Management of Clinically Significant Macular Edema or Diabetic Macular Edema

Diagnosis

Diabetic macular edema is the most frequent cause of visual loss in patients with nonproliferative diabetic retinopathy. Approximately 50,000 people in America have diabetic macular edema.¹ The ETDRS show that the 3-year risk of moderate visual loss for patients with foveal or perifoveal macular edema was 24% for the control group and 12% for the photocoagulation treated group.² However, only 2% of the treated group had three or more lines of improved visual acuity. The limitation of the laser may be the development of small focal scotomas, choroidal neovascularization, macular ischemia, and macular scarring. Often patients have refractory or residual macular edema after several focal or grid laser photocoagulation treatments.

Metamorphopsia on Amsler grid testing can occur 2 to 5 degrees from center fixation. Microperimetry with the scanning laser ophthalmoscope can map macular scotomas in diabetic patients with clinically significant macular edema (CSME).^3–5

There are several ways in which the patient with diabetic macular edema will present to the ophthalmologist. The first is that he or she is referred to the ophthalmologist/retina specialist after having been seen by another eye care practitioner, an optometrist, for having macular edema. A second referral route is through the patient’s primary care practitioner, for an evaluation of a first eye examination. Thirdly, the patient complains of decreased vision. Lastly, the patient is asymptomatic and comes for an evaluation for a chief complaint other than his or her diabetic macular edema. Upon routine examination, the patient is found to have macular edema.

In all of these instances, it is best to document the patient’s duration of diabetes, his or her type of diabetes, Type 1 or Type 2, and obtain from the patient, the latest fasting blood glucose and hemoglobin A1c (HbA1c).

If this patient is unclear about his or her diabetes status or thinks he or she is a “borderline diabetic” but presents with diabetic retinopathy, then the ophthalmologist may send him or her for a physical examination with his or her family practitioner or internist. If the patient has not seen an internist for a year, he or she should be sent for lipid profiles, CBC and electrolytes, fasting blood glucose, and hemoglobin A1c. Another ophthalmic follow-up appointment can be made after the lab values are available. Follow-up appointments with his or her internist and endocrinologist are also suggested. One third of the diabetic population does not know that they have the disease.¹ Thus, undiagnosed diabetic patients may present for a routine exam when they in fact have diabetes and diabetic retinopathy.

Health literacy is defined as a measure of the patients’ ability to read, comprehend, and act on medical instructions. Patient awareness is now being studied in the medical literature. A health literacy study evaluated 114 diabetic patients presenting to general medicine clinics at two urban hospitals in Atlanta, Georgia. The authors found that 94% of the patients with functional health literacy know the symptoms of hypoglycemia versus 50% with inadequate literacy. Poor health literacy is common among racial and ethnic minorities, elderly persons, and patients with chronic conditions, particularly in public-sector settings. Thus, it is important to continue to educate the diabetic patients about their chronic disease and side effects.^6,7

The HbA1c shows that the patient has been compliant with his or her blood sugar over the past 6 months. If the HbA1c is over 7%, there is a high risk of diabetic retinopathy. If the triglyceride is over 150 mg/dL and within the 200 mg/dL range, we would expect to see more hard exudates changes in the retina. If there is hyperlipidemia, obesity, or cardiovascular disease, we will anticipate an accelerated rate of diabetic retinopathy as we follow up the patient (Chapter 7). The HbA1c could be elevated but the fasting glucose could be normal denoting good patient compliance for 24 hours but poor long-term compliance for the past 6 months. We would expect his or her eye findings to show diabetic retinopathy depending on his or her HbA1c status.

In another study evaluating HbA1c status and health literacy, it is found that patients with inadequate health literacy are less likely than patients with adequate health literacy to achieve tight glycemic control (HbA1c ≤7.2%). Those with the lower HbA1c are more likely to achieve tight control than those patients with poor glycemic control (HbA1c ≥9.5%) and to report retinopathy.⁷

In large metropolitan areas with medical schools in the city, patients usually have more laboratory follow-up and they present to the ophthalmologist with full medical evaluations. In large, sprawling suburban or rural areas where there are no nearby medical schools or medical centers, the patient may present to the ophthalmologist with poor vision and fulminant diabetic retinopathy without even knowing that he or she has diabetes.^6,7

Similarly, with macular edema, which can be an insidious disease affecting near vision, the patient may not have seen an eye care provider for many years because he or she “felt fine.” Often, a patient with severe diabetic macular edema presents to the ophthalmologist not knowing that he or she has diabetes.

Chief Complaint

Listen to what the patient is saying. What is the patient’s chief complaint? In the patient’s own words, what bothers him or her? If the clinician finds macular edema but the patient’s reason is his or her failing grade in the driving test, then, the clinician must answer that his or her driving test result is correlated to his or her diabetic macular edema.

Ask about his or her symptoms: Is it a gradual, painless loss of vision? Is it transient visual loss? Is the visual loss at night only? Decreased contrast sensitivity may mean the additional diagnosis of glaucoma which can be associated with diabetes. Is the visual impairment at sunset? Decreased rod function from previous laser photocoagulation for diabetic retinopathy can lead to loss of contrast sensitivity at sunset. All this time, we are taking notes so that we can ask the patient more questions after he or she finishes speaking. Let the patient tell the story.

Past Medical History

The review of systems sheet and history form filled out by the patient provides information about the duration of diabetes, treatment with insulin, without insulin, family history, hypertension, cardiovascular disease, renal disease, thyroid disease, and metabolic syndrome risk factors (Chapter 7). Their answers to the previous questions and their physical habitus may lead to further questioning about their American Diabetes Association Diet, their exercise regimen, their weight gain, eating issues involving weight gain or weight loss, and weight loss surgery.

Red flags are comorbid conditions, obesity, recent hospitalizations for stroke, heart disease, diabetic ketoacidosis, smoking, surgery for any reason, hospitalizations for infections, history of foot ulcers, and previous laser to the eyes for any reason. These mean that the patient may have accelerated diabetic retinopathy issues in the future.

We always send a referral letter to the internist or optometrist or referring ophthalmologist. If the problem is urgent, requiring laser or surgery, we call the referring doctor.

In our office, we have available handouts from the American Diabetes Association, the literature about the pathophysiology of diabetes, the epidemiology of diabetes as it affects the patient. We tailor the statistics to the patient sitting in the exam chair.

The office staff could provide Web site information and handouts about diets recommended by the American Diabetes Association, a list of cookbooks for the diabetes diet, and a list of endocrinologists whom they could see near their geographic region.

Before patients leave, we ask them to sign a medical release form so that our office can obtain their previous lab results from their internist or family care practitioner.

We ask that their future lab results be sent to our office as well as to their internist.

Physical Exam

Our approach to CSME is simple: visual acuity, Amsler grid testing, pupillary testing, slit lamp examination, and then a dilated funduscopic examination with a 90 D lens and a 20 D lens. Fundus photography and Optical Coherence Tomography (OCT) are part of the first visit.

Once we make the diagnosis of CSME, we obtain a fluorescein angiogram depending on the severity of the macular edema and level of retinopathy. Capillary nonperfusion can be documented by fluorescein angiography. Prior to macular laser, fluorescein angiography is extremely helpful in identifying microaneurysms for focal treatment.

We also assess the level of diabetic retinopathy that the patient has in terms of his or her vascular disease (optic nerve appearance, arteriolar changes, venous beading changes, vein-to-artery ratio of 3:1).

Fovea

In examining the fovea, we look for the internal limiting membrane reflex, its relationship to the posterior hyaloid face, the appearance of the fovea, smooth like normal, and whether the surface is cystic or is it irregular because of gliosis from old inflammation or chronic hypertension. This can be verified by the OCT.

Optical Coherence Tomography

When we perform the OCT examination, we look at the central subfield thickness of the fovea expressed in microns. The OCT describes the contour of the fovea and its relationship to the vitreous. This measurement can diagnose early gliosis, macular cysts, and macular edema at the Henle layer. The information is very accessible for all ophthalmologists and eye care practitioners.

ETDRS Classification of Macular Edema

Diagnosis of CSME by the ETDRS criteria is thickening of the retina at or within 500 μm of the center of the macula; hard exudates at or within 500 μm of the center of the macula, if associated with thickening of the adjacent retina (not residual hard exudates remaining after the disappearance of retinal thickening); or a zone or zones of retinal thickening of one disc area or larger, any part of which is within one disc diameter of the center of the macula² (Table 8-1).

The diagnosis of CSME is through slit lamp biomicroscopy and is documented with stereo fundus photography. Fluorescein angiography is required by the ETDRS only after the clinical diagnosis is made by slit lamp biomicroscopy. Thus, fluorescein angiography leakage without clinical thickening does not fulfill the definition of CSME according to the ETDRS criteria.

Now, 20 years after the landmark ETDRS, there are clinical modifications in the retina practice. The use of the OCT is commonplace and noninvasive. Thus, the imaging of macular edema can be identified and quantified easily. The macular cysts and the amount of macular edema can be seen in cross section on OCT for each patient.

While macular edema can present at every stage of diabetic retinopathy, from background diabetic retinopathy to nonproliferative to proliferative diabetic retinopathy, the tools are the same for the diagnosis. The treatment is different depending on the severity of the disease.

Patients with Visual Acuity of 20/20 to 20/30

In asymptomatic patients with the visual acuity of 20/20 to 20/30, with CSME according to the ETDRS guidelines, these patients would be eligible for treatment.² However, because they are asymptomatic, these patients may not want treatment. Patient education with your nurse or assistants over several visits may prepare them for the eventuality of treatment. The emphasis is that laser will keep them at their visual acuity level.

Patients with Visual Acuity of 20/40

The visual acuity of 20/40 is a threshold for treatment for many patients since 20/40 is the driving test vision requirement. At the 20/40 level of visual acuity, the patient is usually symptomatic. The patient needs to understand fully that the laser will preserve his or her vision in the long term. For anxious patients, we perform a central visual field to map the preoperative visual scotoma from the macular edema and then proceed to laser. We make sure that the patient understands that there is always a risk for some immediate vision loss but in the long run, he or she will maintain his or her vision.

Patients with Visual Acuity of 20/50 to 20/80

At this visual acuity of 20/50 or worse, the patient is unhappy and wants treatment. OCT and fluorescein angiography are helpful in documenting the pathology for laser planning. The fluorescein angiographic photos will demonstrate the extent of the diabetic retinopathy to the patient. Patient education is important prior to informed consent.

Patients with Visual Acuity of 20/100 or Worse

Previous laser

The most important question to ask is “why” is the vision 20/100? In eyes with previous laser, ask these questions:

1. Is the patient noncompliant with his or her diabetes treatment?

2. Is the patient obese and has the metabolic syndrome characteristics?

3. Is the patient going to be compliant in our office and follow our instructions for follow-up?

4. Does the patient have renal disease, which would cause fluid retention, and therefore have cystic macular edema?

5. Is the patient infected with a foot ulcer?

6. What are the patient’s HbA1c status, FBS, and lipid profiles?

7. Does the patient have undiagnosed glaucoma? Is it open angle glaucoma or early rubeotic glaucoma?

Those patients who have had previous macular laser will have residual macular edema. They need fluorescein angiography and OCT evaluations of their macula. From the fluorescein angiogram, the clinician will be looking for areas of capillary nonperfusion, areas of abnormal foveal capillary net. Look at the time of the arteriovenous phase transit. If the transit time is significantly longer than the normal expected 15 to 16 seconds, the retina specialist might think of decreased flow to the retina, common with internal carotid disease or poor cardiovascular perfusion. If the flow is abnormal, the retina specialist might consider sending the patient to a cardiologist. The cardiologist would probably perform echocardiogram of the heart, ECG, internal carotid ultrasonography, magnetic resonance angiography, or Holter monitoring of his or her heart.

In these patients with residual macular edema with 20/100 vision of worse would lead the clinician to ask: has the previous laser caused macular scarring that has enlarged and caused additional inflammation and gliosis? Is there a functioning macula with adequate blood flow? From the OCT, the ophthalmologist will be looking at the macular thickness measurement and the abnormalities of Henle layer.

Lastly, examine the patient for glaucoma. The optic nerve, the angle, and the trabecular meshwork mu1.Aim for the area with diffuse leakagest be looked at carefully. Look at the patient’s visual field and visual evoked potential for optic nerve function. Send the patient to a glaucoma specialist if there is no clear reason as to why the vision is decreased.

These previously treated eyes are candidates for additional laser or bevacizumab intravitreal injection. Bevacizumab may be the only treatment option if the macula shows poor perfusion and extensive derangement of foveal capillary net. It is important to warn these patients about a prolonged course of recovery. It must be emphasized that their diabetes must be under control during this time of visual rehabilitation.

No previous laser

In those patients who present for the first time to our office with diabetic macular edema, we order fluorescein angiography, OCT to determine if there is focal or diffuse leakage. We want to ascertain what type of leakage they have in the macula. In addition, how thick is the retinal? Is there massive cyst formation? They are a candidate for macular laser using the ETDRS guidelines.² The fluorescein angiogram can identify hundreds of additional microaneurysms not seen on regular fundus photography of the macular region. If this is the case, focal laser treatment can be performed. The fluorescein angiogram can reveal areas of capillary nonperfusion within the macula. If upon OCT testing there are large foveal cysts, grid laser and bevacizumab may be offered.

Treatment

Patients with CSME should be considered for laser surgery. While a minority of patients have improvement of vision, for the majority of cases, the goal of treatment with laser photocoagulation is the stabilization of vision. Most patients need more than one treatment session. The average number of treatment sessions is 3 to 4 separated by 2 to 4 months, for the retinal thickening to resolve.

OCT and fluoresecein angiography document the macular edema. The fluorescein angiogram is useful in delineating the abnormal derangement of the foveal avascular zone. The extent of the foveal capillary net and the fovea will allow the clinician in planning laser treatment.

Follow-up examination for post-op laser patients with CSME can be scheduled 2 to 4 months after surgery. However, if the patient notes worsening of vision, he or she should come in before the scheduled appointment.

New Treatment Modalities (See Chapter 5)

Combination of laser and triamcinolone, and laser and pegaptanib and bevacizumab, is now done throughout the United States since 2006. The newer agents which are monoclonal antibody intravitreal treatments have not had a large scale multicentered trials yet.^8,9

Treatment Options

These macular edema patients who fulfill the ETDRS criteria can be offered the treatment of laser, and the clinician can provide proof of the macular edema using the OCT and fundus photos and fluorescein angiography. However, if the patient resists treatment, the clinican can offer the Amsler grid testing and ask that they return in 6 weeks, and monitor their hemoglobin A1c and fasting blood sugars in the interim.

If the macular edema is diffuse, and the patient does not want laser or intravitreal bevacizumab, one can offer topical NSAID eye drops for treatment as a temporizing measure.¹⁰

Laser

If the macular edema has discrete microaneurysms with leakage seen on fluorescein, laser is used for those microaneurysms in a “focal” treatment.

For this group of patients who opt for laser, make sure the laser burn is focused on the microaneurysm and that the burn is a light “white burn.” A bright white, oversized burn would mean the risk of a scotoma in the macula in a patient with pre-op visual acuity of 20/20 to 20/30. The light burn would prevent secondary macular gliosis as a secondary consequence.

The laser settings are 100 mW, argon green laser, 100 μm spot size, 0.1 seconds. If you want to use less power, you can use a 50-μm spot size with lower power. Always try a test burn in the far periphery with your desired laser settings (Tables 8-2 and 8-3).

Intravitreal Triamcinolone

Prep the cul-de-sac with topical proparacaine HCl 0.5%, 5% povidone iodine. We use topical proparacaine, instilled over the intended injection site for about 10 to 15 seconds. Continuously apply proparacaine HCl eye drops over the site, with a sterile 4×4 held against the lower eyelid to catch the runoff of the excess eye drops.

Then, we apply 5% povidone iodine to the injection site. We place three drops and ask the patient to close his or her eyes and blink a few times. We wait for 3 minutes before we inject. During this 3-minute waiting period, we get ready to prep the outside of the eye with 10% povidone iodine with sterile 4 × 4 sponges (Table 8-4).

For injection, 4 mg of triamcinolone acetonide is injected intravitreally with a tuberculin syringe with a 30-gauge needle. Other authors have used 25 mg of triamcinolone acetonide intravitreally as well.¹¹

Immediately postoperatively in the office, the patient receives topical timolol maleate XE ½% instilled in their cul-de-sac (Table 8-5). Postoperatively, the patients go home with instructions to use either topical moxifloxacin or gatifloxacin four times daily for 4 days, or erythromycin ophthalmic ointment four times daily for 4 days. Ointment can be used if the patients cannot put in eye drops or if they live alone. The patients are asked to instill timolol maleate XE ½% once a day for a week and then return to see us for an intraocular pressure check the next day.¹

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