Flies carrying Hsap\RALAG23V.GMR have eyes with abnormal external morphology, with the phenotype being more severe if they carry two copies rather than one copy of Hsap\RALAG23V.GMR. The orientation of the ommatidia is irregular, although most ommatidia contain the normal number of photoreceptor rhabdomeres. A severe loss of rhabdomeres and pigmented lattices is seen in flies carrying two copies of Hsap\RALAG23V.GMR. These defects are seen in flies immediately after eclosion, indicating that these defects are not likely to be caused by retinal degeneration. The initial stage of neuronal differentiation in the eye disc in third instar larvae is not disturbed in flies carrying two copies of Hsap\RALAG23V.GMR. At 40 hours after puparium formation (APF) the normal spacing pattern of the ommatidia is disrupted compared to wild type. The number of cone cells and primary pigment cells appears normal, but the arrangement of the cells in the ommatidia is highly disorganised. Secondary and tertiary pigment cells are misshapen compared to wild-type cells at 40 hours APF. More filamentous actin bundles are seen in the ommatidia, especially in the pigment cells. The shapes of the photoreceptor cells and their rhabdomeres is disrupted. Swollen pigment cells are visible between the photoreceptor cells, suggesting that the spreading of cells is impaired. At the basal surface of the wild-type retina, secondary pigment cells elongate radially and form a "petal" pattern with tertiary pigment cells and bristles. This "petal" pattern is highly disorganised in the retina of flies carrying Hsap\RALAG23V.GMR. The retina is nearly normal in flies carrying one copy of Hsap\RALAG23V.GMR; pigment cells extending along and surrounding the rhabdomeres are seen in longitudinal sections and at the floor of the retina a layer of pigment cell feet is seen.