March 2013 Online Photo Diagnosis

By Patrick J. Caroline, FAAO, & Mark P. André, FAAO

Dislocation of the Crystalline Lens

The crystalline lens normally lies behind the iris and in front of the vitreous, held in its position by the zonules. These photos show a dislocated lens, or ectopia lentis, which occurs when the lens is not in its normal position. When a lens is decentered but remains in the papillary area, it is referred to as subluxated. It is estimated that greater than 25 percent of zonular fibers must be disrupted for subluxation to occur¹. Patient symptoms of lens subluxation include decreased vision, monocular diplopia, progressive myopia, and marked astigmatism.

A luxated lens is defined as complete displacement of the crystalline lens from the papillary aperture, implying complete disruption of zonular fibers. The lens may be dislocated forward into the anterior chamber or posteriorly into the vitreous.

Trauma is the most common cause of lens dislocation, accounting for more than half of the cases in most series. Traumatic dislocation of the lens is often accompanied by other evidence of contusive injury to the head or globe.

Ectopia lentis is also a feature of a variety of systemic disorders including Marfan's syndrome and homocystinuria. The lens dislocation in Marfan's syndrome is usually superiorly and temporally, while it is usually inferiorly and nasally with homocystinuria.

Because patients who have Marfan's syndrome may have dilation or dissection of the aorta and cardiac valvular disease, and those who have homocystinuria have a tendency to develop thromboembolism, it is important that the diagnosis be established before any surgical maneuvers are made that could precipitate vascular complications.

In general, dislocated lenses with intact capsules can be well tolerated for long periods of time. If the subluxated lens is clear, refraction usually can be accomplished satisfactorily. Dilation of the pupil may be useful in some cases. If the lens is luxated into the vitreous cavity, an aphakic contact lens correction may be used. Surgical intervention is indicated when the dislocated lens becomes cataractous, either causing decreased visual function or preventing adequate retinoscopy in a child. Lens extraction may also be necessary with a clear lens when the edge is in the papillary axis, precluding suitable phakic or aphakic correction. Other indications include a dislocated lens that is leaking lens protein, leading to a lens-induced uveitis or glaucoma, and irreversible luxation of the lens into the anterior chamber with papillary block.

References

1. Current Ocular Therapy, FT Fraunfelder, FH Roy, W.B. Saunders 1995
2. Jarrett WH, Dislocation of the lens. A study of 166 hospitalized cases. Archives in Ophthalmology 78:289-296, 1967.