How is congenital glaucoma classified into primary congenital glaucoma (PCG) and secondary congenital glaucoma, and what are the further subtypes of each, with reputable source citations?

Classification of Congenital Glaucoma

Congenital glaucoma is fundamentally divided into primary congenital glaucoma (PCG) and secondary childhood glaucomas, with PCG representing isolated trabeculodysgenesis and secondary forms associated with other ocular or systemic abnormalities. 1, 2

Primary Congenital Glaucoma (PCG)

PCG is the most frequent childhood glaucoma and represents isolated developmental anomalies of the trabecular meshwork without associated ocular or systemic conditions. 3, 4

Key Defining Features of PCG:

• Isolated trabeculodysgenesis: Variable trabecular meshwork anomaly without an imperforate membrane, confirmed on histopathology 3
• Age-based presentation: Develops both pre- and postnatally, typically diagnosed in early childhood 5
• Genetic basis: Primarily autosomal recessive transmission, with CYP1B1 being the most well-known causative gene; multiple other genes identified through recessive, dominant, or polygenic mechanisms 3, 5
• No associated anomalies: Absence of other ocular developmental abnormalities or systemic disease distinguishes it from secondary forms 3

Clinical Subtypes of PCG (by age of onset):

While PCG itself is not formally subdivided into distinct subtypes in the literature provided, it is recognized as a spectrum disease with variable age of presentation and severity. 4

Secondary Childhood Glaucomas

Secondary childhood glaucomas are a heterogeneous group associated with other ocular or systemic abnormalities, distinct from PCG in clinical features and treatment response. 1, 2

Major Categories of Secondary Childhood Glaucoma:

1. Glaucoma Associated with Non-Acquired Ocular Anomalies 2

• Axenfeld-Rieger anomaly: Anterior segment dysgenesis with iris and angle abnormalities 2
• Peters anomaly: Corneal opacity with anterior segment malformations 2
• Aniridia: Absence or hypoplasia of the iris with associated angle abnormalities 2

2. Glaucoma Associated with Systemic Disease 2

• Sturge-Weber syndrome: Facial port-wine stain with ipsilateral glaucoma and leptomeningeal angiomatosis 2
• Neurofibromatosis: Phakomatosis with potential angle abnormalities and glaucoma development 2

3. Glaucoma Due to Acquired Conditions 2

• Uveitic glaucoma: Secondary to intraocular inflammation 2
• Traumatic glaucoma: Following ocular injury with angle damage 2
• Tumor-associated glaucoma: Secondary to intraocular masses 2

4. Glaucoma Following Cataract Surgery 2

This represents an important iatrogenic cause of secondary childhood glaucoma, occurring after pediatric cataract extraction. 2

Critical Clinical Distinctions

Surgical Management Differences:

Children with secondary glaucoma undergo significantly more surgical procedures and revisions compared to those with PCG, making surgical management more challenging. 1

Diagnostic Approach:

• PCG diagnosis: Recognition of corneal signs (edema, Haab's striae, enlargement) and symptoms of elevated IOP, with thorough examination to distinguish from secondary forms 3
• Secondary glaucoma diagnosis: Requires identification of associated ocular anomalies or systemic conditions through comprehensive ocular and systemic evaluation 2

Important Clinical Pitfalls

The nomenclature for childhood glaucoma has historically been inconsistent, which can lead to diagnostic confusion. 3 The key is distinguishing isolated trabeculodysgenesis (PCG) from glaucoma with associated developmental, systemic, or acquired conditions (secondary childhood glaucomas). 1, 2, 3

Delayed diagnosis in either primary or secondary forms leads to irreversible visual loss and blindness, making early recognition critical. 5