The 21st century has witnessed a significant revolution in imaging techniques. Continuous innovation in this area has introduced many advanced technologies over the last two decades, including TD-OCT (Time-Domain Optical Coherence Tomography), SD-OCT (Spectral-Domain Optical Coherence Tomography), and SS-OCT (Swept Source OCT). Swept Source is a type of laser incorporated in the device.
Swept Source OCT technology was first introduced to the clinical world around 2012, overshadowing its preceding technologies, namely Time-Domain OCT and Spectral-Domain OCT. This advancement has helped retina specialists and other surgeons overcome the limitations of previous imaging technologies.
Understanding Swept Source OCT and Spectral Domain OCT
How is SD-OCT Different from SS-OCT?
SD-OCT (Spectral-Domain Optical Coherence Tomography) and SS-OCT (Swept-Source Optical Coherence Tomography) differ significantly in their design and hardware, including the bulk optics components, photodetection device, and light source.
For instance, Swept Source OCT’s wavelength is centered around 1 µm, typically in the near-infrared range, providing deeper penetration into tissues. In contrast, SD-OCT uses an 870-nm wavelength light source, which is in the visible to near-infrared range and offers high resolution but with relatively shallower penetration.
The mechanisms of these modalities also differ. SD-OCT reflects different frequencies of light concurrently from the object and then separates these frequencies with the spectrometer’s help. This allows it to capture a broad spectrum of light at once, but it may be limited by the spectral resolution of the spectrometer. On the other hand, SS-OCT uses a laser that sweeps through different wavelengths over time. This method enables the capture of high-speed and high-resolution images with improved depth penetration, requiring a tunable laser and precise wavelength control.
Advantages of Swept Source OCT
SS-OCT offers several quality advantages over its predecessor technologies, such as Time-Domain OCT and Spectral-Domain OCT:
- Deeper and Faster Acquisition Time: Swept Source OCT’s ability to penetrate deeper and acquire images faster allows for obtaining high-resolution images of retinal structures behind pre-retinal hemorrhages, which was challenging with SD-OCT. This deeper penetration aids in visualizing and diagnosing conditions obscured by hemorrhages or other obstructions.
- High Imaging Speed: Another significant advantage of Swept Source OCT is its high imaging speed, which generates high-resolution images while reducing the negative effects of the patient’s eye movements during the scan. This rapid scanning capability ensures better image quality and minimizes motion artifacts. Additionally, compared to SD-OCT, SS-OCT uses a relatively less intense light source, enhancing patient comfort during the examination and reducing potential discomfort or glare.
- Uniform Sensitivity: Swept Source OCT offers uniform sensitivity across the entire scan window, allowing for comprehensive imaging of the vitreous, retina, and deep ocular structures in a single scan. This is a notable improvement over SD-OCT, where variations in sensitivity could limit the ability to capture detailed images of both superficial and deep ocular tissues within the same scan.
Impact of Swept Source OCT on Ophthalmology
SS-OCT has successfully established itself as one of the most innovative imaging technologies with substantial clinical impacts and acceptance in ophthalmology. Below are some critical applications of SS-OCT.
A. OCT in Posterior Segment Disease
Using SS-OCT, detailed visualization of the posterior segment of the eye is possible. This technology effectively identifies the progression of pathologic processes such as retinal diseases and optic nerve conditions and monitors the outcomes of both surgical and non-surgical interventions. It is highly effective for tracking anatomical changes that can occur with macular disease treatment, such as alterations in the macula’s thickness or the presence of fluid, helping assess the effectiveness of therapies and guiding further treatment decisions.
B. OCT in Glaucoma Diagnosis
Swept Source OCT has manifested itself as the dominant visualization modality in detecting and managing glaucoma and retinal diseases. It obtains a high-resolution, clear image of ocular structures, including the choroid, lamina cribrosa, and the optic nerve head. This detailed imaging allows for precise assessment of structural changes associated with glaucoma, such as thinning of the retinal nerve fiber layer and alterations in the optic nerve head. Early detection of glaucoma with the help of SS-OCT is crucial, as it enables timely intervention and management, significantly impacting treatment outcomes and potentially slowing disease progression.
C. OCT in Diabetic Retinopathy
Diabetic Retinopathy is a disease found in patients with diabetes. The increased blood sugar level damages the blood vessels of the eye retina, leading to issues such as leakage, bleeding, and abnormal growth of new blood vessels. If not medicated on time, this disease can severely impair vision and potentially lead to blindness. Swept Source OCT can be beneficial in diagnosing and treating diabetic retinopathy by providing high-resolution cross-sectional images of the retina. This technology allows for detailed visualization of retinal layers, detection of retinal edema, and assessment of the extent of damage, which is crucial for timely and effective treatment to prevent vision loss.
Inphenix is a US-based company that designs and manufactures lasers and light sources with extensive demand in the telecom, sensing, medical, and measurement industries. Their Swept Source OCT possesses multiple salient features such as deep penetration, long coherence length, and high resolution, making it suitable for a wide range of diagnostic and imaging applications. They offer Swept Sources in three different variants—1060nm, 1310nm, and 1550nm windows—each tailored to meet specific needs and optimize performance in various systems. These variants are ideal for OEM integration, providing flexibility and compatibility with diverse equipment and applications in the optical and imaging fields.
