Cataracts

OVERVIEW: 

 

As is the case with humans, Cataracts are some of the most common visual problems found in domestic dogs.  Mammal eyes, including those of dogs, have a clear lens which allows light through much like the lens of a camera.  A cataract is any lack of clearness in the lens, more commonly called opacity.  Because cataracts can block light from passing through the lens, they can have a substantial impact on a dog’s vision.  The impact of a cataract is determined by its size and the degree to which it is opaque.  Very small cataracts usually have no impact on a dog’s vision whatsoever, and will not necessarily grow until they become a problem.  Although not necessarily the case, many cataracts will grow and become more opaque over time.  Moderately sized cataracts often cause blurry vision.  If a cataract is allowed to develop until it is very large and opaque, it can cause total blindness.   Cataracts should not be confused with nuclear sclerosis, the natural hardening of the lens as dog ages, although many dogs do develop both conditions at the same time.  There are many different types of cataracts, each of which has slightly different characteristics.  Veterinarians commonly classify cataracts based on three criteria, development, cause, and age of onset.

 

On a basic level, veterinarians classify cataracts by how advanced they are.  Incipient cataracts are very small and unlikely to interfere with vision.  Immature cataracts are substantial enough to cause blurry vision but neither covers the entire lens nor cause total vision loss.  Mature cataracts have advanced to the point where the entire lens is opaque and the dog is either functionally or entirely blind.  Hypermature cataracts form when the lens of a dog with a mature cataract begins to deteriorate.  Hypermature cataracts are actually smaller than mature cataracts because of the loss of water and proteins from the lens (think of a raisin becoming a grape or a plum becoming a prune).  Sometimes, as the lens deteriorates clear spots open up within the cataract allowing for partial vision restoration, but most hypermature cataracts remain completely opaque.

 

Cataracts are also commonly categorized by their cause.  There are two major classifications of cataract causes and several subgroups within them.  Primary cataracts, also known as hereditary or genetic cataracts, are caused by a dog’s genetic inheritance.  Although they can develop at any time in a dog’s life, primary cataracts are in a dog’s genetic code from birth and can be passed down to its offspring.  A large majority of cataract cases are primary.  There are many different types of polygenic cataracts, and many different breeds are affected.  The exact methods by which cataracts are inherited are unclear in most breeds and may be polygenic, meaning that multiple genes are responsible.  The inheritance methods for some types of cataracts have been discovered for some breeds, but there are still many years of research to go in this field.

 

Secondary cataracts are cataracts caused by some event that happens during a puppy’s gestation or during the dog’s life.  There are numerous causes of secondary cataracts.  The most common cause of secondary cataracts is diabetes mellitus.  More than 75% of dogs with diabetes mellitus develop cataracts within the first year of having the disease.  Diabetic cataracts, as they are sometimes referred, are some of the fastest appearing and developing cataracts and are considered a veterinary emergency.  The second most common cause of secondary cataracts is toxicity of the lens.  The lens may become toxic as a result of a number of infections and conditions and, much more rarely, certain medications.  One of the most common cataract causing conditions is glaucoma, defined as the increase of pressure within the eye.  Commonly referred to as toxic cataracts, these cataracts vary wildly in all aspects from case to case.  Less commonly, cataracts can be caused by trauma suffered as a result of accident or injury.  Most trauma-based cataracts are the result of a lens rupture.  These cataracts can be especially problematic because in many cases it is unclear that the lens has ruptured until cataracts develop, especially in the case of head injuries that do not directly involve the eye.  Much like toxic cataracts, trauma-based cataracts vary wildly depending on the underlying injury.  Cataracts may also be caused by nutritional deficiencies.  Nutritional deficiency cataracts are actually most commonly seen in puppies that were either malnourished in the womb or shortly after birth, but can develop anytime throughout a dog’s life during which it is malnourished.  Many dogs develop secondary cataracts as a part of the aging process, usually after the age of eight.  Such cataracts are usually small and only infrequently interfere with vision.  The previous five causes are responsible for the vast majority of secondary cataracts, but a small minority is caused by rarer factors.  Some of the other potential causes of cataracts in dogs include birth defects and prolonged exposure to radiation such as occurs in many cancer treatments.

 

Cataracts are also classified by the age of the dog upon their onset.  Congenital cataracts are present at birth and first appear when the puppy opens its eyes for the first time.  Congenital cataracts are almost always present in both eyes although there are exceptions.  A sizable majority of congenital cataracts are caused by genetic inheritance, but many are also the result of infections, toxins, and/or malnutrition present in the womb.  Developmental cataracts, also known as early onset cataracts, develop early in a dog’s life, usually between the ages of 2 weeks old and 2 years old.  Like congenital cataracts, the majority of developmental cataracts are primary cataracts, but many cases are secondary cataracts.  Senile cataracts, also known as late onset cataracts, develop in older dogs, usually those which are at least 6 years old.  Senile cataracts are frequently mistaken for nuclear sclerosis, especially by lay people.  Although many secondary cataracts are caused by genetics, these cataracts are significantly more likely to be secondary in nature than congenital or developmental cataracts.

 

Because cataracts are classified in multiple ways, a single case is likely to be defined in several ways.  For example, a single cataract could be an immature, primary, developmental cataract, a hypermature, secondary, senile cataract, or any number of other combinations.

 

Regardless of form or cause, most cataracts develop in a similar manner.  The lens of the eye has a natural composition of about 2/3 water and 1/3 protein.  A complicated maintenance system using sodium water pumps maintains this balance.  If this system malfunctions or is damaged, either too much or too little water goes into the mix, resulting in too little or too much protein respectively.  This results in opaqueness and cataracts.

 

RISK FACTORS: 

 

  • Age – Dogs of any age may develop cataracts, but the condition is most frequently seen in two groups, young dogs under the age of 2 years and older dogs over the age of 6 years.
  • Diabetes Mellitus – Dogs with diabetes mellitus are very likely to develop cataracts.  More than 75% of dogs with diabetes mellitus will have developed cataracts within 1 year of developing the condition.
  • Nutrition – Dogs which have been malnourished, both in the womb and any time after birth, are more likely to develop cataracts.
  • Genetics – Dogs whose close relatives have had cataracts are much more likely to develop them than other dogs.
  • Breed – There are many different breeds that are highly susceptible to developing different types of cataracts, and many breeds are highly susceptible to multiple types of cataracts.  Breeders, breed clubs, and veterinarians are the best source of information for the prevalence of cataracts, and of which type, a particular breed or line is most susceptible to.  Among the breeds most susceptible to primary cataracts include the Afghan Hound, American Cocker Spaniel, Boston Terrier, Chesapeake Bay Retriever, German Shepherd, Golden Retriever, Labrador Retriever, Miniature Schnauzer, Old English Sheepdog, Siberian Husky, Staffordshire Bull Terrier, Standard Poodle, Welsh Springer Spaniel, and West Highland White Terrier.  Among the breeds most likely to develop secondary cataracts as a result of other medical problems common in the breed include the Akita, Beagle, and Cavalier King Charles Spaniel.
SIGNS & SYMPTOMS: 

 

There are two major signs that a dog is suffering from cataracts, physical changes to the eye and behavioral indications that the dog is having difficulty seeing.  Eyes afflicted by cataracts go through two primary changes, they become cloudy and their color can change.  In cases of incipient cataracts, only a small spot or spots on the eye appear cloudy or differently colored while the rest of the eye appears normal.  In cases of immature cataracts, the changes have taken place over a large part of the eye, but not the entire structure.  In cases of mature and hypermature cataracts, the eye is usually completely cloudy and/or differently colored.  Although each case is slightly different and the color will vary according to the light and angle which the eye is viewed from, the color change is usually to a light blue, grey, or green.

 

Dogs with cataracts in the early stages often display no behavioral indications at all, because their vision is often not impacted at all.  As the cataract advances, the dog’s vision increasingly worsens, as do the behavioral changes.  Dogs suffering from vision loss may bump into things on a regular basis.  Many seem to not notice what they usually would, for example a squirrel running in the grass.  It is very common for dogs with poor vision to become hyper reactive to sound or touch.  Many begin to bark excessively, often out of nervousness or fear.  Most dogs with vision become increasingly surprised by mundane events such as being petted or approached by a stranger, because they cannot see it coming.  These reactions may turn into fear and even aggression.

 

DIAGNOSIS & TESTS: 

 

Cataracts are a relatively easy condition to diagnose.  All that is usually necessary is a basic veterinary eye exam using an ophthalmoscope.  Cataracts are especially easy to diagnose in young dogs because there are fewer alternatives.  In older dogs, nuclear sclerosis is often mistaken for cataracts, even by veterinarians.  Because many veterinarians do not have the equipment and expertise necessary to distinguish between cataracts and nuclear sclerosis (especially if the cataracts are incipient cataracts) many veterinarians will refer their patients to a veterinary ophthalmology specialist for a more precise diagnosis.

 

Once a dog has been diagnosed with cataracts, the type of cataract and its cause must be identified.  The dogs age will determine whether the cataract is congenital, developmental, or senile.  The developmental stage of the cataract will be determined by its size and the amount of vision loss experienced by the dog.  The cause of the cataract is often much more challenging to ascertain.  Veterinarians will usually perform a number of tests to determine whether the dog is suffering from an underlying condition or has experienced an unknown trauma.  The exact tests and diagnostic procedures necessary will be determined by which condition is suspected.  For example, many diseases require that blood, urine, and stool samples be collected and tested, while many others require x-rays, physical examinations, and other tests.  It is very important for the advancement and cause of the cataract to be determined because treatment options are heavily dependent on them.  Determining cause is also extremely important because many of the underlying conditions which cause cataracts, such as diabetes mellitus, are considerably more serious than the cataracts themselves, and some can even be fatal.

 

CONVENTIONAL TREATMENT & MANAGEMENT: 

 

The treatment and management options available for cataracts vary from case to case, and are highly influenced by a number of factors.  Unfortunately, there once a cataract has formed, there is no known way to eliminate it without surgery.  The only exceptions to this are cataracts caused by malnutrition, which sometimes improve naturally once proper nutrition is provided, and hypermature cataracts, which sometimes develop clear sports which allow vision.  Most cataracts are not so serious that they require surgery, and surgery is definitely not the first and/or best option in many cases.  In cases of secondary cataracts, the first step is usually to resolve the underlying condition or to get it under control.  This is necessary because if the cause is not resolved, new cataracts are likely to develop, even if previous ones were removed surgically.  In cases of incipient cataracts or early stage immature cataracts, veterinarians will often attempt to slow the cataract’s development in an effort to postpone surgery or make it unnecessary.  There are a number of promising products which have shown some ability to slow the development of cataracts for months or even years.  Most of these products contain nutritional supplements designed to strengthen the eye and/or antioxidants.

 

In order to determine whether to perform a cataract removal surgery, veterinarians have to carefully weigh a number of factors.  The age of the dog is taken into consideration, with some dogs being too old and others being too young.  The extent of vision loss experienced by the dog is taken into consideration, as are the behavioral changes associated with that vision loss.  Whether or not the cataract is advancing is taken into consideration, with those that are progressing the most and the most rapidly being to most likely to be removed.  Other factors which must be considered include other health conditions, the dog’s temperament, financial cost, and likelihood of success.  Veterinarians and owners must always be aware that cataract removal surgery is a quality of life surgery rather than a life saving surgery.

 

If it is decided that surgery is the best or only treatment option available, the dog must undergo the procedure.  Because many veterinarians lack the proper equipment or expertise to conduct cataract removal surgery, many clients are referred to veterinary ophthalmologists or large veterinary hospitals.  Although cataracts are incredibly variable, surgeries to remove them are not.  The dog must be placed under general anesthetic because even the slightest movement can have disastrous results.  A small incision is made in the eye.  The surgeon then enters the capsular bag, the part of the eye that holds the lens.  The next step is photoemulsification, whereby the cloudy lens is emulsified and removed by ultrasonic pulses emitted by a special probe inserted into the capsular bag.  An artificial lens is then placed in the eye to replace the removed, cloudy lens.  This replacement lens is known as an intraocular lens or IOL.  There are many types of intraocular lens available, and the exact type selected will depend on the veterinarian’s personal preference as well as the unique features of a particular case.  When both eyes are impacted by cataracts, cataract removal surgery is usually performed on both eyes at the same time.  When this is not possible, a second surgery may be necessary to remove cataracts from the second eye. 

 

POTENTIAL COMPLICATIONS: 

 

The complications from cataracts themselves are fairly basic.  The most common effects are vision loss, which can sometimes be so severe as to result in total blindness.  Dogs with vision loss are more susceptible to a variety of accidental injury as a result of not being able to see properly.  The next most common complication from cataracts is known as cataract-associated inflammation.  Within a cataract, some of the lens protein becomes liquefied.  In some cases, this liquefied protein leaks into other parts of the eye.  Although this leakage can occur in any eye affected by cataracts, it is easily the most common in hypermature cataracts, especially those which have developed clear sports.  Protein leakage causes uveitis, also known as intraocular inflammation.  When caused by cataracts, the condition is known as cataract-associated inflammation, cataract-associated intraocular inflammation, or lens-induced uveitis.  Cataract-associated inflammation can cause a dog to experience discomfort or pain, and in some cases may even lead to glaucoma, retinal detachment, or intraocular adhesions.

 

The various treatments necessary for cataracts may also have side effects.  There may be a variety of side effects from any of the medications and supplements prescribed to prevent the spread of cataracts, some of which are potentially serious.  There are also a number of risks associated with cataract surgery.  Some dogs are allergic to anesthesia and may experience difficulty breathing, heart problems, anabolic shock, and even death when put under.  There is always a risk of excessive blood loss during surgery, especially if the dog has an undiagnosed blood disorder such as Von Willebrand’s disease.  There are many risks inherently associated with cataract surgery specifically as well.  The eye is an incredibly delicate structure, and even the most careful and experienced surgeon may cause damage to it while performing cataract surgery.  Even more challenging is proper recovery.  Any scarring within the eye may result in vision loss.  Although veterinary ophthalmology surgeons take every precaution to prevent scarring, it is not entirely preventable in all cases.

 

HOLISTIC REMEDIES: 

 

As of yet, no holistic remedies have been discovered that can help cure cataracts.  There is no herb, supplement, or treatment currently available which can remove or shrink a cataract once it has developed.  The exception to this is certain cases of cataracts caused by malnutrition, which can sometimes be improved with vitamins and nutrients.  In the vast majority of cases, holistic treatments are limited to the prevention of the cataract advancing.  There are a number of different holistic remedies that are thought to aid in this goal, many of which may help delay surgery for a substantial period of time and hopefully put it off permanently.  Because many holistic remedies may interact with those prescribed by conventional medication (often negatively) it is highly advisable to consult with a veterinarian before using any.

 

Vitamins A, C, and E and the mineral zincZinc is an essential mineral believed to possess antioxidant properties, which may protect against accelerated aging of the skin and muscles of the body; studies differ as to its effectiveness. In pet foods is considered important in helping to support healthy skin, hair and mucous membranes. Zinc also helps speed up the healing process after an injury. It has antioxidant properties and is also beneficial to the body's immune system. Zinc also helps stimulate the action of more than 100 enzymes, and helps to stimulate the sense of smell, synthesize DNA and RNA, and promotes normal growth and development. all influence vision to some degree, and all are prescribed by holistic veterinarians to fight cataracts.  These treatments may either be consumed in individual supplements or in supplements which combine some or all of them.  The antioxidant Coenzyme Q10 is another commonly recommended, especially for older dogs.  Two of the most commonly recommended herbal treatments for cataracts are Bilberry (Vaccinium myrtalis) and Milk Thistle (Silybum sp), both of which are thought to have substantial impacts on vision and improving the health of the eyes.

 

PREVENTION & HELPFUL TIPS: 

 

When it comes to cataract prevention, a distinction must be made between preventing cataracts from developing and preventing cataracts from worsening once they have developed.  Primary cataracts are inherently caused by genetics and are inherent in a puppy from the time it is conceived.  For this reason they are essentially impossible to prevent.  On the other hand, many cases of secondary cataracts are preventable, although many are not.  The best way to prevent secondary cataracts from developing is to take steps to prevent their underlying causes.  For example, dogs should always be provided with proper nutrition, especially pregnant mothers.  If a puppy is abandoned by its mother and must be bottle fed, special nutritional supplements should be provided.  Owners can also help prevent secondary cataracts from developing by being vigilant and making sure that any illnesses or medical conditions are diagnosed and treated as quickly as possible.  It is also ideal if owners take steps to prevent their dogs from injuring themselves in the first place.

 

Most cataract prevention will lay in improved breeding methods.  Because most cases of cataracts are inherited genetically, any dog that has developed cataracts either from an unknown cause or a known genetic cause should not be bred.  The same goes for the parents, siblings, or offspring of any dog matching that description.  Such precautions are not necessarily required in cases of secondary cataracts, depending on the underlying cause.  The Canine Eye Registration Foundation (CERF) keeps records of dogs which have been diagnosed with visual problems, as well as providing other resources to breeders, owners, and fanciers.

 

Nuclear sclerosis is very frequently mistaken for cataracts, especially in older dogs.  Nuclear sclerosis is a natural part of the canine aging process that is seen in virtually all dogs eventually.  This does not mean that owners should be any less vigilant and should still take their dogs to the veterinarian if their eyes are changing color or becoming cloudy.

 

 

Cataracts are an opacity in the lens of the eye. Most cataracts in dogs are caused by a genetic predisposition, but diabetes mellitus is also a common cause. The only effective treatment is surgical removal.