❖ Subluxation (partial dislocation): The suspension of the lens (the zonulefibers) is slackened, and the lens is only partially within the hyaloid fossa (Fig. 7.23).
❖ Luxation (complete dislocation): The lens is torn completely free andhas migrated into the vitreous body or, less frequently, into the anterior chamber.
There are several causes of lens dislocation (Table 7.5).Mostfrequently, it is due totrauma(see contusion of the eyeball). Later in life,pseudoexfoliation may also lead to subluxation or luxation of the lens. Hereditary causes and metabolic disease produce lens displacementearlyyet on the whole are rare. Additional rare causes include hyperlysinemia (characterized by retarded mental development and seizures) and sulfite oxi-dase deficiency (which leads to mental retardation and excretion of cysteinein the urine).
The most frequent atraumatic causes of lens dislocation are Marfan’s syndrome, homocystinuria, and Weill-Marchesani syndrome.
Slight displacement may be of no functional significance to thepatient. More pronounced displacement produces severe optical distortion with loss of visual acuity.
Cardinal symptoms include tremulous motion ofthe iris and lens when the eye moves (iridodonesis and phacodonesis). These symptoms are detectable under slit-lamp examination.
Optical considerations (see symptoms) and the risk of secondaryangle closure glaucoma from protrusion of the iris and dislocation of the lens into the anterior chamber are indications for removal of the lens.