While this is generally the rule, we all know that there are exceptions to every one :-)

I had ON in both eyes, although one was worse than the other.

My right eye was "legally blind". I could seem some light out of it, but the vison measured 20/400.

My left eye was better, it was only 20/100.

If any of your sisters doctors are thinking that it could be ON, your sister needs to push for IVSM as soon as possible. The longer ON lasts, the more chance of permanent damage.

It took about 10 months from the time I noticed that something wasn't quite right with my vision, till the time I had IVSM.

None of my doctors were very optimistic for a good outcome, because of the time I suffered with it.

At two weeks post IVSM, my vision was 20/35 and 20/75. Nowhere near what my vision was pre-ON, but good enough to make my opthalmologist clap his hands, jump up and down and squeal!!!