Primary Lens Luxation

What is Primary Lens Luxation in dogs?

Chevromist eye diagramPrimary Lens Luxation, also known by its abbreviation PPL, is an often inherited disease of the eye that has been well documented in many breeds of dogs from terriers to the almost hairless Chinese Crested dogs. It is a painful condition that eventually leads to blindness in the affected dog. Dogs that are affected by Primary Lens Luxation undergo breakdown or disintegration of the zonular fibres which are responsible for supporting the lens inside the eye. This results in the lens to fall into the wrong position in the eye. If the lens falls into the anterior chamber, glaucoma and vision loss will affect the dog. Primary Lens Luxation with a hereditary cause is an autosomal recessive disease, but other causes including trauma to the eye can result in the condition.

Genetics of Primary Lens Luxation in dogs

As an autosomal recessive disease, the mutated gene responsible for Primary Lens Luxation needs to be inherited from both parents for the dog to be affected. The particular gene responsible is the ADAMTS17 gene on the canine chromosome 3 and DNA Disease Testing will determine if a tested dog is Clear of the disease (2 normal copies), a Carrier (1 normal copy and one mutated copy) or Affected (2 mutated copies of the gene). Mutated  ADAMTS17 genes have a single mutation at one point of the gene that is detected with DNA screening. Different to most autosomal recessive inherited diseases, carriers do have a very low increased risk of developing the condition, but these cases are quite rare.

What is the severity of Primary Lens Luxation in dogs?

Primary Lens Luxation is considered to be a medium to highly severe disease as untreated dogs will often become blind and suffer from ongoing pain from the dislocated lens. Primary Lens Luxation is not considered a fatal disease but does greatly impact the health and quality of life of an affected dog.

What are the symptoms of Primary Lens Luxation in dogs?

Dogs affected by Primary Lens Luxation vary in the age that they first show any signs of the condition from between 2 and 8 years of age, although some affected dogs may first show symptoms outside of this range. Onset of the clinical symptoms of Primary Lens Luxation can be sudden with the affected dog excessively blinking, squinting and producing copious amount of tears in response to the elevated pressure in the eye from the acute onset of glaucoma. While Primary Lens Luxation usually affects both eyes, often the eyes will be affected at different times from weeks to months apart.

Diagnosis of Primary Lens Luxation in dogs

veterinary eye checkDiagnosis of Primary Lens Luxation can usually be made by veterinarians performing an eye examination to see that the lens has dislocated from its normal position. As other causes are responsible for Primary Lens Luxation other than inheriting mutated genes, such as trauma, infection and inflammation, only a DNA Disease Screen for the mutated ADAMTS17 gene will confirm an inherited cause.

Treatment of dogs with Primary Lens Luxation

Surgery is the best form of treatment for dogs affected by Primary Lens Luxation but this must be performed within 72 hours of the onset if there is to be any chance of saving the affected dogs vision.  After this point, and loss of vision is confirmed the focus of the surgery is often to relieve the pain. Commonly, the decision is made to remove the eye to end the pain caused by the resulting glaucoma resulting in the dog leading a relatively pain free life.

References

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Gharahkhani P, O’Leary C, DuffyD, Bernays M, Kyaw-Tanner M. Primary Lens Luxation in Australian Tenterfield and Miniature Bull Terriers is due to an old ADAMTS17 mutation and is an additive trait. Open Genomics J. 2012 Mar;5:7-13

Gould D, Pettitt L, McLaughlin B, Holmes N, Forman O, Thomas A, Ahonen S, Lohi H, O’Leary C, Sargan D, Mellersh C. ADAMTS17 mutation associated with primary lens luxation is widespread among breeds.Vet Ophthalmol. 2011 Nov;14(6):378-84

Grahn BH et al (2003) Diagnostic ophthalmology. Congenital lens luxation and secondary glaucoma. Can Vet J 44(5):427

Johnsen DA et al (2006) Evaluation of risk factors for development of secondary glaucoma in dogs: 156 cases (1999-2004). J Am Vet Med Assoc 229(8):1270-1274

Lazarus JA et al (1998) Primary lens luxation in the Chinese Shar Pei: clinical and hereditary characteristics. Vet Ophthalmol 1(2-3):101-107

Sargan DR, Withers D, Pettitt L, Squire M, Gould DJ, Mellersh CS. (2007)Mapping the mutation causing lens luxation in several terrier breeds. J Hered. 98(5):534-8

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