Choroidal neovascularization (CNV) is an eye condition where abnormal blood vessels develop beneath the retina. These new vessels can compromise vision, leading to significant impairment if untreated. Optical Coherence Tomography (OCT) is a non-invasive imaging technique that has transformed eye disease diagnosis and management. This article explores how OCT assists in understanding and managing CNV, providing insights into its capabilities.
Understanding Choroidal Neovascularization
Choroidal neovascularization involves the growth of new, irregular blood vessels from the choroid, a vascular layer beneath the retina. These vessels extend into the subretinal space, under the light-sensitive tissues. The most frequent cause for CNV is age-related macular degeneration (AMD), particularly its “wet” form. Other conditions, such as high myopia, ocular histoplasmosis syndrome, or inflammatory eye disorders, can also contribute to its development.
These abnormal blood vessels are often fragile and prone to leakage of fluid, blood, or lipids. This leakage accumulates in or under the macula, the central part of the retina responsible for sharp vision. This accumulation disrupts the normal retinal architecture, leading to distorted or blurred central vision. Persistent leakage and bleeding can result in scar tissue formation, permanently damaging photoreceptors and causing severe, irreversible vision loss.
Individuals experiencing CNV may notice several symptoms. Straight lines may appear wavy or bent. A blurry spot or a blind spot can develop in the center of their vision. Some people report a noticeable decrease in the brightness or intensity of colors.
How Optical Coherence Tomography Works
Optical Coherence Tomography is a non-invasive imaging test that utilizes light waves to create cross-sectional pictures of the retina. It functions similarly to ultrasound, but uses light instead of sound waves, allowing for much higher resolution imaging of the eye’s internal structures. Light waves penetrate the eye, and reflections from different retinal layers are captured to construct a detailed anatomical map.
During an OCT scan, the patient sits comfortably and places their chin on a rest. Patients focus on a target light while the machine scans the eye. The entire process is quick, taking only a few minutes per eye, and is completely painless and non-contact. No special preparation, such as pupil dilation, is typically required, making it convenient for patients.
The primary benefit of OCT is its ability to provide incredibly detailed, micron-level images of the retinal layers. This allows ophthalmologists to visualize structures and subtle changes not discernible with other examination methods. Its speed and non-invasive nature contribute to its widespread adoption in eye care, enabling efficient and precise diagnostics.
Detecting and Monitoring CNV with OCT
Optical Coherence Tomography plays a significant role in identifying choroidal neovascularization by visualizing anatomical changes within the retina and choroid. OCT can directly show the abnormal neovascular membrane itself, often appearing as an irregular elevation of the retinal pigment epithelium (RPE) or a distinct lesion beneath the neurosensory retina. Beyond the membrane, OCT detects fluid accumulation, a hallmark of active CNV. This fluid can be observed as intraretinal fluid (within the retinal layers) or subretinal fluid (between the neurosensory retina and the RPE).
Ophthalmologists meticulously examine OCT scans for several features indicative of CNV activity. Besides fluid, they look for sub-retinal pigment epithelium (sub-RPE) fluid or hemorrhage, appearing as areas of increased reflectivity beneath the RPE. The structural integrity of the outer retina, including photoreceptor layers, is also assessed for signs of disorganization or damage from leaking vessels. Tracking these features allows clinicians to differentiate active, leaking CNV from inactive lesions.
OCT is also used for the ongoing monitoring of CNV, providing a quantitative and objective assessment of disease progression and treatment response. Repeat OCT scans track changes in fluid levels and the size or activity of the neovascular membrane over time. This consistent imaging helps determine the effectiveness of current treatments, such as anti-VEGF injections, by observing reductions in fluid or membrane activity. OCT’s precision enables the detection of subtle changes, indicating early recurrence of CNV activity, even before a patient notices significant vision changes.
The Significance of Early Diagnosis and Ongoing Monitoring
Timely diagnosis of choroidal neovascularization holds considerable importance for preserving vision. Early detection facilitates prompt treatment, which can significantly improve visual outcomes. Addressing the condition quickly helps to limit damage from leaking blood vessels, preventing irreversible vision loss and maintaining a higher level of central vision. Without early intervention, the abnormal vessels can cause extensive and permanent scarring.
Regular OCT monitoring further aids in the effective management of CNV. Consistent scans detect new or recurring disease activity efficiently. This proactive approach enables timely intervention, such as additional injections, and allows for treatment plan adjustments. Monitoring helps prevent further vision deterioration by catching reactivations before extensive damage occurs.
Ultimately, early detection combined with consistent monitoring can preserve a greater amount of vision over a patient’s lifetime. This proactive management strategy contributes significantly to maintaining the patient’s quality of life. It allows individuals to continue performing daily activities that rely on sharp central vision, such as reading, driving, and recognizing faces.
Treatment Approaches for Choroidal Neovascularization
The primary treatment for choroidal neovascularization today involves anti-VEGF (vascular endothelial growth factor) injections. These medications are administered into the vitreous humor of the eye. Their purpose is to block VEGF, a protein that promotes the growth of new blood vessels and increases their permeability, leading to fluid leakage. By inhibiting VEGF, these injections help dry up fluid, reduce bleeding, and prevent further growth of the neovascular membrane.
While anti-VEGF injections are the standard, other treatments have been used historically or in specific cases. Photodynamic therapy (PDT) involves injecting a light-sensitive drug into the bloodstream, activated by a non-thermal laser light applied to the eye. This targets and closes off the abnormal vessels. Laser photocoagulation, which uses a high-energy laser to burn and destroy the abnormal vessels, is generally used less frequently today due to the risk of damaging overlying healthy retinal tissue and creating blind spots.
Treatment decisions for CNV are highly individualized and are often guided by OCT scan findings. The presence and amount of fluid, along with the neovascular membrane characteristics observed on OCT, inform the frequency and type of injections needed. While CNV is a serious condition that can threaten vision, ongoing advancements in diagnostic tools like OCT and effective treatments offer considerable hope for preserving vision and managing the disease.