Anterior Lens Luxation
Anterior lens luxation usually affects middle-aged dogs of the terrier breeds and is seen most frequently in Smooth and Wire Haired Fox Terriers and Jack Russell Terriers. It is associated with zonular defects in the terrier breeds (associated with the ADAMTS17 mutation), whereas in other breeds with inherited cataract formation it is associated with advanced cataract (hypermature) formation. These secondary glaucomas appear as acute corneal edema, increased IOP, blepharospasm, tearing, and ciliary flush. Often, the lens is in front of the pupil and often totally within the anterior chamber. Pupillary blockage with vitreous adherent to the posterior lens capsule and iridocorneal angle closure are common and can markedly increase IOP within the posterior segment. Applanation tonometry from the central cornea may yield erroneous low IOP levels. Direct examination of the posterior segment is not usually possible, and B-scan ultrasonography may be used to evaluate the vitreous and retina.
Treatment consists of lowering IOP to normal levels (usually with mannitol, 1–2 g/kg, IV); transpupillary aqueous humor flow may be reestablished with moderate dilation with 10% phenylephrine. Lens removal, preferably by phacoemulsification or intracapsular extraction, is performed as soon as possible. Postoperative treatment consists of topical and systemic antibiotics and corticosteroids and maintenance of a moderate but moving pupil. IOP is closely monitored and any increases treated with topical β-blockers, topical and systemic carbonic anhydrase inhibitors, and prostaglandin analogs. Longterm postoperative complications include anterior uveitis, secondary glaucoma, and retinal detachment.