Cataract, the clouding of the lens in the eye, can develop due to multiple reasons such as aging or diseases such as diabetes. Posterior capsule opacification (PCO or secondary cataract) is caused by residual lens epithelial cells migration and proliferation, a few months or a few years after cataract removal surgery in up to 50% of treated patients. Residual anterior lens epithelial cells migrate from the equator beside posterior lens capsule towards the pupil centre and they opacificate into lens fibres by their differentiation (globular aglomerates or fusiform Elsching pearls). In that way, the capsule that holds the lens in place becomes clouded. Design and material of different types of intraocular lenses, their accommodation, some eye conditions or illnesses (retinis pigmentosa, glaucoma, pseudoexfoliation syndrome) and patient’s age affect the occurrence of PCO. Surgical technique also has a great influence in preventing the PCO. Symptoms of posterior capsule opacification or secondary cataracts are similar to those of cataracts. For many patients, the first sign of secondary cataract development is a feeling that their vision is cloudy or blurry. A change in visual acuity shown by decreased ability to read a Snellen eye chart occurs when secondary cataract develops and is significant enough to consider correction of secondary cataract with YAG laser. Treatment for secondary cataracts is the procedure called Neodymium YAG laser capsulotomy. YAG is a short for yttrium aluminium garnet, the type of laser used for the procedure. A small hole is made with a laser in the capsule. The procedure takes only a few minutes and is entirely painless. Indication for Nd:YAG laser capsulotomy not only depends on opacification density, but also depends on the patients subjective visual deterioration. Pharmaceutical substance usage for treating this condition is still in its experimental phase.