Bifocals are prescription eyeglasses that contain two lenses. One part of the lens (generally the upper one) is made to see objects far away and the other lens (lower lens) is made to enable vision of objects that are nearer. Bifocal eyeglasses are prescribed for people who have presbyopia, a condition where people find it difficult reading small print, having headaches, and eye strain with reading. This condition is generally caused due to the aging and hardening of the lens of the eye. People who use bifocals may experience headaches, and dizziness.