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Trends in Cataract Surgery

US Sensory Disorders Review, 2006:27-9 DOI:

Presbyopia—The Last Frontier
There is great excitement in the profession, the ophthalmic industry, and in the middle-aged public that implantable lenses can be used for presbyopia and that these devices that will lead to elimination of dependence on spectacles and contact lenses.

Simply put, presbyopia is caused by the normal, agerelated hardening of the lens. This hardening results in the loss of the ability of the eye to change the shape of the lens, thus limiting its ability to change focus from distant to intermediate or near objects. The ability to change focus is called accommodation.

Presently, there are three presbyopia correcting lenses that have been approved by the FDA.Two of these are ‘pseudo-accommodative:’ the ReStor by Alcon Laboratories, and the ReZoom by Advanced Medical Optics. Approved by the FDA as an ‘accommodating’ lens is the CrystaLens from Eyeonics.

A pseudo-accommodating lens is essentially a disc with concentric rings of different optical power. Thus, light entering the eye from distant and nearsources is divided by the rings and focused on the retina simultaneously.The brain selects which one to focus on, that is, which one to pay attention to.As light is divided, there is always a loss of image quality.While they work well, especially relative to the vision of a cataract patient before surgery, they are not perfect.

By contrast, accommodating lenses achieve their visual effects dynamically. True accommodation requires a transient and rapidly reversible change in the power of the visual system. In keeping with the Helmholtz theory of accommodation, the lens must change its shape or move forward and backward in the eye to change its power and focus. Either the lens moves within the eye, or additional power is added to it by some other means. To do that accurately, a complex series of actions must be initiated by muscles in the eye.

Few ophthalmologists today believe that any of the above mentioned lenses are adequate enough in their performance to use them for surgery when the patient only needs reading glasses. However, if the patient has cataracts, which require the removal of the natural lens, then these lenses offer an excellent alternative to traditional mono-focal IOLs.They are also indicated for patients without cataracts who want reduced dependence on reading glasses, but most ophthalmologists do not feel that 45- to 50-year-old presbyopic patients who have normal distance vision in both eyes should be subjected to surgery in hopes of keeping their distance vision normal and eliminating their need for reading glasses.