There are two sides to this, I'd recommend reading both and seeing what you think.

Francis, Delicia et al. 1987 A reassessment of the risk of multiple sclerosis developing in patients with optic neuritis after extended follow-up

- and -

Miller, David et al. 1988 The early risk of multiple sclerosis after optic neuritis

Here's a newer one, but I could only find the abstract.

Beck, Randy et al. 2003 (abstract only)High- and low-risk profiles for the development of multiple sclerosis within 10 years after optic neuritis: experience of the optic neuritis treatment trial

Years ago, Kim had an episode where she completely lost her vision for a few days. This scared her big time. It was only one instance, but certainly a significant one. Ken