Lens luxation is dislocation of the lens inside the eye. The lens is suspended inside the eye by small fibers called zonules. If the zonules break down entirely, the lens shifts forward (anteriorly) inside of the eye (in front of the iris). The lens may also shift backword inside the eye (posterior luxation). A lens luxation may be primary (spontaneous) or secondary to other problems in the eye.
Primary lens luxation
Primary lens luxation occurs due to an inherited weakness or degeneration of the lens zonules. The condition most often occurs in terrier breeds of dogs. Other commonly affected breeds are Shar-Peis, Poodles, Beagles and Border Collies but any breed or mixed breed can be affected.
Lens luxation typically occurs between 3-6 years of age. With primary lens luxation, both eyes are at risk for dislocation of the lens.
Secondary lens luxation
This occurs when a primary disease process inside the eye damages the zonules. Conditions that can result in secondary lens luxation include glaucoma, chronic inflammation inside the eye (uveitis), cataracts, eye trauma, and intraocular tumor.
In cats, lens luxation most often develops due to chronic uveitis
Anterior lens luxations result in discomfort and signs that can be recognized as a problem. With subluxation and posterior luxations, signs are often not apparent. Outward signs of a lens luxation may include:
- Sudden change in the size and shape of the pupil
- Squinting, holding eye closed, and increased tearing or blinking
- Increased eye redness
- Cloudiness or haziness to the cornea
- Increased redness in the white part of the eye
- Visual impairment or loss
A complete ophthalmic exam is necessary for the diagnosis of lens luxations. The pressure inside the eye is also checked with a tonometer, as lens luxation can cause or result from glaucoma. A corneal stain will help to assess the health of the cornea. An ocular ultrasound may be performed to check the stability of the retina, as lens luxation can cause the retina to tear and detach.
Early detection of lens luxation is vitally important. As the lens shifts forward inside the eye, it will often block normal fluid flow inside the eye leading to very high intraocular pressures (glaucoma). The high eye pressure is both painful and blinding, due to pressure damage to the optic nerve and retina. With early detection of anterior lens luxation, the lens can be surgically removed, allowing the pressure to normalize. Anterior lens luxations are considered emergencies.
Medical therapy alone for anterior lens luxation is typically unsuccessful at controlling high eye pressures. Without lens removal, eyes will often become irreversibly blind and painful due to glaucoma, which may necessitate eye removal or placement of a prosthetic implant.
For posterior lens luxation, medications may be prescribed long term to help prevent the lens from shifting forward.
After surgical removal of luxated lenses, the eye is monitored closely for proper healing. The two most common potential complications after surgery to remove luxated lenses are glaucoma and retinal detachment. Both are vision threatening. Long term monitoring of intraocular pressures is important, because many of the breeds of dogs with primary (inherited) lens luxation, are also prone to primary glaucoma. In eyes with lens subluxation (loose yet still attached lenses), periodic examination is important. In between exams, it is imperative to watch for signs of lens shifting. In most situations, lens luxation cannot be prevented.
Vision in eyes following lens removal will be farsighted. Up close vision will be functional and somewhat blurred (much like humans requiring glasses to read a book). The farsightedness does not typically an impediment in everyday activities in our companion animals.