In a significant number of cases, the exact cause of uveitis cannot be determined. In some instances, uveitis (also known as iridocyclitis or iritis) occurs because of a systemic neurological condition, such as rheumatoid arthritis, ankylosing spondylitis, tuberculosis or collagen vascular diseases like lupus.
Concussion injuries to the brain are one cause of such differences, for instance. In other circumstances, a difference in pupil size might be an indicator of certain ocular conditions, neurological disease or a sign of brain injury in the case of head trauma. This is called essential anisocoria, and is not a matter for concern at all, just something to be noted for future reference if necessary, particularly if they are different by more than two millimeters or so. It is not uncommon for people to have small observable differences in pupil size from birth this would be like having one foot slightly larger than the other. Pupil dilating drops, used routinely to give eyecare practitioners a better look into the back of the eye, may cause the pupils to dilate to eight millimeters or more, which is why you need to use dark sunglasses afterwards.Īn eyecare practitioner will usually check the size and shape of the pupils during the early part of a comprehensive vision examination, using either a penlight (see figure 1) in normal room illumination, or with an instrument called a direct ophthalmoscope in a darkened room. In bright daylight outdoors, the pupils should contract to two millimeters or less, while they may dilate in a dim-lit restaurant to six or seven millimeters. Normal pupil size in everyday room illumination is about three to five millimeters in diameter. The iris muscles control the size of the pupil, making it larger in dim light and smaller when the light is bright. The pupil is not actually a structure, but is simply a little window in the center of the colored part of the eye, the iris. The pupil also contracts when the eye changes focus from far away to close up. Anisocoria is the medical term that simply means the pupils are not equal. Christian K.Normally, the pupils of the eyes are equal in size, are both round in shape and both react quickly and equally to light and any change of focus. Several conditions can cause this, such as blood clotting problems, infections, high blood pressure or a mass around the area of the optic nerve, explains Dr. When I no longer constrict in response to light this is often a sign that the dog's eyes are no longer capable of recognizing light on the back of the eye causing blindness. Sometimes, I may also appear dilated in both eyes. "If anisocoria occurs suddenly, you should consider this an emergency situation and seek veterinary care immediately to lessen the chance that your dog's vision will be permanently affected."~ Dr. Cheryl Yuill, VCA Animal Hospital
Is it the dilated one or the constricted one? Also, a very important important piece of information needed is uncovering which pupil is the abnormal one. Just consider that there are many conditions that may cause anisocoria in dogs such as an eye injury, inflammation somewhere within the eye, Horner's syndrome, glaucoma, uveitis, exposure to toxins, head concussions and even cancer. These two muscle basically work in opposition. My size is therefore controlled by two groups of smooth muscles of the dog's iris: the iris sphincter muscle and the iris dilator muscle. When it's bright instead, the iris muscle expands so to constrict me so to allow less light into the dog's eye. When it's dark, the iris muscle contracts so to enlarge me so to allow more light into the dog's eye so he can see. The iris (the colored part of the eye) acts as a camera's shutter and basically regulates how much light should enter and reach me. The amount of light that reaches me therefore elicits the iris to change my size. When it comes to me though, you can think of me as an adjustable opening. I am an Adjustable Openingįor sake of comparison, you can compare your dog's eyes to a camera that takes pictures of the world and sends those images to your dog's brain through the optic nerve. For instance, in goats and horses, I am oval, in cats I am a thin vertical slit, but in dogs and humans I tend to be round. I can be of different shapes and sizes based on the species you are looking at.
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