Lens Subluxation

Lens subluxation (partial dislocation) is displacement of the lens from its normal position with the lens still partly within the pupillary area, due to partial loss of zonular support.

• Traumatic: blunt injury with zonular dialysis (the commonest acquired cause).
• Inherited and systemic:
  • Marfan syndrome (FBN1; superotemporal displacement), the commonest genetic cause.
  • Homocystinuria (cystathionine beta synthase deficiency; inferonasal displacement, thromboembolism, intellectual disability, osteoporosis).
  • Weill-Marchesani syndrome (microspherophakia, short stature, brachydactyly, glaucoma).
  • Ehlers-Danlos syndrome, sulphite oxidase deficiency, hyperlysinaemia, aniridia, simple ectopia lentis.
• Acquired ocular: pseudoexfoliation syndrome (zonular weakness), hypermature cataract, high axial myopia, buphthalmos, intraocular tumours, chronic uveitis, previous surgery, syphilis.

• Blurred vision from induced lenticular astigmatism and myopia (lens becomes more spherical), monocular diplopia when the lens edge crosses the pupil.
• Iridodonesis (trembling iris), phacodonesis (trembling lens), asymmetric anterior chamber depth, vitreous strands in the anterior chamber or pupil, visible lens equator in the pupil.
• Raised intraocular pressure from pupillary block (microspherophakia) or angle recession; retinal detachment risk.
• Marfan: tall stature, arachnodactyly, arm span exceeding height, pectus deformity, aortic root dilatation, mitral valve prolapse.
• Homocystinuria: malar flush, marfanoid habitus, thrombotic events, learning disability.

• Dilated slit lamp examination in supine and upright positions (the lens shifts with posture), noting direction, extent in clock hours of zonular dialysis, and lens shape.
• Ultrasound biomicroscopy and anterior segment optical coherence tomography to image zonules and the lens equator; B-scan if the view is poor.
• Refraction, intraocular pressure, gonioscopy, dilated fundus examination.
• Systemic screen in non-traumatic cases: echocardiography for aortic root and valves, plasma total homocysteine and methionine (homocystinuria; urinary cyanide nitroprusside test), FBN1 sequencing, Marfan systemic score, skeletal survey, blood syphilis serology.
• Family examination.

• Observation with optical correction (refraction through the phakic or aphakic portion of the pupil) when the lens remains clear and vision is good.
• Treat associated glaucoma: miotics for pupillary block in microspherophakia are contraindicated (they worsen block); use cycloplegia (atropine 1 percent) and laser peripheral iridotomy.
• Indications for surgery: loss of vision not correctable with spectacles, pupillary block, lens induced uveitis, lens in the pupil with glare, cataract, or progressive subluxation with risk of dislocation.
• Techniques: lens removal by phacoemulsification with capsule hooks, capsular tension ring or segments, and in-the-bag intraocular lens if support suffices (up to about 4 to 6 clock hours of dialysis); for greater loss, scleral fixated (sutured or intrascleral flanged, Yamane technique) or iris fixated intraocular lens, or pars plana lensectomy and vitrectomy with aphakic contact lens correction in children.
• Homocystinuria: pyridoxine 200 to 1000 mg daily (in responsive patients), folate 5 mg daily, vitamin B12 1 mg monthly, betaine 100 mg/kg/day in divided doses, methionine restricted diet. Before anaesthesia, maintain hydration, avoid nitrous oxide, and use thromboprophylaxis (compression stockings, low molecular weight heparin) because of thrombotic risk.
• Marfan: annual echocardiography, beta blocker (atenolol 50 to 100 mg daily) or losartan 50 to 100 mg daily, avoidance of isometric exertion and contact sport, and cardiology and genetics review.
• Children: amblyopia therapy and early correction.