The refractive state of the eye in Icelandic horses with the Silver mutation.
Abstract: The syndrome Multiple Congenital Ocular Anomalies (MCOA) is a congenital eye disorder in horses. Both the MCOA syndrome and the Silver coat colour in horses are caused by the same missense mutation in the premelanosome protein (PMEL) gene. Horses homozygous for the Silver mutation (TT) are affected by multiple ocular defects causing visual impairment or blindness. Horses heterozygous for the Silver mutation (CT) have less severe clinical signs, usually cysts arising from the ciliary body iris or retina temporally. It is still unknown if the vision is impaired in horses heterozygous for the Silver mutation. A recent study reported that Comtois horses carrying the Silver mutation had significantly deeper anterior chambers of the eye compared to wild-type horses. This could potentially cause refractive errors. The purpose of the present study was to investigate if Icelandic horses with the Silver mutation have refractive errors compared to wild-type horses. One hundred and fifty-two Icelandic horses were included in the study, 71 CT horses and five TT horses. All horses were genotyped for the missense mutation in PMEL. Each CT and TT horse was matched by a wild-type (CC) horse of the same age ± 1 year. Skiascopy and a brief ophthalmic examination were performed in all horses. Association between refraction and age, eye, genotype and sex was tested by linear mixed-effect model analysis. TT horses with controls were not included in the statistical analyses as they were too few. Results: The interaction between age and genotype had a significant impact on the refractive state (P = 0.0001). CT horses older than 16 years were on average more myopic than wild-type horses of the same age. No difference in the refractive state could be observed between genotypes (CT and CC) in horses younger than 16 years. TT horses were myopic (-2 D or more) in one or both eyes regardless of age. Conclusions: Our results indicate that an elderly Icelandic horse (older than 16 years) carrying the Silver mutation is more likely to be myopic than a wild-type horse of the same age.
Publication Date: 2017-06-02 PubMed ID: 28577553PubMed Central: PMC5455091DOI: 10.1186/s12917-017-1059-7Google Scholar: Lookup
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- Journal Article
Summary
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The study examines the refractive state of the eye in Icelandic horses that have the Silver mutation. More specifically, it investigates whether Icelandic horses with the Silver mutation are more prone to refractive errors as compared to wild-type horses.
Background of the Study
- The research context here is a congenital eye disorder known as Multiple Congenital Ocular Anomalies (MCOA) syndrome, common in horses.
- This condition and the Silver coat color in horses are triggered by the same missense mutation in the premelanosome protein (PMEL) gene.
- Horses homozygous or TT for the Silver mutation are usually affected by multiple ocular defects, which cause visual impairments or blindness, but the visual condition of heterozygous or CT horses is unknown.
- The study was prompted by earlier research showing that Comtois horses with the Silver mutation had significantly deeper anterior eye chambers, a fact that could potentially lead to refractive errors.
Purpose and Methodology of the Study
- The goal of the present research was to explore whether Icelandic horses carrying the Silver mutation also have refractive errors.
- A sample of one hundred and fifty-two Icelandic horses, including 71 CT horses and five TT horses, were all genotyped for the PMEL mutation.
- Each of these horses with the Silver mutation was paired with a wild-type or CC horse of about the same age for a comparative study.
- A brief ophthalmic examination was performed on all horses, and a linear mixed-effect model analysis was used to test the association between refraction and factors such as age, eye, genotype and sex.
- Due to the small number of TT horses, these pairs were not included in the statistical analyses.
Results and Conclusion of the Study
- Significant findings from the study reveal that the interaction between age and genotype had a major impact on the refractive state of the eye (as evidenced by a P value of 0.0001).
- CT horses that are older than 16 years were more myopic on average than wild-type horses of the same age. However, no refractive state difference was observed between CT and CC horses that were younger than 16 years old.
- TT horses were myopic in one or both eyes regardless of their age.
- These results imply that the chances of being myopic are higher in an elderly Icelandic horse (aged over 16 years) carrying the Silver mutation compared to a wild-type horse of the same age.
Cite This Article
APA
Johansson MK, Jäderkvist Fegraeus K, Lindgren G, Ekesten B.
(2017).
The refractive state of the eye in Icelandic horses with the Silver mutation.
BMC Vet Res, 13(1), 153.
https://doi.org/10.1186/s12917-017-1059-7 Publication
Researcher Affiliations
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden. mariakjoh@hotmail.com.
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden.
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden.
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden.
MeSH Terms
- Animals
- Eye Diseases / congenital
- Eye Diseases / genetics
- Eye Diseases / veterinary
- Female
- Hair Color / genetics
- Heterozygote
- Homozygote
- Horse Diseases / congenital
- Horse Diseases / genetics
- Horses
- Male
- Mutation, Missense
- Phenotype
- Refraction, Ocular / genetics
- Syndrome
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