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Adjustable intraocular lens technology

2014; Lippincott Williams & Wilkins; Volume: 40; Issue: 7 Linguagem: Inglês

10.1016/j.jcrs.2014.05.013

1873-4502

Nick Mamalis,

Corneal surgery and disorders

The future is ours to see. —Eddie Money Despite the advances in cataract surgery and biometry, incorrect intraocular lens (IOL) power remains one of the most frequent causes of IOL exchange. In the 16th annual ASCRS/ESCRS survey regarding foldable IOL complications and explantations, incorrect IOL power was the third most cited reason for IOL explantation.A The problem with incorrect IOL power may increase in the future as large numbers of baby boomers who have had refractive surgery develop cataracts. Difficulties in adequate measurement of eyes following refractive surgery may increase the frequency of incorrect IOL power postoperatively. Technologies are now emerging that may allow adjustment of the IOL power following cataract surgery. In this issue, my colleagues Joshua Ford, Liliana Werner, and I review adjustable IOL power technology (pages 1209–1224). Adjustable IOL technologies can be broken into 2 major areas: those that require an invasive adjustment and those in which the power change can be performed with a noninvasive adjustment. Intraocular lenses that require secondary procedures for power adjustment are typified by multicomponent IOLs. This idea is not new. It was explored initially with prototypes developed in 1996. The basic idea behind a multicomponent IOL is a base component that is placed in the eye, usually within the capsular bag, and a secondary component that is theoretically exchangeable if the power of the IOL has to be adjusted; ie, only the anterior-most component is removed. While early prototypes of the multicomponent IOL were evaluated in animals, a more recent prototype has been studied in humans. Experimental work is being done on a modular IOL system in which both components are made of a foldable hydrophobic acrylic material that will allow initial insertion through a small incision with docking of the optic component onto the base component. This optic component can be exchanged through a small incision when necessary. Also, the optic component can be manufactured as a monofocal, multifocal, or toric IOL that can be fit into the base component. Additional ways of adjusting IOLs invasively include a mechanically adjustable IOL that can change the power of the IOL by moving a cylinder and a piston relative to each other, changing the optic position. Finally, the concept of a repeatedly adjustable IOL that can change the position of the optic and subsequent power by twisting the optic much like a screw cap has been proposed. Multiple technologies that do not require invasive secondary procedures to adjust the IOL are also being evaluated. One is a magnetically adjustable IOL that can theoretically change the optic position using an external magnetic source. An even more interesting technology involves a liquid-crystal adaptive IOL. This is characterized by an electromechanical accommodating IOL that is activated by pupil constriction during accommodation with a change in the liquid-crystal optic to attain near vision. This type of technology may allow adaptive IOLs that can be driven by an external system to change the power of the IOL. Another interesting technology being evaluated to change the power of an IOL in situ is using the femtosecond laser, which can bombard the electrons of a very thin 50 μm layer of material within the optic of an IOL that can alter the 3-dimensional shape of the material and change its refractive index, inducing power adjustments.B Another way of changing an IOL power in a noninvasive manner uses the principle of 2-photon chemistry. Coumarins are a class of molecules that serve as a photoactive linker group that can be added to a polymer skeleton embedded within an IOL. Bombarding these polymers by a 2-photon treatment can alter the refractive index of the IOL and change its shape. The adjustable lens technology that is the most advanced is the so-called light-adjustable lens (LAL). This technology was developed by Calhoun Vision, Inc. and has been studied extensively in our laboratory.1,2 The light-adjustable IOL is a 3-piece silicone posterior chamber IOL that has silicone macromers containing an ultraviolet (UV) light-activated photo initiator. After implantation of the IOL, the power can be adjusted by activating the photoreactive components by exposure to a special UV light that will cause polymerization/crosslinking in the area of exposure, leading to a diffusion gradient. Unpolymerized macromers will then diffuse into the area of treatment, changing the curvature of the lens and the IOL power in general. This can provide a myopic correction, hyperopic correction, or even cylindrical corrections. Once the desired refraction is obtained, the entire IOL is irradiated, locking in the power. Extensive preclinical studies were performed in our laboratory documenting the reproducibility of the various treatment patterns to the IOL as well as biocompatibility and safety.C Clinical studies have now been performed throughout the world; phase 3 studies documenting the usefulness of this technology are ongoing in the United States. Adjustable IOL technologies are an exciting potential way of correcting postoperative refractive errors without requiring explantation or exchange of an IOL. These technologies include invasive multicomponent or mechanically adjustable IOLs. Intraocular lenses that can be adjusted noninvasively, allowing postoperative IOL power adjustment, appear to be a promising future technology.