Your question is not simple to answer to because what you call 'original sin' can have several meanings and interpretation.
The logic you presented works hardly: it is very simple and do not take into account other "variables". For instance, is the 'first sin' inherited by us?
Also, according to your reasoning, can you individuate the first passage where, in the bible, it's spoken about disability? Then all the facts/events that happen before could be the cause of disability.
This is just to say that having a rigid logic is not, in my opinion, the best approach to the Scripture.
Thus said, like @AffableGeek was suggesting, the passage from John 10 contains some answers: "This man was not born blind because of his sin or his parents' sin, but in order that the glory of the Lord might be shown."
According to this passage, but also other reading other miracles in the Gospel, we understand that:
Sin is not inherited: to actualize it in our daily life, my interpretation is that there is not direct connection with our parent's sins. Hence if my father killed a man, God is not going to punish me for that (to put it veery simply!). However (and this is an angle of view I really like and use often as an approach to the scripture) it DESCRIBES how things work in real life: if my father killed a man, he will be probably have troubles in his life, and it will negatively reflect on my growth as a child, on my personality...
So, the evil (sins) around us can create disabilities: pollution, incests, hazards caused by man not respecting nature and so on.
The scripture invites us to understand not much the CAUSES of the disability, but its purposes! It's revolutionary! We always try to understand why something happened, while in Chirst's view is more imortant to understand how the glory of God can manifestate.
I also worked some time with handicapped people, and I can assure you that staying close to such people OBLIGE you to make a lot of virtuos things like:
- realizing which are the important things in life
- appreciate what you already have
- give love and care to somebody, thus 'training' your hearth not to be selfish
- ... and many others...
So, to answer to your question, I think that the best way to reconcile with the belief that disability is a result of original sin, and sin affecting the world, is:
- accept the disability
- accept that it can eventually come from other (or yours) sins
- MOST IMPORTANT: try to live the real but misterious fact that disability is a place where God want to manifestate his presence.