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Okzanna Articles		   
Chow Chow Eye Disorders
     
Have your Chow Chows tested for common eye problems that may be hereditary before selecting them for breeding.
by Dr. Izak Venter (MMEDVET OPHTH)
A.) Entropion

A comformational defect resulting in an "in-rolling" of one or both of the eyelids which may cause ocular irritation. It is likely that entropion is influenced by several genes (polygenic), defining the skin and other structures which make up the eyelids, the amount and weight of the skin covering the head and face, the orbital contents, and the conformation of the skull.

Breeding advice: NO
B.) Corneal dystrophy-endothelial

Corneal endothelial dystrophy is an abnormal loss of the inner lining of the cornea that causes progressive fluid retention (edema).
With time the edema results in keratitis and decreased vision.

Breeding advice: NO
C.) Persistant pupillary membranes (PPM)

Persistant blood vessel remnants in the anterior chamber of the eye which fail to regress normally during the first three months of life. These strands may bridge from iris to iris, iris to cornea, iris to lens, or form sheets of tissue in the anterior chamber. The last three
forms pose the greatest threat to vision and when severe, vision impairment or blindness may occur.

Major PPM's have been observed in the breed. Many ophthalmologists have observed puppies so severely affected that they are temporarily or permanently blind. The blindness is due to adherence of the membranes to the cornea and/or lens.

Breeding advice: NO
D.) Glaucoma

Glaucoma is characterized by an elevation of intraocular pressure (IOP) which, when sustained, causes intraocular damage resulting in blindness. The elevated intraocular pressure occurs because the fluid cannot leave through the iridocorneal angle. Diagnosis and classification of glaucoma requires measurement of the IOP (tonometry) and examination of the iridocorneal angle (gonioscopy). Neither of these tests are part of a routine screening exam for certification.

Age of onset in the Chow Chow appears to be anywhere between 3-6 years of age and has been observed as a bilateral condition. Gonioscopy has evidenced extremely narrow iridocorneal angles and in many regions no evidence of trabecular meshwork.

Breeding advice: NO
E.) Cataracts

A partial or complete opacity of the lens and/or its capsule. In cases where cataracts are complete and affect both eyes, blindness results.
The prudent approach is to assume cataracts to be hereditary except in cases known to be associated with trauma, other causes of ocular inflammation, specific metabolic diseases, persistant pupillary membrane, persistant hyaloid or nutritional deficiencies. Cataracts may involve the lens completely (diffuse) or in a localized region.

In the Chow Chow, the only reported cataracts is congenital. The clinical appearance is variable, ranging from small nuclear or capsular opacities to generalized opacity. The central lens (nucleus) is most consistently affected with variable involvement of the peripheral lens (cortex). Concurrent ocular anomalies may include entropion, microphthalmia, persistant pupillary membranes, and retinal folds, although any direct relationship of these latter conditions to the cataract is unclear.

Breeding advice: NO


References:
1-ACVO Genetics Committee, 1995 and/or Data from CERF All Breeds Report, 1991-1995.
2-Corcaran KA, Koch SA, et al: Primary glaucoma in the Chow Chow. Prog Vet Comp Ophthal 4:193, 1994.
3-Collins BK, et al: Familal cataracts and concurrent ocular anomalies in Chow Chows, 200:1485, 1992.
Also have your Chows tested for hereditary CANINE HIP & ELBOW DYSPLASIA - described by
Dr. Larry van Niekerk BVSc(Hons), MmedVet(Chirg).		 
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