Dana\Tom insertion.
Differentiation of the photoreceptor precursors is moderately suppressed in the centre of the eye imaginal discs, first seen at the middle third instar stage. Degree of suppression correlates with the severity of defect in the adult eye morphology.
Circumferential reduction of differentiated eye tissue, marked by an anterior indentation from a distinct V to a rectangle and the posterior margin is irregularly shaped. Anterior identation includes flecks of red pigment and supernumerary interommatidial britles, but not ommatidia.