Classification of the glaucomas

The most widely used classification system of the glaucomas separates angle-closure glaucoma from open-angle glaucoma. This fundamental distinction still holds, but with altered emphasis regarding the former condition. Historically, angle-closure disease has been variably defined in terms of pupillary block mechanisms (e.g., ‘miotic induced’), presenting signs and symptoms (e.g., ‘congestive’), or the presumptive time-course of the condition (e.g., ‘subacute’).The most contemporary approach continues to emphasize the final pathogenic pathway mechanism of irido-trabecular obstruction that results in functional angle closure.86 But abetted by technologies that allow direct visualization of angle, lens, and anterior ciliary body structures, the current classification is an amalgam of both a natural history scheme that emphasizes progressive stages of disease, and a mechanistic scheme focusing on discrete sites of dysfunction in the anterior segment (Fig. 1-2).

In open-angle glaucoma, there is relative impairment of flow of aqueous humor through the trabecular meshwork–Schlemm’s canal–venous system; yet on gonioscopy the angle appears to be open (Fig. 1-3). But amidst all the details of classification, one must never lose sight of the ultimate final pathway in all glaucoma as manifest optic nerve damage and ganglion cell demise.

This basic classification scheme continues to be helpful because it clarifies pathogenetic mechanisms and therapeutic approaches. We propose to simplify glaucoma classification into three major divisions, which are subdivided into primary and secondary categories: (1) angle-closure glaucoma; (2) open-angle glaucoma; and

Fig. 1-2  In angle-closure glaucoma, the peripheral iris covers the trabecular meshwork, obstructing aqueous humor outflow.

(3) developmental glaucoma, in which some anomaly of the anterior segment manifests in the first years of life. The category of ‘combined-mechanism glaucoma’ historically referred to either sequential or coincidental presentations of entities from these three basic categories, and usually involved angle-closure mechanisms; hence we relegate these idiosyncratic cases among the secondary angle-closure glaucomas.

A similar classification system divides glaucoma into conditions that affect the internal flow, and conditions that affect the outflow of aqueous humor. Internal flow block is caused by such conditions as pupillary block or malignant glaucoma. Outflow block occurs with diseases of the trabecular meshwork (e.g., neovascularization) or that compromise Schlemm’s canal, collector channels, and the venous system (e.g., elevated episcleral venous pressure).

Alternative classification systems4 are based on other features of the diseases, including (1) the site of the outflow obstruction, which is divided into diseases that affect the pre-trabecular passage of aqueous humor (e.g., posterior synechiae to the lens after ocular inflammation), the trabecular flow (e.g., glaucoma after administration of - chymotrypsin), and the post-trabecular movement of aqueous humor (e.g., increased episcleral venous pressure from a carotid-cavernous sinus fistula); (2) the tissue principally involved (e.g., glaucoma caused by diseases of the lens or diseases of the retina); (3) the proximal initial events (e.g., steroid glaucoma); and (4) the age of the patient (e.g., congenital, juvenile). Specific diseases have also been subclassified, such as POAG types, based on various appearances of the damaged optic nerve,87 or classification of disease stages by visual field damage;87b or the angle-closure glaucomas, based on IOP levels and gonioscopic configurations as correlated with ultrasonic biomicroscopy.88

The reader is cautioned that all classification schemes are arbitrary and limited. Some cases do not fit neatly into one category or another. The classification that follows is not meant to be allinclusive, but to be an aid in thinking about pathogenesis and treatment.

I.Angle-closure glaucoma

A.Primary angle-closure disease

Irido-trabecular contact is the final common pathway of angle closure disease, obstructing aqueous outflow; it can be conceptualized in two complimentary schemes:

1.Natural history

a.Primary angle closure suspect

b.Primary angle closure

c.Primary angle-closure glaucoma

2.Anterior segment mechanisms of closure

a.Iris–pupil obstruction (e.g.,‘pupillary block’)

b.Ciliary body anomalies (e.g.,‘plateau iris syndrome’)

c.Lens–pupil block (e.g.,‘phacomorphic block’ (swollen lens or microspherophakia))

B.Secondary angle-closures

1.Anterior ‘pulling mechanism’

The iris is pulled forward by some process in the angle, often by the contraction of a membrane or peripheral anterior synechiae.

a.Neovascular glaucoma

b.Iridocorneal endothelial syndromes (e.g., Chandler’s syndrome)

c.Posterior polymorphous dystrophy

d.Epithelial downgrowth

e.Fibrous ingrowth

f.Flat anterior chamber

g.Inflammation

h.Penetrating keratoplasty

i.Aniridia

2.Posterior ‘pushing mechanism’

The iris is pushed forward by some condition in the posterior segment. Often the ciliary body is rotated anteriorly, allowing the lens to come forward also.

a.Ciliary block glaucoma (malignant glaucoma)

b.Cysts of the iris and ciliary body

c.Intraocular tumors

d.Nanophthalmos

e.Suprachoroidal hemorrhage

f.Intravitreal air injection (e.g., retinal pneumopexy)

g.Ciliochoroidal effusions (e.g., panretinal photocoagulation)

(a)Inflammation (e.g., posterior scleritis)

(b)Central retinal vein occlusion

h.Scleral buckling procedure

i.Retrolental fibroplasias II. Open-angle glaucoma

A. Primary open-angle glaucoma

1.IOPs higher than ‘normal range’

2.IOPs within ‘normal range’ (low-tension glaucoma)

B.Secondary open-angle glaucoma

1.Pigmentary glaucoma

2.Pseudoexfoliation glaucoma

3.Steroid glaucoma

4.Lens-induced glaucoma

a.Phacolytic glaucoma

b.Lens-particle glaucoma

c.Phacoanaphylaxis

5.Glaucoma after cataract surgery

a.-Chymotrypsin glaucoma

b.Glaucoma with viscoelastics

c.Glaucoma with pigment dispersion and intraocular lens

d.UGH syndrome (uveitis glaucoma hyphema)

e.Glaucoma after neodymium:yttrium-aluminum- garnet (Nd:YAG) laser posterior capsulotomy

f.Glaucoma with vitreous in anterior chamber

6.Glaucoma after trauma

a.Chemical burns

b.Electric shock

c.Radiation

d.Penetrating injury

e.Contusion injury

7.Glaucoma associated with intraocular hemorrhage

a.Ghost cell glaucoma

b.Hemolytic glaucoma

c.Hemosiderosis

8.Glaucoma associated with retinal detachment

9.Glaucoma after vitrectomy

a.Intraocular gas

b.Intraocular silicone oil

10.Glaucoma with uveitis

a.Fuchs’ heterochromic iridocyclitis

b.Glaucomatocyclitic crisis (Posner-Schlossman)

c.Precipitates on trabecular meshwork (trabeculitis)

d.Herpes simplex

e.Herpes zoster

f.Sarcoidosis

g.Juvenile rheumatoid arthritis

h.Syphilis

i.Human immunodeficiency virus (HIV) infection

11.Glaucoma with intraocular tumors

a.Malignant melanoma

b.Metastatic lesions

c.Leukemia and lymphoma

d.Benign lesions (e.g., juvenile xanthogranuloma, neurofibromatosis)

12.Amyloidosis

13.Increased episcleral venous pressure

a.Obstruction of venous drainage (e.g., superior vena cava obstruction)

b.Arteriovenous fistula (e.g., carotid cavernous)

c.Ocular episcleral venous anomalies (e.g., SturgeWeber syndrome)

III.Developmental glaucoma

Anomalies of the anterior segment are present at birth. Glaucoma may be present at birth or may appear in the first decades of life

(see Ch. 20 for detailed classification of pediatric glaucoma diseases).

A.Primary congenital (infantile) glaucoma   1. Congenital glaucoma

  2. Autosomal dominant juvenile glaucoma

  3. Glaucoma associated with systemic abnormalities   4. Glaucoma associated with ocular abnormalities

B.Secondary glaucoma

  1. Traumatic glaucoma

  2. Glaucoma with intraocular neoplasm   3. Uveitis glaucoma

  4. Lens-induced glaucoma

  5. Glaucoma after congenital cataract surgery   6. Steroid-induced glaucoma

  7. Neovascular glaucoma

  8. Secondary angle-closure glaucoma

  9. Glaucoma with elevated episcleral venous pressure

10.Glaucoma secondary to intraocular infection

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