Cataracts
How does a cataract form?
Mechanisms of lens metabolism become damaged resulting in altered hydration and subsequent osmotic effects. Insoluble proteins increase while the soluble proteins decrease. Electrolyte, lipid, and glucose metabolic pathways are affected. Increased hydration results information of vacuoles and water cleft. Lens fibers undergo oxidative damage, which results in retention of sodium and calcium. The lens eventually opcaifies.
How do we classify cataracts?
Several methods are used to classify cataracts:
Age of Animal at onset
Congenital: present at birth; often nuclear; sometimes nuclear and cortical.
Consider removal if cortex is involved.
Some breeds that can inherit cataracts:
Afghan hound, Cocker spaniel, Boston terrier, Chesapeake Bay Retriever, German Shepherd, Golden Retriever, Labrador Retriever, Miniature Schnauzer, Old English Sheepdog, Standard Poodle, West Highland White Terrier
Cataracts can also result from exposure to a toxin or infectious agent in utero
Juvenile: occurs in young animals, less than 6 years of age, usually occurs at 2 to 3 years of age. In many breeds, juvenile cataracts are hereditary.
Senile: develops at 6 years of age and older.
Stage of maturation:
This refers to the appearance of the lens regardless of the age of the animal, or the underlying problem causing the cataract. Not all cataracts progress through each stage of maturation.
Incipient: very small opacity. Less than 15% of the lens is opaque
Immature: more of the lens involved than in an incipient cataract.
The tapetal reflection is still visible.
Definition of tapetal reflection
Mature: there is solid opacity of the lens, and the tapetal reflection is absent. The animal is functionally blind.
Intumescent: the lens has imbibed water and appears swollen. This is common in dogs with diabetes mellitus. Intumescence occurs with immature and mature cataracts.
Hypermature: liquefaction of the lens cortex begins, and the cortex clears. Fractures lens fibers appear opalescent (like snow flakes, sparkles) and the anterior lens capsule appears wrinkled.
Morganian: liquefaction of the cortex with an intact nucleus. The nucleus may drop or sink ventrally to the bottom of the capsular bag when the cortex liquefies.
Location within the Lens:
Capsular: opacity confined to the lens capsule
Subcapsular: most of the opacity involved cortex directly beneath the lens capsule
Cortical: opacity of the lens cortex (may be anterior or posterior cortical)
Nuclear: opacity primarily in the center of the lens (nucleus). This type is frequently congenital and nonprogressive.
Equatorial: opacity is promarily nt he area of the lens equator
Polar/axial: within the pupillary axis. Usually a focal, central opacity
Clock hour: the location of a lens opacity may be described by referring to its position relative to the face of a clock
Anterior/Posterior: used to descibe opactities of the capsular, subcapsular, polar/axial, and cortical areas of the lens.
What Causes Cataracts?
Heritability / Genetics: one of the most common causes of cataracts in dogs. Ophthalmologists perform CERF exams (Canine Eye Registration Foundation) to detect cataracts suspected or proven to be of heritable cause.
Metabolic:
Diabetes mellitus is the most common cause of metabolic cataracts. It is related to abnormal metabolism of glucose by the lens. These cataracts are always bilateral, and form rapidly.
Hypocalemia resulting from renal failure or hypoparathyroidism can cause cataracts in dogs. These tend to be multifocal and bilaterally symmetric.
Secondary to Uveitis: chronic iridiocyclitis can induce cataract formation by altering lens nutrition or microenvironment
Senile: old age frequently caused cataract formation in dogs and horses
Secondary to retinal disease: progressive (PRA) is common in Poodles , Labs, Irish Setters. Check history for evidence of blindness or poor dim light vision before cataracts developed.
Lens Luxation: the luxated lens is no longer located in its nutritional microenvironment and frequently developers a cataract.
Trauma: perforating injury to the cornea and lens frequently induces cataract formationn. Rarely does blunt trauma cause cataracts to form
Nutritional: canine and feline milk replacers (arginine and tryptophan deficinecy)
Electric shock: anterior subcapsular (puppy that bites an electric cord)
Radiation: causes decreased epithelial cell mitosis (young animals are more susceptible)
Toxins: disophenol for hookworms
Treatment:
The only treatment for cataracts is surgery.
Cataract surgery is almost always an elective surgical procedure
Other health problems should be addressed before cataract surgery is considered
A complete ophthalmic examination should always be performed
When will my dog need surgery?
Signs of vision loss are usually not detected by the owner until the cataract occupies 40-50% of the lens. Oftentimes, this needs to occur in both eyes for the dog’s vision to be negatively affected.
What can happen if my dog doesn’t have surgery?
When surgery is not performed, cataracts will most likely progress, and eventually may leak lens proteins and therefore cause lens-induced uveitis. Complications of uveitis include glaucoma and phthisis bulbi. Retinal detachment, subluxation, and luxation have also been observed.
Surgical techniques for lens extraction:
Extracapsular Extraction:
traditional method still performed today if phacoemulsification is not possible
removal of central anterior capsule, nucleus, and cortical material
posterior capsule is left intact to stabilize vitreous and facilitate placement of intraocular lens implant (IOL)
frees the lens protein, contributing to post-operative uveitis
Phacofragmentation / Phacoemulsification:
ultrasound is used to fragment the cataract, which is then aspirated from the eye through a 3mm incision
advantages include a small incision, reduced uveitis due to completeness of lens removal, reduced surgical time, ideal for IOL implantation
success rate is about 94%
both eyes can be operated on at the time of surgery
Intracapsular extraction:
usually only used when there is lens instability
the entire lens with intact capsule is removed
complications: predisposes to vitreous loss because of the attachment of the posterior lens capsule to the anterior vitreous face; retinal detachment is more likely.
What about Laser cataract surgery ?
There is NO SUCH THING.
Cataracts cannot be removed with lasers.
What about Medical Treatment of cataracts ?
There is NO SUCH THING.
Many drugs have been administered, but none are effective.
Treatment of cataracts requires SURGERY.
What are some complications of cataract surgery ?
Anterior uveitits
Ocular hypertension / glaucoma
Ruptures posterior capsule / vitreous herniation
Hyphema / fibrin in the anterior chamber
Shallow anterior chamber / wound dehiscence
Infection
Retinal detachment