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Group of disorders characterized by malformations of
the iridocorneal angle of the anterior chamber of the eye, resulting in
juvenile glaucoma.
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Glaucoma Iridogoniodysgenesis; IGDA
Syndrome.
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Iridogoniodysgenesis Type I (Autosomal Dominant Iridogoniodysgenesis Anomaly): Characterized by iris hypoplasia, goniodysgenesis, and juvenile glaucoma
as a result of aberrant migration or terminal induction of the neural crest
cells involved in formation of the anterior segment of the eye.
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Iridogoniodysgenesis Type II (Iridogoniodysgenesis Syndrome; Autosomal Dominant Iris Hypoplasia with Early-Onset Glaucoma): Characterized by an autosomal dominant iris hypoplasia associated with
early-onset glaucoma caused by maldevelopment of the trabecular meshwork and
the iris. Glaucoma usually is detected in the second decade of life but may
begin at any age.
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Most cases are transmitted as an autosomal
dominant trait with variable expressivity and complete penetrance. Two
chromosomal loci can be involved: 4q25 and 6p25, corresponding to PITX2 (or
RIEG) and FKHL7, respectively. PITX2, the most studied gene, is an homeobox
gene coding for a transcription factor. Different levels of expression of
this gene supposedly are responsible for the phenotypic variability of the
syndrome.
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Abnormal differentiation of neural crest cells
causes “goniodysgenesis” (abnormalities in differentiation of the
iridocorneal angle tissue). The anterior iris stroma is hypoplastic and
associated with increased intraocular pressure, resulting in glaucoma.
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Affected individuals often have an unusual
dark-gray or chocolate-brown eye color as a result of the iris epithelium
showing through the hypoplastic iris stroma. All patients are at risk for
developing juvenile glaucoma, which is often diagnosed in the second decade
of life, although it can begin at any age. The glaucoma is often resistant
to medical therapy and, in the absence of surgical intervention, blindness
may occur. Nonocular features, such as maxillary hypoplasia, dental
anomalies (microdontia, hypodontia), umbilical hernia, and hypospadias, may
present as part of the syndrome.
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Inquire about severity of glaucoma
and associated nonocular features. Obtain a list of topical antiglaucoma
medications: echothiophate (long-acting anticholinesterase, which prolongs
the effects of drugs that are metabolized by plasma cholinesterase such as
succinylcholine, mivacurium, procaine, chloroprocaine, and cocaine),
epinephrine (hypertension and dysrhythmias), and timolol (nonselective
beta-blocker with potential for bradycardia, hypotension, bronchospasm in
asthmatic patients, and decompensation of congestive heart failure).
Selective beta-blockers such as betaxolol are considered safer in
asthmatics.
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The main anesthetic challenge is
avoidance of intraocular pressure increases during direct laryngoscopy and
tracheal intubation, as well as coughing, straining, and vomiting. In the
presence of maxillary hypoplasia, intubation per se should not be
technically difficult because the mandible remains normal. Intravenous
lidocaine, adequate anesthetic depth, and use of a nondepolarizing muscle
relaxant are the key elements in providing minimal changes in intraocular
pressure during tracheal intubation. Like intracranial pressure, intraocular pressure
is increased by hypercarbia and hypoxia and is reduced by hyperventilation,
slight elevation of the head, osmotic diuretics, and carbonic anhydrase
inhibitors.
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The majority of central ...