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Diseases of the Lens
The lens is the fine focusing mechanism of the eye. Changes in the shape of the lens allows one to change the plane of focus from near to far away objects. The lens is a highly transparent and complex structure. Changes or damage to the lens may not only result in loss of vision, but in potentially painful conditions.
The most common problems of the lens include:
What is a cataract?
By definition, cataracts are opacities of the lens. The lens is a highly transparent and complex structure. Disruptions of this fragile system will result in loss of transparency and decrease in vision.
What causes a cataract?
The most common cause cataracts in the dog are genetic. Most breeds and, even mixed breeds, have been found to have of genetic cataracts. The breeds with the highest incidence of cataracts include Boston Terriers, Miniature Poodles, American Cocker Spaniels, Standard Poodles, and Miniature Schnauzers. The average age of onset for genetic cataracts is 4-7 years. However, dogs as young as 6 months have developed genetic cataracts and the younger the age of onset of a genetic cataract, the more rapidly the cataract progresses.
Diabetes is the second most common cause of cataracts in the dog. 80% of diabetic dogs develop cataracts within 6 months of diagnosis. Diabetic cataracts are very aggressive, progress quite rapidly, and can result in sudden vision loss.
Other causes of cataracts include intraocular inflammation, certain retinal diseases, and trauma.
What is the treatment for a cataract?
The treatment for cataracts in dogs is the same as in people, the surgical removal of the lens in a process known as phacoemulsification. This advanced procedure allows for the complete removal of the lens and placement of an artificial lens that will result in the return of normal vision. Success for phacoemulsification in dogs is 90-95%. Success is defined as a visual and comfortable eye.
What may happen if I do not treat the cataract?
Unfortunately, cataracts are not an entirely benign disease. Failure to remove cataracts may not only result in the progressive loss of vision, but if a cataract becomes very advanced, termed a hypermature cataract, it can result in potentially painful complications such as intraocular inflammation, glaucoma, and lens luxation.
What is a lens luxation?
A lens luxation is instability of the lens. The lens is suspended behind the pupil with small fibers termed zonules. Breakdown of these zonules result in instability and possible movement of the lens within the eye. The types of luxations include:
- subluxation - partial but not complete breakdown of the zonules resulting in a lens still in it's proper location but loose.
- posterior luxation - complete breakdown of the zonules with the lens located behind the iris.
- anterior luxation - complete breakdown of the zonules with movement of the lens in front of the iris. This is considered an emergency.
What causes a lens luxation?
The most common cause cataracts in the dog are genetic. Many breeds and, even mixed breeds, have been found to have of genetic lens luxation. The breeds with the highest incidence of cataracts include Terriers and mixed Terriers, Miniature Poodles, American Cocker Spaniels, Border Collies, Shar Pei, German Shephards, and Blue Heelers. The average age of onset for genetic cataracts is 3-6 years.
Other causes of lens luxation include intraocular inflammation, advanced cataracts, senile changes, glaucoma, and trauma.
Why are lens luxations important?
Unfortunately, lens luxation has highly associated with the development of glaucoma, a painful and blinding condition of the eye. Anterior lens luxations are the most urgent leading to glaucoma in 73% of dog eyes, thus considered an emergency. However, even posterior luxations and subluxations can lead to glaucoma.
What is the treatment for a lens luxation?
The treatment for lens luxation varies with the type of luxation. Anterior lens luxations cause significant disruption of the fluid within the eye resulting in significant increases in intraocular pressure, a very painful and potentially blinding condition. The only way to relieve the situation is to surgically remove the lens through a large corneal incision. An anterior lens luxation is considered an emergency and should be treated immediately.
Posterior luxated and subluxated lenses can be treated more conservatively with topical medications to constrict the pupil and decrease the intraocular inflammation. However, these eyes must still be monitored closely for the development of glaucoma.
Even if the lens is completely removed, the eye still had the potential for vision, just not optimal vision. Eyes without lenses are very farsighted. For this reason, an artificial lens can be placed in certain circumstances if a luxated lens needs to be removed.
What is a lens laceration?
A lens laceration is the disruption of the transparent membrane that surrounds the lens, termed the lens capsule. Lens lacerations are always associated of a traumatic puncture of the eye.
What causes a lens laceration?
Lens lacerations are always a result of a penetrating trauma of the eye, usually coupled with a corneal laceration or puncture. Cat scratches to the eye are the most common presentations.
Why are lens lacerations important?
If the disruption of the lens capsule is large enough, it will result in a massive inflammatory reaction within the eye that leads to painful, non-visual globe. This reaction takes time to develop and may not become apparent until 2 weeks after the initial traumatic incident.
What is the treatment for a lens laceration?
The treatment for a lens laceration is the surgical removal of the lens in a process known as phacoemulsification. This advanced procedure allows for the complete removal of the lens and, if the lens capsule is sufficiently intact, placement of an artificial lens that will result in the return of normal vision. A lens laceration is considered an emergency and should be addressed immediately.
