Archive for April, 2016

Aging Changes in your Dog’s Eyes

Monday, April 25th, 2016

Have you noticed that your older dog’s eyes look cloudy? Perhaps you think he has developed cataracts. Well chances are that he does not have cataracts at all!  Older dogs commonly have aging changes in the lenses of their eye.

lenticular sclerosis in a dog

Older dog’s eyes can look cloudy but may not be cataracts.

This condition is called lenticular sclerosis, or nuclear sclerosis. We see it in our patients’ eyes every day. The most relevant point for you, as a dog owner is that a dog’s vision is rarely affected by lenticular sclerosis.

picture of a dog's eye with labels

Anatomy of a dog’s eye from

The ocular lens plays an important role in the vision changes of an aging dog’s eyes.  When you look into your dog’s eyes you can see the pupil as a round black hole, surrounded by colored Iris. The lens is suspended within that pupillary circle.  In a normal eye the lens is a clear oval shaped structure that should be invisible to an observer of the eye. The purpose of the lens is to refract (change direction of) light coming through the eye. This provides a more focused image on the retina at the back of the eye.  Light scatters in a functional way as it moves through the lens.

As an animal ages, the outside margins (cortex) of the lens continually produce new fibers.  Therefore the center of the lens (nucleus) becomes denser as the old fibers  move inward to make room for the new fibers. That density is seen by us (and you) as an opaque appearance to the center of the eye where the lens sits.  Sclerosis is a term used in medicine to define a hardening or consolidation of a tissue. It can be used to define changes in bone, and even soft tissues, such as the lens.

In the picture below of a dog with lenticular sclerosis, we dilated his pupil with a drop of medicine. This allows a full view of the round opaque lens in the center of the eye.

nuclear sclerosis

We illuminated Boston’s eye to show his mild lenticular sclerosis.

The way we know that dogs can still see through their sclerosed lenses is to shine our ocular examination instrument light through the lens. If we can see the retina reflection then we know that light it getting to the retina in order to create an image for the dog. So the dog can see just fine through their denser lens.

Cataracts, on the other hand, will often prevent the reflection of the retina when we shine light into the eye. This translates as a dark spot in the animal’s field of vision.

dog cataract

A drawing of a dog’s eye with a cataract. From

Normal eyes are transparent because the lens fibers are organized in an orderly fashion. Cataracts will disrupt that order, leading to a more opaque lens. This opacification can vary in degree and pattern. Anything from very small and linear, to an all-encompassing opacification of the lens.  Some cataracts in dogs are immature, which translates to no full loss of vision for the dog.  An in depth explanation of the formation and causes of cataracts is beyond the scope of this blog, but one of our veterinarians can certainly answer questions you may have about cataracts.

older dogs eye issues

Dr. Swindell consulting with a client about Boston’s eyes.

Because we have a passion for educating our clients about veterinary medicine and pathology at Carlson Animal Hospital, our doctors would be glad to show you any changes we see in your pet’s eyes.  If the changes are visible with the naked eye, it’s a great opportunity for showing you what we see!  If special instruments are needed to identify changes, then we can use diagrams show you what we are seeing.

Please don’t hesitate to ask us! Schedule your appointment today!

Heartworm Disease and Prevention

Thursday, April 14th, 2016

We want you to have easy access to more information about heartworm disease and the advantages of prevention over treatment. In this post we dispel misconceptions about heartworm, write about what you can do to prevent heartworm, and briefly describe the protocol if the disease occurs. Additionally we’ll give you some links to online resources if you would like to research this further.

As always, our primary message is that we are available to talk with you about any questions or concerns you have about your pet’s health and well-being.


Heartworm Disease and Prevention

Heartworm is a very serious disease in pets and can be life threatening. The prevalence of heartworm in the last decade has increased dramatically in the Chicago area, even though it is an extremely preventable disease. The American Heartworm Society provides maps of the incidence of heartworm in the United States – as well as past years for comparison:

penetration of heartworm in the US

Heartworm incidence in the United States (2103)

What is Heartworm?

A common misconception about heartworm is that it is transmitted by fleas, or by ingestion of contaminated feces, or of a worm itself. It is actually transmitted by mosquitoes, and it only takes one bite by an infected mosquito.

heartworm infecting pets

The life cycles of heartworm in pets


The heartworm life cycles consist of an adult female worm living in a host such as a dog, wolf, coyote, or fox. The adult female produces microfilaria that travel through the host’s bloodstream. When a mosquito takes a blood meal from an infected animal, the microfilaria are ingested as well. In the mosquito, they mature into larvae over a period of 10 to 14 days – the mosquito is now considered infective. When the infected mosquito bites a susceptible animal, the larvae enter through the skin and bite wound of the new host.

incubation of heartworm larvae

6 months for the larvae to mature into adult heartworms

It takes approximately 6 months for the larvae to mature into adult heartworms.

The larva migrate through tissue of the infected host until they become a juvenile worm. At this point they enter the host’s blood stream, making their way to the heart (and pulmonary arteries) – hence the name “heartworm.” Once they are in the heart/lungs, they mature into the adult worm. This is why we test our patients for heartworm annually. The most common heartworm screening test identifies the presence of adult heartworms.

How does Heartworm Affect my Pet?

Heartworm infection in the dog can cause damage to the heart, lungs, kidneys, eyes, central nervous system, and the systemic circulation. Affected animals may have no clinical signs initially. In the earlier phases of the disease they may develop a cough, exercise intolerance, or weight loss which may or may not be due to a loss of appetite. In more serious cases, they can go into heart failure, have severe lung disease or have a sudden cardiovascular collapse.

Heartworm disease in the cat can present with mild signs such as a cough, vomiting, decreased energy or weight loss.

Heartworm Testing

For dogs, heartworm disease can be detected by routine blood screening tests, recommended yearly.

how do you test for heartworm

Simple blood test to detect heartworm.

It requires a small blood sample and results return within 24 hours.

The screening test detects adult heartworms, so if there is concern of exposure it is important to test a patient 6-7 months after the exposure occurred. It is also important to test patients prior to beginning a heartworm preventive medication program, unless they are under 6 months of age.


Annual testing is necessary to allow early treatment if heartworm disease is detected as well as to ensure the preventive medication given has been successful.

How quickly can we test for heartworm

Heartworm test results

If a patient is positive for heartworm disease, dogs with microfilaria could possibly have a reaction to the preventive. Our treatment recommendations will account for this possibility.  The earlier heartworm disease is detected and treated, the better it will be for the patient.

Treatment of a heartworm positive patient

Heartworm disease is a successfully treatable disease in most dogs, but there may be secondary life threatening complications.   We determine a treatment plan by the classification of the heartworm disease in the given patient using clinical symptoms and diagnostic testing results. Once the stage is determined a treatment plan is individualized for each patient.

Medcine to treat heartwom

Treatment for heartworm is customized to each infected patient.

The treatment and medical monitoring does take several months before a final resolution is achieved. Since heartworm disease is preventable, prevention is always the desired form of management.

Heartworm is fatal to cats

No safe treatment for cats with heartworm

Unfortunately, there is no safe treatment for heartworm disease in cats.

The indoor/outdoor cat should be tested and placed on preventive medications.

Heartworm Prevention

Routine prevention eliminates circulating larva before it becomes an adult worm and reaches the heart – this can occur in as little as 51 days. This is why keeping a strict preventive regimen is extremely important. This typically requires a simple oral preventive (often a chewable “treat”) our patients can enjoy once every 30 days.

preventing heartworm

Dr. Leslie giving Brynn her monthly heartworm medication.

Many heartworm preventives also have other medications paired with them to control intestinal worms as well.

Each of our patients is assessed and their individual health conditions is taken into account prior to us recommending and instituting a specific heartworm prevention.

Please call us with any questions, or visit the American Heartworm Society for more information: