Fig. 4. Transmission change in different areas of the corneas of T. hamiltoni (Th; Aii–Eii) and T. pleurogramma (Tp; Ai–Ei) during three stages of light- and dark-adaptation (LA, light-adapted; LA+30 min dark, the halfway point of dark-adaptation; DA, dark-adapted). Mean transmission measurements are shown for five areas of each cornea (see inset). Due to the symmetrical distribution of the pigment in the ventral and the dorsal hemifields, the measurements for Areas 1 and 2 were averaged. The central cornea (Area 3; Ci,ii) shows the largest change in transmission properties during the adaptation change while the properties of the dorsal and ventral rims (Area 1; Ai,ii) remain constant. During dark-adaptation the central areas of the cornea (Areas 3–5; Ci,ii–E,i,ii) transmit increasing amounts of light in the 400–500 nm wavelength band while the reverse is true in Area 2 (Bi,ii), indicating that the pigment is shifted from the center towards the rim of the corneas.

Return to article