This article was reviewed by Florence Cabot, MD
Like space in the “Star Trek” motion picture series, presbyopia remains one of the final frontiers of refractive surgery, but efforts are under way to develop the real restoration of accommodation.
Over the years, the results of accommodative pseudophakic IOLs have been mixed, but that may be ready to change and the last frontier of ophthalmology may be tamed with new lenses that provide options for surgeons and hope for their patients.
Accommodation and presbyopia involve several ocular structures—the ciliary muscle, pupil, lens, zonule, vitreous, and some brain structures and neural pathways as well. This makes restoring accommodation complex. Restoring accommodation means creating a device that has a continuously variable, adjustable, active, near-focusing ability. This can be thought of as similar to the autofocus of a camera. Over the years, several teams have worked on restoring accommodation, whether on the cornea, the lens, or on the sclera.
First generation IOLS
The first generation of accommodative IOLs relied on the Helmholtz theory of accommodation. The lenses are supposed to provide a forward shift, because they have flexible haptics that should respond to the contraction of the ciliary muscle. Results have been disappointing, and the few good results that have been seen were attributed to an increase of optical aberrations rather than an actual movement of the lens.
The Ophthalmic Biophysics Center (OBC) at the Bascom Palmer Eye Institute in Miami, FL, built a unique dual OCT system that provides dynamic imaging, so real-time video of the ciliary muscle can be seen on one side, with the anterior segment seen on the other side.
Researchers used that system to image patients that had received a Crystalens (Bausch + Lomb), a first-generation accommodative lens. They could see that after a 2-D accommodation stimulus the Crystalens was actually showing either a minimal forward axial shift (not able to provide useful accommodation to the patient), or no axial shift at all, or a backward axial shift in some cases.
Modular and multicomponent IOLs
The new-generation accommodative IOLs are modular and multicomponent, and provide postoperative adjustability. In both categories, the exact effective lens position is known. This allows precise IOL calculations and refractive outcomes.
Multicomponent open capsule IOLs
Some lenses do not have continuous adjustability, but allow for an adjustment to be made after the operation, and repeated over time. Within this category there are two subcategories. The first consists of two parts, a base component and an optic component.
The Gemini Capsule from Omega Ophthalmics, the Harmoni from ClarVista Medical, and the Precisight from infiniteVision Optics are this type of lens. These keep the capsule open, thus preventing posterior capsular opacification. The haptics stay in the bag while the optics can be exchanged and adjusted as many times as necessary later on.