What is the most common cause of cystoid macular edema (CME) in a phakic patient without vascular disease?

Most Common Cause of Cystoid Macular Edema in Phakic Patients Without Vascular Disease

Pseudophakic cystoid macular edema (PCME) is the most common cause of cystoid macular edema (CME) in phakic patients without vascular disease, typically occurring after cataract surgery due to postoperative inflammation with disruption of the blood-aqueous and blood-retina barriers.

Pathophysiology and Presentation

• CME is characterized by accumulation of fluid in cyst-like spaces in the outer nuclear layer of the retina, presenting with reduced vision and metamorphopsia 1
• The condition can be detected through optical coherence tomography (OCT) showing cystic spaces in the outer nuclear layer, and fluorescein angiography showing the classical perifoveal petaloid staining pattern 2
• Fluid progressively accumulates in the outer plexiform layer of the retina and pools into cystic spaces, which can be visualized with OCT 3
• In chronic CME, fluid accumulation is associated with thinning of the retina and fibrosis, leading to irreversible lesions that don't respond to medical therapies 3

Common Causes in Phakic Patients

• Inflammation is the primary mechanism for CME in phakic patients without vascular disease, with uveitis being the most significant cause 4
• Intraocular inflammation disturbs the blood-retina barrier, leading to retinal edema 4
• Other potential causes include:
  • Epiretinal membrane formation 1, 5
  • Vitreomacular traction 6
  • Inflammatory diseases such as Vogt-Koyanagi-Harada disease 6

Risk Factors

• Young age, male gender, and black race have been identified as demographic risk factors 7
• Previous history of CME is a strong risk factor for involvement of the fellow eye 7
• Pre-existing conditions such as uveitis increase the risk of developing CME 2
• Intraoperative complications during eye surgery can significantly raise the risk of developing CME postoperatively 2

Diagnostic Approach

• Optical coherence tomography (OCT) is essential for diagnosis, showing cystic spaces in the outer nuclear layer 2
• Fluorescein angiography is indispensable in the workup of CME, showing the classical perifoveal petaloid staining pattern and late leakage of the optic disk 2
• Ultrasound biomicroscopy can be helpful in imaging anterior segment anatomy and pathology, including the cornea, which may contribute to understanding the etiology of CME 6

Treatment Considerations

• First-line treatment typically includes topical nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids, which may have a synergistic effect when combined 8
• Oral carbonic anhydrase inhibitors can be considered complementary as they increase fluid resorption through the retinal pigment epithelium 3, 2
• For refractory cases, intravitreal corticosteroids and anti-vascular endothelial growth factor (anti-VEGF) agents have shown promise 8
• When CME is refractory to medical therapy or associated with significant vitreous involvement, pars plana vitrectomy may improve outcomes 8

Pitfalls and Caveats

• CME must be differentiated from other causes of macular edema such as diabetic macular edema or edema due to vein occlusions 3
• Chronic CME with thinning of the retina and fibrosis may not respond to medical therapies 3
• When using topical carbonic anhydrase inhibitors, be aware that they should not be first-line therapy when endothelial dysfunction is a possible contributing factor, as they may interfere with the endothelial pump 6, 5
• When using prostaglandin analogues to lower intraocular pressure, be cautious as they have potentially inflammatory properties and should be avoided when inflammation is a possible contributing factor 6