Use all OCT functions to best serve patients
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OCT imaging is extremely valuable in the diagnosis and management of retinal conditions, providing high-resolution and repeatable images of retinal structures.
The noninvasive technology produces volumetric images of tissue at rapid scan speeds and has become an integral component of the standard of care for many posterior segment eye diseases.
Effective OCT imaging provides high-resolution scans in customizable patterns. My preferred OCT gives users the ability to scan the macula, the midperipheral region and the peripheral retina, and obtain progression analyses via repeatable scans and deep tissue images of the choroid with enhanced depth imaging (EDI).
I use OCT in practice to manage patients with age-related macular degeneration and diabetic retinopathy (DR) among a variety of other conditions.
Evaluating AMD
Almost 20 million Americans are living with AMD (Rein DB, et al). OCT can reveal signs of the pathophysiology of AMD, including subretinal fluid, intraretinal fluid and subretinal hyperreflective material that is not visible upon clinical exam, making it possible to detect signs of exudation in a patient who might otherwise be misdiagnosed as only having intermediate AMD.
OCT imaging plays a crucial role in determining a patient’s treatment plan and monitoring outcomes. Each time a patient is seen, OCT supports clinical evaluation imperative for effective patient monitoring and individualized disease management.
Approximately 20% of individuals with AMD develop geographic atrophy (GA; Fleckenstein M, et al). As an AMD patient’s disease progresses, OCT can play a pivotal role in monitoring the condition by detecting precursors to and early stages of GA. Biomarkers of disease visible on OCT scans that show patients at significantly increased risk for developing GA include incomplete retinal pigment epithelium and outer retinal atrophy, hyperreflective columns (barcode sign), collapse of large drusenoid retinal pigment epithelium detachment and hyperreflective foci.
The EDI feature I use aids in greater visualization of choroidal stroma and vasculature. To ensure no signs of early AMD are missed, high-density volume scans are conducted, utilizing high-resolution acquisition modes to avoid missing any subtle findings.
Diagnosis, management of diabetic retinopathy
DR is the leading cause of preventable blindness in working-age adults in the United States (Cheung N, et al). Up to 25% of patients in my practice have DR. Diabetic macular edema can develop at any stage of DR, even milder cases, which can affect a patient’s central vision as a result of intraretinal fluid in the macula. These changes can be visible with OCT even when they cannot be detected clinically.
Patients with diabetes can have significant areas of macular ischemia. As the retina becomes more ischemic and capillaries become damaged, OCT can aid in determining whether inner retinal layers have become disorganized or thinned.
Once a diagnosis has been made, OCT is critical in monitoring changes in DR to determine if a patient’s disease has improved or worsened. Visual acuity does not always accurately portray disease severity. In patients who are being treated for DR, this will show whether administered treatments are working and to what extent.
Making the most of a powerful tool
For a patient to benefit from the potential that OCT offers for identifying and monitoring retinal diseases, ordering the correct scan is pertinent. This requires a familiarity with scan options. Each imaging instrument has different scanning strategies, with commonalities among functions.
First, the scan location must be identified. Most routine macular cube scans or radial scans cover about a central 6 mm diameter in the macula, which is adequate in most situations. However, the scan must be adjusted if something is noted on the clinical exam that is not covered by this routine scan area, if there is pathology picked up at the edge of a scan or there is a patient complaint that directs the scan to a different location.
A decision must also be made about the orientation of the scan. Horizontal cube scans provide thickness maps to evaluate tomographic changes over time. The scans may be helpful in discerning the thickness of individual retinal layers.
In radial scans, all slices cut through the fovea, which provides higher sampling of the fovea. Looking at radial scans may aid in the identification of subtle pathologies, such as disorganization of retinal inner layers, photoreceptor atrophy and inner retina ischemia.
Vertically oriented scans present better visualization of some conditions like choroidal folds. They also provide an increased ability to compare the superior hemisphere with the inferior hemisphere, making it useful for pathologies such as branch retinal vein occlusion, branch retinal artery occlusion, glaucoma and non-glaucomatous optic neuropathies.
It is also vital to compare the same scan type at the same location, taken during subsequent visits, to confidently monitor changes over time. I use the OCT’s anatomic positioning system, which uses the center of the fovea and the center of Bruch’s membrane opening as two fixed, structural landmarks, ensuring optimal image comparisons. Additionally, eye tracking alleviates the effects of eye motion, even if the patient blinks or moves and permits precise follow-up examinations.
OCT has irrefutably changed the standard of care provided to patients, while also enhancing the doctor’s ability to appropriately observe and treat any ocular issues that arise. The ways we diagnose and monitor patients are now informed by detailed, real-time retinal imagery. To best serve patients and interpret what is presented on the scans, it is important to understand and use all the unique tools an OCT imaging device can provide.
References:
- Cheung N, et al. Lancet. 2010;doi:10.1016/S0140-6736(09)62124-3.
- Fleckenstein M, et al. Ophthalmology. 2018;doi:10.1016/j.ophtha.2017.08.038.
- Rein DB, et al. JAMA Ophthalmol. 2022;doi:10.1001/jamaophthalmol.2022.4401.
For more information:
Jessica Haynes, OD, FAAO, FORS, is a consultative optometrist at Charles Retina Institute in Germantown, Tennessee, and serves as a consulting faculty member at the Advanced Care Ocular Disease Clinic at Southern College of Optometry in Memphis, Tennessee.
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