Potential side effects associated with progressive lenses include a sensation of headache, nausea, dizziness, distortion and difficulty seeing in low light. Also, there can be distortion in peripheral vision known as the "swim effect" occurring due to changes at the edge of the lenses.
One reason for initial nausea and dizziness when wearing progressive lenses is difficulty adjusting to the different lens powers within the progressive lenses. During the adaptation period, senses of depth perception and distance are altered. Peripheral distortion can occur at first when moving the eyes side to side rather than moving the head to see. The side effects are temporary and should only last a few hours to a few weeks. Sometimes people require minor changes to their lenses over time to help with the adjustment period.