Figure 11.2 True, fixed, ventromedial strabismus (esotropia) is seen here from a dorsal view in a Holstein cow. Degrees of exophthalmos usually accompany this inherited disorder that occurs in several breeds of cattle. A brainstem nuclear defect is believed to cause this problem that may be accompanied by some degree of visual impairment (amaurosis).
Congenital blindness from many diseases can be associated with abnormal eyeball positions and movements. Also, Appaloosa, miniature, Thoroughbred, and Paso Fino horses severely affected with inherited night blindness can have dorsomedial strabismus, which may be noticed when they attempt to visually fix on an object.13,14 The ventromedial rotational positioning of the eyeball seen in many newborn foals disappears by a few weeks of age.15
Figure 11.3 Ventral eye deviation, as seen in this donkey’s left eye while the muzzle is being raised, with or without a left head tilt, is assumed to be left vestibular disease until proven otherwise. In this case, there also is left facial paresis evidenced by the right deviation of the muzzle. These signs were due to involvement of CN VIII and VII caused by the immune‐associated disease polyneuritis equi.
Although many inflammatory, physical, metabolic, toxic, and nutritional disorders may affect the regions of the brainstem where the oculomotor, trochlear, and abducent nuclei are located, prominent signs of fixed strabismus are rarely seen alone in large animals.16,17 However, many severe asymmetric forebrain diseases result in turning of the head and neck and drifting toward one side, usually the side of the lesion. This can also involve the eyes being drawn toward one side, particularly with thalamic involvement, and these signs collectively comprise the adversive syndrome.18,19 The relative dorsomedial rotation of the eyeballs (Figure 11.5) seen in diseases such as polioencephalomalacia, lead poisoning, water intoxication and bacterial meningitis in ruminants, and with meningitis and hypoxic and neonatal encephalopathy in newborn foals, may not be a specific trochlear nerve paralysis. This is because the eye can be moved in all four directions and out of this rotated position, so it might reflect severe forebrain disease involving the central motor pathways controlling eyeball posture. A similar dorsomedial eyeball rotation can also be seen with congenital cerebellar hypoplasia and with cerebellar abiotrophy in several species likely due to alteration in vestibulocerebellar tonic control of extraocular muscles.
Figure 11.4 Ventral and slight lateral deviation of one eyeball relative to the other is the most frequently seen eye deviation in large animals. It is most often due to vestibular disease. Although it can be referred to as strabismus, the eye is not fixed and can be moved away from the ventral position by movement of the head. This lamb is suffering from listeriosis with the encephalitis worse on the left side of the brainstem. Compared with the more normally responding right eye (A), the left eyeball is ventrally deviated (B) while the head is in a normal posture. The ventral deviation became even more prominent with elevation of the nose and head extension.
Figure 11.5 The term dorsomedial (rotational) strabismus is used to describe what is seen here (A and B). The cow (A) has Salmonella sp. sepsis and meningitis, and the ewe (B) has thiamine‐responsive polioencephalomalacia. Both have rotation of the globe such that the medial aspect of the pupil is now rotated to a dorsal and caudal position. The images of each eye have been rotated such that the palpebral fissure is shown perfectly horizontal, and the equators of the eyeballs are indicated by yellow lines. That this is not a fixed strabismus is attested by the fact that with moving the position of the head the eye can be drawn out of this position.
References
1 1 Momke S, Fink S, Wohlke A, Drogemuller C and Distl O. Linkage of bilateral convergent strabismus with exophthalmus (BCSE) to BTA5 and BTA18 in German Brown cattle. Anim Genet 2008; 39(5): 544–549.
2 2 Scacco G, Rambaldi AM, Roccaro M, et al. Bilateral convergent strabismus with exophthalmos in cattle ‐ what do we know? Large Anim Rev 2017; 23(2): 67–71.
3 3 Fink S, Momke S and Distl O. PLXNC1 and RDH13 associated with bilateral convergent strabismus with exophthalmus in German Brown cattle. Mole Vis 2012; 18(235–36): 2229–2240.
4 4 Momke S and Distl O. Bilateral convergent strabismus with exophthalmus (BCSE) in cattle: an overview of clinical signs and genetic traits. Vet J 2007; 173(2): 272–277.
5 5 Regan WM, Gregory PW and Mead SW. Hereditary strabismus in Jersey cattle. J Hered 1944; 35(8): 233–234.
6 6 Holmes JR and Young GB. A note on exophthalmos with strabismus in shorthorn cattle. Vet Rec 1957; 69: 148–149.
7 7 Julian RJ. Bilateral divergent strabismus in a Holstein calf. Vet Med Small Anim Clin 1975; 70(10): 1151.
8 8 Distl O and Scheider A. An unusual eye defect in Highland cattle: diverging unilateral strabismus. Dtsch Tierarztl Wochenschr 1994; 101(5): 202–203.
9 9 Distl O and Gerst M. Association analysis between bilateral convergent strabismus with exophthalmus and milk production traits in dairy cattle. J Vet Med A Physiol Pathol Clin Med 2000; 47(1): 31–36.
10 10 Mayhew IG. Neuro‐ophthalmology: a review. Equine Vet J Suppl 2010( 37): 80–88.
11 11 Johnson PJ, Constantinescu GM and Frappier BL. The vestibular system. Part I: Anatomy, physiology and clinical signs from altered vestibular function. Equine Vet Educ 2001; 13(2): 105–109.
12 12 Thomson C and Hahn C. Veterinary neuroanatomy: a clinical approach. 1st ed. Saunders Elsevier. 2012; 208.
13 13 Nunnery C, Pickett JP and Zimmerman KL. Congenital stationary night blindness in a Thoroughbred and a Paso Fino. Vet Ophthalmol 2005; 8(6): 415–419.
14 14 Sandmeyer LS, Bellone RR, Archer S, et al. Congenital stationary night blindness is associated with the leopard complex in the Miniature Horse. Vet Ophthalmol 2012; 15(1): 18–22.
15 15 Leiva M, Pena T and Monreal L. Ocular findings in healthy newborn foals according to age. Equine Vet Educ 2011; 23(1): 40–45.
16 16 Jacob SI, Drees R, Pinkerton ME, Bentley EM and Peek SF. Cavernous sinus syndrome in a Holstein bull. Vet Ophthalmol 2015; 18(2): 164–167.
17 17 Myrna KE. Neuro‐ophthalmology in the Horse. Vet Clin North Am Equine Pract 2017; 33(3): 541–549.
18 18 Robillard A, Saint‐Hilaire JM, Mercier M and Bouvier G. The lateralizing and localizing value of adversion in epileptic seizures. Neurology 1983; 33(9): 1241–1242.
19 19 Schiff MM, Esmond WG and Himwich HE. Forced circling movements (adversive syndrome): correction with dinenhydrinate