How much to expect from this settlement? Should I write a letter?

I have a lawsuit that has been going on for two years. Back in 2005 I was diagnose with a severe eye ulcer from the re nu solution which resulted in excruciating pain and left me with corneal scarring. I understand there were several other plaintiffs as well. I recently got a call and she told me they were going to get in contact with me about a settlement by the end of the month. Just curious on how much something like this will be? The lady that called also told me if I had anything else to tell her such as any long term effects that I may have forgot to tell her to let her know. I was thinking of wring a letter of what I went through...will this be better for my case? I'm not really sure what to do...I've never done this.