Yes, as long as we can prove that the loss is over and above what you would have experienced naturally because of the pre-existing condition. If for example, you were suffering from a pre-existing condition and an injury at work meant you lost your eyesight a lot sooner than you would have otherwise have done, we would be able to make a claim for you. On the other hand if the progression of your pre-existing condition meant that you would have lost your eyesight regardless of the accident, there is less likely to be a claim.
As this is really complicated we can only answer this question fully on a case by case basis. Don’t allow the fact that you have a pre-existing condition to stop you from talking to an expert. You have nothing to lose and everything to gain.