Say a soldier sustained some defect that caused him to go blind while he was still in the middle of his term. Due to the physical setback of not being able to see, will he receive an honorary discharge? Or would his officers find some light duties for him to do?
I think this question can be best answered by appealing to the P.Oxy.39, papyrus, Oxyrhynchus, Egypt, AD 52, which deals with a man named Tryphon who was released from Imperial service due to a cataract, which of course caused Tryphon to have poor sight. Some do debate whether the source actually deals with Tryphon being part of the army or whether he was simply a part of imperial administration, but either way, partial or full blindness certainly seems to have been a cause for release from imperial service, be it in the armed forces or in the administration.
We're perhaps inclined to think it deals with the army, simply as surely the administration could still make use of Tryphon's skills without his sight. However, the source also state's Tryphone to have been a weaver, and most would imagine sight being a crucial sense for weaving! Whether or not he weaved in imperial service under some capacity, many Roman soldiers often made use of their prior careers whilst in service, can merely be speculated upon. Regardless, he was released from service due to his poor eyesight.
I hope this has helped answer your question!
Sources:
P.Oxy.39, papyrus, Oxyrhynchus, Egypt, AD 52
The Complete Roman Army - Adrian Goldsworthy