The IOL horizon: accommodative intraocular lenses

Polymeric Materials for Eye Surface and Intraocular Applications

Ocular applications of polymeric materials have been widely investigated for medical diagnostics, treatment, and vision improvement. The human eye is a vital organ that connects us to the outside world so when the eye is injured, infected, or impaired, it needs immediate medical treatment to maintain clear vision and quality of life. Moreover, several essential parts of the eye lose their functions upon aging, causing diminished vision. Modern polymer science and polymeric materials offer various alternatives, such as corneal and scleral implants, artificial ocular lenses, and vitreous substitutes, to replace the damaged parts of the eye. In addition to the use of polymers for medical treatment, polymeric contact lenses can provide not only vision correction, but they can also be used as wearable electronics. In this Review, we highlight the evolution of polymeric materials for specific ocular applications such as intraocular lenses and current state-of-the-art polymeric systems with unique properties for contact lens, corneal, scleral, and vitreous body applications. We organize this Review paper by following the path of light as it travels through the eye. Starting from the outside of the eye (contact lenses), we move onto the eye's surface (cornea and sclera) and conclude with intraocular applications (intraocular lens and vitreous body) of mostly synthetic polymers and several biopolymers. Initially, we briefly describe the anatomy and physiology of the eye as a reminder of the eye parts and their functions. The rest of the Review provides an overview of recent advancements in next-generation contact lenses and contact lens sensors, corneal and scleral implants, solid and injectable intraocular lenses, and artificial vitreous body. Current limitations for future improvements are also briefly discussed.

Restoration of accommodation: surgical options for correction of presbyopia

Accommodation is a dioptric change in the power of the eye to see clearly at near. Ciliary muscle contraction causes a release in zonular tension at the lens equator, which permits the elastic capsule to mould the young lens into an accommodated form. Presbyopia, the gradual age-related loss of accommodation, occurs primarily through a gradual age-related stiffening of the lens. While there are many possible options for relieving the symptoms of presbyopia, only relatively recently has consideration been given to surgical restoration of accommodation to the presbyopic eye. To understand how this might be achieved, it is necessary to understand the accommodative anatomy, the mechanism of accommodation and the causes of presbyopia. A variety of different kinds of surgical procedures has been considered for restoring accommodation to the presbyopic eye, including surgical expansion of the sclera, using femtosecond lasers to treat the lens or with so-called accommodative intraocular lenses (IOLs). Evidence suggests that scleral expansion cannot and does not restore accommodation. Laser treatments of the lens are in their early infancy. Development and testing of accommodative IOLs are proliferating. They are designed to produce a myopic refractive change in the eye in response to ciliary muscle contraction either through a movement of an optic or through a change in surface curvature. Three general design principles are being considered. These are single optic IOLs that rely on a forward shift of the optic, dual optic IOLs that rely on an increased separation between the two optics, or IOLs that permit a change in surface curvature to produce an increase in optical power in response to ciliary muscle contraction. Several of these different IOLs are available and being used clinically, while many are still in research and development.