The ophthalmological pathologies that dogs can suffer from are multiple and can affect various ocular structures. One of them is lens dislocation, an alteration characterized by the displacement of the lens to an abnormal location as a result of the rupture of the ligaments that keep it suspended. Some types of dislocations constitute a medical emergency and require immediate ophthalmological treatment. Therefore, it is important to know the signs that may be associated with this disease in order to act early.
What is lens luxation in dogs?
Before explaining what lens dislocation is, it is convenient that we review the structure of the eye to understand what this pathology consists of.
The crystalline lens is a biconvex lens that allows objects located at different distances to be focused. This lens is located between the anterior chamber, which contains the aqueous humor, and the vitreous cavity, which contains the vitreous humor. Under normal conditions, the lens is located right in the center and behind the pupil, suspended by so-called zonular fibers or ligaments
When the zonular fibers break, the lens loses its normal anatomical location, is displaced, and what is known as a lens dislocation. This pathology can occur in dogs of any age, and there are certain breeds predisposed to suffer from it, mainly terriers, miniature schnauzers and poodles.
Types of lens luxation in dogs
Lens dislocations can be classified based on different criteria. Depending on whether the rupture of the zonular fibers is complete or incomplete, we speak of:
- Lens dislocation: when the zonular fibers break completely, in 360º, a complete displacement of the lens occurs.
- Lens subluxation: When only part of the fibers break, a partial displacement of the lens occurs.
In addition, depending on the chamber towards which the lens dislocates, we can find:
- Anterior dislocation: in this case, the lens passes through the pupil and is located in the anterior chamber, just behind the cornea. Anterior dislocations are considered an ophthalmological emergency.
- Posterior dislocation: when the lens is positioned in the vitreous cavity.
However, it is worth mentioning that it is not uncommon for the lens to change position depending on the position of the animal's head, given that the lens can pass from the anterior chamber to the vitreous through the pupil.
Finally, depending on the cause, we can speak of two types of lens dislocation in dogs:
- Primary dislocation: it is caused by a defect in the proteins that form the zonule. It occurs in young animals with a congenital weakness of the zonules or in older dogs due to chronic degeneration of the zonules.
- Secondary dislocation: the rupture of the zonule occurs as a result of a previous disease, such as trauma, eye perforation, cataract, glaucoma, intraocular tumors or uveitis.
Causes of lens luxation in dogs
The causes that can produce a luxation or subluxation of the lens in dogs are the following:
- Congenital structural weakness of the zonule fibers: There are certain breeds, especially terriers, that are born with a structural weakness of the zonules, which favors the rupture of the zonules at a given moment and the lens dislocation. These cases of dislocation usually occur in young animals.
- Advanced age: With age, chronic degeneration of the zonules can occur, triggering a total or partial rupture of the zonules.
- Other ocular pathologies that secondarily trigger lens dislocation: such as eye or head trauma, glaucoma, cataracts, tumors intraocular that displace the lens or uveitis that destroy the zonular fibers.
Symptoms of lens luxation in dogs
Clinical signs that can be seen in dogs with lens luxation are:
- Signs of eye pain: tearing (epiphora), closed eye (blepharospasm), photophobia, and depressed mood.
- Vision disturbances: signs of low vision or blindness.
- Changes in the transparency of the eye: both changes in the transparency of the cornea (due to the appearance of corneal edema) or of the cornea itself lens (due to development of a cataract in the dislocated lens). Therefore, if you notice an opacity in the dog's lens, it may be a dislocation.
- Aphakic crescent or aphakic moon: When the lens is displaced from the center of the pupil, a silhouette is created in the shape crescent moon This sign is typical of lens subluxations.
- Iridonesis: These are abnormal movements or tremors of the iris (colored part of the eye) that occur at the same time as eye movements.
- Lenticulodonesis: abnormal movements of the lens.
In the case of secondary dislocations, it will also be possible to observe the clinical signs associated with the primary pathology that triggers the dislocation.
In addition, it is possible to detect complications associated with lens dislocation. The most frequent and important is the development of a glaucoma in the affected eye. In these cases, it is common to observe congestion of the vessels of the sclera, corneal edema, pupil dilation (mydriasis), eye pain and loss of vision.
Diagnosis of lens luxation in dogs
The diagnosis of this pathology can be more or less simple depending on whether it is a subluxation, an anterior or posterior dislocation. In either case, the diagnostic protocol may include the following steps:
- Ophthalmological examination: in case of lens subluxation, the aforementioned aphakic crescent will be observed, in case of posterior dislocation it will be possible to observe it with simple View the retinal vessels (without the need to do an eye fundus) and in cases of anterior dislocation, the lens will be observed in front of the iris. In case the lens has developed a cataract, the diagnosis will be easier than if the lens is still transparent. Sometimes it may be necessary to perform a slit lamp scan for greater accuracy.
- Ocular ultrasound: In cases where the diagnosis is complicated, it may be useful to perform an ocular ultrasound to determine more accurately lens displacement.
Treatment and surgery for lens luxation in dogs
The treatment of this ocular pathology depends fundamentally on the type of dislocation that has been diagnosed:
- Surgery: In subluxations and anterior dislocations, the treatment of choice is surgery and consists of lens extraction.
- Treatment of clinical signs and complications: In posterior subluxations, the lens is usually left in the vitreous cavity and only a therapy to palliate the clinical signs and possible complications of the dislocation.
- Treatment of primary pathologies: in the case of secondary dislocations, it is important to establish treatment for the primary pathology that triggered the dislocation, since it is possible that it is a disease that can also affect the other eye.
It is important to note that there are certain dislocations that are an ophthalmological emergency a and that, however, may not be considered an emergency by the caregivers. Often, the guardians of dogs with this problem are alarmed to detect a serious loss of vision in the affected eye, however, these cases are usually chronic processes in which it is difficult or impossible to recover vision, so it is not They consider it a real emergency. However, Recent dislocations in which a visual deficit has not yet occurred are true medical emergencies that require immediate ophthalmological treatment. For this reason, in the event of any ocular sign compatible with a lens dislocation, it is essential to go to an emergency veterinary center to avoid serious complications.
