Impact of facial conformation on canine health: corneal ulceration - PubMed (original) (raw)

Impact of facial conformation on canine health: corneal ulceration

Rowena M A Packer et al. PLoS One. 2015.

Abstract

Concern has arisen in recent years that selection for extreme facial morphology in the domestic dog may be leading to an increased frequency of eye disorders. Corneal ulcers are a common and painful eye problem in domestic dogs that can lead to scarring and/or perforation of the cornea, potentially causing blindness. Exaggerated juvenile-like craniofacial conformations and wide eyes have been suspected as risk factors for corneal ulceration. This study aimed to quantify the relationship between corneal ulceration risk and conformational factors including relative eyelid aperture width, brachycephalic (short-muzzled) skull shape, the presence of a nasal fold (wrinkle), and exposed eye-white. A 14 month cross-sectional study of dogs entering a large UK based small animal referral hospital for both corneal ulcers and unrelated disorders was carried out. Dogs were classed as affected if they were diagnosed with a corneal ulcer using fluorescein dye while at the hospital (whether referred for this disorder or not), or if a previous diagnosis of corneal ulcer(s) was documented in the dogs' histories. Of 700 dogs recruited, measured and clinically examined, 31 were affected by corneal ulcers. Most cases were male (71%), small breed dogs (mean± SE weight: 11.4±1.1 kg), with the most commonly diagnosed breed being the Pug. Dogs with nasal folds were nearly five times more likely to be affected by corneal ulcers than those without, and brachycephalic dogs (craniofacial ratio <0.5) were twenty times more likely to be affected than non-brachycephalic dogs. A 10% increase in relative eyelid aperture width more than tripled the ulcer risk. Exposed eye-white was associated with a nearly three times increased risk. The results demonstrate that artificially selecting for these facial characteristics greatly heightens the risk of corneal ulcers, and such selection should thus be discouraged to improve canine welfare.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1

Fig 1. A 2 year old male Pug diagnosed and undergoing treatment for a corneal ulcer in his left eye.

Fig 2

Fig 2. Quantifying muzzle length (A-B), cranial length (B-C) and palpebral fissure width (D-E).

A, left: Muzzle length is defined as the distance (mm) from the dorsal tip of the nasal planum to the stop. Cranial length is defined as the distance (mm) from the stop to the occipital protruberance. B, right: Palpebral fissure width is defined as the straight-line distance (mm) between the medial and lateral canthus. As an example, this Cavalier King Charles Spaniel has a craniofacial ratio of 0.27 (muzzle length 28mm / cranial length 102mm), and a relative palpebral fissure width value of 33.3% ((palpebral fissure width 34mm / cranial length 102mm) *100)

Fig 3

Fig 3. Example of dogs with and without nasal folds.

A Bulldog with a marked nasal fold obscuring the nasal planum (A), and a relatively longer muzzled American Bulldog lacking this feature (B).

Fig 4

Fig 4. Probability of being affected by a corneal ulcer across the relative palpebral fissure width spectrum.

The curves are generated from a generalised linear mixed model that included the presence of a nasal fold, relative palpebral fissure width and craniofacial conformation as predictors for corneal ulceration, and breed as a random effect. Brachycephaly, the presence of a nasal fold, and a relatively wider palpebral fissure all significantly increased the risk of ulceration. Brachycephalic dogs with and without nasal folds, and non brachycephalic dogs without nasal folds are represented, with brachycephalic dogs with skin folds at highest risk throughout the spectrum.

Fig 5

Fig 5. Probability of being affected by a corneal ulcer across the craniofacial ratio spectrum.

The curve is generated from a generalised linear mixed model with craniofacial ratio as a single continuous factor to examine its effect on ulcer risk in isolation. As craniofacial ratio increases (and muzzles become relatively longer), corneal ulcer risk decreases.

Fig 6

Fig 6. Differentiating between higher and lower risk eye morphologies.

The Pug in (A) exhibits an extremely high-risk conformation for corneal ulcers, with a relative palpebral fissure width of 35%, compared to the Pug in (B), who exhibits a lower relative palpebral fissure width of 30% and correspondingly lower risk. It should be noted that 30% is still a high risk morphology, and should not be aimed for in most breeding programmes. The amount of visible sclera is easily discernible between these two dogs. Both dogs have a prominent nasal fold and are extremely brachycephalic.

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This study was funded by UFAW (www.ufaw.org.uk) while the primary author was supported by a joint BBSRC/RVC doctoral studentship (www.bbsrc.ac.uk; www.rvc.ac.uk). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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