Crystalline Lens Subluxation
Signs and Symptoms: While crystalline lens subluxation can occur in any patient, these three profiles are most prone: significant blunt trauma to the eye or head; systemic conditions such as Marfan's syndrome, homocystinuria, hyperlysinuria, familial ectopia lentis, sulfite oxidase deficiency, Weill-Marchesani syndrome, aniridia and Ehlers-Danlos syndrome; hypermature cataract in which zonular support has been lost.
Symptoms of lens subluxation includes visual disturbance from extreme hyperopic or myopic shift, astigmatism or acquired aphakia. Occasionally, the vision fluctuates dramatically as the patient may alternate between phakic and aphakic vision. Monocular diplopia may also manifest. In most cases, there are no physical sensations except when the lens blocks the pupil, leading to secondary angle closure. In that case, the patient will manifest all of the symptoms of an acute angle closure glaucoma attack.
At the slit lamp you will note a displaced crystalline lens. This appears as a black crescent at the edge of the lens against a red reflex from the fundus. The lens can be up and out, down and in, down and out, nasal or temporal, or completely displaced into the posterior or anterior chamber. Phacodonesis (tremulousness of the lens due to loss of zonular support) and iridodonesis (tremulousness of the iris) may also exist. With pupillary block, there may be inflammation, corneal edema, angle closure and markedly elevated intraocular pressure.
Pathophysiology: Subluxation implies displacement of the crystalline lens, whereas luxation refers to a lens that is totally dislocated. The term ectopia lentis has been used interchangeably with subluxation, although this term should be reserved for bilateral cases.
Lens subluxation can be either acquired or due to congenital systemic causes. Infants are rarely born with displaced lenses; rather, they develop due to a predisposing systemic condition.
Acquired subluxation is slightly more common than lens displacement associated with underlying systemic disorders. Trauma accounts for a large percentage of all acquired lens subluxations, with mechanical stretching of the zonules. This occurs as the eye is compressed in an anterior-posterior direction, such as with impact by a fist or ball. The subsequent distention of the globe in the medial-lateral plane ruptures the zonular fibers. Other acquired causes include chronic cyclitis, syphilis, buphthalmos, ciliary body tumor and severe or pathological myopia.
The pathophysiologic mechanism of lens subluxation from congenital causes varies depending on the condition. The direction of displacement in each case is characteristic, although not completely diagnostic. In Marfan's syndrome, the lenses tend to displace supero-temporally due to abnormal collagen vascular tissue and faulty lens zonules. It is typically present at birth and is non-progressive. Because the zonules are still attached to the lens, some accommodation remains.
Homocystinuria, a defect in amino acid metabolism, results in brittle zonules that rupture. This allows the lens to displace inferonasally or even into the anterior chamber. There is no accommodation, and the condition may progress.
Two other conditions worth mentioning are simple ectopia lentis and ectopia lentis et pupillae. Simple ectopia lentis is an autosomal-dominant condition where the lenses are dislocated superotemporally, but there are no other associated systemic abnormalities. Ectopia lentis et pupillae is likewise an isolated inherited condition, albeit autosomal-recessive, where the lenses displace temporally in opposite directions.
The main concern with lens subluxation is the development of secondary angle closure glaucoma. Anytime the crystalline lens displaces, there is always the possibility that the lens can come into apposition with the back surface of the iris (or the front surface of the iris during complete lens dislocation into the anterior chamber). This will lead to pupillary block, iris bombé and secondary angle closure. Also, if the lens completely dislocates into the anterior chamber, the lens may touch the cornea, irreversibly damaging the endothelial cells with subsequent corneal edema and decompensation.
Management: Extraction of a dislocated lens can be difficult, so a subluxated lens itself is not sufficient reason to pursue surgery. In the absence of pupillary-block glaucoma, corneal decompensation, inflammation or intractable visual disability, leave the subluxated lens alone in favor of non-surgical options. For stable induced refractive errors, visual correction with glasses or contact lenses may be an option.
If the lens luxates into the posterior chamber but no inflammation ensues, simply monitor the condition. However, if inflammation does occur and the threat of retinal damage presents, vitrectomy and lens extraction are necessary.
Avoid dilating cases in which you suspect loss of zonular adherence (as with hypermature cataracts) with subsequent risk of dislocation into the anterior chamber until you obtain a surgical consultation. If the lens has already spontaneously dislocated into the anterior chamber, or where the patient was dilated with subsequent anterior dislocation, follow this protocol: Recline the patient (who can be dilated, if the dislocation happened spontaneously), then carefully manipulate the head until the lens falls back into place in the fossa. Apply pilocarpine solution and obtain a surgical consultation.
If pupillary-block, angle-closure glaucoma develops, laser peripheral iridotomy is indicated as soon as possible. However, this rarely manages the condition successfully. Thus, the patient should then undergo lens extraction with intraocular lens implantation. While some surgeons have had success with posterior chamber implants, anterior chamber lenses are typically the modality of choice.
1. Cross HE, Jensen AD. Ocular manifestations in the Marfan's syndrome and homocystenuria. Am J Ophthalmol 1973; 75:405.
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