Fig. 3: Non-uniform sampling of visual space established by µCT of the Drosophila eye.
From: Eye structure shapes neuron function in Drosophila motion vision
a, Schematic of the Drosophila visual system, highlighting the retina. b, Maximal intensity projection of a whole fly head scanned with µCT. Lenses are labelled with white spheres in the left half. Scale bar, 50 μm. c, Magnified cross-section (boxed region in b) showing lenses and photoreceptors, with example tip–lens pair defining the viewing direction of that ommatidium. Scale bar, 10 μm. d, Magnification of boxed region in c. Photoreceptors in each ommatidium are arranged in an ‘n’ or ‘u’ shape above or below the equator30. Scale bar, 20 μm. e, Right eye ommatidia directions represented by points [x, y, z] on a unit sphere. The +h row is based on d, and +v divides approximately equal halves. f, Mollweide projection of three-dimensional (3D) ommatidia directions (‘Eye | Moll’) and inter-ommatidial angles (ΔΦ, averaged over six neighbours). Contour lines show iso-levels. g, A unit hexagon with seven columns (home column and surrounding six), illustrating the conventions used to characterize the geometry of the eye’s viewing directions. The +h axis is the line from the centre of two right neighbours to two left neighbours, and the +v axis is the line from bottom neighbour to top. Shear angle α is the angle between +h and +v axes. Inter-ommatidial angles include six-neighbour ΔΦ = mean(|v1|, |v2|, |v3|, |v4|, |v5|, |v6|), vertical-neighbour ΔΦv = mean(|v1|, |v4|), horizontal-neighbour ΔΦh = mean(|v2v6|, |v3v5|). Using small-angle approximation, angles are computed using the Euclidean distance (\(| \cdot | \)) of points on the unit sphere in e. h, Spatial distribution of ΔΦv and ΔΦh. Points represent ommatidia directions as in f. i, Distribution of shear angles across the right eye, with three example unit hexagons from the same vertical grid line, each aligned to the meridian line through its home column. Inset histogram shows all shear angles. Vertical scale bar corresponds to a uniform distribution. In h,i, points lacking a complete neighbour set are empty circles. Points not matched to medulla columns (Fig. 4a) are not plotted.
