OCT in the Diagnosis of Vitreomacular Disease
Optical coherence tomography (OCT) is a noninvasive diagnostic tool for practitioners, utilizing light waves to provide cross-section imaging of the retina. The OCT provides invaluable data within minutes that allows the practitioner to quickly and accurately diagnose patients. The technology has advanced tremendously over the years and has allowed for improved patient care on both ends.
The OCT evaluates the posterior pole, supplying information on the vitreous, optic nerve, and retina. The vitreous is a gel-like liquid that maintains the eyes shape, it is composed of water, hyalocytes, collagen, and glycosaminoglycans. This gel connects to the retina via several attachment points of varying strengths. Over the course of our lives, the vitreous’s composition degrades in a process called liquefaction–effectively creating a more liquid entity that weakens the adhesions to the retina. The attachment point between the vitreous and the optic nerve is commonly separated over time, leading to what we call a posterior vitreous detachment or PVD. The sudden detachment of the vitreous at this location may lead to a pesky floater that a patient complains about as well as flashes of light. The presence of a PVD can lead to several other ocular conditions down the road. OCT imaging can successfully track this process by capturing the location of the vitreous attachment points to the macula and can reveal when these two structures split. This allows practitioners to provide patients with updates on their posterior pole and anticipate changes that may occur over time.
In cases where the vitreous causes disruption at the retinal surface, we see a condition called vitreomacular traction (VMT). This occurs when the vitreous pulls on the macula, creating tension and distorting the normal macular structure. Vitreomacular traction would cause no pain to the patient, however it may cause blurry vision or metamorphopsia. Oftentimes, patients complain of straight lines appearing wavy or bent. The symptoms that arise in office are similar to those seen in age-related macular degeneration. OCT imaging can be used to distinguish between the two. Vitreomacular traction occurs on the retinal surface, in most instances appearing as disrupted foveal contour. The connection between the vitreous and macula may show areas that seem as if they are pulling away from each other. On the other hand, macular degeneration presents in the lower levels of the retina at the RPE layer or at the bottom of the image. Management for vitreomacular traction involves observation until best corrected vision is affected, this involves in office follow ups and at home amsler grid monitoring. Some cases may resolve on their own and intervention may not be necessary. A vitrectomy is an option for advanced cases of vitreomacular traction. This is a surgery in which the vitreous is removed in order to relieve the tension on the macula. A non-surgical option for treatment would be Jetra–a drug treatment that is injected into the eye. It works to target the adhesions between the vitreous and macula in order to provide relief. The use of OCT imaging for VMT diagnosis provides opportunity to catch changes before they occur in order to intervene in a timely manner.
In extreme cases, vitreomacular traction can lead to macular holes which can greatly affect vision. A full thickness macular hole occurs when the vitreous pulls on the macula with enough force to pull off a section of it, creating a gap in the retinal layers that is apparent on OCT imaging. Common symptoms of a macular hole are similar to that of VMT–blurry or distorted vision. A blind spot in your central vision can occur in late stages of a macular hole. Risk factors for a macular hole are being of 60 years or older, high myopia, and eye injuries/surgeries. There are four stages of macular holes: stage one involves a yellow spot or ring in the fovea, stage two is a small full thickness hole, stage three is a full thickness hole with no PVD, and stage four is a full thickness hole with a complete PVD. Treatment involves observation until best corrected vision is affected, this typically begins to occur at stage 2. A vitrectomy with a gas bubble injection can act as a bandage to hold the macula together. This functions to restore the macular structure and vision to its previous state in most cases. A macular hole left untreated can progress to a detached retina. An OCT can help determine when treatment is necessary, the cross section imaging details whether the macular hole is full thickness or not. The details found on OCT can track patient progression in a timely manner, presenting an opportunity for the practitioner to intervene when vision is jeopardized.
A partial thickness macular hole or a lamellar hole is possible and does not have as many ocular effects. A partial hole occurs when a PVD pulls away from the retina and leaves displaced tissue, however the outer retinal layer remains intact. This is easily diagnosed on OCT by observing the percentage of the retina that is displaced. Symptoms for a partial macular hole is similar to that of a full thickness macular hole, but in most cases vision will remain stable over time. Treatment is generally unnecessary for lamellar holes as they do not tend to progress. A lamellar hole can progress to a full macular hole but it is uncommon. If this does occur, this is treated with a vitrectomy and gas bubble.
A posterior vitreous detachment can oftentimes lead to an epiretinal membrane (ERM) or cellophane maculopathy. This condition occurs due to a proliferation of glial cells on the retinal surface that forms a membranous sheet. This membrane can contract over time, creating tension that may lead to visual distortions. Those who are over 50 and have had a PVD are more at risk to develop an epiretinal membrane. It is most commonly associated with ocular conditions such as prior retinal detachments, diabetic retinopathy, and is often seen in post-surgical patients. An ERM is typically asymptomatic in most patients and is diagnosed with an OCT or dilated retinal exam. On OCT, an ERM appears as a hyper reflective layer overlying the inner retinal surface and is described as having peg-like attachments to the retina. In some cases, loss of foveal depression is seen when traction due to the ERM is present. On ocular exam, an ERM may appear as a fine glistening membrane over the macula. Most ERMS remain fairly stable and so monitoring is the first step in management. In cases where vision is affected, surgical intervention may be required. A vitrectomy is performed to provide access to the ERM where it is peeled off the surface with forceps. This procedure has a high success rate and most patients achieve visual improvement within 3 months, however it may take up to a full year to recover.
The use of OCT in the office opens up opportunities for more accurate and advanced medical care for patients. Understanding how to analyze the imaging provided by the OCT is imperative for practitioners to improve quality of care. OCT plays a vital role in the diagnosis and management of diseases of the vitreous, retina, and optic nerve. This non-invasive diagnostic tool provides information such as cross sectional imaging of the macula, RNFL measurements, and more. This information can assist in treatment decisions and in understanding what the next steps are. Timely diagnosis can prevent sight threatening situations and preserve optimum visual conditions. OCT can function as a teaching tool in the office by providing imaging that the practitioner can reference and explain to the patient, improving their overall understanding of what is happening in their eye. In addition, the presence of an OCT in office acts as a crutch for the practitioner that can boost their confidence in their decision making. The images provided remove any guesswork out of the fundus examination as some macular conditions may appear subtle with the naked eye. If you are thinking of incorporating an OCT into your practice, consider your patient demographic and the pros/cons of diagnostic equipment. Do you cater to a predominantly older population? Can you justify the cost of the equipment with your current revenue? Do you feel confident diagnosing macular conditions without an OCT? There are a lot of aspects to consider when incorporating new equipment into the office, however OCT can be invaluable in many respects in terms of patient care.
If you would like to hear more about this topic, please join us for an awesome Woo U continuing education course coming up on December 12, 2023 with Dr. Julie Rodman, OD, MSc, FAAO. She will be reviewing many of the topics discussed in this article, including OCT imaging and vitreomacular disease in depth.
This FREE course will earn you 1 hour of CE and will be a great way to review examples of diagnostic imaging to assist in your own clinical practice. This is a great way to review important topics with the ability to ask questions in a live setting.
You may register for the event at this link.
Image credit to Dr. Rodman, thank you for your contribution.
Written by Dr. Hannah Alegado, O.D.
