are still exploring how to optimize the OCT artificial intelligence model, innovators on the clinical front line have begun to rewrite patients' destinies with this technology. From subtle retinal lesions to fatal plaques in coronary arteries, from cancer cells beneath the skin to subtle swells of nerve fibers - this faint light of OCT, which piercings through the fog of life, is quietly reshaping the cognitive boundaries of modern medicine.

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Common causes: tractional retinal detachment (TRD) is mainly caused by the traction of the fibrous vascular membrane on the surface of the retina or within the vitreous. Adult TRD is most commonly seen in proliferative diabetic retinopathy (PDR), retinal vein occlusion (RVO), retinal vasculitis and proliferative vitreoretinopathy (PVR). In addition, trauma, sickle cell retinopathy and uveitis, etc. can also lead to TRD. TRD in children is commonly seen in congenital diseases such as familial exudative vitreoretinopathy (FEVR), retinopathy of prematurity (ROP), and persistent primary vitreous hyperplasia (PHPV).

Clinical manifestations: The patient's symptoms are closely related to the location and extent of the traction. Typical manifestations include: Decreased vision: Posterior pole detachment can cause a sharp decline in central vision, while early peripheral detachment may be asymptomatic. Visual field defect: Fixed direction black shadow occlusion, a certain area of the visual field: "curtain" -like occlusion. Floaters and flashes of light: When the eyes move, brief "lightning-like" or "fire-like" flashes appear before the eyes, mostly around the visual field. Sudden drop in central vision + distorted vision: This highly indicates macular involvement. If not treated promptly, it may cause irreversible vision damage, such as scar formation and photoreceptor cell necrosis.

Diagnostic method: Fundus examination: After mydriasis dilation, the indirect ophthalmoscope can reveal the fibrous vascular membrane and its traction on the retina, with or without vitreous hemorrhage. Optical coherence tomography (OCT) : High-resolution display of the morphology of each layer of the retina, assessment of the position of the traction membrane and the involvement of the macular area. B-ultrasound: It is suitable for patients with severe vitreous opacity to assess the degree of traction and the extent of detachment. Fluorescein fundus angiography: It helps identify neovascularization, non-perfusion areas and lesion distribution, which is beneficial for surgical planning.

Treatment and prognosis: Vitrectomy (PPV) : Removing the proliferative membrane and releasing traction, combined with gas or silicone oil filling to reposition the retina, is the preferred surgical method for TRD. Laser photocoagulation: Targeting ischemic areas or around holes, it reduces new blood vessels and leakage. Anti-vegf drugs: Preoperative injection can reduce the vascular activity of the proliferative membrane and lower the risk of intraoperative bleeding. External scleral compression surgery: It is suitable for peripheral detachment and reduces vitreous traction through external pressure. Postoperative management: Regular follow-up is necessary. Avoid strenuous exercise and intraocular pressure fluctuations. Supplement neurotrophic drugs (such as vitamin B1 and adenosine triphosphate) to promote functional recovery.

Preventive strategies: Control underlying diseases: For instance, patients with diabetes and hypertension need to strictly manage their blood sugar and blood pressure to delay the progression of retinopathy. Regular ophthalmic screening: High-risk groups (patients with high myopia and diabetes) should have fundus examinations every year. Avoid ocular trauma: Especially for those engaged in high-risk occupations, protective equipment should be worn. Timely treatment of vitreous hemorrhage: Early intervention can reduce the formation of organized membranes.

The symptoms of tractional retinal detachment are centered around painless visual abnormalities. In the early stage, they may only present as mild floaters or flashes, which are easily overlooked. As the traction intensifies, visual field defects, distorted vision and decreased vision gradually occur. Due to the significant individual differences in symptoms, especially among high-risk groups such as diabetes and high myopia, even if there are no obvious discomforts, regular fundus screening (such as OCT and fundus fluorescein angiography) is still necessary to avoid delaying treatment due to "asymptomatic" conditions. Once the above warning signals occur, it is essential to visit an ophthalmologist as soon as possible and undergo surgery (such as vitrectomy) to relieve the traction and reposition the retina, so as to save vision to the greatest extent.

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