Background
While any type of glaucoma can be unilateral, primary open-angle glaucoma, primary angle-closure glaucoma, primary infantile glaucoma, juvenile-onset glaucoma, and pigmentary glaucoma are generally bilateral diseases, the severity of which may be asymmetric in the two eyes.
This article reviews glaucoma associated with increased episcleral venous pressure (EVP) and glaucoma associated with iridocorneal endothelial (ICE) syndrome.
Several etiologies of unilateral glaucoma are discussed in detail in other articles, including Glaucoma, Pseudoexfoliation; Glaucoma, Uveitic; Glaucoma, Lens-Particle; Glaucoma, Drug-Induced; Glaucoma, Neovascular; Glaucoma, Intraocular Tumors; Glaucoma, Hyphema; Glaucoma, Angle Recession; and Glaucoma, Malignant.
Pathophysiology
Increased EVP
In the early 1900s, Lauber provided histological evidence that the canal of Schlemm was connected to the episcleral venous network. Aqueous humor drains via the anterior surface of the ciliary body or through the trabecular meshwork, Schlemm canal, collector channels, and, subsequently, aqueous veins. These pathways have been termed unconventional and conventional, respectively.
While the unconventional pathway is independent of pressure, outflow via the conventional route is passive and depends largely on the difference between the intraocular pressure (IOP) and EVP; as EVP increases relative to IOP, or as resistance increases, flow decreases.
The 3 general pathophysiological mechanisms of increased EVP are arteriovenous anomalies, venous obstruction, and idiopathic. Arteriovenous anomalies associated with increased EVP include carotid-cavernous sinus fistula, orbital varix, Sturge-Weber syndrome, orbital-meningeal shunts, carotid-jugular venous shunts, and intraocular vascular shunts. Venous obstruction may be caused by a retrobulbar tumor, thyroid ophthalmopathy, superior vena cava syndrome, congestive heart failure, thrombosis of the cavernous sinus or orbital vein, vasculitis involving the episcleral or orbital vein, and jugular vein obstruction.
ICE syndrome
The pathophysiological mechanism underlying ICE syndrome remains unknown. However, the finding of chronic inflammatory cells in the corneal specimens of patients with ICE syndrome suggests a viral etiology. In a study using polymerase chain reaction techniques, 16 of 25 corneas from patients with ICE syndrome and 4 of 6 patients with herpetic keratitis were positive for herpes simplex virus.
Glaucoma associated with ICE syndrome is believed to be due to trabecular meshwork obstruction caused by peripheral anterior synechiae or, less commonly, an abnormal cellular membrane.
Epidemiology
Frequency
United States
The frequency of glaucoma associated with increased EVP or with ICE syndrome is unknown.
Glaucoma has been reported to occur in 30% of patients with Sturge-Weber syndrome, 5% of patients with thyroid ophthalmopathy, 11.6% of patients with scleritis, and 4% of patients with episcleritis.
Mortality/Morbidity
- Glaucoma is the third leading cause of blindness in the United States.
- Because glaucoma may progress insidiously without causing symptoms, progressive glaucomatous damage may occur without the patient even being aware of the diagnosis.
- Prompt and continued control of IOP can prevent ocular damage due to glaucoma.
Sex
- Traumatic carotid-cavernous sinus fistulae occur more commonly in males than in females.
- ICE syndrome occurs more commonly in females than in males.
Age
- Spontaneous carotid-cavernous sinus fistulae typically occur in middle-aged to elderly individuals, while traumatic carotid-cavernous sinus fistulae occur most commonly in young persons.
- It has been reported that 60% of patients with glaucoma associated with Sturge-Weber syndrome acquire glaucoma before age 2 years, and the remaining patients develop glaucoma later in childhood or in early adulthood.
- The onset of ICE syndrome generally occurs in early to middle adulthood.
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