In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Q: The retina does not feel pain , so damage may not be felt for hours .
A: 
The retina has no sensitivity to pain , and the effects of retinal damage may not appear for hours , so there is no warning that injury is occurring .