In a minority of eyes, corneal refractive surgery is not the procedure of choice. This can be due to a number of reasons, such as insufficient reserves of corneal tissue, unusually high refractive errors or a high risk of corneal ectasia. Whatever the reason, we are only interested in the best possible outcome, so in these cases we may recommend artificial lens implantation. Artificial lenses can provide a useful – and sometimes the only – solution to a difficult refractive surgical problem.
A variety of different options are available for treating refractive errors with lens implants, including phakic intaocular lenses (IOLs), clear lens exchange (CLE) and intracorneal lenses (ICL). These are implanted with the expectation of permanence, although they can be removed surgically if necessary.
Phakic IOLs, also known as implantable contact lenses, are surgically placed either between the cornea and the iris (anterior chamber) or between the iris and the natural crystalline lens (posterior chamber). Anterior chamber phakic IOLs have been found to cause long term loss of function of the water-regulating mechanism of the cornea, and are no longer popular among most ophthalmologists. Posterior chamber IOLs are thought to accelerate the formation of cataract, but can be a useful option nonetheless. The IOL functions to modify (augment or reduce) the power of the natural lens, the focusing ability (accommodation) of which is preserved for near tasks such as reading.
CLE involves removing the natural lens before it develops a cataract specifically to treat a refractive error. An IOL is placed in the lens capsule. This procedure incurs all the risks of cataract surgery, including blindness, and should only be considered when every other available option has been exhausted. In contrast, laser refractive surgery carries a much lower risk to the eye. CLE can be recommended, however, in the treatment of narrow angle glaucoma.
ICLs, or corneal inlays, are still under investigation as a treatment for presbyopia. Early results suggests that they can be associated with high levels of patient intolerance due to the optical aberrations these devices induce. Evidence suggests that Laser Blended Vision is a far superior treatment for presbyopia.