Glaucoma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Rohan Bir Singh, M.B.B.S.[2]

The glaucoma is typically classified is as open angle or closed angle and as primary or secondary. There have been multiple schemes proposed for the classification for glaucoma. However the classification of the glaucomas based on initial events and classification based on mechanisms of outflow obstruction are commonly used.

Classification based on angle

Open-angle Glaucoma
Primary open-angle glaucoma (POAG)	not associated with known ocular or systemic disorders that cause increased resistance to aqueous outflow or damage to optic nerve usually associated with elevated IOP
Normal-tension glaucoma	considered in continuum of POAG; often used when IOP is not elevated
Juvenile open-angle glaucoma	used when open-angle glaucoma diagnosed at young age (typically 10-30 years of age)
Glaucoma suspect	normal optic disc and visual field associated with elevated IOP suspicious optic disc and/or visual field with normal IOP
Secondary open-angle glaucoma	increased resistance to trabecular meshwork outflow associated with other conditions (e.g. pigmentary-, phacolytic-, steroid-induced-) increased posttrabecular resistance to outflow secondary to elevated episcleral venous pressure (e.g. carotid cavernous sinus fistula)

Angle-Closure Glaucoma
Primary ACG with relative pupillary block	movement of aqueous humor from posterior chamber to anterior chamber restricted peripheral iris in contact with trabecular meshwork
Acute angle closure	occurs when IOP rises rapidly as a result of relatively sudden blockage of the trabecular meshwork
Subacute angle closure (intermittent angle closure)	repeated, brief episodes of angle closure with mild symptoms and elevated IOP, often a prelude to acute angle closure
Chronic angle closure	IOP elevation caused by variable portions of anterior chamber angle being permanently closed by PAS
Secondary ACG with pupillary block	e.g. swollen lens, secluded pupil
Secondary ACG without pupillary block	posterior pushing mechanism: lens-iris diaphragm pushed forward (e.g. posterior segment tumor, scleral buckling procedure, uveal effusion) anterior pulling mechanism: anterior segment process pulling iris forward to form PAS (e.g. iridocorneal endothelial syndrome, neovascular glaucoma, inflammation)
Plateau iris syndrome	primary angle closure with or without component of pupillary block, but pupillary block is not predominant mechanism of angle closure

Childhood Glaucoma
Primary congenital/infantile glaucoma	primary glaucoma present from birth to first few years of life
Glaucoma associated with congenital anomalies	associated with ocular disorders (e.g. anterior segment dysgenesis, aniridia) associated with systemic disorders (e.g. rubella, Lowe syndrome)
Secondary glaucoma in infants and children	e.g. glaucoma secondary to retinoblastoma or trauma

Classification on based on initial event

Congenital and Developmental Glaucoma (Q15.0)

• Developmental glaucoma

• Primary congenital glaucoma
• Infantile glaucoma
• Glaucoma associated with hereditary of familial diseases

Primary Glaucoma and its Variants (H40.1-H40.2)

• Primary glaucoma

• Primary open-angle glaucoma, also known as chronic open-angle glaucoma, chronic simple glaucoma, glaucoma simplex
• Low-tension glaucoma
• Primary angle-closure glaucoma, also known as primary closed-angle glaucoma, narrow-angle glaucoma, iris- block glaucoma, acute congestive glaucoma

• Acute angle-closure glaucoma
• Chronic angle-closure glaucoma
• Intermittent angle-closure glaucoma
• Superimposed on chronic open-angle closure glaucoma (combined mechanism)

• Variants of primary glaucoma

• Pigmentary glaucoma
• Exfoliation glaucoma, also known as pseudoexfoliative glaucoma or glaucoma capsulare

Secondary Glaucoma (H40.3-H40.6)

• Secondary glaucoma

• Inflammatory glaucoma

• Uveitis of all types
• Fuchs heterochromic iridocyclitis

• Phacogenic glaucoma

• Angle-closure glaucoma with mature cataract
• Phacoanaphylactic glaucoma secondary to rupture of lens capsule
• Phacolytic glaucoma due to phacotoxic meshwork blockage
• Subluxation of lens

• Glaucoma secondary to intraocular hemorrhage

• Hyphema
• Hemolytic glaucoma, also known as erythroclastic glaucoma

• Traumatic glaucoma

• Angle recession glaucoma: Traumatic recession on anterior chamber angle
• Postsurgical glaucoma

• Aphakic pupillary block
• Ciliary block glaucoma

• Neovascular glaucoma
• Drug-induced glaucoma

• Corticosteroid induced glaucoma
• Alpha- chymotrypsin glaucoma. Postoperative ocular hypertension from use of alpha chymotrypsin.

• Glaucoma of miscellaneous origin

• Associated with intraocular tumors
• Associated with retinal detachments
• Secondary to severe chemical burns of the eye
• Associated with essential iris atrophy

Absolute Glaucoma (H44.5)

• Absolute glaucoma

Classification based on mechanism of outflow obstruction

Open Angle Glaucoma Mechanisms

1. Pre-trabecular (membrane overgrowth)

   • fibrovascular membrane (neovascular glaucoma)
   • endothelial layer, often with Descemet-like membrane (iridocorneal endothelial syndrome, posterior polymorphous dystrophy, penetrating and non-penetrating trauma)
   • epithelial downgrowth
   • fibrous ingrowth
   • inflammatory membrane (Fuchs heterochromic iridocyclitis,luetic interstitial keratitis)

2. Trabecular

   • idiopathic (chronic open-angle glaucoma, juvenile open-angle glaucoma)
   • “clogging” of trabecular meshwork

   • red blood cells (hemorrhagic-, ghost cell-, sickled red blood cells)
   • macrophages (hemolytic-, phacolytic-, melanomalytic-)
   • neoplastic cells (primary ocular tumors, neoplastic tumors, juvenile xanthogranuloma)
   • pigment particles (pigmentary-, exfoliation syndrome / glaucoma capsulare, malignant melanoma)
   • protein (uveitis, lens-induced glaucoma)
   • viscoelastic agents
   • α-chymotrypsin-induced glaucoma
   • vitreous

   • alterations of the trabecular meshwork

   • steroid-induced glaucoma
   • edema (uveitis, scleritis, episcleritis, alkali burns)
   • trauma (angle recession)
   • intraocular foreign bodies (hemosiderin, chalcosis)

3. Post-trabecular

   • obstruction of Schlemm’s canal (e.g. collapse at canal)
   • elevated episcleral venous pressure
   • carotid cavernous fistula
   • cavernous sinus thrombosis
   • retrobulbar tumors
   • thyroid ophthalmopathy
   • superior vena cava obstruction
   • mediastinal tumors
   • Sturge-Weber syndrome
   • familial episcleral venous pressure elevation

Angle Closure Glaucoma Mechanisms

1. Anterior (“pulling”)

   • contracture of membranes

   • neovascular glaucoma
   • iridocorneal endothelial syndrome
   • posterior polymorphous dystrophy
   • penetrating and non-penetrating trauma

   • consolidation of inflammatory products

2. Posterior (“pushing”)

   • with pupillary block

   • pupillary block glaucoma
   • lens-induced mechanisms (phacomorphic lens, ectopia lentis)
   • posterior synechiae (iris-vitreous block, pseudophakia, uveitis)

   • without pupillary block

   • ciliary block (malignant) glaucoma
   • lens-induced mechanisms (phacomorphic lens, ectopia lentis)
   • following lens extraction (forward vitreous shift)
   • anterior rotation of ciliary body (following scleral buckling or panretinal photocoagulation, central retinal vein occlusion)
   • intraocular tumors (retinoblastoma, malignant melanoma)
   • cysts of the iris and ciliary body
   • retrolenticular tissue contracture (retinopathy of prematurity, persistent hyperplastic primary vitreous)

Developmental Anomalies of Angle

1. incomplete development of trabecular meshwork / Schlemm’s canal

   • congenital (infantile) glaucoma
   • Axenfeld-Rieger syndrome
   • Peter’s anomaly
   • glaucomas associated with other developmental anomalies

2. iridocorneal adhesions

   • broad strands (Axenfeld-Rieger syndrome)
   • fine strands that contract to close angle (aniridia)

Combined Mechanism Glaucoma

1. Combination of two or more forms of glaucoma present either sequentially or simultaneously
2. IOP elevation can occur as a result of either or both of the following:

   • the intrinsic resistance of the trabecular meshwork to aqueous outflow in open-angle glaucoma
   • the direct anatomic obstruction of the filtering meshwork by synechiae in ACG