SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
1 . menace the animal by moving the hand toward each eye . The entire visual system must be intact to get a positive response . Although this primarily involves II and VII , there are multiple influences . - afferent pathway : - ipsilateral eye and optic nerve ( II ) - optic chiasm - contralateral optic tract - lateral geniculate nucleus ( thalamus ), optic radiation , occipital visual cortex - efferent pathway : from the contralateral visual cortex to the ipsilateral facial nucleus
- The cerebellum exerts influences on cerebral function , including visual responses . Horses with cerebellar disease often lack a menace response , but are not blind . 2 . If the menace is doubtful , observe the animal in an obstacle course . 3 . Direct and consensual responses to light . ( This also tests the oculomotor nerve .) 4 . An ophthalmoscopic examination of the fundus may be important .
5 . The menace is normally absent in neonates until several days of age .
C . Parasympathetic to pupil – Oculomotor Nerve ( III )
1 . Both pupils should constrict symmetrically when a light is shone into either eye .
2 . Pupillary size should be symmetrical and neither abnormally constricted or dilated .
3 . Recognize Horner ’ s Syndrome :
Damage to the sympathetic supply of the eyeball results in Horner ’ s syndrome , seen as a slight ptosis of the upper lid , a miosis ( constriction ) of the pupil and a slight protrusion of the nictitating membrane . Vision and the pupillary light response are unaffected . In the horse , lesions involving the sympathetic supply to the head result in these ophthalmic signs and additional signs consisting of dilation of facial blood vessels , hyperemia of nasal and conjuctival mucous membranes and increased temperature and sweating of the face . This latter sign is most prominent at the base of the ear and is present over the neck down to about the level of the axis . These signs have been seen with lesions of the sympathetic pathways in the guttural pouches , in the area of the cervical vagosympathetic trunk , and at the thoracic inlet .
Equine Horner ’ s syndrome can be expected from large lesions involving the descending sympathetic pathways in the brainstem and the cervical spinal cord . In such cases , there will also be excessive sweating over the whole affected side of the body because all the sympathetic pathways leaving the spinal cord have lost their central ( upper motor neuron ) connections .
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