What causes fluid accumulation behind a cataract lens, also known as cystoid macular edema (CME)?

Causes of Fluid Accumulation Behind Cataract Lens

The primary cause of fluid accumulation behind a cataract lens, known as capsular bag distension syndrome or capsular block syndrome, is characterized by an accumulation of milky or clear fluid behind the lens optic that can cause anterior displacement of the lens, decreased vision, and myopic refractive shift. 1

Mechanism and Characteristics

• Capsular bag distension syndrome (capsular block syndrome) is an uncommon condition that can develop following cataract surgery, causing fluid to accumulate in the space between the posterior capsule and the intraocular lens (IOL) 1
• This condition is characterized by:
  • Accumulation of milky or clear fluid behind the lens optic 1
  • Anterior displacement of the lens 1
  • Decreased vision 1
  • Myopic refractive shift (change in refraction toward nearsightedness) 1

Related Conditions and Complications

• Cystoid macular edema (CME) is a distinct but related condition that can occur following cataract surgery, characterized by fluid accumulation in cyst-like spaces in the outer nuclear layer of the retina 2, 3
• The incidence of clinical CME following modern cataract surgery is approximately 0.1-2.35% 3, 4
• Risk factors that increase the likelihood of developing post-surgical fluid accumulation include:
  • Diabetes mellitus 3, 5
  • Uveitis (ocular inflammation) 3, 5
  • Retinal vein occlusion 2, 5
  • Epiretinal membrane 2, 5
  • Intraoperative complications during cataract surgery 3, 4

Pathophysiological Mechanisms

• Postoperative inflammatory processes are believed to be a primary causative factor in fluid accumulation behind the lens 3, 4
• Prolapsed or incarcerated vitreous can contribute to the development of fluid accumulation 3, 4
• In capsular block syndrome specifically, the anterior capsulorrhexis may completely seal against the IOL optic, trapping fluid that cannot escape 1
• Inflammatory mediators can disrupt the blood-retinal barrier, leading to increased vascular permeability and fluid accumulation 6

Diagnostic Features

• Fluid accumulation behind the lens can be visualized during slit-lamp examination 1
• Optical coherence tomography (OCT) is a useful diagnostic tool that can display cystic spaces in the outer nuclear layer in cases of CME 3, 4
• Fluorescein angiography typically shows a classical perifoveal petaloid staining pattern and late leakage of the optic disk in CME 3, 4
• Patients may report blurred or variable vision, often with a diurnal pattern (worse upon waking and clearer later in the day) 1

Treatment Approaches

• Laser posterior capsulotomy is an effective surgical procedure to treat capsular bag distension syndrome 1
• For CME, first-line treatment typically includes:
  • Topical nonsteroidal anti-inflammatory drugs (NSAIDs) 3, 7
  • Topical corticosteroids 3, 7
  • Oral carbonic anhydrase inhibitors can be considered as complementary therapy 3, 6
• In cases of resistant CME, periocular or intraocular corticosteroids may be an option 3, 4
• Antiangiogenic agents, though experimental, can be considered for nonresponsive persistent CME 3, 4

Preventive Measures

• Proper surgical technique during cataract surgery is essential to minimize the risk of capsular block syndrome 1
• Ensuring the anterior capsulorrhexis is properly sized and positioned can help prevent fluid accumulation 1
• Prophylactic use of topical NSAIDs, either alone or in combination with corticosteroids, may reduce the risk of developing CME 7, 5

Clinical Course and Prognosis

• Most cases of pseudophakic CME resolve spontaneously 3, 4
• Capsular block syndrome typically requires intervention with laser posterior capsulotomy for resolution 1
• Chronic fluid accumulation can lead to permanent visual impairment if left untreated 3, 4