From the Guidelines
Macular edema is diagnosed through a comprehensive eye examination by an ophthalmologist or retina specialist, with Optical Coherence Tomography (OCT) being the most important diagnostic tool. The process typically begins with a dilated eye exam where drops are used to widen the pupil, allowing the doctor to examine the retina and macula. Visual acuity testing is performed to assess how the condition affects vision. According to the diabetic retinopathy preferred practice pattern 1, OCT is the best way to detect and quantitate center-involved diabetic macular edema (CI-DME).
Diagnostic Criteria
The diagnosis of macular edema considers both the presence of fluid in the macula and the underlying cause, which could include diabetic retinopathy, retinal vein occlusion, age-related macular degeneration, or inflammatory conditions. Historically, CSME is defined by the ETDRS to include any of the following features:
- 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, when associated with adjacent retinal thickening
- A zone or zones of retinal thickening 1 disc area or larger, where any portion of the thickening is within 1 disc diameter of the center of the macula 1.
Diagnostic Tools
In addition to OCT, other diagnostic tools may be used, including:
- Fluorescein angiography, which involves an injection of dye into the arm, to identify leaking vessels causing the edema
- Fundus photography, to document the appearance of the retina for comparison over time
- Amsler grid testing, to detect distortions in central vision
- Slit-lamp biomicroscopy, to evaluate the posterior pole and midperipheral retina
- Indirect ophthalmoscopy, to examine the far peripheral retina 1.
Importance of Early Diagnosis
Early diagnosis is crucial as prompt treatment can prevent permanent vision loss. Macular edema can cause a substantial decrease in vision-related quality of life, and treatment options such as anti-VEGF injections, focal laser treatment, and intravitreal steroids have demonstrated therapeutic benefit 1. Therefore, a comprehensive eye examination and retinal imaging are essential for diagnosing macular edema and guiding treatment.
From the Research
Diagnosis of Macular Edema
To diagnose macular edema, the following methods can be used:
- A detailed examination of the fundus, if possible with a slit-lamp and a contact or non-contact lens, to check for swelling of the retina and presence of hard exudates in the macular region 2
- Fluorescence angiography to achieve a correct differential diagnosis and to reveal capillary leakage, cystoid macular edema, leaking points, or choroidal neovascularization 2
- Optical coherence tomography (OCT) to image retinal thickness and structure, producing cross-sectional and three-dimensional images of the central retina 3
- Fundus biomicroscopy by ophthalmologists or stereophotography by ophthalmologists or other trained personnel to diagnose diabetic macular oedema (DMO) and clinically significant macular oedema (CSMO) 3
Parameters for Clinical Evaluation
The following parameters are relevant for clinical evaluation of macular edema:
- Extent of the macular edema (i.e., the area that shows increased retinal thickness)
- Distribution of the edema in the macular area (i.e., focal versus diffuse macular edema)
- Central foveal involvement (central area 500 μm)
- Fluorescein leakage (evidence of alteration of the blood-retinal barrier or 'open barrier') and intraretinal cysts
- Signs of ischemia (broken perifoveolar capillary arcade and/or areas of capillary closure)
- Presence or absence of vitreous traction
- Increase in retinal thickness and cysts in the retina (inner or outer)
- Chronicity of the edema (i.e., time elapsed since initial diagnosis and response to therapy) 4
Diagnostic Accuracy of OCT
The diagnostic accuracy of OCT for detecting DMO and CSMO is as follows: