dye photocoagulator, by placing green laser burns circumferentially outside the iris sphincter, or with a Nd:YAG photodisruptor, by creating approximately 4 partial sphincterotomies.

Adverse Effects, Complications, and Patient Dissatisfaction with Multifocal IOLs

Patient complaints after multifocal IOL implantation can generally be divided into 2 categories: blurred vision and photic phenomena (glare, halos). Patients may experience both groups of symptoms. These symptoms can occur even after uneventful surgery with a well-centered multifocal IOL.

Patients with multifocal IOLs are more likely to have significant glare, halos, and ghosting than are patients with monofocal, toric, or accommodating IOLs. These issues stem from a variety of different etiologies, including intrinsic IOL problems. The reports of halos tend to subside over several months, perhaps from the patient’s neural adaptation, but they may be persistent. Because of a reduction in contrast sensitivity, the subjective quality of vision after multifocal IOL insertion may not be as good as after monofocal IOL implantation. The trade-off of decreased quality of vision in return for reduced dependence on glasses must be discussed fully with the patient preoperatively. With multifocal IOLs, intermediate vision may be weaker than distance or near acuity. Some surgeons implant different models of multifocal IOLs, called mixing and matching, in the 2 eyes of a patient to maximize the range of visual function.

A small percentage of patients never adapt to multifocal IOLs and require IOL explantation and exchange to recover vision. All patients should be counseled as to this possibility before surgery. Patients with multifocal IOLs appear to be much more sensitive to lesser extents of posterior capsule opacification (PCO) than are individuals with monofocal IOLs. These patients benefit from Nd:YAG capsulotomy; however, tolerance of the multifocal IOL must be determined before undergoing the Nd:YAG capsulotomy, as an open posterior capsule significantly complicates IOL explantation and exchange. Intrinsic IOL symptoms usually appear very early if not immediately in the postoperative course and do not generally worsen over time. In contrast, symptoms from PCO are not present initially but gradually worsen over the first few weeks to months after surgery.

Agresta B, Knorz MC, Kohnen T, Donatti C, Jackson D. Distance and near visual acuity improvement after implantation of multifocal intraocular lenses in cataract patients with presbyopia: a systematic review. J Refract Surg. 2012;28:426–435.

Cillino S, Casuccio A, Di Pace F, et al. One-year outcomes with new-generation multifocal intraocular lenses. Ophthalmology. 2008;115(9):1508–1516. Epub 2008 Jun 5.

Cionni RJ, Osher RH, Snyder ME, Nordlund ML. Visual outcome comparison of unilateral versus bilateral implantation of apodized diffractive multifocal intraocular lenses after cataract extraction: prospective 6-month study. J Cataract Refract Surg. 2009;35(6): 1033–1039.

Packer M, Chu YR, Waltz KL, et al. Evaluation of the aspheric Tecnis multifocal intraocular lens: one-year results from the first cohort of the Food and Drug Administration clinical trial. Am J Ophthalmol. 2010;149(4):577–584. Epub 2010 Feb 6.

Rosenfeld SI, O’Brien TP. The dissatisfied presbyopia-correcting IOL patient. Focal Points: Clinical Modules for Ophthalmologists. San Francisco: American Academy of Ophthalmology; 2011, module 8.

Woodward MA, Randleman JB, Stulting RD. Dissatisfaction after multifocal intraocular lens implantation. J Cataract Refract Surg. 2009;35(6):992–997.

Bioptics

The term bioptics was suggested by Zaldivar in the late 1990s and is now used to describe the combination of 2 refractive procedures—one intraocular and one corneal—to treat patients with refractive errors that are suboptimally treated with a single procedure. Examples include extreme myopia, high myopia or hyperopia with significant astigmatism, and multifocal IOL implantation in patients with significant astigmatism. In these cases, the intraocular procedure is performed first, with keratorefractive surgery performed after both anatomical and refractive stability are achieved, usually 1–3 months after the initial surgery.

Bioptics with LASIK or surface ablation are reasonable alternatives, depending on patient

parameters. As new treatment options are developed, the possibilities for other combinations of refractive surgery will increase.

The ability to successfully combine refractive procedures further expands the limits of refractive surgery. The predictability, stability, and safety of LASIK increase when smaller refractive errors are treated. In addition, there is usually sufficient corneal tissue to maximize the treatment zone diameter without exceeding the limits of ablation depth. The LASIK procedure provides the feature of adjustability in the overall refractive operation. These benefits must be balanced against the combined risks of performing 2 surgeries rather than 1 surgery.

Alfonso JF, Fernández-Vega L, Montés-Micó R, Valcárcel B. Femtosecond laser for residual refractive error correction after refractive lens exchange with multifocal intraocular lens implantation. Am J Ophthalmol. 2008;146(2):244–250. Epub 2008 May 23.

Güell JL, Vázquez M, Gris O. Adjustable refractive surgery: 6-mm Artisan lens plus laser in situ keratomileusis for the correction of high myopia. Ophthalmology. 2001;108(5): 945–952.

CHAPTER 9

Accommodative and Nonaccommodative

Treatment of Presbyopia

Introduction

Presbyopia, the normal progressive loss of accommodation, affects all individuals beginning in middle age, regardless of any underlying refractive error. This relentless loss of near vision and dependency on glasses may be particularly distressing for individuals with emmetropic vision who have previously enjoyed excellent uncorrected vision. The possibility of “curing” or reducing the effects of presbyopia remains the “Holy Grail” of refractive surgery.

A number of procedures intended to increase the amplitude of accommodation are being investigated. Some of these techniques rely on various types of so-called scleral expansion. Others involve implantation of intraocular lenses (IOLs) capable of anteroposterior movement, with a subsequent change in effective lens power. Still others involve the creation of a multifocal cornea or use of a multifocal IOL. Some procedures were initially developed partly on the basis of rejection of the long-accepted Helmholtz theory of accommodation. Because several proposed types of surgery for presbyopia stem from new theories of accommodation, the discussion begins by examining the different theories of accommodation.

Theories of Accommodation

Vision scientists do not yet have a complete understanding of the relationship between the effect of ciliary muscle contraction and zonular tension on the equatorial lens. In addition, a few markedly different anatomical relationships have been described between the origin of the zonular fibers and the insertion of these fibers into the lens.

The Helmholtz hypothesis, or capsular theory, of accommodation states that during distance vision, the ciliary muscle is relaxed and the zonular fibers that cross the circumlental space between the ciliary body and the lens equator are at a “resting” tension. With accommodative effort, circumferential ciliary muscle contraction releases this tension on the zonules. An anterior movement of the ciliary muscle annular ring also occurs during accommodation. The reduced zonular tension allows the elastic capsule of the lens to contract, causing a decrease in equatorial lens diameter and an increase in the curvatures of the anterior and posterior lens surfaces. This “rounding up” of the lens yields a corresponding increase in its dioptric power, as is necessary for near vision (Fig 9-1). When the accommodative effort ceases, the ciliary muscle relaxes and the zonular tension on the lens equator rises to its resting state. This increased tension on the lens equator causes a flattening of the lens, a decrease in the curvature of the anterior and posterior lens surfaces, and a decrease in the dioptric power of the unaccommodated eye.

Figure 9-1 Schematic representation of the Helmholtz theory of accommodation, in which contraction of the ciliary muscle during accommodation (bottom) leads to relaxation of the zonular fibers. The reduced zonular tension allows the elastic capsule of the lens to contract, causing an increase in the anterior and posterior lens curvature. (Illustration by Jeanne Koelling.)

In the Helmholtz theory, the equatorial edge of the lens moves away from the sclera during accommodation and toward the sclera when accommodation ends. In this theory, all zonular fibers are relaxed during accommodation and all are under tension when the accommodative effort ends. According to Helmholtz, presbyopia results from the loss of lens elasticity with age. When the zonules are relaxed, the older lens does not change its shape to the same degree as the young lens does; therefore, presbyopia is an aging process that can be reversed only by changing the elasticity of the lens or its capsule.

Diametrically opposed to the Helmholtz hypothesis is the Schachar theory of accommodation. Schachar suggests that during accommodation, ciliary muscle contraction leads to a selective increase in equatorial zonular tension—rather than to the uniform decrease (anterior, equatorial, and posterior) proposed by the Helmholtz theory—with a subsequent pulling of the equatorial lens outward toward the sclera (Fig 9-2). Schachar postulates that accommodation occurs through the direct effect of zonular tension (as opposed to the passive effect proposed by Helmholtz), causing an increase in lens curvature. In this theory, the loss of accommodation with age is a result of the continued growth of the lens, leading to increasing lens diameter and a decrease in the lens–ciliary body distance, which results in a loss of zonular tension. Anything that increases resting zonular

tension (eg, scleral expansion) should restore accommodation.

Figure 9-2 Schematic depiction of the Schachar theory, which proposes that only the equatorial zonules are under tension during accommodation and that the anterior and posterior zonular fibers serve solely as passive support structures for the

lens. (Illustration by Jeanne Koelling.)

Schachar proposed that the mechanism for functional lens shape change is equatorial stretching by the zonules, which would decrease the peripheral lens volume and increase the central volume, thus producing central steepening of the anterior central lens capsule (Fig 9-3). During accommodation and ciliary muscle contraction, tension on the equatorial zonular fibers increases, whereas tension on the anterior and posterior zonules is reduced. These actions would allow the lens to maintain a stable position at all times, even as it undergoes changes in shape. Schachar theorized that the anterior and posterior zonules serve as passive support structures for the lens, whereas the equatorial zonules are the active components in determining the optical power of the lens.

Figure 9-3 The Schachar theory proposes that the increase in equatorial zonular tension causes a decrease in peripheral lens volume and, thus, an increase in central lens volume and central lens curvature. (Illustration by Jeanne Koelling.)

Evidence from recent studies on human and nonhuman primates contest Schachar’s theories on accommodation and presbyopia. Investigations in human tissues and with scanning electron microscopy reveal no zonular insertions (equatorial or otherwise) at the iris root or anterior ciliary muscle. Various imaging techniques consistently indicate that the diameter of the crystalline lens decreases with accommodation so that the equator moves away from the ciliary body. In vitro laser scanning imaging shows that the crystalline lens does not change focal length when increasing and decreasing radial stretching forces are applied. This evidence thus runs contrary to Schachar’s