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

Abstract

Purpose To describe the most common ocular abnormalities in the Icelandic horse with focus on equine recurrent uveitis (ERU) and association between ocular abnormalities and summer eczema and coat colors. Methods A descriptive cross‐sectional study. A complete physical and ophthalmic examination as well as measurement of serum titers for Leptospira serovariants was performed on Icelandic horses from Denmark (DK) and the United States (USA). Results One hundred and twelve Icelandic horses living in DK and 26 Icelandic horses living in the United States were included in this study (total of 138 horses, 274 eyes). The three most common ocular abnormalities were follicular conjunctivitis (55.8%, 153/274 eyes), cataracts (27.4%, 75/274 eyes), and multifocal chorioretinopathy (“bullet holes”; 19%, 52/274 eyes). The prevalence for ERU among Icelandic horses aged “eight years and older” was 8% (6/75 horses). The “insidious ERU” type was found in 83% of the ERU cohort (5/6 horses), while “classic ERU” was found in 17% (1/6 horses). A correlation between ERU and cataracts was found in the population (p < .01). Leptospiral serology results were not associated with ERU in either DK or US‐Icelandic horses (p = 1.00, p = 1.00, respectively). ERU was not associated with summer eczema (p = .49), and no coat colors were associated with the ocular abnormalities found in the Icelandic horse (all p‐values > .05). Conclusion Follicular conjunctivitis, cataracts, and multifocal chorioretinopathy were the three most common ocular abnormalities findings. Icelandic horses who were 8 years or older had an 8% prevalence for ERU. Summer eczema and coat color were not associated with evidence of ERU or other ocular abnormalities.

A review of investigated risk factors for developing equine recurrent uveitis

“…The Appaloosa and breeds with similar coat spotting patterns, along with Icelandic horses and draft breeds, have been reported to have a predisposition for insidious uveitis 29,108,109 . The prevalence for insidious uveitis among Icelandic horses over 8 years old was 6.7% in a recent investigation with horses from Denmark and the USA 109 .…”

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

“…Sample collections from the Danish Icelandic horses were approved by the Danish research animal committee. All US and Danish horse owners gave informed consent as noted in Henriksen et al (2021).…”

“…Eight years was used as the control threshold age for inclusion, as was previously done in Sandmeyer et al (2020). A complete ophthalmic examination was performed on each horse, consistent with methods used in Henriksen et al (2021). Inclusion criteria for ERU cases included two or more of the following clinical findings: phthisis bulbi, aqueous flare, keratic precipitates, iris hyperpigmentation, anterior or posterior synechiae, hyphema, hypopyon, cells in aqueous humor, fibrin in anterior chamber, corpora nigra atrophy, immature, mature or hypermature cataracts, vitritis, glaucoma, retinal detachment, active chorioretinitis, chronic chorioretinal degeneration/scars as a butterfly lesion, tapetal hyperreflectivity, optic nerve head atrophy and intraocular pressure below or above normal range of 10-30 mmHg as well as a history of recurrent uveitis from their referral veterinarian (Table S1, Gilger & Hollingsworth, 2017).…”

“…The Icelandic horse was also recently reported to be predisposed to ERU (Henriksen et al, 2021). To date, no studies have investigated the genetic risk for ERU in this breed.…”

Chronic Intraocular Leptospiral Infection Relying on Biofilm Formation inside the Vitreous Cavity Leads to Recurrent Uveitis in Horses

“…), which accounts for a large proportion of affected horses in the United States, was also classified as ERU. In other studies, the percentage of horses affected with ERU ranges from 7 to 10% [54][55][56], with up to one-third of the horses suffering from the disease on both sides [3,34,57]. The attacks of uveitis in both eyes often do not start at the same time, but with a time delay of several months up to about 2 years [34].…”