One thing you can see in all the breeds is that they are trimmed a certain way on the head/face & this can make the eyes look bigger too. When you are talking genetics, Chiari is both hereditary AND congenital. Chiari is a deformity at the base of the skull & runs in specific breeds & ALL of these breeds, Yorkie, Chi, pom, ShihTzus all have that against them due to greeders such as this. When you are talking a deformity such as this, you WILL get more pups then not with the condition/deformity especially if you keep breeding the lines over & over. The round and/or square shape is what they breed for & is the cause of the deformity & unfortunately is a VERY STRONG defect meaning it doesn't take many rebreedings of lines to one another to make it predominant & will have most offspring with it. Take a look at the King Charles Cavilier Spaniel, it is said that all King Charles have a degree of Chiari witch causes the big bulgy eyes & hydrocephalus. It is because of people breeding yorkies to have the squaty compact body & that term Baby Doll face meaning very short muzzle & the very round or square face that causes the Chiari malformation as that is not the normal shape the head should be. The breeder that we got our Sassy from did this & now our vally is FULL of yorkies with Chiari
