While meditating on a couple of verses in the Gospel of Matthew, King James Version, I found myself considering just what I was seeing. Jesus used the words "evil" and "single" to describe the person's eye. Here I quote those verses:
"The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness!" - (Matthew 6:22-23 -- KJV)
We speak of being enlighten. Our eyes light up our understanding, opening us to Truth or are they blocking Godly Wisdom. In the above quote I see Jesus telling us to look with single sight to God for understanding and not to "evil" worldly answers to life's problems.
To choose which type of eye we are going look out with is the question. A good, clear, single eye is focused on God's will and message. This brings light into the person. If we choose to focus on evil, bad things of the world order we bring darkness into our Soul or mind. The ways of the world lead to darkness.
The old Hymn "Keep your eyes on Jesus" is a good way to live successful life.