The cave-dwelling Typhlotriton spelaeus larvas live in daylight. The l
arvas undergo a metamorphosis when the thyroxin level (T3 and T4) incr
eases. They leave aquatic life for terrestrial and subterranean aphoti
c life. The larval eyes are normal and show good vision response to te
sts. On the contrary, in the oldest larva and the adult, the eyes are
small with poor vision or no vision at all. The lens can disappear but
in any case the eyelids grow over the eye. The retinal degeneration t
akes place during and after metamorphosis. The admitted statement that
''after metamorphosis . . . the developing lids close over the eye an
d invade the cornea'' is not confirmed concerning the invasion, becaus
e it is now evident that the eyelids separate spatially from the resid
ual cornea. Consequently, the fibroblasts of the eyelids are not able
to invade the corneal stroma. In fact, the periocular tissues do not i
nvade the cornea but invade the eyelids' tissues. We are able to confi
rm that the development of the larval eyes is complete and apparently
normal. After metamorphosis, the eyes decrease in size. The cornea ''s
inks'' with the eye into orbit tissues. The eyelids cover the eye and
are themselves replaced by a supraocular skin. This fits the descripti
on of the human cryptophthalmia. We also demonstrate that even in the
degenerate eye the residual cornea retains the main structure of a nor
mal salamander cornea. The preservation of the endothelium and of the
Descemet membrane is exceptional in blind cave-dwelling vertebrates be
cause in the other degenerate corneas the edema of the stroma depends
on the spatial disjunction of the underepithelial stroma and the supra
endothelial stroma. Perhaps, the, very advanced development of the eye
and the late start of the degenerative processes could explain the re
lative preservation of the cornea. Thus, the arguments put forward ten
d to prove that the thyroxinic metamorphosis sets off the growth and f
usion of the eyelids but that the eye degeneration is related to hered
itary processes.