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 (this is highlighted in the species accounts).
Most other non-trichoniscid woodlice (with a few notable exceptions. e.g. Eluma caleata) have the eye composed of many (usually more than 10) well pigmented ocelli.