Idiopathic Unilateral Transient Miosis in Dogs.

Idiopathic unilateral transient miosis is benign, self-limiting, occurring predominantly in young Australian Shepherds.

This descriptive study characterizes idiopathic unilateral transient miosis in dogs through analysis of 78 cases meeting strict inclusion criteria. The condition predominantly affects young dogs, with mean onset at 6.5 months, and shows marked breed predisposition toward Australian Shepherds, Miniature Australian Shepherds, and merle-phenotype dogs. Clinical presentation is typically benign, with episodes lasting a median of 30 minutes and most commonly occurring after sleep (74%) or physical activity (22%). Blue-eyed dogs were disproportionately affected (76%), as were females (61%). Notably, 71% of affected dogs experienced recurrent episodes with alternating sides in 62% of cases. The condition occurs in the absence of other ocular or systemic abnormalities, distinguishing it as a benign idiopathic phenomenon. This represents the first formal characterization of this condition in veterinary medicine, establishing baseline clinical features that may guide diagnosis and client education regarding this self-limiting presentation.

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