Diabetic retinopathy is a complication of diabetes that damages the small blood vessels in the retina, the light-sensitive tissue at the back of the eye. Over time, this damage can lead to fluid leakage and swelling, potentially causing significant vision loss if not properly managed. Ophthalmologists use a non-invasive imaging technology called Optical Coherence Tomography, or OCT, to diagnose and manage the effects of this condition. This scan provides detailed, three-dimensional images of the retina, allowing for a comprehensive assessment of its health.
Understanding Optical Coherence Tomography
Optical Coherence Tomography is an imaging method that provides cross-sectional pictures of the retina. It functions similarly to an ultrasound but uses light waves instead of sound waves. The OCT machine directs a beam of invisible infrared light into the eye and measures how that light reflects off the retinal structures, generating a detailed map of the retina’s layers.
The primary advantage is its high resolution, which allows specialists to see each retinal layer and measure its thickness with precision. This capability distinguishes it from standard retinal photography, which only captures a surface image. The scan produces a two- or three-dimensional map of the retinal anatomy, enabling a thorough evaluation of any changes caused by disease.
The OCT Examination Process
In many cases, an ophthalmologist will first administer eye drops to dilate the pupils. These drops widen the pupils to provide a clearer view of the retina, though they can cause temporary light sensitivity and blurred vision. Not every OCT examination requires dilation, and the decision depends on the specific clinical situation.
Patients are seated in front of the OCT machine, placing their chin on a rest to keep their head still. They are then asked to focus on a target light while the device scans the eye, a painless and non-invasive process that takes only a few minutes.
Key Findings in Diabetic Retinopathy
A scan of a healthy macula shows organized layers and a characteristic dip in the center, the foveal contour. In diabetic retinopathy, an OCT is sensitive in detecting structural changes. The most common finding is Diabetic Macular Edema (DME), which is swelling in the macula from leaking blood vessels.
On the scan, DME causes a loss of the foveal dip as the area thickens. This can appear as a spongy thickening of the retina or as distinct, dark pockets of fluid known as intraretinal cysts. OCT machines can also generate color-coded maps where warmer colors indicate swollen areas.
The scan can also identify an epiretinal membrane (ERM), a thin layer of scar tissue on the retinal surface. An OCT shows an ERM as a bright, reflective line that can wrinkle the underlying retinal layers, and this pulling can contribute to swelling.
Another finding is vitreomacular traction (VMT), which occurs when the vitreous gel, which normally pulls away with age, remains stuck to the macula and exerts a pulling force. An OCT scan visualizes this attachment and its distorting effect on the retinal contour.
Interpreting an OCT Scan
Interpreting an OCT scan involves comparing the patient’s retinal structure to a normal reference. A healthy macula has a thickness in the range of 200 to 275 microns and a recognizable pattern of light and dark bands. In diabetic retinopathy, this normal architecture is disrupted by the changes described previously.
By comparing a patient’s current scan to a normal reference and to their own previous scans, an ophthalmologist can precisely quantify the extent of the disease.
Guiding Treatment and Monitoring
Information from an OCT scan guides treatment decisions for diabetic retinopathy. The quantitative measurement of central retinal thickness is a biomarker used to determine the need for intervention. If significant swelling is detected, a doctor may recommend treatments such as injections of medication into the eye. These medications, known as anti-VEGF agents, work to reduce leakage from abnormal blood vessels and decrease macular edema.
OCT is also used for monitoring the retina’s response to therapy. After treatment, follow-up scans assess effectiveness, with a reduction in retinal thickness indicating a positive response. For instance, a macular thickness of over 400 microns might decrease to under 300 microns after a successful injection.
This objective data allows clinicians to tailor treatment plans. Based on the OCT findings, a doctor can decide if a patient needs further injections, if the interval between treatments can be extended, or if a different therapeutic approach is warranted. This continuous monitoring helps in managing the condition effectively, with the goal of stabilizing the retina and preserving vision long-term.