Genetic welfare problems of companion animals
Brachycephalic Ocular Syndrome
Condition: Brachycephalic Ocular Syndrome
Related terms: brachycephalic ocular disease, exophthalmos, exposure keratopathy, exposure keratopathy syndrome, keratitis syndrome, pigmentary keratisis, macropalpebral fissure syndrome, medial canthus syndrome
Outline: Because of their extreme brachycephalic (short) head shape and its consequences on the anatomy (shape and positioning) of the eyes and surrounding tissues, Pugs are prone to several eye conditions that tend to lead to chronic irritation and pain. It seems likely that prevalence of these diseases will be lower in those with less extremely abnormal head shapes (compared with more typical canine head shape).
Summary of Information
(for more information click on the links below)
1. Brief description
Brachycephaly is the term used to describe animals that have greatly shortened upper jaws and noses. Decreased depth of the orbits (the bony eye sockets) is also common. Of the dog breeds, the Pug has an extreme brachycephalic head shape, with large, prominent eyes and almost complete lack of muzzle.
Brachycephalic ocular disease is the name given to a syndrome seen in brachycephelic animals that often combines lesions of the eyelid, conjunctiva (the tissues lining the eyeballs and eyelids) and cornea (the tissue forming the clear front surface to the eyeball) (Maggs et al 2008).
Dogs affected by this syndrome may show various conformational abnormalities of the eye including exophthalmos (abnormal protrusion of the eyes), macropalpebral fissure (an excessively wide opening of the eyelids compared to the size of the eye) and lagophthalmia (inability to close the eyelids completely) (Maggs et al 2008, Bedford and Jones 2001). The abnormal head shape may lead to other problems also including: lower medial entropion ( inward rotation of the eyelid or eyelid fur which rubs on the eye), nasal fold trichiasis (skin fold and hairs on the nose comes in constant direct contact with the corneas), distichiasis (abnormally placed eyelashes that rub on the eye), poor tear production and/or quality (which means the cornea is more prone to damage as potential abrasive particles that come into contact with it are not washed away), pigmentary keratitis or exposure keratopathy (long term damage to the corneas), and epiphora (tears running onto the face) (Maggs et al 2008).
Depending on the type and severity of the above problems, affected dogs can show signs that include: excessive tear production (lacrimation), holding of their eyelids partially closed, excessive blinking and sensitivity to light, discharge from the eyes, inflammation and redness of the conjunctiva, damage to the cornea which may lead to partial or complete blindness, frequent rubbing at the face and eyes, and tear staining on the face.
With less of the globe sitting tightly enclosed by the skull, brachycephalic dogs are more prone to eye prolapse (dislocation of the eye beyond the plane of the eyelids) compared to other dogs. Minor forms of trauma are all that are needed to cause prolapse in extreme brachycephalic breeds (Mould 1993, Bedford and Jones 2001).
2. Intensity of welfare impact
Without treatment, the various conditions, outlined above, that make up brachycephalic ocular syndrome, lead to irritation of the cornea and surrounding tissues causing constant discomfort, pain and possibly blindness.
Surgical treatments may help, although some Pugs need multiple operations which themselves can cause distress and discomfort. Despite surgery, many dogs will need ongoing veterinary visits and frequent topical eye medications. For some individuals both of these are difficult and distressing.
Prolapse of the eyeball is a veterinary emergency that can lead to blindness. The distress shown by dogs with a prolapsed eyeball indicates that it is very painful (Mould 1993).
3. Duration of welfare impact
Without surgical treatment brachycephalic ocular syndrome is life-long. Surgery cannot correct all the anatomical defects involved in this syndrome. Life-long medical treatment may alleviate some signs.
4. Number of animals affected
Probably all Pugs have this condition to some degree.
From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are Pugs (Lucy Asher 2011, personal communication), we estimate that the UK population size of this breed may be around 30,000.
Brachycephalic ocular syndrome is suspected in any Pug showing any of the signs outlined . Diagnosis of the extent and severity of the abnormalities requires thorough examination of the eyes.
Brachycephalic ocular syndrome is a result of selective breeding for brachycephaly – abnormal, short-muzzled, head shape. As far as we are aware, the genetic changes that underlie this inherited defect are not fully understood but at least two genes are thought to be significantly involved.
7. How do you know if an animal is a carrier or likely to become affected?
All Pugs have a brachycephalic head shape therefore probably all are affected with brachycephalic ocular syndrome to a greater or lesser extent. Examination of any puppy prior to purchase is essential, along with its dam and sire. Dogs showing any signs of brachycephalic ocular syndrome, or whose parents have any signs or have had surgical procedures or medical treatments to alleviate the condition should not be purchased (because if there is, instead, a demand for unaffected animals, the population will soon be comprised of healthier relatives less at risk of these chronic and serious painful conditions).
8. Methods and prospects for elimination of the problem
As brachycephalic ocular syndrome is a consequence of the brachycephalic head shape, it seems unlikely that it will be possible to elimination the condition from Pugs without changing the conformation of the breed (and their breed standard) significantly, although it may be possible to select for lines that are less severely affected. Unfortunately, as the Pug is one of the most severely brachycephalic of breeds, it may be impossible to eliminate this problem, or to do so in a reasonable time, without out-crossing to breeds that are less, or are not, brachycephalic. Opinions differ as to whether it is ethically acceptable to breed animals whose welfare is likely to be compromised.
For further details about this condition, please click on the following:
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
The term “brachycephaly” comes from the Greek words for short and head. The term applies to all breeds of dog (and cat) with short heads. The brachycephalic dog and cat breeds include: Pugs, English bulldogs, Pekingese, French bulldogs, Lhasa Apsos, Boxers, Shih Tzus, Boston terriers and Persian cats.
The brachycephalic head shape is due to an inherited defect in development of the bones of the skull (Stockard 1941). The length is markedly reduced, with severe shortening of the muzzle and skull (Stockard 1941). However, the soft tissues of the head are not similarly reduced in size. There are a number of serious medical conditions associated with the brachycephalic shape – these include brachycephalic airway obstruction syndrome (BAOS) (discussed in detail elsewhere, see BAOS in English bulldog), difficulties giving birth (see foetal pelvic disproportion in Boston terriers), dental problems caused by maxillary brachygnathism (the top jaw is abnormally short), and exophthalmos and brachycephalic ocular syndrome discussed here.
Figure 1. The brachycephalic skull is characterised by its shortening, particularly of the muzzle and by shallow eye sockets and deformed jaw. This image depicts an English Bulldog. Similar characteristics are shown, to varying degrees by all brachycephalic breeds.