Subretinal injection is a specialized surgical technique that delivers therapeutic agents directly into the subretinal space, a confined area between the neurosensory retina and the retinal pigment epithelium (RPE). This precise method allows for the targeted delivery of medications, genetic material, or cells to the affected tissues. The direct application ensures that the therapeutic agents reach their intended cellular targets with greater efficiency, a significant advantage over systemic or less localized delivery methods.
Conditions Treated
Subretinal injection is a treatment for specific eye conditions that affect the photoreceptors or the retinal pigment epithelium. Inherited retinal diseases (IRDs), such as Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP), are frequently targeted with this approach. In these genetic disorders, the photoreceptor cells or the RPE are impaired, leading to progressive vision loss. Age-related macular degeneration (AMD), particularly its wet form, can also be treated using subretinal injections, sometimes involving the delivery of tissue plasminogen activator (tPA) to manage submacular hemorrhages. Stargardt disease, another inherited macular degeneration, is also a candidate for subretinal therapies.
The Procedure Explained
Subretinal injection is a delicate surgical procedure performed in an operating room. Patients receive either local or general anesthesia to ensure comfort and immobility during the operation. Local anesthesia often involves a sub-Tenon block, which numbs the eye and surrounding tissues, while general anesthesia provides a deeper state of unconsciousness.
The standard technique involves a vitrectomy, where small incisions are made in the sclera, the white outer layer of the eye, to insert tiny instruments. This allows the surgeon to remove the vitreous gel, the clear, jelly-like substance that fills the eye.
A fine cannula is then carefully guided through a small opening created in the retina, known as a retinotomy, to access the subretinal space. Once the cannula is positioned, the therapeutic agent is slowly injected, creating a small, temporary detachment of the retina, often referred to as a “bleb.” The entire process requires specialized surgical skills to minimize trauma to the retinal tissues.
Recovery and Post-Procedure Care
Following a subretinal injection, patients can expect a recovery period lasting one to two weeks, during which it is important to avoid strenuous activities. Some common post-operative sensations include a “scratchy” or “sandy” feeling in the eye, which can be alleviated with artificial tear drops or gel. It is important to avoid rubbing the treated eye to prevent complications.
A small red spot or area of blood on the white of the eye at the injection site is a common occurrence, usually resolving within a couple of weeks. Patients will be prescribed eye drops, antibiotics and steroids, to prevent infection and manage inflammation. These drops are used for several weeks, with instructions provided by the surgeon regarding frequency and duration.
Follow-up appointments are scheduled to monitor the healing process and assess the eye’s response to the treatment. Any sudden worsening of vision, increased pain, or new symptoms like a significant increase in floaters should be reported to the medical team immediately. Maintaining good hygiene, avoiding getting water directly into the eye during showering for the first 24 hours, and refraining from swimming for at least a month are also recommended to prevent potential infections.
Potential Outcomes and Considerations
Subretinal injections aim to stabilize vision or slow the progression of retinal diseases, rather than always providing a complete restoration of sight. For instance, in inherited retinal diseases like Leber congenital amaurosis (LCA), gene therapy delivered via subretinal injection has shown improvements in visual function and retinal stability. Similarly, in certain cases of wet age-related macular degeneration (AMD), subretinal delivery of agents can aid in displacing submacular hemorrhages, potentially preserving central vision.
The effectiveness of the treatment can vary among individuals, depending on the specific condition, its severity, and the patient’s overall health. Temporary discomfort and the need for ongoing monitoring are common considerations. Continued observation is part of the long-term care to assess the sustained benefits and address any changes that may arise.
Advancements in Subretinal Therapies
Subretinal injection is recognized as a delivery method for advanced therapies beyond traditional medications. Its ability to place therapeutic agents directly at the photoreceptor and retinal pigment epithelium (RPE) layers makes it suitable for gene therapy. Gene therapies for inherited retinal diseases, such as those targeting RPE65 mutations in Leber congenital amaurosis (LCA) or MERTK-related retinitis pigmentosa, have demonstrated success through subretinal delivery. This approach allows for the introduction of functional genes into the cells to correct genetic defects causing vision loss.
The technique is also being explored for cell-based therapies, including the transplantation of stem cells or stem cell-derived RPE cells, for conditions like age-related macular degeneration and Stargardt disease. These cells are intended to replace damaged retinal cells or provide supportive factors to preserve existing ones. Research evaluates the therapeutic potential of stem cells delivered into the subretinal space. This allows these treatments to target specific cell types, offering new possibilities for restoring or preserving vision in previously untreatable conditions.