Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

Toy Poddle

Toy Poodle

Distichiasis

Related terms: distichia, abnormal eyelash growth

(NB this is a different condition from trichiasis).

Outline: In distichiasis the position and direction of growth of some eyelashes is abnormal so that they touch the surface of the eyeball. Depending on the extent of the number, the degree of contact, the bristliness of the eyelashes, and perhaps other factors, this can lead to abrasion, ulceration, inflammation and infection of eye tissues which can cause serious discomfort, pain and untreated to partial blindness. It is said to be a common disease of poodles. It tends to occur from early in life and persist throughout life. The genetics have not been determined but it seems likely that avoiding breeding from affected animals would lead to reduction in prevalence and elimination of the disease.


Summary of Information

(for more information click on the links below)

1. Brief description

Distichiasis is an eye disease caused by extra or abnormally positioned eyelashes causing irritation and damage to the surface of the eye. Eyelids are lined by Meibomian glands, whose openings lie between the normal line of eyelashes and the surface of the eye. In distichiasis, which is a common genetic abnormality in some breeds of dogs, some eyelashes grow out of the Meibomian gland openings and these tend to abrade and irritate the eyes. This can cause mild irritation and discomfort through to severe and painful disease if the cornea becomes damaged and infected.

2. Intensity of welfare impact   

This varies from mild to severe depending on whether the cornea becomes damaged, inflamed and infected.

3. Duration of welfare impact

Most affected animals show signs of the disease from early in their life and these persist unless treated, although how badly affected the poodle is by the disease may vary as misdirected eyelashes grow and are shed.

4. Number of animals affected

Distichiasis is considered to be one of the commonest genetic diseases of dogs and it is often stated in the veterinary literature that poodles are especially prone to the disease (Bedford 1973, Long 1991, Gray 2007). However, as far as we are aware, there are no published data on the proportion of poodles affected. From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are poodles (Lucy Asher, 2011, personal communication), we estimate that the UK population size of this breed may be around 80,000.

5. Diagnosis

Distichiasis is diagnosed by careful examination of the eyelid margins of the poodle, using magnification if necessary. There is no genetic test for distichiasis in dogs.

6. Genetics

Distichiasis is said to be a dominant genetic trait but, as far as we are aware, the genetics have not been investigated in any detail. The disease is influenced by abnormal position and direction of eyelash growth, the nature of the eyelash hair – whether thick and bristly or thin and soft, and possibly by the nature of the growth cycles of the eyelashes, ie how long they grow before being shed. It is likely that these aspects, all of which may influence the likelihood and severity of disease, are under the control of various genes or sets of genes. 

7. How do you know if an animal is a carrier or likely to become affected?

The disease can often be detected from a young age through examination of the eye and eyelid. The genetics have not been elucidated but the fact that the disease is common in poodles suggests that there is a genetic link and that affected animals are more likely than non-affected animals to produce young that suffer from the disease.

8. Methods and prospects for elimination of the problem

As far as we are aware, there are currently no breeding schemes aimed at reducing the prevalence of, or eliminating, this disease. Animals with distichiasis should not be used for breeding.


For further details about this condition, please click on the following:
(these link to items down this page)


1. Clinical and pathological effects

Distichiasis is an eye disease caused by extra or abnormally positioned eyelashes causing irritation and damage to the surface of the eye (Lawson 1973). Dogs normally have eyelashes (cilia) only in the upper of their eyelids and these typically point away from the eye and do not touch it. Another structure of the eyelid are the sebaceous Meibomiam glands whose secretions help normal eye function. The openings to these glands are found on the inner rim of the eyelid, adjacent to the eyelashes. In distichiasis, eyelashes grow out of these Meibomian gland openings (Lawson 1973). These abnormal eyelashes tend to grow so that the hairs touch the surface of the eyeball (the cornea or the conjunctiva).

Distichiasis figure 1

Figure 1. The diagram on the left is shows a normal eye: the eyelashes grow away from the eye. The diagram on the right illustrates eyelash growth out of the Meibomian gland, directed towards the eye, leading to abrasion and irritation of the cornea. (The image is the property of ‘Eye Care for Animals’- www.eyecareforanimals.com to whom we are grateful for permission to reproduce it here).  

Whether or not these abnormal eyelashes cause a problem depends mostly on their structure: whether they are fine and soft or thick and hard. Fine, soft hairs seem to cause affected dogs few problems; thick, hard hairs more. The number of abnormally placed hairs varies greatly and the more there are the greater the likelihood of more severe consequences. Sometimes groups of hairs emerging together from a Meibomian gland opening become matted and may appear as a single hair.

It is the tissue of the eye, the cornea (the clear surface of the eyeball) and the conjunctiva (the tissues lining the eyelids and attaching to the eyeball) that are affected by the disease. These are very sensitive and the presence of an object rubbing on them is irritating. The first sign of this is increased blinking or holding the eye slightly closed. The irritation also often causes excessive tear production (Lawson 1973).

Distichiasis figure 2

Figure 2. A moderate case of distichiasis - there is, as yet, no apparent damage to the cornea of the eye despite inverted eyelashes coming in to contact with the eye itself.

 

Distichiasis figure 3

Figure 3. This dog is likely to be at a higher risk of corneal damage due to the thickness and number of hairs growing in the direction of the eyeball.  In both cases there are signs of increased tear production, which may be the result of distichiasis. (Images property of Susan Jacobi at www.vision4pets.com, to whom we are grateful for permission for their reproduction).

More severe problems occur when the abnormal hair is thicker and harder and when the irritation has been of longer standing. The animal may involuntarily draw its eye into the socket. This may cause the eyelids to roll inwards (spastic entropion) leading to further irritation of the cornea, as more eyelashes are brought into contact with it, and escalation of the problem. The eyelids themselves may be held tightly closed which in itself is painful due to muscle fatigue.

Irritation of the conjunctiva commonly causes inflammation. The conjunctiva becomes red and swollen and at increased risk of desiccation and infection. Chronic irritation leads to the cornea becoming cloudy, scarred, pigmented, and ulcerated and, in response to this, blood vessels grow across it. When ulcerated, the cornea is very painful. Long-term corneal damage can lead to partial blindness.

Distichiasis figure 4

Figure 4. More severe cases of distichiasis can occur in entropion (inversion of the edge of the eyelid), causing larger numbers of hairs come in to contact with the eye resulting in damage to the cornea and surrounding conjunctiva.

 

Distichiasis figure 5

Figure 5. Distichiasis may also cause the dog to hold the eyelid closed, which can cause further pain and have further impacts on the welfare of the animal. (Images property of Susan Jacobi at www.vision4pets.com, to whom we are grateful for permission for their inclusion).

 

The condition is best treated by removing the abnormally located hairs, under anaesthesia using cryotherapy or electroepilation. Treatment can be very effective but sometimes has to be repeated (Chambers & Slater 1984). Older methods of treatment involving surgery or cautery are no longer recommended.

Return to top

2. Intensity of welfare impact

Depending on the nature and level of damage to the eye, the welfare effects of distichiasis on the affected poodle will range from mild and intermittent discomfort through to severe and chronic discomfort and pain.

Return to top

3. Duration of welfare impact

Most affected animals show signs of the disease from early in their life and these persist unless treated. The effects of the disease, may be intermittent and vary in intensity as misdirected eyelashes grow and are shed.

Return to top

4. Number of animals affected

Distichiasis is considered to be one of the commonest genetic diseases of dogs and it is usually stated in the veterinary literature that poodles are especially prone to the disease (Bedford 1973, Long 1991, Gray 2007). However, as far as we are aware, there are no published data on the proportion of poodles affected. From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are poodles (Lucy Asher, 2011, personal communication), we estimate that the UK population size of this breed may be around 80,000.

Return to top

5. Diagnosis

Distichiasis is diagnosed by careful examination of the eyelid margins, using magnification if necessary. For those dogs that are reluctant to keep still during examination, sedation or anaesthesia may be needed. Lawson (1973) found that using the x25 lens of an operating microscope was necessary to detect half of the abnormal eyelashes present. Furthermore, it can be difficult to tell whether an abnormal eyelash observed is the actual cause of the eye problems experienced by the presenting dog. Small, abnormally positioned wispy eyelash hairs may be present in dogs in cases when the cause of eye disease is found not to be these, but some other factor e.g. an infection or eye trauma. In such cases, it may be necessary to trial-treat by removing the abnormal eyelashes to observe what difference this makes. However, eyelashes, even if wispy, should not normally touch the surface of the eye and any tendency to do so is an abnormality which is likely to increase the risk of complications.

Return to top

6. Genetics

Distichiasis is said to be a dominant genetic trait but, as far as we are aware, the genetics have not been investigated in any detail. The disease is influenced by abnormal position and direction of eyelash growth, the nature of the eyelash hair – whether thick and bristly or thin and soft, and may be also by the nature of the growth cycles of the eyelashes, ie how long they grow before being shed. It is likely that these aspects, all of which may influence the likelihood and severity of disease, are under the control of various genes or sets of genes.

With dominant traits a single gene, coming from either one of parents is expected to cause the abnormality (eg in this case, tendency for abnormal direction of growth of eyelashes). However, dominant genes may have incomplete penetration – that is - not all individuals with the gene always develop the problem or go on to develop it to the same extent.

There is no genetic test for distichiasis in Miniature and Toy poodles.

Return to top

7. How do you know if an animal is a carrier or likely to become affected?

The disease can often be detected in affected animals from a young age through examination of the eye and eyelid. The genetics have not been elucidated but the fact that the disease is common in poodles suggests that there is a genetic link and that affected animals are more likely than non-affected animals to have affected offspring. If the eyes and eyelids are found to be normal on examination at two to three years of age then it is unlikely that the dog has this problem or will go onto develop it.

Return to top

8. Methods and prospects for elimination of the problem

As far as we are aware, there are currently no breeding schemes aimed at reducing the prevalence of, or eliminating, this disease. Dogs with distichiasis should not be used for breeding

However, since distichiasis is considered to be very common in poodles, there is a risk that limiting breeding to only unaffected animals, might limit the size of the breeding population such that other genetic diseases may increase in prevalence, unless these are also taken into consideration. This problem would be likely to be avoided by out-crossing and breeding with unaffected dogs of other breeds.

Return to top

9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Stephanie Kaufman for assistance in illustrating it.

Return to top

10. References

Bedford PGC (1973) Distichiasis and its treatment by the method of partial tarsal plate excision. Journal of Small Animal Practice 14: 1-5

Carter JD (1995) The eyelids. In: Veterinary paediatrics, dogs and cats from birth to six months, second edition. Edited by JD Hoskins. WB Saunders, Philadelphia

Chambers ED and Slatter DH (1984) Cryotherapy (N20) of canine distichiasis and trichiasis: an experimental and clinical report Journal of Small Animal Practice 25: 641-659

Gray H (2007) Distichiasis. VIN Associate, accessed 24.11.2010. http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=2933

Hallwell WH (1967) Surgical management of canine distichia. Journal of the American Veterinary Medical Association 150: 874-879

Lawson DD (1973) Canine distichiasis. Journal of Small Animal Practice 14: 469-8

Long RD (1991) Treatment of distichiasis by conjunctival resection. Journal of Small Animal Practice 32: 146-148

© UFAW 2011


Credit for main photo above:

http://depositphotos.com/10575590/stock-photo-toy-poodle-puppy-on-green-grass.html ©Depositphotos.com/FotoJagodka