Why Ear Disease Can Affect The Eye

By | June 30, 2010

Jane Lilley raises the spectre of Horner’s syndrome and describes a number of dogs with drooping eyes, some of which had suspected ear infections as a root cause, but others had no apparent cause at all. Horner’s syndrome is of curse a human medical term and how our doctors love to confuse their subject by naming diseases asy syndromes So what is Horner’s syndrome and how can diseases of the eat cause these symptoms in the eye?

Spaghetti Junction: Those knowledgeable in anatomy will know that many of the major nerves to the head emerge from the skull just around the inner ear and some of these supply the eye and surrounding structures. In fact the area behind the lower jaw, just below the ear, is probably the anatomical equivalent of spaghetti junction, only far more important and far more of a problem if anything goes wrong. In this small area of the body there are a myriad of nerves and ganglia, major arteries supplying the head and brain, major veins draining blood from the head, a salivary gland and towards the inner portion of this area there is the throat. It is not surprising therefore to find tht any inflammation in this area can cause problems and in particular can affect the eye. Now, as inflamed ears are fairly common in dogs all the structures in this area are vulnerable. So, especially where the inflammation and infection is severe enough to extend out of the ear canal into the surrounding soft tissue or even into the middle ear, there is a high probability that nerves will become involved. This is where Horner’s syndrome comes from, being caused by damage to the delicate nerve fibres supplying the eye. The nerves become involved through pressure or inflammation and are rendered useless for a time. But we still have not yet defined Hormer’s syndrome: It is the drooping of the upper eye lid, with slight drooping lower lid and a constricted pupil. In adddition the third eyelid is often drawn across part of the eye and the eye seems to sink back into the socket. The eye looks a little like a gunslinger in a classic western with narrowed eyelids and a tight pupil. For the owner this is a dramatic conditin because Horner’s syndrome tends to be one-sided so the good eye makes the afflicted eye look quite peculiar. So now it is clear, a nasty ear infection can involve the nerves that pass close to the eye and thus interfere with their function. Logical and believable but it is not the whole story. For Horner’s syndrome can occur without ear infection. It can also happen due to damage to the neck or even the spine in the first part of the chest. This is really the clue to the basis of the syndrome, for this is not a problem associated with the classic nervous system we all know about. The nerves we all understand are those that power the striped muscle fibres of the body, like the muscles that move limbs, help us breath and make hearts beat. There is a part of the nervous system we all tend to ignore: the so-called autonomic system that powers smooth muscle fibres such as those involved in blood vessels, lungs and the iris of the eye. A large proportion of these autonomic nerves lie outside the spine running up and down the body parallel to it. They power those muscle fibres over we have no direct control (thus the name autonomic). These muscles operate in relation to other stimuli. For example, they control blood flow to tissues, or the waves of contraction in the bowel that aid in digestion, or the dilation of the pupil in the eye depending on the amount of light available. You have no control over these muscles, they are controlled by other factors such as homones. It is smooth muscle fibres that keep the third eyelid retracted and probably also assist in keeping the eyelids in place when awake. Thus it is not surprising that damage to the autonomic system can cause the signs described as Horner’s syndrone. As the ganglia around the base of the ear are part of the autonomic system it is not surprising that ear infection can disrupt their function. Equally, autonomic nerves running along the neck or even in the front part of the thoracis spine are also prone to damage from a variety of sources. Choke chains, tumbles in the park or bites and stings are all capable of causing this syndrome.

Spinal injuries: It is amazing how far the autonomic nerves spread their influence and how im- portant they are to normal everyday functions that we are largely unconscious of. Horner’s syndrome is one obvious manifestation of what can happen when damage occurs. The basis of Horner’s syndrome can be varied. It is true that ear infection is a common cause. But tumours or spinal injuries are also capable of causing the syndrome too. All of the dogs Jane Lilley described got better in time and thankfully this is a usual result, but more permanent damage caused by injury or tumours can produce a more long lived or permanent set of symptoms. So, while Horner’s syndrome can turn out to be quite an involved diagnosis and definitely frightening for the owner, the eventual result is usually a good one but not always. This simple terminology describes the clinical effects of a whole range of root causes that may be quite removed from the eye, which is the site (sorry, bad pun) of the syndrome. Because of this, any treatment may be directed at an entirely different location, a long way from the eye. So if your vet x-rays your dog’s neck when it has a funny looking eye, maybe you will not think he or she is going crazy.

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