Ectopia lentis is a displacement of the lens that may be congenital, developmental, or acquired. A subluxated lens is partially displaced from its normal position but remains in the pupillary area. A luxated, or dislocated, lens is completely displaced from the pupil, implying separation of all zonular attachments. Findings associated with lens subluxation include decreased vision, marked astigmatism, monocular diplopia, and iridodonesis (tremulous iris). Potential complications of ectopia lentis include cataract and displacement of the lens into the anterior chamber or the vitreous space. Dislocation into the anterior chamber or pupil may cause pupillary block and angle-closure glaucoma. Dislocation of the lens posteriorly into the vitreous cavity often has no adverse sequelae aside from a profound change in refractive error.
Trauma is the most common cause of acquired lens displacement. Nontraumatic ectopia lentis is commonly associated with Marfan syndrome, homocystinuria, aniridia, and congenital glaucoma. Less frequently, it appears in association with Ehlers-Danlos syndrome, hyperlysinemia, Weill-Marchesani syndrome, and sulfite oxidase deficiency. Ectopia lentis may occur as an isolated anomaly (simple ectopia lentis), which is usually inherited as an autosomal dominant trait. Ectopia lentis can also be associated with pupillary abnormalities in the ocular syndrome ectopia lentis et pupillae (discussed later in this chapter).
Marfan syndrome is a heritable disorder with ocular, cardiovascular, and skeletal manifestations. Though usually inherited as an autosomal dominant trait, the disorder appears in individuals with no family history in approximately 15% of cases. Marfan syndrome is caused by mutations in the fibrillin gene on chromosome 15. Affected individuals are tall, with arachnodactyly (Fig 4-18A) and chest wall deformities. Associated cardiovascular abnormalities include dilated aortic root and mitral valve prolapse.
Between 50% and 80% of patients with Marfan syndrome exhibit ectopia lentis (Fig 4-18B). The lens subluxation tends to be bilateral and symmetric (usually superior and temporal), but variations do occur. The zonular attachments commonly remain intact but become stretched and elongated. Ectopia lentis in Marfan syndrome is probably congenital in most cases. Progression of lens subluxation occurs in some patients over time, but in many patients the lens position remains stable.
Other ocular abnormalities associated with Marfan syndrome include axial myopia and an increased risk of retinal detachment. Patients with Marfan syndrome may develop pupillary block glaucoma if the lens dislocates into the pupil or anterior chamber. Openangle glaucoma may also occur. Amblyopia may develop in children with lens subluxation if their refractive error shows significant asymmetry or remains uncorrected in early childhood. Spectacle or contact lens correction of the refractive error provides satisfactory vision in most cases. Pupillary dilation is sometimes helpful. The clinician may refract both the phakic and the aphakic portions of the pupil to determine the optimum visual acuity. A reading add is often necessary because the subluxated lens lacks sufficient accommodation.
In some cases, adequate visual acuity cannot be obtained with spectacle or contact lens correction, and removal of the lens may be indicated. Lens extraction—either extracapsular or intracapsular—in patients with Marfan syndrome is associated with a high rate of complications such as vitreous loss and complex retinal detachment. Advanced surgical techniques, including the use of capsular tension rings and capsular tension segments, are increasingly being used to improve outcomes in these cases (see Chapter 12, Preparing for Cataract Surgery in Special Situations).
Figure 4-18 Marfan syndrome. A, Arachnodactyly in a patient with Marfan syndrome. B, Subluxated lens in Marfan syndrome.
(Part A courtesy of Karla J. Johns, MD.)
Homocystinuria is an inborn error of methionine metabolism in which serum levels of homocysteine and methionine are elevated. Homocystinuria is transmitted in an autosomal recessive pattern. Affected individuals are healthy at birth; however, seizures and osteoporosis typically develop within the first year of life, and cognitive impairment soon becomes apparent. These individuals are usually tall and have light-colored hair. Persons with homocystinuria are prone to thromboembolic episodes, and surgery and general anesthesia are thought to increase the risk of thromboembolism.
Lens dislocation in individuals with homocystinuria tends to be bilateral and symmetric. The dislocation appears in infancy in approximately 30% of affected individuals, and by the age of 15 years, it appears in 80% of those affected. The lenses are usually subluxated inferiorly and nasally, but variations have been reported. Because zonular fibers of the lens are known to have a high concentration of cysteine, deficiency of cysteine is thought to disrupt normal zonular development; affected fibers tend to be brittle and easily disrupted. In studies of infants with homocystinuria treated with a low-methionine, high-cysteine diet and vitamin supplementation with the coenzyme pyridoxine (vitamin B6), the incidence of sequelae, including ectopia lentis, was reduced in some patients who received this therapy. (See also BCSC Section 6, Pediatric Ophthalmology and Strabismus.)
Hyperlysinemia, an inborn error of metabolism of the amino acid lysine, is associated with ectopia lentis. Affected individuals also show cognitive impairment and muscular hypotony.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.