This three year old Labrador is presented to you as the owner is concerned about its eyes, although vision seems to be normal. What is wrong and what tests would you do to determine what is wrong?
There is mild inward strabismus (esotropia) bilaterally, only seen well with distant direct ophthalmoscopy as here. Direct fundoscopy also shows some fine nystagmus with the fast phase outwards. Assessing eye movements on moving the head (passive duction test) followed by grasping the globe conjunctiva after local anaesthetic and moving the eye laterally (forced duction test) shows no abnormality. In the labrador the strabismus is probably neurological as it is in Siamese cats, while in this Cavalier King Charles spaniel it was impossible to move the globe medially and there was a lateral post-traumatic restritive strabismus which the owners chose not to treat as the dog was not impaired by the problem.