Presbyopia: Ageing results in weak ciliary muscles. This reduces the power of accommodation of eyes. As a result, the person finds it difficult to see nearby as well as distant objects. This defect is rectified by using bi-focal lens.
Astigmatism: This condition develops because of irregular curvature of cornea. A person suffering from this defect is unable to differentiate between vertical and horizontal planes. This defect is rectified by using cylindrical lens.
