Alsalamu Alaykum
The Messenger of Allah (saw) said: "For everything there is a face and the face of your religion is prayers. So see to it that none from amongst you damages and disfigures the face of his religion." (Source: Biharul Anwar, Volume 82, Page 209) & “If Your Salaat is accepted then all your other deeds /Aamal are accepted"
Before responding this question, we shall know that Salat or Namaz is the most important and a complete system of worship in Islam. Literal meaning of salat is DUA. Considering salat as insignificant or taking it lightly (Istekhfaf-e-Salat) is a major sin. A person, who offers salat, but does not care about the masail (rules and laws) of salat, is like one who considers salat as insignificant. For some persons, the lack of knowledge of some masail of salat, wudu and ghusl, may be an acceptable excuse, but for many other persons, the lack of knowledge is no excuse, and the Islamic sharia may require such persons, in some cases, even to repeat the salat of whole life with the correct method. Hence it is necessary for every Muslim to know and understand the masail of salat carefully so that he gains full benefit of this act of worship and he is also not considered as one who is careless about salat.
However, concerning to the above mentioned question, we shall know that according to Islamic rules in this regard, closing the eyes during prayer is permissible but it is Makrooh (undesirable), it means it is better to leave that during praying.
Read more in;
http://www.sistani.org/english/qa/01280/page/2/#14915
http://www.islamic-laws.com/salaat.htm