An imaging method called optical coherence tomography (OCT) makes use of light waves to produce high-resolution and cross-sectional pictures of biological tissues. It functions similarly to ultrasonic imaging, except it employs light waves to probe tissues rather than sound waves and making micrometer-scale features visible. Time-domain OCT (TD-OCT) the original kind of OCT measured the time delay of light reflected from the tissue using a moving reference mirror.
SD-OCT is an advanced version of OCT that uses a spectrometer to capture a broad spectrum of light reflected from tissues. It records the full interference pattern of light at a given time, allowing for rapid, high-resolution imaging without the need for mechanical scanning. The interference pattern known as the spectral signal is analyzed to extract spatial information. In SD-OCT, light from a broadband source is split into 2 beams, one directed at the tissue and the other at a reference mirror. The reflected light is combined to create an interference signal which is captured by a spectrometer. This information is used to reconstruct an image of the tissue showing details like retina layers and blood vessels. SD-OCT captures the full spectrum of light in a single scan and enabling faster and more detailed imaging.
SD-OCT gives faster image capture and higher resolution compared to TD-OCT which requires mechanical scanning and can cause distortion due to motion artifacts. This is particularly useful in clinical settings where time efficiency is crucial. SD-OCT captures data in parallel and allowing faster acquisition without compromising resolution. Its higher axial resolution around 5 to 7 mm enables visualization of fine retinal structures, which is crucial for monitoring conditions like macular edema, retinal detachment or diabetic retinopathy.
SD-OCT offers improved signal-to-noise ratio (SNR) and three-dimensional (3D) imaging allowing clinicians to detect subtle changes in the retina that may not be visible with previous technologies. This is particularly beneficial when imaging the retina where light scattering and absorption can limit image quality. SD-OCT generates volumetric data through rapid cross-sectional scans and providing a more comprehensive view of the tissue compared to traditional 2D imaging. Its faster scanning speeds reduce motion artifacts and optical aberrations, enhancing visualization of retinal layers, making it easier for clinicians to detect and monitor diseases like macular degeneration, diabetic retinopathy and glaucoma.
Indications
Macular diseases:
Age-Related Macular Degeneration (AMD): It detects early changes in the macula enabling early disease progression monitoring.
Diabetes Macular Edema (DME): It helps to identify the extent of macular edema, measuring retinal thickness and assessing fluid accumulation.
Macular hole: It is used to visualize the size, location and depth of a macular hole and assessing associated features.
Myopic maculopathy: It monitors changes associated with high myopia and guiding management decisions and preventing vision loss.
Glaucoma:
Optic nerve head assessment: It is useful for optic nerve head assessment. Glaucoma is a group of diseases characterized by progressive damage to the optic nerve. SD-OCT is used to measure the thickness of the retinal nerve fiber layer (RNFL) and analyze the optic nerve head (ONH) for early signs of glaucoma.
Retinal Nerve Fiber Layer (RNFL) evaluation: SD-OCT allows for detailed measurement of the RNFL which consists of the axons of retinal ganglion cells.
Angle-Closure Glaucoma: SD-OCT can be used to assess the anatomy of the anterior chamber and evaluate the angle between the cornea and the iris. This helps in determining the risk of angle closure and planning surgical interventions.
Diabetic Retinopathy:
To assess the Diabetic Macular Edema (DME): SD-OCT is essential to indetify subtle changes in the retinal layers like retinal thickening or fluid leakage, indicative of diabetic macular edema (DME). It helps to determine the need for interventions like intravitreal injections, laser therapy or corticosteroid treatment.
Retinal Detachments and Vitreoretinal Diseases: SD-OCT is used in the diagnosis and management of retinal detachment. It gives detailed information on the macula’s involvement, critical for treatment planning.
Optic Nerve Diseases: SD-OCT can be used to assess optic neuropathies, papilledema and corneal diseases.
Corneal Diseases and Anterior Segment Imaging: SD-OCT is used for retinal imaging, corneal thickness, stromal structure and epithelial layer. It is used for evaluating the anatomy of the anterior chamber especially in conditions like angle-closure glaucoma.
Pediatric Ocular Conditions: SD-OCT helps in assessing retinal development and abnormal vascular changes in premature infants. It is useful in evaluating various congenital retinal diseases.
Post-Surgical Monitoring: Post-Vitrectomy and post-Laser Treatment can monitor the retinal structure for potential complications.
Contraindications
Inability to maintain fixation: Patients who cannot remain still or fixate on a target (children and elderly with cognitive impairments).
Severe photophobia or sensitivity to light: Patients with extreme light sensitivity may find the light used in SD-OCT uncomfortable.
Severe cataracts or opaque media: Significant opacities in the cornea, lens or vitreous body that obstruct the light required for SD-OCT.
Vitreous hemorrhage: Blood in the vitreous body that obscures the retina and reduces clarity of SD-OCT images.
Severe retinal detachment or tear: Distorted retina in cases of large or complex retinal detachment, hindering light reflection for accurate imaging.
Intraocular lenses (IOLs): Non-diffractive or complex IOLs may cause light scattering and distorting OCT images.
Retinal prostheses or other ocular implants: Metal or refractive materials in ocular implants may interfere with SD-OCT light and distort the imaging.
Outcomes
Equipment
Light source like super luminescent diode (SLD)
Interferometer
Optical scanner
Photodetector
Pupil alignment and eye tracking system
Patient preparation
Pre-Procedure Assessment: Collect the medical and ocular history of patinet to tailor the exam and identify any contraindications. Assess symptoms like vision changes or eye pain to focus the scan appropriately.
Informed Consent: Explain the non-invasive nature of the procedure, potential minor discomforts and reassure that no radiation is used which is important for pregnant patients.
Pupil Dilation: If needed, use eye drops to dilate the pupil for better retinal visualization. This takes 15 to 30 minutes and patients should be informed about potential side effects like light sensitivity. Advising sunglasses for aftercare is recommended.
Comfortable Positioning: Ensure the patient sits comfortably in front of the SD-OCT device with their chin and forehead supported to prevent movement during the scan. Proper alignment is key to obtaining accurate images.
Instruct the Patient on Procedure Steps: Instruct the patient to focus on a target light, stay still and avoid excessive blinking or movement to prevent artifacts.
Minimize External Factors: Advise removing eyewear and limiting external light interference for optimal imaging quality. For children or uncooperative patients, sedation may be considered. Patients with disabilities may require additional assistance to ensure comfort and understanding of the procedure.
Addressing Pre-Existing Conditions: If the patient has dry eyes or active eye conditions, appropriate measures (lubricating drops) should be taken to improve comfort and image quality.
Pregnant Patients: SD-OCT is safe for pregnant patients but it is important to assess the necessity of the procedure and ensure their comfort especially in later stages of pregnancy.
Patient position
The patient should be seated comfortably in front of the SD-OCT device, facing the scanning system for easy access and alignment. The patient’s chin should be placed on the chin rest to stabilize the head and maintain the appropriate distance between the eye and the scanner. The patient’s forehead should be supported to prevent tilting. Eye alignment should be done with the SD-OCT scanner and the patient should focus on a target light or fixation point. Comfort is crucial to prevent motion artifacts and maintain image quality. A relaxed posture is also essential.
Technique
Step 1: Patient preparation:
The patient should be seated comfortably in front of the SD-OCT device aligned with their chin and forehead. If pupil dilation is necessary, administer dilating eye drops and allow 15 to 30 minutes for effect. Ensure the patient remains still and focuses on the target light during the scan.
Step 2: Patient position:
To ensure proper scan alignment, position the patient’s chin on the chin rest and forehead against the forehead support. Adjust the device’s alignment to center the eye in front of the scanner using an alignment system. The patient should focus on the target light provided by the system.
Step 3: Eye alignment and focus:
The clinician uses an SD-OCT system to focus on the patient’s eye and ensuring it is within the scanner’s field of view. Real-time images or guidance are displayed to help align the eye and optimize focus which can be fine-tuned using on-screen guides.
Step 4: Scan acquisition
The SD-OCT device captures high-resolution images of the eye’s structures including the retina, optic nerve and other ocular tissues after the patient is in position and aligned. Different scanning protocols like macula scan, optic nerve head scan or volume scan may be selected based on the clinical indication. Macula scan focuses on the retina while optic nerve head scan evaluates glaucoma or optic neuropathy. Volume scan acquires a series of high-resolution images to create a 3D map. The scan is typically performed in several phases taking multiple cross-sectional images in different locations.
The SD-OCT system may require multiple captures or image passes with clinicians adjusting parameters like frame count, resolution or pattern to optimize images and may capture both horizontal and vertical retina cross-sections.
Step 5: Image quality:
The SD-OCT system ensures high-quality images after a scan providing real-time feedback to ensure clarity. Additional scans may be necessary if unclear or motion artifacts occur. The system calculates key parameters for diagnosis and monitoring, generates automated reports and allows images for detailed review for diagnostic interpretation. Some systems may allow post-processing to adjust contrast or other parameters.
Step 6: Analysis:
The SD-OCT system generates automated reports with measurements and images, saving them in the patient’s medical record for clinician review and documentation of relevant findings for further management.
Step 7: Post procedural care:
Pupil dilation may cause blurry vision and light sensitivity, so advise sunglasses. Discuss findings, follow-up appointments, treatments and schedule additional diagnostic tests or imaging if needed.
An imaging method called optical coherence tomography (OCT) makes use of light waves to produce high-resolution and cross-sectional pictures of biological tissues. It functions similarly to ultrasonic imaging, except it employs light waves to probe tissues rather than sound waves and making micrometer-scale features visible. Time-domain OCT (TD-OCT) the original kind of OCT measured the time delay of light reflected from the tissue using a moving reference mirror.
SD-OCT is an advanced version of OCT that uses a spectrometer to capture a broad spectrum of light reflected from tissues. It records the full interference pattern of light at a given time, allowing for rapid, high-resolution imaging without the need for mechanical scanning. The interference pattern known as the spectral signal is analyzed to extract spatial information. In SD-OCT, light from a broadband source is split into 2 beams, one directed at the tissue and the other at a reference mirror. The reflected light is combined to create an interference signal which is captured by a spectrometer. This information is used to reconstruct an image of the tissue showing details like retina layers and blood vessels. SD-OCT captures the full spectrum of light in a single scan and enabling faster and more detailed imaging.
SD-OCT gives faster image capture and higher resolution compared to TD-OCT which requires mechanical scanning and can cause distortion due to motion artifacts. This is particularly useful in clinical settings where time efficiency is crucial. SD-OCT captures data in parallel and allowing faster acquisition without compromising resolution. Its higher axial resolution around 5 to 7 mm enables visualization of fine retinal structures, which is crucial for monitoring conditions like macular edema, retinal detachment or diabetic retinopathy.
SD-OCT offers improved signal-to-noise ratio (SNR) and three-dimensional (3D) imaging allowing clinicians to detect subtle changes in the retina that may not be visible with previous technologies. This is particularly beneficial when imaging the retina where light scattering and absorption can limit image quality. SD-OCT generates volumetric data through rapid cross-sectional scans and providing a more comprehensive view of the tissue compared to traditional 2D imaging. Its faster scanning speeds reduce motion artifacts and optical aberrations, enhancing visualization of retinal layers, making it easier for clinicians to detect and monitor diseases like macular degeneration, diabetic retinopathy and glaucoma.
Macular diseases:
Age-Related Macular Degeneration (AMD): It detects early changes in the macula enabling early disease progression monitoring.
Diabetes Macular Edema (DME): It helps to identify the extent of macular edema, measuring retinal thickness and assessing fluid accumulation.
Macular hole: It is used to visualize the size, location and depth of a macular hole and assessing associated features.
Myopic maculopathy: It monitors changes associated with high myopia and guiding management decisions and preventing vision loss.
Glaucoma:
Optic nerve head assessment: It is useful for optic nerve head assessment. Glaucoma is a group of diseases characterized by progressive damage to the optic nerve. SD-OCT is used to measure the thickness of the retinal nerve fiber layer (RNFL) and analyze the optic nerve head (ONH) for early signs of glaucoma.
Retinal Nerve Fiber Layer (RNFL) evaluation: SD-OCT allows for detailed measurement of the RNFL which consists of the axons of retinal ganglion cells.
Angle-Closure Glaucoma: SD-OCT can be used to assess the anatomy of the anterior chamber and evaluate the angle between the cornea and the iris. This helps in determining the risk of angle closure and planning surgical interventions.
Diabetic Retinopathy:
To assess the Diabetic Macular Edema (DME): SD-OCT is essential to indetify subtle changes in the retinal layers like retinal thickening or fluid leakage, indicative of diabetic macular edema (DME). It helps to determine the need for interventions like intravitreal injections, laser therapy or corticosteroid treatment.
Retinal Detachments and Vitreoretinal Diseases: SD-OCT is used in the diagnosis and management of retinal detachment. It gives detailed information on the macula’s involvement, critical for treatment planning.
Optic Nerve Diseases: SD-OCT can be used to assess optic neuropathies, papilledema and corneal diseases.
Corneal Diseases and Anterior Segment Imaging: SD-OCT is used for retinal imaging, corneal thickness, stromal structure and epithelial layer. It is used for evaluating the anatomy of the anterior chamber especially in conditions like angle-closure glaucoma.
Pediatric Ocular Conditions: SD-OCT helps in assessing retinal development and abnormal vascular changes in premature infants. It is useful in evaluating various congenital retinal diseases.
Post-Surgical Monitoring: Post-Vitrectomy and post-Laser Treatment can monitor the retinal structure for potential complications.
Inability to maintain fixation: Patients who cannot remain still or fixate on a target (children and elderly with cognitive impairments).
Severe photophobia or sensitivity to light: Patients with extreme light sensitivity may find the light used in SD-OCT uncomfortable.
Severe cataracts or opaque media: Significant opacities in the cornea, lens or vitreous body that obstruct the light required for SD-OCT.
Vitreous hemorrhage: Blood in the vitreous body that obscures the retina and reduces clarity of SD-OCT images.
Severe retinal detachment or tear: Distorted retina in cases of large or complex retinal detachment, hindering light reflection for accurate imaging.
Intraocular lenses (IOLs): Non-diffractive or complex IOLs may cause light scattering and distorting OCT images.
Retinal prostheses or other ocular implants: Metal or refractive materials in ocular implants may interfere with SD-OCT light and distort the imaging.
Light source like super luminescent diode (SLD)
Interferometer
Optical scanner
Photodetector
Pupil alignment and eye tracking system
Patient preparation
Pre-Procedure Assessment: Collect the medical and ocular history of patinet to tailor the exam and identify any contraindications. Assess symptoms like vision changes or eye pain to focus the scan appropriately.
Informed Consent: Explain the non-invasive nature of the procedure, potential minor discomforts and reassure that no radiation is used which is important for pregnant patients.
Pupil Dilation: If needed, use eye drops to dilate the pupil for better retinal visualization. This takes 15 to 30 minutes and patients should be informed about potential side effects like light sensitivity. Advising sunglasses for aftercare is recommended.
Comfortable Positioning: Ensure the patient sits comfortably in front of the SD-OCT device with their chin and forehead supported to prevent movement during the scan. Proper alignment is key to obtaining accurate images.
Instruct the Patient on Procedure Steps: Instruct the patient to focus on a target light, stay still and avoid excessive blinking or movement to prevent artifacts.
Minimize External Factors: Advise removing eyewear and limiting external light interference for optimal imaging quality. For children or uncooperative patients, sedation may be considered. Patients with disabilities may require additional assistance to ensure comfort and understanding of the procedure.
Addressing Pre-Existing Conditions: If the patient has dry eyes or active eye conditions, appropriate measures (lubricating drops) should be taken to improve comfort and image quality.
Pregnant Patients: SD-OCT is safe for pregnant patients but it is important to assess the necessity of the procedure and ensure their comfort especially in later stages of pregnancy.
Patient position
The patient should be seated comfortably in front of the SD-OCT device, facing the scanning system for easy access and alignment. The patient’s chin should be placed on the chin rest to stabilize the head and maintain the appropriate distance between the eye and the scanner. The patient’s forehead should be supported to prevent tilting. Eye alignment should be done with the SD-OCT scanner and the patient should focus on a target light or fixation point. Comfort is crucial to prevent motion artifacts and maintain image quality. A relaxed posture is also essential.
Step 1: Patient preparation:
The patient should be seated comfortably in front of the SD-OCT device aligned with their chin and forehead. If pupil dilation is necessary, administer dilating eye drops and allow 15 to 30 minutes for effect. Ensure the patient remains still and focuses on the target light during the scan.
Step 2: Patient position:
To ensure proper scan alignment, position the patient’s chin on the chin rest and forehead against the forehead support. Adjust the device’s alignment to center the eye in front of the scanner using an alignment system. The patient should focus on the target light provided by the system.
Step 3: Eye alignment and focus:
The clinician uses an SD-OCT system to focus on the patient’s eye and ensuring it is within the scanner’s field of view. Real-time images or guidance are displayed to help align the eye and optimize focus which can be fine-tuned using on-screen guides.
Step 4: Scan acquisition
The SD-OCT device captures high-resolution images of the eye’s structures including the retina, optic nerve and other ocular tissues after the patient is in position and aligned. Different scanning protocols like macula scan, optic nerve head scan or volume scan may be selected based on the clinical indication. Macula scan focuses on the retina while optic nerve head scan evaluates glaucoma or optic neuropathy. Volume scan acquires a series of high-resolution images to create a 3D map. The scan is typically performed in several phases taking multiple cross-sectional images in different locations.
The SD-OCT system may require multiple captures or image passes with clinicians adjusting parameters like frame count, resolution or pattern to optimize images and may capture both horizontal and vertical retina cross-sections.
Step 5: Image quality:
The SD-OCT system ensures high-quality images after a scan providing real-time feedback to ensure clarity. Additional scans may be necessary if unclear or motion artifacts occur. The system calculates key parameters for diagnosis and monitoring, generates automated reports and allows images for detailed review for diagnostic interpretation. Some systems may allow post-processing to adjust contrast or other parameters.
Step 6: Analysis:
The SD-OCT system generates automated reports with measurements and images, saving them in the patient’s medical record for clinician review and documentation of relevant findings for further management.
Step 7: Post procedural care:
Pupil dilation may cause blurry vision and light sensitivity, so advise sunglasses. Discuss findings, follow-up appointments, treatments and schedule additional diagnostic tests or imaging if needed.
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