Complications and Comorbidities> Ophthalmology/Otology>

DEFINITION

• The macula is a small and highly sensitive part of the retina, located roughly in the center of the retina and just temporal to the optic nerve. 
• Macular edema occurs due to fluid and protein leaking from blood vessels within the macula causing it to swell and thicken.
• Focal macular edema is caused by foci of vascular abnormalities, primarily microaneurysms, which tend to leak fluid.
• Diffuse macular edema is caused by dilated retinal capillaries in the retina.
• Clinically significant macular edema (CSME) was defined by the Early Treatment Diabetic Retinopathy Study Group (EDTRS) -- see Diagnosis section for full definition.

EPIDEMIOLOGY

• Accounts for three-quarters of visual loss associated with diabetes (Sutter).
• Prevalence of CSME reported as 5.9% and 7.5% for individuals with younger- and older-onset of diabetes (<30 versus >30 years), respectively (Hirai).
• Higher incidence of macular edema associated with male sex, severe diabetic retinopathy, higher glycosylated hemoglobin, proteinuria, higher systolic and diastolic blood pressure, and greater pack-years of smoking (Klein).
• Can occur at any stage of diabetic retinopathy, although more likely to occur as retinopathy progresses.
• CSME associated with decreased survival in persons with older-onset diabetes mellitus (Hirai).

DIAGNOSIS

• The ETDRS defined CSME as: 1) retinal edema located at or within 500 µm of the center of the macula; or 2) hard exudates at or within 500 µm of the center if associated with thickening of adjacent retina; or 3) a zone of thickening larger than 1 disc area if located within 1 disc diameter of the center of the macula (ETDRS)
• Diagnosis best made by ophthalmologist using slit-lamp binocular steroscopic ophthalmoscopy of the posterior pole using a contact lens
• Funduscopic exam with direct ophthalmoscope may reveal hard exudates and microaneurysms surrounding or within the macula, however, does not provide stereoscopic view for diagnosis.

SIGNS AND SYMPTOMS

• Blurring of vision in the middle or just to the side of the central visual field
• Visual loss can progress over a period of months
• Visual acuity may be 20/20 in some cases of CSME
• Patient may complain of being unable to focus clearly
• Symptoms may be unilateral or bilateral

CLINICAL TREATMENT

• Laser treatment considered first-line therapy: focal (for focal disease) and grid (for diffuse disease).
• ETDRS demonstrated that eyes with CSME benefited from focal argon laser photocoagulation treatment when compared to untreated eyes in controls. Treatment reduced the risk of moderate visual loss by 50%, increased the chance of visual improvement, and was associated with only minor losses of visual field (ETDRS).
• Eyes with retinal edema not meeting the criteria of CSME showed no significant difference between the treatment and control group.
• Preferable to initiate focal laser for macular edema prior to either panretinal laser treatment for high-risk proliferative diabetic retinopathy or cataract surgery because of potential risk for progression of macular edema.
• Side effects of focal laser include paracentral scotoma, transient increased edema, decreased vision, choroidal neovascularization, subretinal fibrosis, photocoagulation scar expansion, inadvertent foveolar burns (Kim).
• ETDRS demonstrated that subretinal fibrosis occurred less often in laser-treated eyes than in untreated control eyes.
• Intravitreal administration of corticosteroids has been shown to be useful in cases of refractory CSME, however side effects of corticosteroid use include 2-3 times increase in cataract surgery and a 4-8 times increase in intraocular pressure (Martidis).
• Pars plana vitrectomy and detachment of the posterior hyaloid may also be useful in treating diabetic macular edema (Kaiser).
• Medical treatment including topical NSAIDs and steroid eye drops can be used but laser treatment is preferred and more beneficial.
• Risk factor management of hypertension, hyperlipidemia and hyperglycemia is also important to prevent macular edema progression (Ciulla).

FOLLOW UP

• A dilated fundoscopic exam by an ophthalmologist should be performed every 2-4 months until resolution of CSME.

EXPERT COMMENTS

• Visual acuity is not a criteria in the diagnosis and/or treatment of CSME but may be helpful in following clinical course.
• Requires exam by ophthalmologist for diagnosis.

REFERENCES