Bhashya
चक्षुरेव ऋक् आत्मा साम ।आत्मेति च्छायात्मा,तत्स्थत्वात्साम ॥
In plain words
The eye itself is the ṛk, and the self is the sāman. This self is the shadow in the eye, and because it rests there, it is known as the sāman.
Close to the Sanskrit
The eye indeed is ṛk, the self is sāman. The self thus is the shadow-self, because of abiding therein, it is sāman.