Part of the official UK Kennel Club testing scheme in Shar Pei
Both primary lens luxation (PLL) and primary open angle glaucoma (POAG) have been diagnosed in Shar Pei that are homozygous (carry two copies) for the 6 bp deletion in ADAMTS17 . Currently it remains unclear whether this single mutation can indeed cause both PLL and POAG, or whether the mutation causes POAG and the fact that both POAG and PLL have been diagnosed in dogs that are homozygous for the mutation is that it can be difficult to differentiate between the two conditions (because POAG can lead to secondary lens luxation and PLL can lead to secondary glaucoma). As a result, until POAG and PLL in Shar-Pei can be further characterized, we suggest they might be considered together as POAG-PLL in this breed.
Th early clinical signs of primary open angle glaucoma (POAG) can be detected by a veterinary ophthalmologist when dogs are between 3 and 4 years of age. The initial signs are a small, sustained rise in intraocular pressure (IOP) and lens subluxation. Unlike primary closed angle glaucoma, which is the more common form of glaucoma in dogs, there is no pectinate ligament abnormality and the iridocorneal angle remains open until the late stages of the disease. POAG is not painful in its early stages and the slow progression of this disease means that often owners are not aware their dog is affected until they notice their dogs’ eyes have become enlarged (due to the increased pressure) or a vision problem becomes noticeable. POAG is progressive, however, and the continued rise in IOP will eventually lead to pain and blindness.
PLL is the term given to the spontaneous displacement or movement of the lens from its normal position within the eye, as a result of rupture of the lens zonules that hold the lens in its normal position. The zonules are a network of tiny fibres that attach the edge of the lens to the ciliary muscle that circles the eye, in the same way that springs attach a trampoline to its frame. Following zonule rupture the lens usually moves to the anterior chamber at the front to the eye where it can cause damage and rapid onset glaucoma by obstructing the drainage of fluid out of the eye resulting in an increase of pressure within the eye. Glaucoma can cause irreversible vision loss if not treated quickly. PLL is invariably bilateral (occurs in both eyes), although a period of several weeks or months might separate luxation of the two lenses. Clinical signs of PLL include sudden onset of eye pain, clouding of the cornea (the front of the eye will look blue), redness of the “white” of the eye and a reluctance to exercise. PLL should be considered an emergency and veterinary assistance sought immediately.