PEER REVIEWED

Decisions for Imaging in DME

A brief guide to diagnosis and management with images

AMEEN MARASHI, MD

Usually, after examining patients with diabetic macular edema, we order ancillary tests that help us to document the case, plan treatment, offer a prognosis, and confirm the diagnosis. The most ordered tests are optical coherence tomography and fundus fluorescein angiography (FFA).

Ordering both imaging examinations at the first visit may be necessary in some cases, while other times, we choose one or the other. When and why should we order FFA or OCT, and what should we look for when we order them?

OPTICAL COHERENCE TOMOGRAPHY

When and Why?

At the first visit, ordering OCT (particularly when best-corrected visual acuity is less than 20/20) is important because it will help us to document and learn about the pattern, location, thickness (Figures 1 and 2), and vitreomacular interface status of the edema, all of which can affect our treatment plan and visual prognosis.

Figure 1. Pretreatment OCT of diabetic macular edema.

Figure 2. Three-dimensional OCT map of DME before treatment.

OCT can be ordered again after 18 weeks based on treatment plan (Figures 3 and 4), to monitor the effectiveness of treatment. Further, it can help us decide whether it is mandatory to change, stop, or continue with the treatment plan.

Figure 3. The same patient as in Figures 1 and 2, following four anti-VEGF injections.

Figure 4. Three-dimensional OCT map for the patient in Figures 1, 2, and 3, after four anti-VEGF injections.

What Are We Looking For?

When examining the OCT of DME patients, we should consider several points:

Macular thickness. Worse baseline VA has been associated with greater central subfield thickness.

Location of edema — central or not. OCT can be used as a guide in some cases for laser photocoagulation, particularly when planning modified grid laser (Figure 5).

Figure 5. Three-dimensional OCT map showing the location of DME.

Disorganization of the retinal inner layers. Disorganization of the retinal inner layers (DRIL) is associated with reduced visual acuity, especially in patients with center-involved DME (Figure 6) in more than 50% of or within 1 mm of the foveal center and in the presence of large cysts.¹

Figure 6. Optical coherence tomography showing a large cyst with disorganization of the retinal inner layers.

For example, each 299-µm increase in the extent of DRIL over a four-month period was associated with a 1-line decrease in visual acuity at eight months. Nevertheless, an independent factor in reduced VA is the disruption of the photoreceptor inner segment/outer segment layer, because it reflects damage to the photoreceptors, which may reflect chronic macular edema, along with a diffuse pattern.

DME pattern. The pattern of DME can include diffuse macular thickness (Figure 7), cystoid macular edema (Figure 6), serous retinal detachment (Figure 8), and vitreomacular interface abnormalities (Figure 9). The improvements in VA and macular thickness are better in CME and worse in vitreomacular interface abnormalities after injecting intravitreal anti-VEGF agents.²

Figure 7. Optical coherence tomography showing diffuse macular thickness.

Figure 8. Optical coherence tomography showing subretinal fluid with an intraretinal cyst.

Figure 9. Fundus photo and OCT showing vitreomacular interface abnormality with a tractional element.

Vitreomacular interface integrity. The integrity of vitreous macular interface is so important because when the tractional element (Figure 9) is responsible for DME (especially when focal attachments of epiretinal membranes disturb the inner surface of the retina), our management would be pars plana vitrectomy with ERM peeling, instead of intravitreal anti-VEGF blockade, which would be a relative contraindication because of the risk of increased traction.

However, when ERM is present, but the main element of DME is a microvascular abnormality (Figure 10), intravitreal anti-VEGF has reduced effects, with the risk of inducing traction, particularly in vascularized membranes. VEGF blockade should be a second-line approach, with the first line being intravitreal triamcinolone acetonide or laser photocoagulation.

Figure 10. Fundus photo and OCT showing a vitreomacular interface abnormality with a vascular element.

FUNDUS FLUORESCEIN ANGIOGRAPHY

When and Why?

At the first visit, ordering FFA (especially when the BCVA is approximately 20/20) is important (Figures 11 and 12) because it will help us to document the presence of clinically significant macular edema (CSME) as defined by the ETDRS, and the measurement of VA is insufficiently sensitive to detect DME.³ Treating such cases with focal laser photocoagulation may maintain good vision for approximately 18 weeks in cases of good control of diabetes and blood pressure.

Figure 11. Fundus photo of the eye of a patient with DME and BCVA of 20/20.

Figure 12. Image from the same patient as in Figure 11, showing focal leakage and clinically significant edema.

Ordering FFA at the first visit is mandatory in cases of featureless retina with very poor BCVA to exclude ischemic DME because these patients have poor prognoses and will not benefit from any treatment in which OCT cannot detect ischemic diabetic maculopathy⁴ but may show evidence of ganglion cell layer damage.⁵

Fundus FA can be ordered as a guide for locating leaking microaneurysms. Further, in cases of CSME, when planning to perform laser photocoagulation, FFA can be performed either promptly (at one week) or deferred (at 24 weeks) until after intravitreal injections (anti-VEGF or steroids), depending on the case.

What Are We Looking For?

When examining FFA images of eyes with DME, we should consider several points.

Perfusion status. The perfusion status of the macula and retinal periphery with ischemia (Figures 13 and 14) indicates a poor prognosis with no beneficial treatment. Such cases can present as a large foveal avascular zone (FAZ) or a FAZ with irregular borders.

Figure 13. Fundus photo of featureless retina with signs of macular ischemia. BCVA was counting figures.

Figure 14. Fundus FA of the patient in Figures 12 and 13 shows a large FAZ and capillary dropout.

The presence of significant nonperfusion of the retinal periphery (Figures 15 and 16) is a prognostic factor for proliferative diabetic retinopathy, which requires prompt panretinal laser photocoagulation. Placing laser burns in nonperfused areas of the retinal periphery when treating PDR is recommended to preserve the visual fields as much as possible, especially in patients with compromised visual fields, such as those with glaucoma.

Figure 15. Fundus photo showing peripheral retinal ischemia with DME.

Figure 16. Fundus FA of the patient in Figure 15 showing peripheral retinal ischemia with clinically significant edema.

Clinically significant macular edema. The presence of CSME, defined as any edema⁶ (which presents as leaking microaneurysms on angiography) within 500 µm of the center of the fovea, hard exudate within 500 µm of the center of the fovea adjacent to the edema, or one disc diameter of edema within one disc diameter of the center of the fovea, is an indication for FFA.

Location and leakage. If the edema is far from the center and does not meet the criteria for CSME, or it is near to or inside a FAZ, it is important to decide whether it would be safe or dangerous to treat the eye with continuous wave laser photocoagulation or whether a switch to micropulse mode wave laser photocoagulation, anti-VEGF therapy, or intravitreal steroid injection is warranted (Figures 17 and 18).

Figure 17. Noncentral macular edema in a patient with BCVA of 20/25.

Figure 18. In the same patient as in Figure 17, FFA shows leaking microaneurysms far from the fovea and centrally.

Type of edema. It is important to consider whether the edema is focal, multifocal, or diffuse because this information will have an effect on the treatment plan (Figures 19 and 20).

Figure 19. Fundus photo of a patient with diffuse DME.

Figure 20. Fundus FA of the same patient in Figure 19 showing diffuse DME.

It can be important to correlate the angiogram and fundus exam; for example, when a circinate lipid ring is present, it can present as a cluster of leaking microaneurysms on angiography, while zones of intraretinal microvascular abnormalities may be highlighted as capillary nonperfusion (Figures 21 and 22).

Figure 21. Fundus photo showing a circinate lipid ring adjacent to intraretinal microvascular abnormalities.

Figure 22. FFA of the same patient, with a cluster of microaneurysms corresponding to the ring next to capillary nonperfusion.

CONCLUSIONS

When it comes to using imaging as a guide for laser photocoagulation, OCT maps and FFA can be somewhat similar. However, while OCT is a minimally invasive imaging method, fewer laser shots are needed to treat DME after FFA.⁷

Ordering OCT can help us to learn about the edema, to determine the visual prognosis, to choose our treatment plan, and to monitor the effectiveness of treatment. DRIL, CST, and disruption of the photoreceptor IS/OS layer are visual prognostic factors, while vitreous macular interface integrity, in conjunction of the edema pattern, is important for treatment planning. Ordering FFA can help us to learn about the perfusion status of the retina, the location and type of macular edema, and the presence of CSME in choosing our treatment plan. RP

REFERENCES