The human eye is like other tools. It means if we use it correctly the result will be good and vice versa. We are not allowed to use our eyes as we wish, as we are not allowed to use a knife to injure or kill others. Hence, prohibited items must be known to avoid committing them. For example it is forbidden to look at unfamiliar (Na-Mahram) women. It does not mean that we should close our eyes completely since then we cannot walk or we might fall down on the ground, but it means we can reduce the amount that we see by limiting our view. Imam Sadiq (the sixth Imam of Muslims) said: “One look after another will sow the seeds of desire in the heart, and it is sufficient temptation for the person.” (Wasa’il al-Shi’ah, v.14, p.139)
A dirty look will also tear down the veils of modesty and chastity. There are many people whose life is ruined due to a dirty look. Only for instance it can be said that dirty look of a married man at unfamiliar (Na-Mahram) woman or girl will sow the seeds of desire in his heart and he will be in love with her gradually and it can ruin the family. And it is also forbidden for women because the same reason.
We should remember that dirty look, is a major reason for the spread of adultery.