Several types of IOLs are used for cataract surgery. The most common is the monofocal IOL, which allows for focus at a fixed distance. A disadvantage of the monofocal IOL is the requirement of the patient to wear corrective lenses after cataract surgery. Monofocal lenses include both spheric and aspheric IOLs. The difference between the two is in the surface of the lens, whether it is spherical or aspherical. This curvature is related to the correction of spherical aberration, or the excessive refractive power of the cornea at its periphery. Aspheric lenses are generally considered to be superior. They have been shown to produce clearer vision and greater contrast sensitivity. In the Nordic region 90% of the market is aspheric. Southern Europe uses more spherical lenses while Germany uses more aspheric. However, the use of aspheric IOLs involves a trade-off, with conventional (spheric) IOLs having been shown to produce better depth of focus and near vision.
LASERs, which stands for Light Amplification (by) Stimulated Emission (of) Radiation, were developed in 1960 by Theodore Maiman. Lasers were quickly adopted for ophthalmology with the first instance of their clinical use appearing in 1963. Over the last 50 years ophthalmic lasers have proliferated in both types of lasers and indications. Despite this diversity, all lasers function on the same fundamental principles. Lasers are created when the electrons in atoms in special glasses, crystal or gases absorb energy from an electrical current or another laser and become excited/elevated to a higher energy state. Electron orbits are less stable at these higher energy states, thus energy is released in the form of a photon which allows the electron to return to its ground state. Photons are particles of light, however, what makes laser photons unique is that they are all of the same wavelength, directional, and coherent (meaning the crests and troughs of the light waves are aligned) whereas ordinary light comprises multiple wavelengths and is not coherent.