MG act as springs in the retina to hold the neural retina together. (A) To test the biophysical properties of retinas lacking MG, we used AFM to pull on the tissue. (B) Tissue deformation was not significantly different for measurements at 33 hpf or 48 hpf (mean ± SEM [error bars], n = 10 retinas). (C) At 72 hpf, retinas deformed significantly more when no MG were present in the tissue than controls (mean ± SEM [error bars], n = 10 retinas). (D) To test if MG are under strain within the retinal tissue, we applied a laser ablation technique to specifically target the apical or basal processes of GFAP:GFP MG in vivo. Ablating the apical process resulted in its retraction of the process and displacement of the cell body basally to the IPL. Ablation of the basal process resulted in its rapid retraction and in cell displacement apically in the INL. The merge is the overlay between each time point. Red lines delineate the regions of ablation. (E and F) Confocal images showing the expanded GCL labeled in the ath5:gapRFP;vsx1:GFP transgenic fish after DAPT treatment. (G) In the absence of MG, we noted a significant increase specifically in the thickness of the GCL (n = 20 retinas, mean + SEM [error bars], P < 0.01). (H) Stiffness measurements at the time of treatment (∼45 hpf), 72 hpf, and 96 hpf of control and DAPT-treated retinae (n = 20 retinas, mean + SEM [error bars], P < 0.01). IPL, inner plexiform layer; ONL, outer nuclear layer. Bars, 15 µm.