Pigment Dispersion Syndrome and Glaucoma: Exploring the Connection

Introduction

Pigment dispersion syndrome (PDS) is glaucoma (increased intraocular pressure resulting in optic nerve damage) of the open-angle type. Even with a high incidence, the condition stays relatively undiagnosed. The syndrome is characterized by the dispersion of the iris pigments originating from the iris pigment epithelium and getting deposited at the back of the corneal endothelium and the anterior segment. The condition occurs bilaterally in both eyes, more commonly in myopic youngsters. The pigmentation may be accompanied by secondary pigmentary granuloma.

Who Is Susceptible to Pigment Dispersion Syndrome?

Owing to the asymptomatic nature of the condition, the condition is often misdiagnosed. The condition has been positively identified in about two to four percent of the population in the past 40 years. Around 15 percent of the patients with PDS develop pigmentary glaucoma after the age of 15. Individuals of African descent have shown a prevalence of 15 per 100,000 individuals. About 26 percent of the patients reporting for refractive surgery to correct myopia (nearsightedness) have had pigment dispersion in the eyes. The prevalence of pigmented glaucoma preceded by PDS has been recorded as 37.5 percent in Latin Americans and 2.45 percent in the States. 20 percent of PDS patients report ocular hypertension, and 25 percent have pigmented glaucoma. About 35 to 50 percent of PDS patients carry the risk of ending up with glaucoma. About 85 percent of PDS patients developed pigmented glaucoma within the first decade.

What Causes Pigment Dispersion Syndrome?

The primary cause of PDS is the existence of a concave iris that results in the rubbing of the iris’s posterior surface against the zonular fibers during pupillary movement. Due to this friction, pigmented granules are released through the epithelial membrane of the iris and deposited in the anterior segment of the eye. There is a marked elevation in the intraocular pressure due to a reduction in trabecular meshwork outflow caused by pigment deposition within the meshwork.

The genetic causality of PDS reports the involvement of various genes on multiple loci, such as 7q35-q366 and 18q11-q21.5,6,93. The condition does not develop with a single mutated gene; rather, it is a combination of various mutations. Studies have also proposed that congenital mesodermal abnormalities and degenerative iris changes are also related to PDS etiopathogenesis.

What Is the Pathophysiology of Pigment Dispersion Syndrome?

PDS is a collective effect of pigment deposition, increased intraocular pressure, and loss of the trabeculae. Progressively, the endothelial cells of the trabecular meshwork and the collagen beams suffer pathologic changes, which hinder the aqueous outflow, causing a further rise in intraocular pressure and secondary glaucoma. Studies have shown a comparatively denser pigment concentration in the anterior chambers of PDS patients than in normal.

The pigment release is a normal process during pupillary movement, requiring irido-zonular contact, which is maximum during blinking. Blinking shunts aqueous humor from the posterior chamber to the anterior, further increasing the intraocular pressure in the anterior chamber. This increase in pressure causes posterior iris bowing, leading to reverse pupillary block. This block can be reduced by reducing blinking. When the ciliary muscles contract during accommodation, the contact increases as the accommodation process pushes the lens surface forwards. The pigment dispersion is associated with pupillary movement, intraocular pressure elevation after workouts, trauma, and lens rubbing with the iris’s posterior surface.

What Are the Risk Factors for Pigment Dispersion Syndrome?

PDS has reported male dominance with a ratio between 2:1 to 5:1 with an age predilection to the 20s in males and 40s in females. PDS is also seen between the ages of 40 and 60 in Caucasians and younger ages in Americans. Patients with myopic errors between -3 dioptre to -4 dioptre are susceptible to PDS. Although PDS is more common in the African American population, transillumination disorders are difficult to diagnose in them owing to their thick irises. Individuals with a flatter cornea have an excessive gush of aqueous humor from the posterior to the anterior chamber, which makes them vulnerable to this condition. The disease can run in families as it has been reported to show an autosomal dominant inheritance pattern with incomplete penetrance.

Additionally, increased trabecular network pigmentation, iridolenticular contact, and intraocular pressure can progress PDS into pigmentary granuloma. About 15 to 50 percent of the cases show this progression.

PDS affects two to four percent of individuals between the second and fourth decade of life, with a prevalence of 15 cases per 100,000 African Americans. About 16 percent of patients requiring refractive surgeries have reported PDS. In the US white population, PDS was reported in 2.5 percent of the ones participating in the study. Reports suggest that 35 to 50 percent of PDS patients develop glaucoma.

What Are the Clinical Features of Pigment Dispersion Syndrome?

The most common clinical features of pigment dispersion syndrome are:

• Pain.

• Redness.

• Photophobia (sensitivity to light).

• Glare.

• Halos (optical phenomenon due to developing eye disorder).

• Myopia.

• Field loss.

• Defective vision.

Findings in different parts of the eye:

• Anterior Chamber: Deep chamber, pigmented disposition, and melanin granules.

• Anterior Chamber Angle: Pigment band (Sampaolesi's line) and angle reduction.

• Cornea: Pigment deposition in the inferior corneal endothelium and at the back of the cornea.

• Iris: Transillumination defects, radial spoke-like defects, melanin deposition, loss of pupillary ruff, heterochromia, and iris bowed backward.

• Lens: Deposition on the anterior surface in a line or ring.

• Fundus: Peripheral retinal depigmentation, myopic disc, tessellated background, glaucomatous optic atrophy, myopic macular degeneration, lattice degeneration, holes, tears, and retinal detachment

How to Diagnose Pigment Dispersion Syndrome?

The diagnosis of PDS is based on clinical and imaging studies:

• Clinical Examination of Vision: Uncorrected and corrected visual acuity is recorded.

• Measurement of Intraocular Pressure: This is done by noncontact tonometry (NCT) and gold standard applanation tonometry (GAT) which draws a picture of ocular hypertension.

• Gonioscopy: This is done to check for glaucoma and visualize the anterior chamber. This also detects any concavity or bowing of the iris and pigmentation patterns.

• Visual Field Analysis: This is done to extrapolate the degree of glaucomatous and nasal optic disc damage.

• Anterior Segment Optical Coherence Tomography: This is an important diagnostic tool to assess anterior chamber depth and width, the volume of the iris, and iris concavity.

• Optic Nerve Head Optical Coherence Tomography: This tests for the presence of optic nerve head, retinal nerve fiber layer, cupping, and ganglion cell complex morphology. The result of this test is used to classify the condition as PDS or pigmentary glaucoma and can also be used to predict the path of disease progression.

• Optical Coherence Tomography Angiography: This is a vascular test implemented to study retinal and optic nerve blood flow.

• Ultrasound Biomicroscopy: This is a non-invasive tool used to study the detailed anatomy of angle structures and factors predisposing to irido-zonular and irido-lenticular contact. The tools visualize the relationship between the iris and zonular structures.

How to Treat Pigment Dispersion Syndrome?

The treatment regimen for PDS can be categorized under various measures:

• Lifestyle Measures: Avoiding exercises and behaviors that precipitate PDS.

• Pharmacotherapy: Miotics (Pilocarpine), selective alpha-adrenergic antagonists (topical Thymoxamine), Prostaglandin (Latanoprost) analogs, beta-adrenergic blockers, carbonic anhydrase inhibitors, and alpha agonists.

• Laser Treatments: Laser trabeculoplasty and laser peripheral Iridotomy.

• Surgical Interventions:

• Filtration surgery.
• Glaucoma drainage devices.
• Minimal invasive glaucoma surgery.
• Trabectome.
• Goniotomy.
• Canaloplasty.

What Is the Prognosis of Pigment Dispersion Syndrome?

The condition shows variable prognosis based on its severity and other factors like myopia and nerve damage. Adequately managed PDS shows a favorable prognosis with rare permanent blindness. PDS patients with normal intraocular pressure and normal aqueous humor dynamics do not usually progress to pigmentary glaucoma and carry good prognostic values.

What Is the Differential Diagnosis of Pigment Dispersion Syndrome?

• Pseudoexfoliation syndrome (deposition of abnormal fibrillary material within various body tissues).

• Bilateral acute iris transillumination (BAIT).

• Bilateral acute depigmentation of the iris (BADI).

• Vogt-Koyanagi-Harada syndrome (central nervous system disorder affecting vision and hearing).

• Sympathetic ophthalmia (an inflammation-mediated eye disorder).

• Acute autoimmune uveitis (uveal components are attacked by autoimmunity).

• Posner-Schlossman syndrome (elevated intraocular pressure and non-granulomatous anterior chamber inflammation).

• Viral uveitis (herpetic).

• Fuch uveitic syndrome (chronic form of unilateral uveitis).

• Traumatic uveitis (inflammation of uveal components due to trauma).

• Horner syndrome (drooping upper eyelid, constricted pupil, and absence of sweating).

• Acute angle-closure glaucoma (rapid or sudden increase in pressure inside the eye.

• Iris melanoma (malignant neoplasm).

What Are the Complications of Pigment Dispersion Syndrome?

Medical Complications

• Corneal edema.

• Non-resolving uveitis (uveal inflammation remains unresolved).

• Angle-closure glaucoma.

• Iris atrophy (iris degeneration).

• Iridoplegia (paralysis of the iris sphincter).

• Relative afferent pupillary defect.

• Intractable glaucoma.

• Surgical Complications

• Wound leak.

• Late bleb leak.

• Blebitis (microbial infection of the glaucoma filtering bleb).

• Intraocular pressure spike.

• Pupillary block.

• Malignant glaucoma.

• Over filtration.

• Flat bleb.

• Vascularized bleb (episcleral fibrosis).

• Encapsulated bleb (tenon cyst).

• Hypotony (intraocular pressure less than 6.5 mmHg).

• Macular snuff out.

• Endophthalmitis (inflammation of the inner coats of the eye).

• Panophthalmitis (infection within the vitreous, sometimes cornea and sclera).

• Blindness.

Conclusion

Pigment dispersion syndrome is a rare condition with potentially serious complications. Individuals must undergo ophthalmological evaluations as part of annual health check-ups. When detected, PDS can be managed, and debilitating progression can be prevented. The patient must be explained about the disease and its potential consequence of non-treatment. Multimodal therapy can help manage the condition, and the patient can have normal-corrected vision.