The hyperiid amphipod, Paraphronima gracilis, apparently thrives with giant eyes that dominate nearly half its body

The eyes of Paraphronima are large and nearly transparent, with the exception of the small, orange retinas. The ommatidia of the eyes are arranged in rows perpendicular to the body axis. 

A single row of ommatidia may function together to boost the light gathering ability of the eye, using a process called spatial summation. 

In most other animals using spatial summation, a circular group of ommatidia may pool the light signal, boosting light sensitivity at the cost of spatial resolution. 

In Paraphronima, summation may occur in a linear, not circular, fashion. Spatial summation in one axis would allow the eye to gather more light, while reducing the cost to spatial resolution in one axis.  

We suspect that Paraphronima is mainly concerned with detecting linear appearing targets, like small siphonophores which could easily be targeted in a single axis.

 
http://nmnh.typepad.com/no_bones/2015/01/the-strange-and-wonderful-eyes-of-paraphronima-gracilis.html