mercoledì 1 settembre 2010
Bilateral ectopia lentis
Figure 1: Axial noncontrast CT of the head at the level of the orbits demonstrates posterior dislocation of both lenses, which now rest dependently in the vitreous. The etiology in this particular patient was repetitive trauma from serial falls.
Diagnosis: Bilateral ectopia lentis
The crystalline lens of the eye is designed to refract the light entering the iris and project/focus it onto the retina. The lens itself contains no vasculature, nerves, or connective tissue. It sits behind the iris and the front of the lens is in contact with the aqueous fluid of the anterior chamber while the posterior surface of the lens is in contact with the vitreous. The lens is held in place by zonular fibers, otherwise known as suspensory ligaments. These fibers connect to the cilliary body around the circumference of the lens.
Subluxation (partial dislocation) or luxation (complete dislocation) of the crystalline lens, otherwise known as ectopia lentis, is caused by dysfunction or disruption of these zonular fibers. Trauma is the most common cause of this disorder. The absence of a traumatic history should prompt consideration of hereditary causes of zonular fiber dysfunction; predisposing conditions include Marfan syndrome, homocystinurea, tertiary syphilis, and Weil-Marchesani syndrome.
Patients will complain of monocular diplopia, markedly decreased visual acuity in the affected eye(s), and/or poor near vision.
Treatment is determined by lens position, with anterior chamber dislocation often being a surgical emergency. As the aqueous humor of the eye flows in the anterior chamber, around the iris from the cilliary body to the canal of Schlemm, this route can become acutely obstructed with anterior dislocation leading to acute glaucoma. The cornea and iris are also at risk for damage. Posterior dislocation may be treated conservatively depending on lens position, but may also lead to uveitis or glaucoma in some cases.