Originally published on TheHorse.com
Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C.
Most equestrians who have purchased horses are familiar with the concept of a prepurchase examination. Ensuring horses are in sound health prior to signing a check helps instill confidence in new owners about their purchase. One key area of the prepurechase exam is the ocular evaluation, and while not all eye anomalies are detrimental to vision, others can cause sale talks to cease.
At the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C., Andrew Matthews, PhD, Dipl. ECEIM, hon Member ACVO, FRCVS, an equine practitioner and ophthalmologist from Ayrshire, Scotland, reviewed the ocular portion of the prepurchase examination.
If an abnormality is identified, Matthews said the veterinarian should consider two questions prior to making his or her recommendation as to whether the horse is suitable for purchase:
By arming the potential purchaser with that information, the veterinarian is allowing him or her to make an informed decision about the horse's purchase, he said.
And he reminded attendees, "It is not possible to objectively assess vision in horses unless the horse is actually blind."
Next, Matthews reviewed some of the common ocular anomalies practitioners might encounter during a prepurchase exam and shared his thoughts on whether affected horses are suitable for purchase:
Congenital leukomas (corneal opacities) can develop from a variety of causes; however, because they are nonprogressive, affected horses are generally considered suitable for purchase by an informed owner.
Corneal fibrosis ("dense, white leukoma, sometimes with superficial pigmentation and frequently with a single small blood vessel in the area," Matthews explained) in most cases are nonprogressive, and affected horses are suitable for purchase. Matthews cautioned that "a very small minority" of affected eyes could be immunologically compromised, and recurrent bouts of nonulcerative keratitis could become an issue.
Corneal edema (fluid swelling) can affect a horse's suitability for purchase depending on the degree of edema present, Matthews relayed. For instance, focal edema is often associated with a mass in the eye's anterior chamber (melanoma, for example) and more generalized edema with inflammatory debris in the eye (termed keratic precipitates, or KPs). Horses with these conditions are not suitable for purchase, he said. On the other hand, local edema in a quiet cornea can resolve in a few months; these horses could be suitable for purchase by an informed owner, he said.
Linear keratopathy (striate opacities in Descemet's membrane, which covers the inner surface of the cornea) are incidental findings, and Matthews considers affected horses suitable for purchase.
Iris cysts typically don't affect purchase recommendations, Matthews said. He cautioned, however, that these growths can very rarely interfere with the corneal endothelium, obstruct the pupil, or detach and float freely in the anterior chamber.
Granulae iridica cysts are typically small enough to have little to no effect on horses' vision, meaning affected animals are suitable for purchase. If the growths are large, however, they are likely to obstruct the pupil's functionality, Matthews said.
Iris colobomas, in which some of the structures of the eye are absent due to incomplete development during gestation, generally have little impact on horses, and affected animals are suitable for purchase, Matthews said.
Stromal cysts have only been identified in Welsh ponies, he relayed, and most commonly develop in hypopigmented (lack of color) or hypotrophic (loss of physical structure) irises. Horses with stromal cysts are generally suitable for purchase, he added.
Anterior segment dysgenesis, a combination of developmental anomalies in the anterior chamber, generally don't affect a horse's purchase by an informed owner because the lesions are typically nonprogressive.
Lesions from previous uveitic episodes should be considered carefully on prepurchase exam, Matthews said. In most cases affected horses are not suitable for purchase; however, he said, affected horses might be suitable for purchase by an informed owner if:
Lens lesions are usually nonprogressive and most have little to no effect on equine vision, making affect horses suitable for purchase. However, Matthews cautioned that opacities in the posterior central nucleus, visual axis, or peripheral nucleus and cortex of the eye have the potential to affect vision at some stage and should be considered with caution.
Retrolental opacities, which are remnants of the embryonic uvea, don't affect a horse's purchase unless the opacities are extensive, Matthews said.
Capsular cataracts alone typically are not a problem; however, if any other signs of prior uveitis are present along with the small focal opacities, give careful thought to the horse's suitability for purchase, Matthews suggested.
Polar cataracts are generally nonprogressive and small and should not affect a sale.
Dense sutural cataracts--a type of congenital opacity--located in the visual axis can cause vision problems, which render affected horses unsuitable for purchase.
Nuclear cataracts are generally nonprogressive; however, they affect the eye's nucleus, are typically bilateral, and are often located on the visual axis, all of which can lead to visual deficits and make a horse unsuitable for purchase, said Matthews.
Floaters in the eye's vitreous are a common finding, Matthews said. Most horses with floaters, unless extensive, are acceptable for purchase. "But note," he cautioned. "There are reports in the literature associated vitreal floaters with headshaking. However, the vast majority of horses with floaters show no behavioral abnormalities."
Pathologic vitreal inclusions are similar to floaters but often associated with more serious ocular inflammatory disease, Matthews said. Affected horses are not suitable for purchase, he added.
Optic atrophy, a condition that affects the optic disc, is another cause for concern. Affected eyes are blind, Matthews said, so these horses aren't acceptable for purchase.
Optic disc lesions are typically nonprogressive lesions that don't often affect vision, so affected horses are suitable for purchase. Matthews noted that in rare instances, extensive optic disc lesions can occur; because this problem is typically associated with prior systemic disease and significant visual problems, these animals aren't suitable for purchase.
It's important, when considering purchasing a horse, to have your veterinarian carry out a complete prepurchase examination; an important part of that exam is the ocular evaluation. Ensuring a horse has healthy vision prior to sale can help reduce future veterinary bills and disappointment for a new owner.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.