Ocular Conditions of Great Danes

OCULAR CONDITIONS OF GREAT DANES

Rachel Lockhart BVM&S CertVOphthal MRCVS

Dogs of any breed can suffer from a variety of ocular defects, disease or abnormality. Some conditions have a proven hereditary basis, some are predisposed in certain breeds due to their anatomy or conformation and some are acquired. Potential defects may have welfare consequences for the individual and their future progeny and may impact on the breed as a whole. Various health schemes are in place to help identify individuals which may be affected by, or carrying genes for, certain condition. By selecting away from these traits the hope is these unwanted characteristics can be “bred out”.

The British Veterinary Association (BVA) operates a hereditary eye disease screening programme in conjunction with the Kennel Club (KC) and the International Sheep Dog Society (ISDS). The Eye Scheme covers 11 hereditary eye conditions in over 50 breeds of dog. There are 33 appointed eye panelists around the country who examine dogs to help ensure that those individuals used for breeding show no evidence of hereditary eye disease. An exam is valid for one year so dogs should be certiﬁed annually to ensure that conditions that may develop later in life have not appeared. These exams do not guarantee that the dog is not a carrier of genetic ocular disease; rather, a test to prove that at that time no genetic ocular disease was clinically apparent. Some abnormalities are congenital and not progressive such that the problems may be diagnosed early. Litters of puppies can be screened for congenital conditions when they are between six and twelve weeks of age.

The diseases included in the Eye Scheme are classified into Schedule A (those with an identifiable genetic cause) and Schedule B (conditions currently under investigation). Great Danes are not included in Schedule A. However, they are listed in Schedule B as being under investigation for a specific form of Primary Glaucoma (increased pressure within the eye) called Goniodysgenesis.

As a breed Great Danes can also be predisposed to several conditions affecting the eyelids and soft tissues surrounding the globes. These abnormalities do not have a proven hereditary basis but may potentially compromise ocular health and therefore the health and welfare of the dog overall. Breeding from affected dogs is therefore strongly discouraged. The Kennel Club Breed Watch is a relatively new scheme which has arisen in response to recent controversies surrounding the impact of intensive inbreeding in certain dog breeds. 43 breeds are listed as potentially developing problems which may impact on health and welfare. 14 of these breeds are classed as high profile and require veterinary inspections at dog shows. The remaining breeds (including Great Danes) have specific undesirable traits which if present are visible with the naked eye and therefore attract special attention by show judges. In comparison, ocular conditions included under the KC/BVA/ISDS Eye Scheme require specialised equipment and veterinary expertise to diagnose. The only condition listed for Great Danes by the KC Breed Watch is “Loose Eyelids”.

For the purpose of this talk I will cover the following conditions: Goniodysgenesis (Primary Glaucoma), Loose Eyelids (Entropion/Ectropion) and Ocular Soft Tissue Abnormalities (Cherry Eye/ Scrolled Cartilage). I will also briefly mention Merle Ocular Dysgenesis if time allows.

GONIODYSGENESIS (Primary Glaucoma)

There is a constant process occurring within the eye whereby clear fluid is formed called Aqueous Humor. This fluid flows through the eye providing nutrition and oxygen to the internal tissues. It then circulates out through a sieve like drainage system and is then eliminated in the general circulation. The rate of fluid production and drainage remains constant so that a stable pressure is maintained within the eye. Glaucoma is an eye disease where the fluid produced inside the eye cannot escape and so the pressure inside the eye increases. This pressure, if high enough, can cause significant pain and blindness. There are numerous causes of glaucoma in the dog. Certain breeds including Great Danes, Basset Hounds, Siberian Husky, English & American Cocker Spaniels, English and Welsh Springer Spaniels, Flatcoat, Golden and Labrador Retrievers amongst others can be born with a deformed drainage angle (Goniodysgenesis). These breeds can therefore produce more fluid within the eye than they can naturally drain and are at risk of developing Primary Glaucoma. Goniodysgenesis usually affects both eyes. However, the degree of deformity can vary quite considerably between individual dogs and between individual eyes of the same dog. Some dogs affected with the condition may therefore be lucky and do not develop clinical glaucoma or may do so only in one eye.

A normal drainage system can become blocked as a result of other eye problems such as inflammation, haemorrhage, or physical changes or damage to the tissue structures within the eye. This type of glaucoma is secondary to other causes and can potentially occur in any breed of dog.

Symptoms

Clinical signs of glaucoma depend on the pressure within the eye and in the early stages may wax and wane. Outward signs can range from a red sore eye (often misdiagnosed as conjunctivitis), blue discolouration of the cornea, physical swelling of the globe, visual disturbances and pain.

Diagnosis

The drainage angle can be examined using a technique called Gonioscopy. This technique is difficult to master requiring specific training and equipment so in general is only performed by Veterinary Ophthalmologists.

Pressure within the eye can also be measured using a machine called a Tonometer. There are several types of Tonometer available. They are expensive but easy to use and your own vet may have one.

Treatment

Goniodysgenesis is a physical abnormality deep within the eye therefore once clinical glaucoma develops it can generally only be controlled rather than cured. Glaucoma is an emergency. If high pressure in the eye is not controlled chronic pain and blindness can quickly result. Control is most commonly achieved with the use of daily eye drops which either slow the production of fluid or increase its drainage through alternative routes. Various surgical procedures have been extrapolated from human Ophthalmology to try and treat glaucoma but in dogs their effects are usually short lived.

In many cases control is only achieved for so long and if a dog is left with a chronically painful blind eye it is often kinder to consider removing the eye surgically. Enucleation can be quite an upsetting idea for humans but from the dogs point of view it usually a relief. Dogs can adapt remarkably well to vision loss as long as they are pain-free and the majority can continue living happy healthy lives.

CONFORMATIONAL DEFECTS OF THE UPPER AND/OR LOWER EYE LIDS (“LOOSE” EYELIDS)

Conformational defects of the upper and/or lower eyelids affect the eyelid margins so they are not in normal contact with the eye when the dog is in its natural pose. Eyelid margins may turn in, out or both at the same time.

Breed-associated conformational defects of the eyelids can occur in many breeds of dog including giant breeds (St. Bernards, Mastiffs, Great Danes), Gun Dog breeds (Spaniels, Retrievers), and any breed with loose facial skin (Bloodhounds, Bassets).

Conformational defects are usually evident at a young age. Eyelid defects can also be acquired due to loss of facial/orbital musculature or skin tension due to age or illness. They can also be secondary to eyelid injuries and scarring or may be intermittent being caused by fatigue or drowsiness. True conformational defects must also be distinguished from abnormal eyelid alignment, induced in an otherwise normal eye, due to reflex globe retraction due to ocular pain.

Ectropion

The margin of the eyelid rolls outward exposing the palpebral conjunctiva (the tissue that lines the inner lids) and the Third Eyelid (Nictitating Membrane). It can result in exposure of the ocular tissue, poor blink motion and poor tear distribution which may predispose to inflammation, infection and ocular trauma.

Entropion

The margin of the eyelid turns inward resulting in contact between eyelashes/facial hair and the ocular tissue. It can result in chronic irritation, excess tearing and painful corneal trauma.

Treatment

Young dogs with eyelid abnormalities are often said to “grow out” of them but this is very rarely the case. In general breed-related conformational defects are only corrected surgically. The defect needs very careful examination to decide exactly what procedure (or combination of procedures) is required to correct the defect. If defects are worsened, or caused, by other ocular disorders these must be corrected first. Otherwise there is a risk of “over correcting”.

CHERRY EYE (PROLAPSED NICTITANS GLAND)

This condition is usually seen in young dogs. It can be seen in any breed big or small including Mastiffs, Great Danes, Cocker Spaniels, Lhasa-Apsos, Shih-Tzus, Poodles, Beagles and Bulldogs.

The Third Eyelid (also known as the Nictitating Membrane) is a triangular fold of conjunctival mucous membrane found in the corner of the eye in dogs, cats and several other mammals and birds. It is normally partially hidden in a normal eye. It contains a T-shaped cartilage with a secretory gland located at the base of the T. This gland is important for the dog providing about 40% of its total tear production.

The gland is normally held down at the base of the third eyelid by a ligament. In Cherry eye the ligament is weaker than normal and it either stretches or breaks allowing the gland to pop up out of position and protrude through the conjunctiva lining the back of the Third Eyelid as a reddish mass (rather like a cherry)! This condition is usually quite painless but if left the overlying exposed tissue will become irritated and inflamed. Secondary infection and corneal trauma are also possible. This condition may occur in just one eye, but eventually the gland of the other eye may prolapse too.

Treatment

In the early stages some glands can be massaged back into place. However, eventually most glands become permanently prolapsed. An old-fashioned treatment was simply to remove the gland but this can cause a permanent deficiency in tear production, with potentially disastrous results. The correct treatment is to surgically replace the gland so that it is protected, and can continue to function normally.

The surgical procedures used can vary according to preference, but most commonly a ‘Pocket’ technique is used. Another method involves anchoring the gland to the bone surrounding the eye. Success rates can be affected by how long the gland was prolapsed before surgery. In cases where the gland has been exposed for some time repeat surgeries may therefore be required. SCROLLING OF THE CARTILAGE OF THE THIRD EYELID

In this condition the T-shaped cartilage within the Third Eyelid buckles causing the leading edge to scroll out away from the surface of the globe. Due to its appearance it is also sometimes referred to as “Leaf Roll”. This again can occur in any breed but is seen most often in Great Danes, German Short-Haired Pointers, Weimeraners, Saint Bernards and Newfoundlands. The treatment is also surgical and involves removal of the ‘buckled’ piece of cartilage.

MERLE OCULAR DYSGENESIS

Merle is a pattern in a dog's coat, though commonly incorrectly referred to as a colour. The merle gene creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well. Merle is a pattern seen in several breeds including the Great Dane where it is part of the genetic makeup that creates the harlequin coloring. The merle gene is an incomplete dominant, meaning only one copy of the gene is needed to show the merle effect. If two such dogs are mated, on average one quarter of the puppies will be "double merles" carrying two copies of the gene. It is these double merle puppies (who may be predominantly white) who could be born with congenital deafness, blindness, or other debilitating ocular issues. Knowledgeable breeders who want to produce merle puppies mate a merle with a non-merle dog. Roughly half the puppies will carry one copy of the merle gene and will therefore have the merle pattern without the risk of ocular or hearing defects associated with double merle dogs.

Ocular defects may include:

 Microphthalmia (congenitally small eyes)  Iris hypoplasia (thinning) or colobomas (holes)  Persistent pupillary membranes  Scleral Colobomas  Congenital cataracts  Retina/Optic nerve abnormalities