Eye regrowth declines with increasing age.
The Regrowth Index (RI) is a measure of eye regrowth quality (Kha et al., 2018). Each regrown eye is assigned to one of four phenotypes: full (comparable to an unoperated control eye), partial (minor abnormalities with some reduction in size), weak (no lens and small size), and none (no regrowth). To obtain the RI value, the number of tadpoles in each category is multiplied by: 3 (full), 2 (partial), 1 (weak), or 0 (none), added together, and then divided by total number of tadpoles. A value of 300 denotes full regrowth in all individuals in the group whereas a value of 0 denotes no regrowth in all individuals. (A) At 5 days post surgery (dps): developmental stage. 27, RI = 281 (n> 100); st. 28 RI = 251 (n = 67); st. 29–30, RI = 159 (n = 142); st. 31, RI = 82 (n = 106); st. 32, RI = 37 (n =113); and st. 33–34, RI = 10 (n = 70). *P < 0.01, vs. st. 27. (B) Representative images showing resulting eyes at 5 dps. Corresponding top and bottom panel show side and top views of the same tadpole. (B1, B1’) Unoperated control eye indicated by yellow arrowheads. (B2, B2’) st. 27. (B3, B3’) st. 28. (B4, B4’) st. 29–30. (B5, B5’) st. 31. (B6, B6’) st. 32. (B7, B7’) st. 33–34. Green arrowheads: Full regrown eyes; orange arrowheads: partial eye regrowth; red arrowheads: no regrowth. Top panels: dorsal is up and anterior is to the left. Bottom panels: anterior is up. Scale bar: 500 µm.