Apex domains cannot have CNAME records.
Question and response
Question
dig opticien-valais.com. NS
Answer
opticien-valais.com. 5 NS ns1.opticien-valais.com.
opticien-valais.com. 5 NS ns2.opticien-valais.com.
Authority
The response has no authority records.
Additional
ns1.opticien-valais.com. 5 A 194.54.185.162
ns2.opticien-valais.com. 5 A 194.54.185.184
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0