In some breeds, such as the Siberian Husky, both irides can be blue ( Figure 10.1). In many breeds, a unilateral completely blue iris is acceptable for that breed standard in other breeds a unilateral blue iris is rejected for registration. Heterochromia iridis indicates multiple colors within one iris or between the irides. The anatomic divisions are also useful clinically, as often the anterior and posterior uvea are affected by separate clinical disorders. The visual pathway (Figure 2 ) is composed of the retina, optic nerve (also known as cranial nerve II), lateral geniculate nuclei (LGN) in the thalamus, and occipital cortex in the cerebrum.The canine uveal tract is divided into anterior (iris and ciliary body) and posterior (choroid) portions. Miosis refers to smaller than normal pupil size, while mydriasis refers to larger than normal pupil size.

What is the difference between miosis and mydriasis? Holmberg DVM, MS, PHD, DACVO, in Small Animal Critical Care Medicine (Second Edition), 2015 Mydriasis is due to stimulation of the iris dilator muscle or compromise of the parasympathetic tone of the iris sphincter muscle, or both. What do you need to know about mydriasis in animals? Highly stressed patients, particularly cats, can have dilated pupils and poor to absent pupillary light responses (PLRs). However, unlike miosis, mydriasis is associated with many conditions. The first step in treating Myiasis in dogs is cleaning and disinfecting the area.Īs with miosis, mydriasis can be pharmacologically induced with agents such as atropine. These small carnivorous “worms” can cause secondary pathologies, so you should never try to cure Myiasis without the help of a specialist. Treatment of Myiasis in dogs should always be done under the supervision of a veterinarian. What should you do if your dog has myiasis? Pacing, circling, or turning the wrong way when called. Contusion of the muscle results in a transient mydriasis, while tears to the muscle fibers can cause permanent injury.Ĭommon signs that your dog might be having a stroke include: Loss of balance. Symptoms include eye pain, blurry vision and photophobia. Traumatic mydriasis: Direct blunt trauma to the sphincter muscle of the iris can cause traumatic mydriasis. Anisocoria refers to pupil asymmetry, or when the two pupils of the eyes in a dog are different sizes. While not a life-threatening condition in itself, anisocoria is a symptom that may be indicative of a serious or irreversible condition. The mechanism by which mydriasis occurs in glaucoma is not entirely clear, but likely involves iris or optic nerve dysfunction associated with elevated intraocular pressure. Glaucoma (increased intraocular pressure) can cause a unilateral mydriasis. Transient traumatic mydriasis or miosis may last for days after blunt eye trauma.

When a dog is feeling tense, his eyes may appear rounder than normal, or they may show a lot of white around the outside (sometimes known as a “whale eye”.) Dilated pupils can also be a sign of fear or arousal-these can make the eyes look “glassy,” indicating that a dog is feeling threatened, stressed or frightened. When should I worry about my dogs dilated pupils? Occasionally, the anisocoria will resolve on its own. This is a symptom of a wide range of underlying causes, including head trauma, degeneration of the eye, or exposure to chemicals. Anisocoria is a condition in which a dog’s two pupils are unequal in size.

Dog unequal pupil size