Ocular abnormalities in the Icelandic horse with a focus on equine recurrent uveitis: 112 Icelandic horses living in Denmark and 26 Icelandic horses living in the United States

A survey of ocular pathology in Warmblood horses in South Africa

BACKGROUND

Warmblood horses are a popular breed around the world for equestrian sports. Previous studies have investigated ocular findings in other breeds of horses; however, no studies exist for the Warmblood breed.

OBJECTIVES

To determine the prevalence of ocular abnormalities in a convenience sample of Warmblood horses in South Africa and to determine if the prevalence of lens and chorioretinal lesions increase with age.

STUDY DESIGN

Descriptive, observational study.

METHODS

Warmblood horses underwent a full ophthalmic examination which included a Schirmer tear test (STT), tonometry, fluorescein dye testing, slit lamp biomicroscopy and indirect ophthalmoscopy. Age was categorised into three groups namely <8 years old, 8-13 years old and 14+ years old for statistical analysis. Prevalence of lens and chorioretinal lesions were compared between age categories.

RESULTS

One hundred and four horses (208 eyes) were examined. The age range was 5 months to 30 years (mean 11 years, standard deviation [SD] 6 years). Ocular pathology was noted in 125 eyes (60.1%) and 79 horses (76%). The highest number of lesions were noted in the choroid and retina, iris and lens. Chorioretinal lesions were seen in 100 eyes (48.1%) and in 65 horses (62.5%). Iridial lesions were seen in 19 eyes (9.1%) and 12 horses (11.5%). Cataracts were seen in 19 eyes (9.1%) and in 13 horses (12.5%). The presence of total chorioretinal lesions (eye level [p = 0.002]; horse level [p = 0.004]), focal chorioretinal lesions (eye level [p = 0.004]; horse level [p = 0.008]) and cataract (eye [p = 0.03]; horse level [p = 0.02]) were all shown to statistically increase with age.

MAIN LIMITATIONS

A small sample size and limited geographic area.

CONCLUSIONS

There was a high prevalence of ocular pathology in this population of Warmblood horses in South Africa. This reiterates the importance of an ocular examination as a part of routine health checks, as well as during prepurchase examinations.

A review of investigated risk factors for developing equine recurrent uveitis

Equine recurrent uveitis (ERU) is an ocular inflammatory disease that can be difficult to manage clinically. As such, it is the leading cause of bilateral blindness for horses. ERU is suspected to have a complex autoimmune etiology with both environmental and genetic risk factors contributing to onset and disease progression in some or all cases. Work in recent years has aimed at unraveling the primary triggers, such as infectious agents and inherited breed-specific risk factors, for disease onset, persistence, and progression. This review has aimed at encompassing those factors that have been associated, implicated, or substantiated as contributors to ERU, as well as identifying areas for which additional knowledge is needed to better understand risk for disease onset and progression. A greater understanding of the risk factors for ERU will enable earlier detection and better prognosis through prevention and new therapeutics.

A genetic investigation of equine recurrent uveitis in the Icelandic horse breed

Equine recurrent uveitis (ERU) is an autoimmune disease defined by inflammation of the uveal tract of the eye. The cause of ERU is thought to be complex, involving both genetic and environmental factors. The purpose of this study was to investigate potential genetic risk factors for ERU in the Icelandic horse. Fifty-six Icelandic horses (11 affected with ERU and 45 controls) living in Denmark and the USA, eight years or older, were included in the study. A case-control GWAS was performed using the GGP Equine 80K array on the Illumina Infinium HD Beadchip using 40 horses. A mixed linear model analysis identified a single SNP on ECA 11 (BIEC2_141650; NC_009154.3:g.3817009A>G) that reached genome-wide significance (p = 1.79 × 10^-7 ). This variant was within an intron of tissue inhibitor of metalloproteinase 2 (TIMP2), a gene previously implicated in ERU. Sanger sequencing identified a single coding variant in this gene; however it was a synonymous mutation (NC_009154.3:g.3858193C>T) and was not perfectly concordant with ERU phenotype (p = 0.68). Further investigation of TIMP2 is warranted. Additional horses and markers are needed to identify other potential loci worthy of further investigation as contributors to ERU risk in Icelandic horses.