Eye Disease in the English Springer Spaniel

Dr.  Cynthia A. Wheeler, DVM, MS, DACVO Animal Eye Care of Michigan 5265 Alward Rd. Laingsburg, MI 48848 Cwheeler7@msn.com

Introduction

A variety of ocular diseases have been reported in the English Springer Spaniel (ESS) over the past century. Some of these diseases are inherited and some are not. Some are diagnosed in the young puppy (congenital) and some in the middle aged to older dog. In 1990, the American College of Veterinary Ophthalmologists (ACVO) established a Genetics Committee to be charged with the task of reporting diseases considered heritable in purebred dogs. The result was the text, Ocular Disorders Presumed to be Inherited in Purebred Dogs. This has formed the basis of data collection for the Canine Eye Registration Foundation (CERF) in North America. Listed under the ESS are the following disorders: entropion, corneal dystrophy (lipid), persistent papillary membranes, cataract, glaucoma, retinal dysplasia (RD) and generalized progressive retinal atrophy (PRA). These disorders will be discussed with emphasis on important clinical signs, diagnosis and breeding recommendations.

Note: In Europe, various examination procedures exist for each country with harmonization coming through active work of the European College of Veterinary Ophthalmologists and Kennel Clubs as well as regional groups. In general, what I present here falls under the general consensus of all these schemes.

External diseases of the eye

Entropion is a conformational defect causing the eyelid margins to roll in causing irritation to the cornea. Both lower and upper lids may be affected. It may be difficult to determine if the condition is primary and inherited (having no other associated cause) or secondary (associated with infection or injury). The disorder is likely influenced by several genes defining the skull shape and orbit depth, the skin weight and how much is present around the eyes as well as the size and position of the eye. It is therefore difficult to determine the precise cause. Unless cause can be determined, breeding recommendations are not to breed affected animals.

Treatment consists of plastic surgery to restore the lid margins to their normal position.

Corneal dystrophy is a non-inflammatory corneal opacity present in one or more of the corenal layers. Usually bilateral white to gray areas are aseen in the cornea. Early middle-age is the most common age of onset. Very few dogs are visually impaired due to this type of corneal dystrophy. It is the clinical impression of this author that most corneal "dystrophy" seen in the ESS is related to the diet fed. Certain types of fats and fats in excess as well as certain grains may lead to elevated circulating lipids causing deposition in the central cornea as a calcium cholesterol grain. In these cases reducing dietary fat or reassessing the types of fats in the diet may cause the lesions to disappear over time. Some cases may be associated with hypothyroidism. The disorder likely has a genetic basis but this has not been defined. It is the breeder's option to decide whether or not to breed an affected dog.

Diseases of the Interal Structures of the Eye

Persistent papillary membranes (PPM) are remnants of a layer of vascular tissue that spanned the pupil area in the neonatal eye. These vessels are necessary for the normal development of the eye, particularly the lens and cornea. At birth they normally break up and disappear forming the opening we know of as the pupil. Strands of this membrane may be retained into adulthood. They may be found as loose strands near the pupil edge or form solid attachments across the pupil (iris to iris), from the iris to the lens or iris to cornea. In severe cases parts or all of the tissue sheet may be retained. These may result in vision impairment or blindness when severe. The disorder is visible in young puppies and is usually bilateral. In minor cases, with the normal growth and development of the anterior structures of the eye, the PPM's may "disappear" but most persist throughout life without change. Diagnosis is made on routine examination with ophthalmoscope and slit lamp. In cases of iris remnants attached only to iris the breeding choice is left to the owner. Where lens or cornea are involved, breeding is discouraged.

Cataract is defined as any opacity in the lens and/or its capsule. It may be present in one or both eyes, and may involve all or part of the lens. Minor opacities do not affect vision. In cases where cataracts are bilateral and complete the dog will be blind. Diagnosis is made after dilating the pupils with a mydriatic during eye examination with an ophthalmoscope or slitlamp. Complete cataract is typically visible even without dilating the pupil.

Cataracts may be primary, and generally considered hereditary, or secondary, as in the case of diabetic cataract. Cataract diagnosed in the young puppy is called congenital (present at birth) and may or may not be heritable. Non-hereditary causes of cataracts include trauma, nutritional deficiency, infection or metabolic disorders. Juvenile cataract is a "loose" term used for cataracts that occur in young adult dogs, while senile cataract is seen in older dogs (older than 8 years of age). In the ESS, juvenile cataracts are seen involving the posterior region of the lens and developing slowly with time. Though the changes do progress with times, most dogs seldom develop severe visual impairment requiring surgery to remove the cataract. The mode of inheritance for cataract in most breeds appears as a familial trait, but it has not been elucidated in the ESS.

Treatment for cataract is by surgery. Lens extraction and replacement with an artificial intraocular lens are performed by veterinary eye specialists all over the world.

Dogs with cataract should not be used for breeding purposes.

Glaucoma is a complex disease entity, the major clinical sign being an elevation of the intraocular pressure. This causes damage to the internal structures of the eye , pain and ultimately blindness. The disease can be differentiated in to primary and secondary types, of which primary glaucoma is recognized as an hereditary condition in the ESS. The age of onset of glaucoma in the breed ranges from 3-12 years, with a mean age of 6 years. Usually affected dogs show unilateral signs of glaucoma with the other eye becoming affected months to years later. Typical signs are a red, painful eye, dilated pupils that do not constrict, or do so slowly, with light stimulation, and a grayish or white discoloration to the cornea. Diagnosis is made by routine examination of the eye including the measurement of pressure in the eye (by tonometry) and evaluation of the iridocorneal angle (also called the filtration angle) in the anterior portion of the eye by gonioscopy.

Pectinate ligament dysplasia (PLD) is a defect of the iridocorneal angle of the eye. The space bridged by the pectinate ligaments- the iridocorneal angle- is important for the circulation of fluids out of the eye. This fluid flow maintains a normal intraocular pressure inside the eye. A recent study by Bjerkas et al, 2002, showed that the prevealence of PLD is 25.5% in the ESS breed. Another frequent defect seein in the breed and associated with PLD, is narrowing of the relative width of the ciliary cleft, another important structure in the same region of the eye. Studies of the iridocorneal angle can be done using a technique called gonioscopy. This was one with a large group of normal ESS dogs and narrow iridocorneal angles with or without concurrent PLD was shown. This study demonstrated a clear relationship between glaucoma and the narrowing of the angle as well as between glaucoma and the degree of PLD. Consequently, both factors may contribute additively as well as independently to the development of glaucoma in the breed. The defects may also serve as markers of abnormalities in the deeper parts of the outflow pathways of the eye which may predispose to glaucoma.

The exact mode of inheritance of primary glaucoma in the ESS has yet to be demonstrated but a polygenic mode is suspected. Affected dogs should not be bred.

Retinal dysplasia (RD) is a congenital defect in the development and layering of the retina resulting in folding and abnormal growth of cells especially in the outer retina. The defect can be primary, and most often due to hereditary factors, or secondary, due to local or systemic inflammatory or infectious processes that affect the retina during development and maturation. Studies indicate that RD in the ESS is inherited and suggest it is an autosomal recessive trait. RD is a congenital disorder developing around 48 days gestation. Affected puppies are born with the lesions already present. The defect may be focal, involving solitary folds in the central parts of the retina; multifocal, with several folded structures in the central and midperipheral area; geographic, in which a localized area in the retina is partially detached; or complete, in which most or all of the retina is abnormal and detached. The defect is most often bilateral but not always with similar degrees of involvement in the two eyes. The appearance of RD during examination with an ophthalmoscope is linear, triangular, curved or curvilinear foci of retinal folding that may be single or multiple, most prevalent in the central tapetal area, near the main retina vessels. In more severe cases scarring with pigmentation and thinning of the retina are seen as well as partial or total detachments.

Clinical signs depend on the severity of the defect. Complete RD causes blindness, while focal RD may not cause any obvious visual problems. Clinical signs of RD usually do not change with age, but there are exceptions. Multiple abnormal areas near each other may progress slowly to full detachment in time. Also, solitary minor changes will partially or completely "heal" with age to a state where they cannot be seen by the examiner. It is therefore important that puppies be examined at a young age (6-12 weeks) to identify this congenital disorder.

None of the forms of RD are desirable and affected dogs should not be used for breeding.

Progressive retinal atrophy (PRA) is a slowly progressive disease of the rod and cone visual cells of the retina. Dogs are born with normal vision but become visually impaired over the course of 2-5 years. Initially there is night vision loss which progresses slowly into day vision loss. For the ESS a great variation of onset and progression of clinical signs has been noted (between 2-13 years). There is some indication that PRA in the ESS is similar to PRA found in the English and American cocker spaniels (progressive rod-cone degeneration- prcd).

Retinal abnormalities in the eye may be observed at examination using and ophthalmoscope after pupils are dilated with a mydriatic. Initially there are color changes at the peripheral tapetal retina early in the disease, the changes in reflectivity of the tapetal retina indicating a generalized thinning of the retinal layers and finally a reduction and thinning of the retinal vasculature. Dogs affected with PRA frequently have secondary cataract that may make diagnosis difficult. In these cases, diagnosis with electroretinography (ERG) is recommended. Through an elaborate testing procedure a diagnosis may be made, often before clinical signs are apparent.

There is no effective treatment for PRA. Affected dogs become blind. The disease is transmitted as an autosomal recessive trait. Affected dogs should not be used for breeding. In Sweden, it is not recommended to breed carriers, such as the parents of an affected dog or offspring of an affected dog.

References

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