'Floating lens sign' in traumatic lens dislocations.

Sir,

Though a multitude of causes can lead to dislocation of the crystalline lens, the most common among them is trauma. Partial or complete disruption of zonular fibers leads to subluxation or dislocation of the lens into the posterior chamber. Surgery is usually indicated due to the high incidence of delayed complications. Herein, we report a case of completely dislocated lens that demonstrates a “floating lens sign” on computed tomography (CT) thereby indicating complete zonular disruption. The differentiation between complete and partial zonular tear is essential as it can alter management.

A 42-year-old male presented to the emergency after having been battered. He reported being beaten and kicked with a transient loss of consciousness. He complained primarily of pain to the face. On examination, he had swelling and ecchymosis of the right eyelid and orbital area. There were lacerations involving the right eyelid and eye opening was not possible. Hence, vision testing and slit lamp examination could not be done. CT scan of the head and the face on the axial scans [Figure 1a] showed the crystalline lens to lie within the vitreous chamber posteriorly in a dependent position. On the coronal scans [Figure 1b], which were acquired after hyperextension of the neck of the patient, the lens had moved within the vitreous to the superior part of the eyeball again lying in a dependent position. We called this the “floating lens” sign, and this indicated complete posterior dislocation of the crystalline lens into the vitreous. The free “floating” of the lens to a dependent position indicates complete zonular disruption with no attachment of the lens to the ciliary zonules.

Figure 1

Axial computed tomography (CT) (a) of the head through the orbit with the patient lying in a supine position with the head in a neutral position reveals that the crystalline lens is lying posteriorly within the eyeball (arrow) in a dependent position. Coronal CT (b) of the head through the orbit with the patient lying in a supine position with the head in a hyperextended position reveals that the crystalline lens has now shifted to the superior aspect of the vitreous chamber in the eyeball (arrow) which is again the dependent position with respect to the new patient position

DISCUSSION

Blunt trauma may cause sudden compressive deformation of the globe causing transient shortening of the eye in the anterio-posterior direction displacing the cornea and anterior sclera posteriorly. This causes a compensatory expansion of the globe in the equatorial plane, which can stretch or break the zonules.1 Traumatic zonular dialysis is a major cause of lens subluxation and dislocation in which partial zonular dialysis may lead to subluxation and complete zonular rupture leads to dislocation. Beside trauma, lens dislocation is seen in hereditary disorder like congenital aniridia, congenital glaucoma, cystathionine b-synthase deficiency, Ehlers-Danlos syndrome, focal dermal hypoplasia, homocystinuria, Kniest dysplasia, Marfan's syndrome, molybdenum cofactor deficiency, sulfite oxidase deficiency, Weill-Marchesani syndrome.

It was traditionally believed that posteriorly dislocated crystalline lenses may be well tolerated for years and that the patient may simply be treated with aphakic contact lenses. However, recently a number of delayed complications are being recognized like delayed retinal detachment,2 allergic uveitis,3 leakage of dissolved lens leading to phacolytic glaucoma4 and impaction in the vitreous and retina. The distinction between partial subluxation and complete dislocation is important. While phacoemulsification and use of capsular support devices may be sufficient for partial subluxation, vitreoretinal surgery in the form of pars plana vitrectomy is necessary in cases of complete dislocation.1

Though radiologic imaging is not a substitute for a thorough direct ophthalmologic examination,5 it may be of occasional help in cases where a direct examination is not immediately possible which may be the case in a noncooperative patient (inebriated or posttraumatic) or due to extensive soft tissue injury (as was the case in our patient). Thus, knowledge of this condition is essential and meticulous evaluation of the orbit and its contents is imperative in all routine CT scan of the heads, not only for medicolegal documentation purposes but also for prompt recognition and intervention.