**Question:** In haemolytic glaucoma, the mechanisms are all except:

A. Increased aqueous humor production
B. Reduced aqueous humor outflow
C. Increased intraocular pressure (IOP)
D. External factors causing damage to the trabecular meshwork

**Core Concept:**
Haemolytic glaucoma is a rare and severe form of open-angle glaucoma characterized by a sudden increase in intraocular pressure (IOP) due to the breakdown of red blood cells (haemolysis) within the trabecular meshwork and the resulting release of heme pigments, which impair the outflow of aqueous humor.

**Why the Correct Answer is Right:**
In haemolytic glaucoma, the primary mechanisms causing increased IOP involve:

1. **Increased aqueous humor production (A)**: This is the main driver of IOP elevation in haemolytic glaucoma as the excessive red blood cell breakdown produces more aqueous humor, leading to increased pressure within the eye.
2. **Reduced aqueous humor outflow (B)**: The release of heme pigments from haemolyzed red blood cells (RBCs) disrupts the outflow of aqueous humor through the trabecular meshwork, further increasing IOP.
3. **Increased intraocular pressure (C)**: The primary consequence of the above two mechanisms results in a significant rise in IOP.
4. **External factors causing damage to the trabecular meshwork (D)**: Haemolytic glaucoma is not primarily caused by external factors damaging the trabecular meshwork; rather, it is a result of internal processes within the eye.

**Why Each Wrong Option is Incorrect:**

Option A (Increased aqueous humor production) is incorrect because haemolytic glaucoma is a primary intraocular process, not directly related to aqueous humor production.

Option B (Reduced aqueous humor outflow) is incorrect as the primary cause is the release of heme pigments disrupting aqueous humor outflow through the trabecular meshwork.

Option C (Increased intraocular pressure) is incorrect as the actual cause of this increase is the disruption of aqueous humor outflow by the heme pigments, not IOP itself.

Option D (External factors causing damage to the trabecular meshwork) is incorrect as haemolytic glaucoma is an intraocular process, not a result of external factors damaging the trabecular meshwork.

**Clinical Pearls:**

Haemolytic glaucoma is a rare and potentially sight-threatening condition, which emphasizes the importance of prompt recognition and management. In cases of sudden onset ocular pain, redness, and visual disturbances, haemolytic glaucoma should be considered in the differential diagnosis, even in the absence of typical risk factors for primary open-angle glaucoma.