Q. What is the most common type of secondary open-angle glaucoma (OAG)?
A) Pigmentary glaucoma
B) Neovascular glaucoma
C) Pseudoexfoliative glaucoma
D) Uveitic glaucoma
Answer: C) Pseudoexfoliative glaucoma
Explanation: Pseudoexfoliative glaucoma (PXFG) is the most common type of secondary open-angle glaucoma (OAG). It develops from pseudoexfoliation syndrome (PXF), where abnormal protein deposits in the eye lead to increased intraocular pressure and glaucoma.
👁️ Pseudoexfoliative Glaucoma (PXG)
A secondary open-angle glaucoma caused by pseudoexfoliation syndrome (PXS)
🧬 Definition
Pseudoexfoliative glaucoma (PXG) is a secondary open-angle glaucoma resulting from the accumulation of pseudoexfoliative (PXF) material—a fibrillar, amyloid-like protein—within the anterior segment structures of the eye, particularly in the trabecular meshwork. This leads to increased resistance to aqueous outflow and elevated intraocular pressure (IOP), eventually causing optic nerve damage and visual field loss.
PXG is more aggressive and more resistant to treatment than primary open-angle glaucoma (POAG), with greater IOP fluctuations and faster progression.
📌 Etiology and Pathogenesis
🧪 Pseudoexfoliation Syndrome (PXS):
- A systemic disorder of extracellular matrix metabolism that leads to the accumulation of PXF material on ocular and extraocular tissues.
- PXF is composed of elastin-like microfibrils, laminin, fibrillin-1, and cross-linked glycoproteins.
- Deposits form on the lens capsule, ciliary body, zonules, iris, corneal endothelium, and trabecular meshwork.
🔬 Mechanisms Leading to Glaucoma:
- Trabecular Meshwork Obstruction:
- PXF material and liberated pigment granules from the iris accumulate in the trabecular meshwork.
- Causes mechanical blockage and degeneration of trabecular endothelial cells.
- Leads to increased outflow resistance and elevated IOP.
- Iris Dysfunction:
- PXF deposits on the iris pigment epithelium result in rubbing and pigment dispersion.
- Leads to pupillary ruff atrophy, poor dilation, and transillumination defects.
- Zonular Weakness:
- PXF deposits on zonules cause zonular fragility, increasing risk during cataract surgery.
- Increased Oxidative Stress:
- Decreased antioxidant defense mechanisms contribute to damage of the trabecular meshwork and other ocular tissues.
- Systemic Associations:
- PXF may also deposit in the skin, lungs, heart, and blood vessels, though systemic glaucoma risk is ocular-specific.
🌍 Epidemiology
- Most common identifiable cause of secondary open-angle glaucoma worldwide.
- Prevalence varies by geography:
- High in Scandinavia (up to 30% of elderly)
- Moderate in Mediterranean, Russia, South India, and Iceland
- Incidence increases with age (rare <50 years)
- Typically unilateral initially, though can progress to bilateral disease in 40–80% over time.
- Slight female predominance
🧬 Genetics
- Strong association with polymorphisms in the LOXL1 gene (Lysyl Oxidase-Like 1), located on chromosome 15q24.
- LOXL1 is involved in cross-linking of elastin and collagen in the extracellular matrix.
- SNPs (e.g., rs1048661, rs3825942) are highly associated with PXF and PXG.
- Genetic risk is modulated by environmental and epigenetic factors; LOXL1 variants are necessary but not sufficient for disease expression.
🔍 Clinical Features
Anterior Segment Findings:
| Finding | Description |
|---|---|
| PXF material on anterior lens capsule | Central disc with peripheral radial striae and clear intermediate zone (classic “target” or “bullseye” pattern) |
| Iris transillumination defects | Moth-eaten appearance due to pigment loss from posterior iris epithelium |
| Poor pupillary dilation | Due to atrophic and rigid iris |
| Sampaolesi’s line | Pigmented line anterior to Schwalbe’s line seen on gonioscopy |
| Pigment dispersion in angle and TM | Often more pronounced than in POAG |
| Corneal endothelial pigment dusting | Krukenberg spindle may occur |
| Phacodonesis or lens subluxation | Due to zonular weakness |
Glaucoma Features:
- Higher IOP at diagnosis (often >30 mmHg)
- Wider IOP fluctuations
- Greater optic nerve head damage
- Faster visual field progression
- Poorer response to medical therapy
🧪 Diagnosis
Slit-Lamp Examination:
- PXF material on the lens capsule, iris, and pupillary margin.
- Iris atrophy, transillumination defects, poor dilation.
Gonioscopy:
- Open angles with heavy trabecular pigmentation.
- Sampaolesi’s line is often visible.
Tonometry:
- Often markedly elevated IOP, with diurnal variability.
Fundus Exam:
- Optic nerve cupping similar to POAG but more pronounced at presentation.
Visual Field Testing:
- Arcuate defects, nasal steps, and generalized depression seen.
OCT:
- Thinning of retinal nerve fiber layer (RNFL).
- Macular ganglion cell loss may occur earlier in PXG than in POAG.
📉 Progression
PXG is typically:
- More aggressive than POAG
- Faster progressing, with earlier optic nerve and field damage
- Resistant to medication, requiring earlier laser or surgical intervention
- Associated with higher risk of visual morbidity
💊 Management and Treatment
1. Medical Therapy
Often first-line, but less effective long-term than in POAG.
| Class | Drug | Notes |
|---|---|---|
| Prostaglandin analogues | Latanoprost, Travoprost | First-line; effective IOP reduction |
| Beta-blockers | Timolol | Use cautiously in elderly/comorbid patients |
| Alpha agonists | Brimonidine | Useful adjunct |
| Carbonic anhydrase inhibitors | Dorzolamide | Good combination therapy |
- Patients often need multiple medications due to high IOP.
2. Laser Trabeculoplasty (e.g., SLT)
- SLT is effective due to pigmented TM, but results may be less durable.
- Can be repeated.
- Often used early to reduce medication burden.
3. Surgical Intervention
Due to the aggressive nature of PXG, earlier surgical intervention may be needed:
a. Trabeculectomy:
- Effective but has a higher failure rate due to inflammation and fibrosis.
b. Glaucoma Drainage Devices (e.g., Ahmed, Baerveldt):
- Used in advanced or refractory cases.
c. Minimally Invasive Glaucoma Surgery (MIGS):
- iStent, Hydrus microstent, etc.
- May be combined with cataract surgery in mild-to-moderate cases.
🏥 Surgical Considerations (Cataract Surgery)
PXG patients are at higher risk of:
- Zonular dialysis
- Capsular instability
- Phacodonesis
- Poor dilation and iris prolapse
- Post-op IOP spikes
Preoperative planning and use of:
- Capsular tension rings (CTR)
- Iris hooks
- Viscomydriasis can improve safety.
Summary Table: Pseudoexfoliative Glaucoma
| Feature | Description |
|---|---|
| Type | Secondary open-angle glaucoma |
| Cause | Accumulation of PXF material in anterior segment |
| Pathogenesis | TM obstruction + oxidative stress + zonular instability |
| IOP | Often higher, fluctuates, progresses faster |
| Laterality | Unilateral early; becomes bilateral |
| Clinical Clues | Lens PXF material, Sampaolesi line, iris changes |
| Progression | Faster optic nerve and field damage |
| Treatment | Meds → SLT → Surgery (earlier than POAG) |
| Surgical Risk | Cataract surgery complications higher |