Ocular pathology in Warmblood horses (Equus caballus) in South Africa

Abstract

OBJECTIVE : To determine the prevalence of ocular abnormalities in Warmblood horses (Equus caballus) in South Africa. BACKGROUND : Warmblood horses have become one of the most popular horse breeds around the world, as well as in South Africa, and are commonly utilised for the equestrian sports of show jumping, dressage and eventing. The presence of vision-threatening abnormalities in such horses could have severe consequences. This prompted the current investigation into assessment of ocular abnormalities in Warmblood horses, which have no history of previous vision problems. DESIGN : Descriptive, observational study MATERIALS: One hundred and four Warmblood horses around various locations in the Gauteng and North West Provinces of South Africa. METHODS : Ophthalmic examination was performed using Schirmer tear test (STT) examination, tonometry, fluorescein dye testing, slit lamp biomicroscopy and direct ophthalmoscopy. Pupils were dilated in all horses for comprehensive examination of the fundus. Age, gender, Warmblood type, coat colour, date and time of examination, utility and housing type were all recorded at time of examination. RESULTS : Age range was 0.4-30 years (mean 10.69 years, median 9 years); with 8 stallions (7.7%), 33 mares (31.7%) and 63 geldings (60.6%). Age was categorised into 4 quartiles namely, 0-6 year old, 7-9 year old, 10-15 year old and 15+ years olds. STT results were 24.4mm/min for the right eye and 25.0mm/min for the left eye, and there was no statistical difference between eyes, genders or age categories. Intraocular pressure (IOP) for the right eye was 36.5mmHg and for the left eye was 32.6mmHg, and there was no statistical difference between eyes, gender or age categories. Cataracts were seen in 19 eyes (9.1%) and in 13 horses (12.5%). The presence of cataracts increased with age, however was only statistically significant in horses older than 15 years old. Chorioretinal lesions were seen in 100 eyes (48.1%) and in 65 horses (62.5%). Of the 100 eyes affected, 7 eyes had peripapillary 'butterfly' chorioretinal lesions (3.4%), 14 eyes had non-peripapillary chorioretinal lesions (6.7%), 88 eyes had focal ‘bullet hole’ chorioretinal lesions (42.3%). The presence of chorioretinal lesions increased with age, however was only statistically significant in horses aged 7-9 years old and 15+ years old. Embryological remnants were detected in 140 eyes - anterior lens capsule opacity 1 (0.5%) and iris to iris persistent pupillary membranes (PPM) 139 (67.3%). Other findings included iris hyperpigmentation 16 eyes (7.7%), conjunctivitis 12 eyes (5.8%), vitreal degeneration 8 eyes (3.9%), asteroid hyalosis 4 eyes (1.9%), uveal cyst 3 eyes (1.4%), linear chorioretinal scar 3 eyes (1.4%), eyelid scar 2 eyes (1%), eyelid mass 2 eyes (1%), prominent conjunctival follicles 2 eyes (1%), conjunctival mass 2 eyes (1%), corneal fibrosis 2 eyes (1%), linear keratopathy 1 eye (0.5%), corpora nigra hyperplasia 1 eye (0.5%), torn corpora nigra 1 eye (0.5%), posterior synechiae 1 eye (0.5%), vitreal herniation 1 eye (0.5%), chalazion 1 eye (0.5%) and an optic nerve mass 1 eye (0.5%). CONCLUSIONS AND CLINICAL RELEVANCE : Chorioretinopathies and cataract formation were the most common lesions observed in Warmblood horses in South Africa. Such lesions have the ability to result in significant visual impairment and even blindness. This reiterates the importance of ocular examination as a part of routine health checks, as well as during pre-purchase examinations, especially in horses utilised for equestrian sports.