Lens luxation refers to the dislocation of the lens inside the eye. Sometimes, this can be a primary inherited problem, for example, in terrier breeds, and sometimes, it can be secondary to other conditions (such as long-standing cataracts, chronic uveitis, or glaucoma). Accurate diagnosis of the cause of lens luxation is extremely important in managing the condition.

The fluid in the eye (aqueous) is produced by the ciliary body and is secreted into the posterior chamber. From there, it moves through the pupil into the anterior chamber and then drains out through the iridocorneal angle.

Primary lens luxation occurs when the ligaments holding the lens in place (the zonules) are abnormal. The lens then becomes loose inside the eye, and if it moves through the pupil into the anterior chamber, it can block the flow of aqueous. The aqueous can no longer escape from the eye; the pressure rises, leading to secondary glaucoma.

However, lens luxation can also be secondary to glaucoma if the eye enlarges due to chronic elevation in intraocular pressure (IOP). The stretching caused by the eye enlarging can lead to the breakdown of the zonules. It is thus vital to determine if the lens luxation is causing the glaucoma or if the glaucoma is the cause of the lens luxation. Incorrect diagnosis leads to disastrous consequences for the eye as the treatment for these conditions is entirely different, and treating with the wrong medication can make the condition much worse. Referral to a specialist in veterinary ophthalmology ensures the best possible decision-making about the condition.

Primary lens luxation

Primary lens luxation is inherited in many terrier breeds and Border Collies. In this condition, the ligaments holding the lens in place (the zonules) are inherently weak, leading to them breaking down. When enough of these zonules break down, the lens begins to wobble (phacodonesis), and as the lens rests against the iris, the iris can also be seen to wobble (iridodonesis). When all the zonules break down, the lens can dislocate (i.e. luxate). If the lens falls backwards (posterior lens luxation), the IOP can remain normal, but vision becomes blurred as the lens no longer helps to focus the image on the retina. Such animals are long-sighted, but they generally cope well with this situation. However, when the lens changes position like this, there is an increased risk that the eye could become blind from a retinal detachment.

Lens luxation is more serious when the lens becomes trapped in the pupil or moves through the pupil into the anterior chamber (anterior lens luxation). This blocks fluid flow in the eye and results in acute elevation in IOP, with painful and blinding consequences for the eye. Urgent surgical treatment is required for primary anterior lens luxation.

Symptoms

Early symptoms may include lens wobble or iris wobble, or sometimes the vitreous can move around between broken zonules and be visible coming through the pupil. These are very subtle signs but can be recognised by a specialist in ophthalmology who is monitoring the eye for signs preceding lens luxation in cases of known predisposition.

More obvious signs include distortion of the pupil, or sometimes the lens is seen in the anterior chamber before the onset of disastrous complications such as glaucoma. Usually, however, the first sign of anterior lens luxation is the development of a sudden onset glaucoma. This rapidly leads to a red, cloudy, painful blind eye.

When these symptoms develop in terrier breeds or Border Collies primary lens luxation urgently needs to be ruled out.

Secondary lens luxation

Sometimes primary lens luxation leads to secondary glaucoma, but chronic primary glaucoma can also lead to secondary lens luxation. It is vital to determine whether the lens luxation is primary or secondary because treatment for the two conditions is completely different.

Chronic glaucoma can lead to the eye enlarging (termed buphthalmos). This enlargement leads to stretching of the zonules supporting the lens, and eventually, lens luxation can result. Sometimes, long-standing cataracts and chronic inflammation (uveitis) lead to degradation of the zonules and can lead to lens luxation.

Most lens luxations in cats are secondary to chronic uveitis. A specialist in ophthalmology will be able to determine whether the lens luxation is primary or secondary by using a combination of slit lamp biomicroscopy, gonioscopy and ultrasound examination (see diagnostic facilities). This examination will then allow the best treatment for the eye and the fellow predisposed eye to help prevent similar problems.

Other Common Issues

Organise a consultation