28.1 Introduction

Intraocular lens (IOL) surgery has, like so many other innovations in medicine, a history strewn with a number of sometimes breathtaking successes as well as some failures and dead end-streets. In less than 70 years—since the pioneering days of Sir Alfred Ridley—IOL implantation has evolved from a freak method angrily denounced by Ridley’s peers in the late 1940s to a procedure that outranks any other medical intervention in sheer numbers (at least in the industrialized world) and in success rates. Today patients expect IOL surgery not only to be the means to overcome cataract but in many cases to “cure” a long-existing ametropia during the same intervention.

To improve an already highly successful, safe, and effective therapy is certainly a challenge, but it is a challenge that inventors, designers, and ophthalmologists strive hard to meet as is evidenced by the ongoing introduction of new types of adjustable IOLs and of new surgical techniques that may allow for even better precision and reproducibility of IOL placement.

28.2 Enhancing Depth of Focus

Some new generation of IOLs are extending the depth of vision (EDOF) to correct presbyopia. The Tecnis Symfony (lens model ZXR00 and toric lens models ZXT100, ZXT150, ZXT225, ZXT300, and ZXT375, Abbott Medical Optics, Abbott Park, IL) received the CE (European Conformity) mark in the summer of 2014 (Fig. 28.1 a). It incorporates a proprietary wavefront-designed aspheric or toric-aspheric anterior optic with a squared posterior optic edge that provides a 360° barrier (Fig. 28.1 b). The edge of the optic has a frosted design to reduce potential edge glare effects. The posterior optic of the lenses has a proprietary achromatic diffractive surface designed to reduce chromatic aberration for enhanced contrast sensitivity (Fig. 28.1 c) and a unique Echelette feature to extend the depth of focus (Fig. 28.1 d). This Echelette provides a novel pattern of light diffraction and is supposed to generate a wide focal range leading to a continuous extended range of vision and not, like multifocal lenses, a fixed number of focal points. Tecnis Symfony IOLs have pupil-independent lens performance in any lighting condition and are designed to minimize dysphotopsia (Fig. 28.2).

Early clinical reports (published in ophthalmological news media rather than in peer-reviewed journals) are speaking of an uncompromised distance vision with a very low number of patients requiring glasses for intermediate vision (about 5%). Data reported at the ESCRS meeting in London (September 2014) indicate that 81% of patients had uncorrected 20/20 visual acuity at far distances and 65% having uncorrected 20/20 vision at intermediate distances. According to these reports, 98% of patients were performing daily activities comfortably without glasses at far distance, 96% at intermediate distance, and 73% at reading distance. The amount of halo and glare is supposed to be comparable to a monofocal IOL, the visual experience has been described as smooth and similar to a zoom lens on a camera. Three months after implantation, 97% of Tecnis Symfony IOL subjects indicated that they would elect to have the lens implanted again.

28.3 Adjusting IOL Power: Light

Missing the intended target refraction is one of the more frequent problems that emerge after IOL implantation and which can lead to patient dissatisfaction. Although studies like those conducted by Murphy et al, who reported 72.3% of 1,676 eyes having been within 1 diopter (D) and 6.4% beyond 2 D of the planned refraction following cataract surgery, are a couple of years old, ¹ there is no question that incorrect IOL power remains a cause of less than optimal postoperative function. Ford et al have named technological inadequacies, mechanical issues, unpredictable effects of wound healing, and untreated astigmatism as the major causes of such an outcome. ² In these cases, the ability to postoperatively alter the IOL power seems desirable.

Probably the clinically most used of these lenses is the light adjustable intraocular lens (LAL, Calhoun Vision, Inc.) whose shape and, thus, refractive power can be changed by UV exposure of photoreactive components incorporated in the silicone lens matrix (Fig. 28.3 and Fig. 28.4). In 2003, Schwartz published the first in vitro and in vivo data regarding the LAL.s. Literatur The light delivery device (LDD) consists of a 365 nm ultraviolet (UV) light source and control interface mounted on a standard slit lamp (Fig. 28.5). When irradiated with this UV light, the macromers of the LAL undergo a chemical change known as photopolymerization, which leads to a predictable change in the shape of the LAL’s surface and, hence, the power of the lens. The principle of this system is as follows: irradiation of the lens by UV light causes macromers to polymerize and form silicone polymers in the irradiated area only. This creates an unstable diffusion gradient that is usually corrected in 12 to 15 hours as macromers diffuse toward the depleted irradiated area to re-create a uniform concentration of macromers throughout the lens. The diffusion of macromers in the depleted area induces a swelling in the irradiated zone, thus inducing a change in radius curvature of the lens (Fig. 28.6). Once the appropriate lens power adjustment is achieved, the whole lens is irradiated (“lock-in” irradiation) to polymerize the remaining macromers. The adjustment process may be repeated as often as necessary until the desired lens power is achieved. Once this power is obtained, the whole lens is irradiated in a lock-in step that removes all macromers, thereby ensuring that no further adjustment can be made to the lens power. Precise selection of target area, beam intensity, exposure time, and spatial intensity profile achieve the amount of lens power change required by each patient. The refractive index of the macromers is similar to the silicone matrix; therefore, the power change of the lens after irradiation is due to a change in lens shape and not to a change in lens refractive index. ^{2 ,​ 4}

In an early study with the LAL, 20 out of 21 patients (96%) were within ± 0.5 D of the intended refractive outcome, and 17 (81%) were within ± 0.25 D after lock-in. Postoperative spherical and cylindrical errors of up to 2 D can be corrected with this innovation. ⁵ In presbyopic patients, there is the option to create a customized near add (CNA) that is based on the individual patient’s pupil size in one eye after correction of any residual refractive error (sphere and cylinder). The fellow eye is corrected for emmetropia. In a group of 15 patients near, intermediate, and distance vision were deemed fair to good after the final lock-in. ⁶ We had very satisfactory outcomes using the so-called adjustable mini monovision, with the dominant eye adjusted for monovision and the nondominant eye targeted for − 1.25 D myopia. If well tolerated, a further adjustment for more myopia—depending on the patient’s reading habits and preferred near distance—is possible. The long-term stability of the adjustment has been proven in 122 eyes of 91 patients who underwent a follow-up of 18 months (Fig. 28.5); the average postoperative refractive error of + 0.96 spherical diopters had by then been reduced to a refractive error of 0.04 D. ⁷ The adjustments are generally well tolerated; in addition, in vitro studies showed no evidence for endothelial cell toxicity by the maximum dose of UV-A light employed during LAL treatment. ⁸

Although the postoperative UV-A irradiation itself poses no hassle, organizing the process of adjustment can be demanding for patients and clinical staff due to the number of necessary visits. The next generation of LAL may have a posteriorly placed UV-enhanced layer, which is currently tested and might decrease the number of postoperative adjustment procedures by specifically targeting and thinning this layer.

In the United States, the Calhoun LAL has not been approved yet by the Food and Drug Administration (FDA). Phases 1 and 2 of the required FDA clinical investigation have been completed; the third and final phase of this clinical trial is still ongoing. However, the Calhoun Vision LAL is commercially available in several countries in South America, as well as in Europe, where this lens has been CE marked in 2008.