Third instar larvae have detectable dendritic arborisation of the lateral neurons in only 9% of cases. Optic lobes are completely missing in mutant animals and no retinal axons enter the brain, but eyelet cell boies and projections are present.

Mutant larvae show no significant response to light (as measured by a "checker assay").

Wild-type larvae reduce their path lengths and show increased head swinging when exposed to light. This response is abolished in so^mda larvae. Wild-type larvae show a greater change in direction when lights are turned on or off (light (L) to dark (D), or D to L transition) than in the absence of a light transition (D to D). The amplitude of change of direction is greater for the D to L than for the L to D transition. The difference in the amplitude of change of direction at all transitions is abolished in so^mda larvae.

Aberrant development of the larval photoreceptor (Bolwigs) organ and the optic lobe primordium of the embryo. Adult photoreceptors fail to project axons into the optic ganglion, as a consequence optic lobe development is aborted and photoreceptor cells show age-dependent retinal degeneration and exhibit severe defects in the light evoked response. Peripheral regions of the eye show indentations or depressions. Heterozygotes with so¹ are wild type.