Duane syndrome: A congenital eye movement disorder in which there is miswiring of the eye muscles, causing some eye muscles to contract when they should not and other eye muscles not to contract when they should. People with the syndrome have a limited (and sometimes no) ability to move the eye outward toward the ear (to abduct the eye) and, in most cases, a limited ability to move the eye inward toward the nose (to adduct the eye). Often, when the eye moves toward the nose, the eyeball also pulls into the socket (retracts), the eye opening narrows and, in some cases, the eye moves upward or downward. Many patients with Duane syndrome turn their face to maintain binocular vision and compensate for improper turning of the eyes.
Duane syndrome is unilateral (with only one eye affected) in about 80% of cases. The remaining 20% of cases are bilateral (with both eyes affected) with one eye usually more severely affected than the other.
Duane syndrome is isolated (it is the only disorder the individual has) in 70% of cases. The remaining 30% of the time Duane syndrome occurs in association with malformations of the skeleton, ears, eyes, kidneys and nervous system and as a component of Okihiro syndrome (an association of Duane syndrome with forearm malformation and hearing loss), Wildervanck syndrome (fusion of neck vertebrae and hearing loss), Holt-Oram syndrome (abnormalities of the upper limbs and heart), Morning Glory syndrome (abnormalities of the optic disc or "blind spot"), and Goldenhar syndrome (malformation of the jaw, cheek and ear, usually on one side of the face).
Clinically, Duane syndrome is often subdivided into three types:
- Type 1 -- The affected eye, or eyes, has limited ability to move outward toward the ear, but the ability to move inward toward the nose is normal or nearly so. The eye opening narrows and the eyeball pulls in when looking inward toward the nose, however the reverse occurs when looking outward toward the ear. About 78% of all Duane syndrome cases are Type 1.
- Type 2 -- The affected eye, or eyes, has limited ability to move inward toward the nose, but the ability to move outward toward the ear is normal or nearly so. The eye opening narrows and the eyeball pulls in when looking inward toward the nose. About 7% of all Duane syndrome cases are Type 2.
- Type 3 -- The affected eye, or eyes, has limited ability to move both inward toward the nose and outward toward the ears. The eye opening narrows and the eyeball pulls in when looking inward toward the nose. About 15% of all Duane syndrome cases are Type 3.
- Subgroup A -- The affected eye is turned inward toward the nose (esotropia).
- Subgroup B -- The affected eye is turned outward toward the ear (exotropia).
- Subgroup C -- The eyes are in a straight, primary position.
Duane syndrome is due to a miswiring of the medial and the lateral rectus muscles, the muscles that move the eyes. Also, patients with the syndrome lack the abducens nerve, the sixth cranial nerve, which is involved in eye movement. Genetic and environmental factors are believed to play a role in Duane syndrome. The syndrome can be inherited as an autosomal dominant or recessive trait. Genes involved in the development of Duane syndrome are located on chromosomes 2q13 and 8q13.