Sight Rot

This gruesome infection causes bleeding from the eyes and, if left untreated, eventual blindness. This disease is transmitted to beasts and humanoids through contaminated water.
A beast or humanoid who drinks of water tainted by the disease must succeed on a DC 15 Constitution saving throw or become infected at stage 1. While infected, the creature must repeat the saving throw once every 24 hours. On a successful save, the creature's condition decreases a stage. If they fail the save, the condition progresses a stage. If the creature successfully saves while on stage 1, the disease is shaken off and they are no longer infected.

Type

Bacterial

Stage 1
The infected creature begins to feel pain and discomfort in their eyes as well as blurred vision. Creatures at this stage have disadvantage on Wisdom (perception) checks and Intelligence (investigation) checks.
Stage 2
Blood begins to flow from the infected creature's eyes. This gives them a -1 to attack rolls and ability checks that require sight. This penalty grows by 1 ever 24 hours until stage 3 is reached.
Stage 3
This stage cannot be reached by failing a daily save from stage 2. This stage can only be reached when the infected creature has a penalty of -5 or higher due to the effect of stage 2. At this stage, the afflicted creature loses its sight and is permanently blinded.