Closing one's eyes enhances the experience by allowing you to focus on the tactile senses which are more critical during cunnilingus. Sight can be distracting due to the close proximity. People's eyes don't focus well on things very close up. The feel of the woman's inner thigh brushing against your face, the flesh of her legs moving in your hands, the sensation of your tongue gliding across her labia. It also allows for you to hear her moaning better. The tactile and auditory senses provide more than enough feedback to gauge a women's pleasure.