Principle of AS-OCT

AS-OCT uses near-infrared light to produce detailed images of the anterior eye. The technology measures the time delay and intensity of light reflected from different ocular structures to create cross-sectional images.

• Wavelength: Uses longer wavelengths (~1300 nm) than posterior segment OCT, optimizing visualization of the anterior segment.
• Resolution: High spatial resolution (5–20 microns) enables detailed assessment of small structures.

Applications of AS-OCT

Corneal Evaluation:

• Measures corneal thickness and curvature (pachymetry and topography).
• Identifies and monitors keratoconus, corneal edema, dystrophies, and scars.
• Assesses surgical outcomes like LASIK flap thickness or corneal grafts.

Anterior Chamber Angle Assessment:

• Evaluates angle structures in glaucoma, particularly in angle-closure glaucoma.
• Measures parameters like angle opening distance (AOD) and trabecular-iris space area (TISA).

Iris and Ciliary Body:

• Visualizes iris lesions, cysts, and abnormalities.
• Examines the effect of angle closure or pupillary block.

Pre- and Post-Surgical Assessment:

• Determines suitability for refractive surgeries like LASIK or SMILE.
• Evaluates outcomes of keratoplasty, cataract surgery, and anterior segment implants (e.g., phakic IOLs).

Lens and Cataract:

• Measures lens thickness and position.
• Useful in evaluating subluxated lenses or anterior segment changes post-surgery.

Anterior Segment Tumors and Cysts:

• Detects and monitors anterior segment masses with high accuracy.

Trauma Assessment:

• Detects structural changes like anterior chamber depth reduction, lens displacement, or iris injuries.

Advantages of AS-OCT

Non-Invasive:

• Provides detailed imaging without contact or anesthesia, enhancing patient comfort.

High Resolution:

• Offers fine structural detail, surpassing ultrasound biomicroscopy in some applications.

Rapid and Efficient:

• Quick imaging with minimal preparation or patient cooperation.

Quantitative Analysis:

• Measures parameters like corneal thickness, anterior chamber depth, and angle dimensions.

Wide Applicability:

• Useful in diagnostics, surgical planning, and postoperative follow-up.

Limitations of AS-OCT

Penetration Depth:

• Limited ability to image deeper structures like the ciliary body or sclera.

Shadowing Artifacts:

• Structures behind highly reflective tissues (e.g., corneal scars) may be obscured.

Cost and Accessibility:

• Advanced systems may not be readily available in all clinics.

Dependence on Optical Clarity:

• Opacities in the cornea or anterior chamber can interfere with image quality.

Limited Field of View:

• Smaller imaging area compared to ultrasound biomicroscopy.

Techniques in AS-OCT Imaging

Corneal Imaging:

• Pachymetry: Maps corneal thickness across its entirety.
• Keratoconus detection: Identifies thinning and steepening patterns.

Angle Imaging:

• Evaluates open and narrow angles, aiding in glaucoma diagnosis.
• Dynamic imaging under different lighting conditions to assess angle changes.

Post-Surgical Imaging:

• Assesses LASIK flaps, corneal grafts, or IOL positioning.

Anterior Chamber Depth (ACD):

• Measures the distance from the corneal endothelium to the lens.