Whereas any type of glaucoma can be unilateral, primary open-angle glaucoma, primary angle-closure glaucoma, primary infantile glaucoma, juvenile-onset glaucoma, and pigmentary glaucoma generally are bilateral diseases, the severity 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.
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.
Whereas 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 three 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.[1]
The pathophysiological mechanism underlying iridocorneal endothelial (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 four of six 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.[2]
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.
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.
Traumatic carotid-cavernous sinus fistulae occur more commonly in males than in females.
ICE syndrome occurs more commonly in females than in males.
Spontaneous carotid-cavernous sinus fistulae typically occur in middle-aged to elderly individuals, whereas 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.[2]
Elicit history of trauma, thyroid disease, congestive heart failure, vasculitis, malignancy, and other systemic diseases.
Diplopia may be a presenting complaint of patients with a carotid-cavernous sinus fistula, thyroid ophthalmopathy, or retrobulbar tumor.
Carotid-cavernous sinus fistulae often present after the following:
Increased EVP may cause pulsating exophthalmos, conjunctival chemosis, engorgement of the episcleral vein, restricted ocular motility, ocular bruit, and ocular ischemia.
Dilated episcleral vessels are a prominent feature of Sturge-Weber syndrome; choroidal hemangioma is present in 31-50% of patients with Sturge-Weber syndrome.
A common clinical sign of an orbital varix is intermittent exophthalmos (exophthalmos occurring when the head is placed in a dependent position, when the patient sneezes, or when the patient performs a Valsalva maneuver).
Orbital tumors may cause proptosis and restricted ocular motility.
Thyroid ophthalmopathy may cause proptosis, restricted ocular motility, conjunctival chemosis, epiphora, exposure keratitis, and optic nerve compression.
Presenting signs of the superior vena cava syndrome include edema of the lid, face, and conjunctiva; vascular engorgement of the fundus, episclera, and conjunctiva; proptosis; optic nerve edema; and glaucoma.
IOP may increase while supine and may decrease while sitting.
The most common presenting manifestations of ICE syndrome are iris abnormalities (eg, iris atrophy, corectopia, ectropion uveae, peripheral anterior synechiae, iris nevi), decreased vision, and pain. Other features of the syndrome may include fine-hammered silver appearance of the posterior cornea and corneal edema.
Glaucoma associated with EVP is due to increased resistance of aqueous outflow from the Schlemm canal and is associated with arteriovenous anomalies, venous obstruction, and idiopathic anomalies.
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.
Lab studies are indicated based on the suspected etiology (eg, thyroid function test, vasculitis workup) of unilateral glaucoma.
B-scan echography to evaluate for orbital tumor, foreign body, and extraocular muscle enlargement (in thyroid ophthalmopathy and other conditions with EVP); also indicated if fundus cannot be visualized[3]
CT scan of orbits to evaluate orbital fracture, foreign body, dilation of superior ophthalmic vein, and enlargement of cavernous sinus (present with carotid-cavernous sinus fistulae)[4]
Angiography to evaluate for arteriovenous anomalies
Orbital venography to evaluate for orbital varix
Color Doppler to evaluate for orbital varix
In patients with increased EVP, gonioscopic examination may reveal reflux of blood in the Schlemm canal.
Ocular pulse amplitude, as measured by pneumotonometry, is a useful noninvasive tool to evaluate patients with carotid-cavernous fistulae.[5]
Malignancy workup for patients with superior vena cava syndrome, orbital tumors
Cardiac workup for patients with congestive heart failure
Although topical glaucoma medications and oral carbonic anhydrase inhibitors may be used initially to control IOP, the underlying etiology must be resolved to achieve long-term IOP control.
Medications that decrease aqueous production are more effective than drugs that increase aqueous outflow.
Medications that reduce aqueous production often can control the early stages of glaucoma.
Epinephrine may be effective in some cases.
The benefit of topical prostaglandins remains to be demonstrated.
Miotics generally are ineffective due to mechanical obstruction of the trabecular meshwork.
Laser trabeculoplasty is generally ineffective unless there are secondary changes in the outflow channels.
Glaucoma filtering surgery may be necessary in cases refractory to medical therapy to completely bypass the resistance due to increased EVP; ciliochoroidal effusions or suprachoroidal hemorrhage may complicate filtering surgery.
The optimal treatment of a direct carotid-cavernous sinus fistula is closure of the abnormal arteriovenous communication with preservation of internal carotid artery patency. Techniques to achieve this result include surgical repair of the damaged portion of the intracavernous internal carotid artery, electrothrombosis, embolization, or balloon occlusion of the fistula.
Dural carotid-cavernous sinus fistulae may close spontaneously, but, for those lesions causing progressive or unacceptable symptoms and signs, standard embolization or endovascular balloon occlusion generally is performed. If these techniques are unsuccessful, direct surgery on the cavernous sinus may be considered. In cases where anatomy makes a standard intravascular approach impossible, the superior ophthalmic vein can be cannulated and a balloon or coil can be threaded into the area of a direct communication.[6, 7, 8, 9]
Laser trabeculoplasty usually is ineffective.
Patients with ICE syndrome generally do well with glaucoma filtering surgery, although late failure may develop due to endothelialization of the fistula, which, in some cases, may be reopened with the Nd:YAG laser.
Consultation is indicated depending on the coexisting conditions, as follows:
Cornea consultation for management of corneal edema
Medications used to decrease aqueous production include ophthalmic beta-blockers, carbonic anhydrase inhibitors (ophthalmic and/or oral), ophthalmic prostaglandins, and ophthalmic alpha 2-agonists. Various combinations of these agents are also available.
Clinical Context: May reduce elevated and normal IOP, with or without glaucoma, by reducing production of aqueous humor or by outflow.
Clinical Context: Nonselective beta-adrenergic blocking agent that lowers IOP by reducing aqueous humor production and possibly increases outflow of aqueous humor.
Clinical Context: Blocks beta 1- and beta 2-receptors and has mild intrinsic sympathomimetic effects.
Clinical Context: Selectively blocks beta 1-adrenergic receptors with little or no effect on beta 2-receptors. Reduces IOP by reducing production of aqueous humor.
Decrease IOP by reducing aqueous production. Reduce elevated and normal IOP, with or without glaucoma.
Clinical Context: Selective alpha 2-receptor that reduces aqueous humor formation and increases uveoscleral outflow.
Clinical Context: Reduces elevated, as well as normal, IOP whether or not accompanied by glaucoma. A relatively selective alpha-adrenergic agonist that does not have significant local anesthetic activity. Has minimal cardiovascular effects.
Clinical Context: Inhibits enzyme CA, reducing the rate of aqueous humor formation, which, in turn, reduces IOP. Used for adjunctive treatment of chronic simple (open angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when delay of surgery desired to lower IOP.
Clinical Context: Used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer the drugs at least 10 min apart. Reversibly inhibits CA, reducing hydrogen ion secretion at renal tubule and increasing renal excretion of sodium, potassium bicarbonate, and water to decrease production of aqueous humor.
Clinical Context: Reduces aqueous humor formation by inhibiting the carbonic anhydrase enzyme, which results in decreased IOP.
Clinical Context: Catalyzes reversible reaction involving hydration of carbon dioxide and dehydration of carbonic acid. May use concomitantly with other topical ophthalmic drug products to lower IOP. If more than one topical ophthalmic drug is being used, administer drugs at least 10 min apart.
Enzyme found in many tissues of the body, including the eye. Catalyzes a reversible reaction where carbon dioxide becomes hydrated and carbonic acid dehydrated. By slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport, it may inhibit CA in the ciliary processes of the eye. This effect decreases aqueous humor secretion, reducing IOP.
Clinical Context: A prostamide analogue with ocular hypotensive activity. Mimics the IOP-lowering activity of prostamides via the prostamide pathway. Used to reduce IOP in open-angle glaucoma or ocular hypertension.
Clinical Context: Indicated to reduce intraocular pressure in patients with open-angle glaucoma or ocular hypertension. Implanted by intracameral injection procedure.
Clinical Context: Prostaglandin F2-alpha analog. Selective FP prostanoid receptor agonist believed to reduce IOP by increasing uveoscleral outflow. Used to treat open-angle glaucoma or ocular hypertension.
Clinical Context: Indicated to reduce intraocular pressure in patients with open-angle glaucoma or ocular hypertension. Implanted by intracameral injection procedure.
Clinical Context: Prostanoid selective FP receptor agonist believed to reduce IOP by increasing outflow of aqueous humor. Human and animal studies suggest the main mechanism of action is increased uveoscleral outflow.
Clinical Context: Dual mechanism, dual pathway molecule which increases aqueous humor outflow through the uveoscleral pathway (mediated by latanoprost acid) and increases the facility of aqueous humor outflow through the trabecular meshwork pathway (mediated by nitrous oxide)
Clinical Context: Fluorinated prostaglandin F2-alpha analogue believed to reduce IOP by increasing outflow of aqueous humor via the uveoscleral pathway.
These agents may decrease intraocular pressure by increasing the outflow of aqueous humor.
They are administered once per day. Potential adverse effects of these medications are similar to latanoprost (eg, eyelash growth, increased iris pigmentation). These agents are considered by some glaucoma specialists as first-line agents for glaucoma, mainly because of the lack of systemic adverse effects.
Clinical Context: Rho Kinase inhibitor which increases trabecular meshwork outflow facility, decreases episcleral venous pressure, and decreases aqueous humor production.
Rho Kinase inhibitors increase drainage of intraocular fluid by improving outflow of the trabecular meshwork.
Close monitoring of IOP and vigilance for evidence of glaucomatous injury (as manifested by examination of the patient's optic discs and by visual field testing) are warranted.
If the patient does not comply with the use of medications, further deterioration of the visual field may occur.
The prognosis for glaucoma is favorable if IOP can be maintained over the lifetime of the patient.[10]
For patient education resources, see the Glaucoma Center, as well as Glaucoma FAQs and Understanding Glaucoma Medications.