If the difference between the eyes is up to 3 diopters, iseikonic lenses can compensate. At a difference of 3 diopters the lenses would however be very visibly different — one lens would need to be at least 3 mm thicker and have a base curve increased by 7.5 spheres. Example
Consider a pair of spectacles to correct for myopia with a prescription of −1.00 m−1 in one eye and −4.00 m−1 in the other.
In the elderly, it can be caused by deterioration of bone, although rare. In children, the majority of flail chest injuries result from common blunt force traumas or metabolic bone diseases, including a group of genetic disorders known as osteogenesis imperfecta. Diagnosis
Diagnosis is by physical examination performed by a physician. The diagnosis may be assisted or confirmed by use of medical imaging with either plain X ray or CT scan. Treatment
Treatment of the flail chest initially follows the principles of advanced trauma life support. Further treatment includes:

Good pain management includes early regional anesthesia (e.g. intercostal blocks or erector spinae plane blocks) and avoiding opioid pain medication as much as possible. This allows much better ventilation, with improved tidal volume, and increased blood oxygenation. Positive pressure ventilation, meticulously adjusting the ventilator settings to avoid pulmonary barotrauma. Chest tubes as required. Adjustment of position to make the person most comfortable and provide relief of pain. Aggressive pulmonary toiletA person may be intubated with a double lumen tracheal tube. In a double lumen endotracheal tube, each lumen may be connected to a different ventilator. Usually one side of the chest is affected more than the other, so each lung may require drastically different pressures and flows to adequately ventilate. Surgical fixation can help in significantly reducing the duration of ventilatory support and in conserving the pulmonary function.