Question 6: What is the difference between pigment dispersion syndrome, pigmentary ocular hypertension (POHT), and pigmentary glaucoma?

Question 6: What is the difference between pigment dispersion syndrome, pigmentary ocular hypertension (POHT), and pigmentary glaucoma?

Answer:

Pigment dispersion syndrome (PDS) is a relatively common and usually underdiagnosed phenomenon produced by spontaneous release of pigment from the iris into the anterior segment. PDS can cause pigment-related ocular hypertension (POHT) or pigmentary glaucoma (PG). Therefore, early detection and understanding of the pathogenesis are of relevance for establishing adequate therapy to prevent vision loss.

In pigment dispersion syndrome, symptoms may be absent or vary significantly, ranging from mild redness and discomfort to severe ocular pain, photophobia, blurred and halo vision. Exercise often triggers symptoms In young patients. Clinical signs in PDS include

• Krukenberg spindle
• Mid-peripheral iris concavity with a spoke-like 360 degree transillumination defects
• Pigment deposition on the anterior surface of the iris, especially within iris furrows or anterior lens capsule

Of note, Krukenberg spindle is not always present in PDS and is not pathognomonic of the entity. Additionally, it is crucial to differentiate pigment from inflammatory cells, as this can lead to misdiagnosing PDS as acute anterior uveitis in a patient with prominent symptoms. Inflammatory cells are generally round, bigger, and whiter, while the pigment is small, tanned-brown particles with sharper edges.

Gonioscopy and fundus examination are essential in the assessment of PDS patients. The angle is usually open, and characteristic pigment deposition is often seen in the inferior trabecular meshwork. In some cases, pigmentation of the Schwalbe line occurs, giving the appearance of a Sampaolesi line, a brown pigment at or anterior to Schwalbe line observed in PDS or pseudoexfoliation syndrome. Another important gonioscopic finding in PDS is backward-bowing of the iris.

Two entities in pigment dispersion syndrome are pigmentary ocular hypertension (POHT) and pigmentary glaucoma (PG). POHT shares the same clinical findings as PDS but with elevated IOP and is more common in males. Monitoring the IOP must be rigorous since each 1 mmHg rise above 21 mmHg increases the risk for developing PG by 1.4 times.(Siddiqui et al 2003) Symptoms include ocular pain, injection, photophobia, and halo vision. Patients may experience symptomatology during or after exercise.

PG is a form of secondary open angle glaucoma and occurs when there is structural optic nerve damage and/or visual field changes. Although PDS tends to affect men and women in almost equal numbers, as previously noted, PG development is far more common in men. A community-based retrospective study found a low risk for developing PG due to PDS with an estimated conversion rate of 10% at 5 years, increasing to 15% at 15 years. This study also demonstrated that the most important predictive factor for the conversion is an IOP >21 mmHg at the initial diagnosis. (Siddiqui et al 2003)

PG patients tend to have a more prominent Krukenberg spindle related to the pigment showers that occur while exercising. Some patients might have subacute attacks characterised by corneal edema and blurred vision. Optic nerve cupping

and visual field defects point, corresponding with the anatomical damage in the retinal nerve fibre layer and ganglion cell complex, suggest diagnosis of PG. Visual field defects are also present and tend to progress unless adequate treatment controls the IOP.

The prevalence of myopia in patients with PDS ranges from 38% to 100%. Moreover, the higher the degree of myopia, the greater the risk for developing PG. The presence of POHT (IOP >21 mmHg) at the moment of PDS diagnosis is the most important risk factor for conversion to PG.(Siddiqui et al 2003)

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