Many Trichoniscids have a single omatidium on each side of the head. In species, such as Trichoniscus sp. the eye comprises three ommatidia in a tight goup (but separated in juveniles). Some species, such as Metatrichoniscoides sp. are blind; completely lacking ommatidia.
Following preservation in alcohol some species lose their eye pigment and may appear blind - TAKE CARE with preserved material.
Most other non-trichoniscid woodlice (with a few notable exceptions) have the eye composed of many (more than 3) well pigmented ocelli.