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Ocular Disorders - Cataracts

What You Should Know About Cataracts: A Report of the Health and Longevity Committee 

By Cathy Sands 

I first became aware of cataracts in dogs in 1989. My vet saw cataracts in a litter of puppies at five weeks of age and referred me to the specialists at Colorado State University (CSU). I missed a day of the 1989 National Specialty Show (in Denver, Colorado) in order to take the litter of five to see two CSU veterinarians Glenn A. Severin, DVM, DACVO, and Steven M. Roberts, DVM, DACVO. 

At that point in time there was no reference to cataracts in Newfoundlands in the CERF (Canine Eye Registry Foundation) data. The doctors were puzzled because some of the puppies had unilateral (one eye only) affected and others had bilateral cataracts. They questioned me about the health of the mother before and while in whelp. The veterinarians requested both parents be brought in for screening. Both parents had normal eyes. 

The final diagnosis was "canine juvenile cataracts;' which means cataracts that occur in a dog less than five years of age. That term is now considered to be obsolete. Cataracts are now identified by the type and the location. 


Of that litter, one puppy was totally blind by 10 weeks of age and was eventually euthanized. The other puppy with bilateral cataracts grew, bur his cataracts did not. Eventually he could see around the cataracts. While he always had a depth perception problem, he did lead a normal lifestyle. The other three puppies-the ones that only had cataracts in one eye-had cataracts that progressed to blinding them in that eye, but they also managed to live normal lives. 


Cataracts are now a known condition in Newfoundland dogs. The data on cataracts in Newfoundlands from the 1999 CERF Manual appears to the right. Cataracts are one of the most common problems affecting the eyes of the dog. There are many different forms and causes of cataract formation. They affect all breeds and ages of dogs. 

cataracts table

What are cataracts? The word cataract literally means, "to break down” This breakdown refers to the disruption of the normal arrangement of the lens fibers or its capsule. This disruption results in the loss of transparency and the resultant reduction in vision. Cataracts often appear to have a white or crushed ice appearance and are found in the lens of the eye. 


What is nuclear sclerosis?
Most people think of cataracts as something seen only in older dogs. The vast majority of older dogs do not have cataracts but have the much more common condition known as nuclear sclerosis. Nuclear sclerosis is a normal change that occurs in the lens of older dogs. Nuclear sclerosis appears as a slight graying of the lens. It usually occurs in both eyes at the same time and occurs in most dogs over six years of age. The loss of transparency occurs because of compression of the linear fibers in the lens. The condition does not significantly affect the vision of the dog, and treatment is not recommended. 


How do cataracts form? Despite the fact that there are several different forms and causes of cataracts, they all develop in a similar fashion. The normal lens is maintained in a dehydrated state. It consists of 66 percent water and 33 percent protein. There is a complicated sodium water pump system in the lens that keeps this water/protein balance in check. When the biomechanical system in the lens is damaged, this pump system begins to fail and extra water moves into the lens. In addition, the percentage of insoluble protein increases. These changes result in the loss of transparency and cataract formation. 

How do we classify cataracts? Cataracts are classified by age at onset, disease, or trauma. 

Age of Animal at onset: The age at which a dog develops cataracts is very important in classifying the type of cataract. The age of onset is particularly important for determining if the cataracts are the result of a hereditary trait in certain breeds of dogs. Inherited cataracts in the dog may occur independently or in association with other ocular disease. If a dog is diagnosed with inherited cataracts, the dog should obviously not be used for breeding because of the likelihood of perpetuating the disease in the offspring. 

• Developmental (Early Onset) Cataracts:
Developmental cataracts are those that develop early on in life. As with congenital cataracts, they may be inherited. They are present at birth; often nuclear; sometimes nuclear and cortical in their location on the lens. These cataracts usually occur in both eyes. Despite the fact that the animal is born with them, they are not necessarily inherited. Infections or toxins may cause the formation of these cataracts while the puppies are still in utero. Primary congenital cataracts, such as those found in Miniature Schnauzers, are inherited. Inherited cataracts at this age are more common in several breeds including Afghan hounds and Standard Poodles. 


• Juvenile Cataracts:
Juvenile cataracts occur in young animals, less than six years of age, but in the Newfoundland these usually occur between 2 to 3 years of age. In many breeds, juvenile cataracts are hereditary. 


• Senile (Late Onset) Cataracts: 
The cataracts that occur in dogs over six years of age are called senile cataracts. They occur much less frequently in dogs than in humans. Nuclear sclerosis, which is not considered to be a medical problem, is often confused with cataracts at this age. 

Disease: The most common metabolic disorder resulting in cataract formation in the dog is diabetes mellitus. If diabetic dogs were followed for a year or more, almost all of them would develop cataracts. In diabetic dogs, the glucose concentration in the lens increases. The extra glucose is converted into sorbitol, which causes an increase in the influx of water to the lens. The water causes a breakdown of the lens fibers and a resulting cataract. 
Cataracts in diabetic dogs can develop extremely rapidly if the dog is not regulated. They generally affect both eyes. Surgical removal of the lens can be successfully performed in the diabetic dog if the animal has been regulated successfully for at least three months. 

Trauma: Trauma from an automobile accident or penetration of a thorn, shotgun pellet or other object may damage the lens and a cataract may develop. These types of cataracts usually only occur in one eye and can be treated successfully with surgical removal. 

Maturation and location of cataracts: 

The stage of maturation 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. 

cataracts

 

• Incipient: Very small opacity. Less than 15 percent 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-The reflection from the tapetum lumidum, the iridescent pigment epithelium of the choroid of animals, which gives their eyes the property of shining in the dark.) 
• 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. Fractured 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 primarily in the 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. Its size can be described in how many clock hours it spans. 
Anterior/Posterior: Used to describe opacities of the capsular, subcapsular, polar/axial, and cortical areas of the lens. 


What Causes Cataracts - 

Heritability/Genetics: This is one of the most common causes of cataracts in dogs. Board Certified ophthalmologists perform CERF exams (Canine Eye Registration Foundation) to detect eye conditions, such as cataracts. 
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 causes cataract formation in dogs and horses. 
Secondary to retinal disease: Progressive (PRA) is common in Poodles, Labradors, and 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 develops a cataract.
Trauma: Perforating injury to the cornea and lens frequently induces cataract formation. Rarely does blunt trauma cause cataracts to form 
Nutritional: Canine and feline milk replacers (arginine and tryptophan deficiency). 
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.


A Reminder: 
It is recommended that all dogs over 12 months of age have CERF evaluations. This will provide a clearer picture of the incidence of cataracts and other eye problems in our breed. 

 

Reprinted from NewfTide 2007

 
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