are they hereditary? especaily if dog only 19 months old? would it be more likely to be because of a trauma  like banging into something?

Yes - hereditary juvenile cataracts can affect any dog and eye testing under the BVA/KC is recommended for several breeds.  Eyes can be tested from upwards of one year of age and thereafter breed club recommendations in my own breed for example are within a 12 month period prior to a dog or bitch being bred from.

There's info on the KC website re a DNA test developed for some breeds already (Boston Terriers and something or other .... ?)

HTH, Teri 

Depends on what type.  There are so many types out there it's hard to say and unless the dog is DNA clear or both parents DNA clear it's a chance it is herditary.

One of our old boys had PPC at 17 months.

both parents clear tested annualy and glaucma clear

IMO it is still likely to be hereditary, although the parents are not suffers it will be in the line somewhere and why we place so much emphasis on checking the dogs pedigrees and the health of the ancestors back as far as possible before selecting a stud or deciding to breed a bitch.

In most cases they can be removed with little problem and your vet will tell you when this is best undertaken, however your dog should not be bred.

So you don't have a DNA test then?  Annually clear could mean both parents are carriers (if of course it works as simple as that)

Our boy's parents where tested clear untill they were no longer being bred from.  He had a PPC from a young age. 

Many dogs in my breed will test clear every year untill 7/8 which is too late, most have already been bred from, with their offspring having been bred from!

this dog is a pet and is netured so will not be bred from but the owner concered asked my opinion and i didnt know much about cateracts

I should think an opthalmologist should be able to identify if the cause was due to trauma .....  but I'm not sure.
Being certified clear of any conditions (and there are a great many different ones) does not mean the dog(s) are not carriers.  This is exactly why DNA testing is being introduced wherever possible.

regards, Teri