Extended Data Fig. 4: Ommatidia viewing directions in Drosophila compound eye maps.

Related to Fig. 3. a, Left: a high-resolution confocal image showing autofluorescence from ommatidia (green, retina) and GFP-labelled Mi1 neurons (green, medulla). Lamina and medulla neuropils are visible (grey) due to nc82 antibody staining. Right: a different cross-section showing the arrangement of individual photoreceptors near the equator. Six dots (R1–R6) arranged as an “n” or “u” shape can be readily seen in each ommatidium. The 7th smaller dot (R7 + R8) in the centre is also often visible. Image is representative of >10 imaged samples. b, Comparison of ommatidia directions defined by lens-photoreceptor tip pairs (grey, used in this study) and by surface normal (red). The surface normal is a typical approximation for the viewing direction, but this estimate differs substantially from that based on the high-resolution structure of each ommatidium. Two corresponding rows are connected with grey lines to illustrate the differences in different eye regions. Notably, these differences are small near the centre of the eye and very large towards the front of the eye. c, Comparison of Mollweide vs. Mercator projections. Red circles show the amount of distortion (Tissot’s indicatrix) with respect to an infinitesimal circle on a sphere. See Methods for a discussion of our choice. d, Ommatidia directions and field of views (contours) for both eyes of the same fly as in Fig. 3. e, Six-neighbour inter-ommatidial angle (ΔΦ) along the equator (+/−15° elevation) for this same fly. f, Ommatidia directions and ΔΦ for two additional female flies. g, Shear angles for these two female flies, plotted as in Fig. 3i. h, Least squares spherical fit to the central 19 lenses shows the centre of the eye is flatter than the edges. i, The least-square circle fits to neighbouring lenses in vertical and horizontal directions, showing increasing curvature near the eye’s periphery.