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OCT useful in management of DME
The imaging device allows physicians to see pathology earlier and more clearly.
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Nearly 30.26 million Americans have type 1 or type 2 diabetes, and of those, 4.2 million adults aged 40 and older, or 29%, have diabetic retinopathy. An estimated 11% of all diabetic patients have diabetic macular edema, and 1% to 3% of those have vision loss. These alarming statistics have propelled research and fueled demand for better treatment options. As a result, we have experienced a significant paradigm shift away from laser therapy as the first line of treatment and moved toward the realm of pharmacological therapy, including intravitreal anti-VEGF and steroidal treatments.
When diagnosing and monitoring patients with DME, spectral-domain OCT is a primary driving force in determining when to start therapy. OCT is an objective tool that can help us to identify early DME, guide us in selecting the best treatment and closely monitor response to treatment.
Treatment determination
OCT has become a standard tool in the diagnosis and management of my patients with DME, and I base my decision for therapy primarily on the evaluation of OCT results. This allows for earlier intervention before the patient presents with what has traditionally been referred to as “clinically significant macular edema” and significant vision loss. Although vision is still an important factor of consideration, the swelling indicated on the OCT scan determines when I initiate treatment. For example, if a patient has 20/20 vision and the OCT report indicates minor swelling, I am unlikely to treat the patient for DME. However, if vision digresses from 20/25 to 20/40 and swelling is evident on the OCT, I will begin treatment. This is a change from the subjective exam toward reliance upon the objective measure provided by OCT.
This objectivity is helpful when I consider continuing or switching treatment modalities. A decrease in central retinal thickness, as seen on OCT, of 10 µm or more is typically considered a positive response. However, when we encounter suboptimal results, we can consider switching to a new medication. The DRCR.net Protocol T study demonstrated that all anti-VEGF treatments are effective in treating DME in patients with good vision, but as vision worsened, the spread of efficacy became wider between the agents. From the Protocol T study, we can also conclude that tailoring treatments to patients for their particular pathology may allow for maximum benefit vs. beginning with one standard modality and then switching to another. This study offers a compelling reason for changing not only how we treat patients with DME, but also how we evaluate them. OCT images, in the context of a patient’s visual function, can provide us with the best overall picture to make these decisions.
Typically, OCT response tracks parallel to a patient’s visual acuity response. In the event of deviation, we may be looking at a patient who has had DME for a long time or somebody who has already undergone multiple treatment modalities. Conversely, if the central retinal thickness improves but best corrected visual acuity remains static, I will hold the course and explain to the patient that the DME has improved and that he may be experiencing a delayed vision response to the improving central retinal thickness. In these situations, the OCT scan is the most accurate picture. Another scenario might be if a patient has 20/20 BCVA but the OCT shows central retinal thickening of 50 µm to 100 µm since the last scan. In this case, I discuss and show the findings to the patient so that we can keep a close watch on it. As soon as the patient or an exam indicates a negative impact on visual function, we can begin treatment. Generally, diabetes swelling tends to be more forgiving than macular degeneration in terms of returning vision and OCT thickness to baseline even after the resurgence of the edema. It is also important to consider that discordance between the anatomy, and OCT can also indicate that there are other factors affecting the diabetic DME patient, including anything from anterior segment complications to vein occlusion to cataract.
Avoid the black hole
OCT gives us the ability to see pathology earlier and more clearly. Using the Spectralis OCT device (Heidelberg Engineering), I have access to multimodality diagnostic imaging of the eye. The Spectralis has enhanced the role of spectral-domain OCT by integrating it with confocal scanning laser ophthalmoscopy. This combination of technology enables me to see unique views of the structure and function of the eye. Its image capability provides active eye tracking with enhanced anatomical details, an overall thickness map and line scans. At follow-up scans, the device automatically re-scans, placing the scan in exactly the same location, thus bypassing operator variability. I am able to compare and contrast the overall thickness map and line scans with precise imagery.
It is highly advantageous and simply a good practice to review all the information the OCT provides, regardless of platform, and not base conclusions off an absolute number. Focusing on the absolute number can lead us into a black hole where we miss the important contributing factors.
- References:
- Diabetes and blindness due to DME. International Diabetes Federation Europe. https://www.idf.org/sites/default/files/IDF%2520Toolkit_Backgrounder_FINAL.pdf. Accessed Sept. 24, 2015.
- Statistics about diabetes. American Diabetes Association. http://www.diabetes.org/diabetes-basics/statistics/. Published June 10, 2014. Accessed Sept. 24, 2015.
- For more information:
- Szilárd Kiss, MD, can be reached at Department of Ophthalmology, Weill Cornell Medical College, 1305 York Ave., 11th Floor, New York, NY 10021; email: szk7001@med.cornell.edu.
Disclosure: Kiss reports no relevant financial disclosures.