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Chapter 42 – Indications for Lens Surgery and Different Techniques

Section 4 – Lens surgery

 

 

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Chapter 42 – Indications for Lens Surgery and Different Techniques

 

HARRY B. GRABOW

 

 

 

 

 

KEY FEATURES

• Lens surgery is the most common eye operation.

• Technical indications for lens surgery are divided into two main categories: medical and optical.

• Socioeconomic conditions play a role in the indications for lens surgery.

• All lens surgery should be considered form of refractive surgery.

• Lens surgery may be divided into four major categories by technique:

• Lens repositioning (couching)

• Lens removal

• Lens replacement

• Lens enhancement

 

 

 

INTRODUCTION

The technical indications for lens surgery today may be classified into two main categories: medical, which might more properly be called surgical or pathological indications, and optical—currently known as refractive indications. Medical indications arise from pathological states of the lens of varying causes, usually related to lens clarity, lens position, or other lens-related conditions, such as inflammation or glaucoma. Non-lens-related conditions may also be an indication for lens surgery, such as aniridia. Surgical or pathological indications have existed for centuries, if not millennia, and are generally indisputable. Refractive indications for lens surgery, in contrast, include clear-lens ametropic refractive states. These are relatively new indications, only decades old, and they may or may not be considered pathological conditions. In some settings, surgery for such conditions is considered controversial, if not contraindicated. However, the ophthalmic subspecialty of refractive surgery gained a secure foothold in the late 1990s, and refractive lens surgery is rapidly becoming a common tool in the armamentarium of both cataract and refractive surgeons. The lens plays such a significant role in the visual refractive system of the eye that many, if not all, of the medical conditions of the lens also interfere with its optics. Similarly, surgical removal of the lens immediately and permanently alters the refractive state of the eye. Today, therefore, all lens surgery, for whatever indication, has properly come to be considered refractive surgery.

In addition to medical and optical indications, a third set of indications exists, particularly pertaining to cataract surgery, that relates not so much to the condition of the eye as it does to economic conditions in the various societies of the world. Thus, the socioeconomic conditions of a country may determine when lens removal is performed, how it is performed, and how available it is for a given population.

 

 

 

MEDICAL (PATHOLOGICAL) INDICATIONS FOR LENS SURGERY

 

I.

Lenticular opacification (cataract)

 

II.

Lenticular malposition

 

A.

Subluxation

 

B.

Dislocation

 

III.

Lenticular malformation

 

A.

Coloboma

 

B.

Lenticonus

 

C.

Lentiglobus

 

D.

Spherophakia

 

IV.

Uveal malformation

 

A.

Partial iris coloboma

 

B.

Total aniridia

 

V.

Lens-induced inflammation

 

A.

Phacoanaphylactic endophthalmitis

 

VI.

Lens-induced (phacolytic) glaucoma

 

VII.

Postoperative retained lenticular material

 

A.

Capsule

 

B.

Cortex

 

C.

Nucleus

 

VIII.

Postoperative complications

 

A.

Capsular ophthalmic visco-surgical device block

 

B.

Capsular hematoma

 

C.

Propioni endophthalmitis

 

IX.

Postoperative capsular opacification

 

A.

Anterior

 

B.

Posterior

 

C.

Synechia

 

X.

Lenticular tumor

 

A.

Epithelioma

 

B.

Epitheliocarcinoma

 

 

 

MEDICAL INDICATIONS FOR LENS SURGERY

Lenticular Opacification (Cataract)

The medical indications for lens surgery ( Box 42-1 ) are true pathological states, some of which threaten the integrity of the whole organ (the eye). They also interfere with a major ocular function, focused vision. Lenticular opacification obstructs the pathway of light; reduces the available quantity of light; scatters light off axis; reduces contrast sensitivity; diminishes color intensity; reduces resolution acuity; may alter lens texture in such a way to contribute to a decrease in accommodation amplitude, particularly in the case of presenile nuclear sclerosis; and, in the case of progressive nuclear sclerosis, often results in a myopic alteration of a previously stable lifelong refractive state.

Lens opacification is by far the most common indication for lens surgery, and lens surgery is the most common eye operation, if not the most frequently performed of all human operations; yet cataract persists today as the most prevalent cause of

 

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human blindness on earth. However, with the rapid acceptance, by both surgeons and patients, of corneal refractive surgery, particularly LASIK, and with the prevalence of ametropia far exceeding the prevalence of cataract in the world population, it may be only a few years before the number of cataract operations is exceeded by the number of refractive procedures.

Cataract, depending on severity, is a condition of the eye that, by interfering with vision, can simultaneously interfere with certain activities in life. It is generally agreed that surgical intervention is indicated when there is “functional” visual impairment. The levels of functional visual impairment necessitating surgical intervention, however, vary from culture to culture. In highly developed societies, the mere loss of the ability to follow a golf ball may qualify an eye for surgery; in third-world countries, leukocoria may precede nutritional deprivation, and lens surgery may be a matter of survival.

In highly structured societies, governments or third-party health insurance carriers pay for such surgical procedures, and these same institutions often set standards for lens surgery indications. Therefore, in developed societies where surgical technology is advanced, perceived economic conditions may be the factors that determine the prevalence and definition of “cataract blindness” for a population, and this changes as conditions change. In many underdeveloped nations, the prevalence of cataract blindness is determined by the availability of care.

In the United States, cataract surgeons often refer to measurable standards of visual performance as indications for cataract surgery. Visual acuity of 20/50 or worse as measured on a Snellen chart in dim ambient (mesopic) illumination with maximal refractive correction is an acceptable level of cataract to indicate surgery, according to the American Academy of Ophthalmology. Visual acuity of 20/50 or worse when tested with bright light imposition on the pupil, or glare testing, is considered a surgical level of cataract dysfunction in many states in the United States. Reduction of contrast sensitivity can be demonstrated and quantified, and the type and degree of lens opacification may be subjectively quantified by slit-lamp examination and categorized according to the Lens Opacification System III (LOCS-III) devised by Chylack et al.[1] The degree to which the opacification obstructs light can, additionally, be measured by laser interferometry.[2] Progressive changes in cataract density over time can be documented by Scheimpflug photography of nuclear cataracts[3] and by Neitz-Kawara retroillumination photography of posterior subcapsular cataracts. [4]

However, in structured economic societies, third-party payers and governmental regulatory agencies are not interested in the results of these sophisticated methods of analyzing loss of lens function; they are more interested in how the loss of lens function interferes with life functions. Loss of functional impairment due to visual impairment may range from minor impairment in luxury lifestyles, such as inability to follow a golf ball; to moderate impairment, such as inability to see well enough to drive an automobile; to severe impairment of life support functions, such as inability to see the units on an insulin syringe or the instructions on a bottle of cardiac medication—or even food on the table. Examples of such tests are the Visual Function Index (VF-14) [5] [6] [7] [8] and the Activities of Daily Vision Scale (ADVS). [9] [10]

CATARACT IN THE PRESENCE OF OTHER OCULAR DISORDERS.

The decision to remove a cataract in an otherwise healthy eye usually depends on the cataract’s impact on the visual function of the eye and the impact of that level of visual impairment on the person’s life. In healthy eyes whose only disorder is cataract, the presumed outcome after uncomplicated surgery is better vision than before surgery. Indeed, in the most technologically advanced societies, patients are requesting emmetropia, and even restoration of accommodation. In such “healthy” eyes, cataract surgeons experience a rate of intraoperative and postoperative complications of less than 2% or, conversely, an uncomplicated rate of 98%. Thus, when one applies a risk-benefit ratio with such a high degree of success, surgery is usually the mutually agreed on course.

However, such may not be the case when the cataract is associated with other disorders, especially if they are contributing factors to the loss of vision of an eye. Therefore, such conditions as amblyopia, corneal opacification, vitreous opacification, maculopathy, retinopathy, glaucoma, and optic neuropathy may alter or delay the decision to operate, based not so much on the expected risks but rather on the limited benefits. In some cases, lens surgery is indicated to preserve peripheral vision only for functional ambulation. In other cases, a progressive condition of the posterior segment is an indication for lens surgery, even when the expectation for visual improvement may be minimal.[11]

Systemic conditions may also play a role in deciding whether and when to remove a cataract. Is the patient’s diabetes under control? Has there been a stroke with hemianopia? Is the patient on systemic anticoagulants? Is the patient terminally ill or immunologically suppressed? Does the patient have Alzheimer’s disease or severe mental retardation?

Thus, the decision to remove a cataract may become a collaborative endeavor with participation by the patient, the patient’s family, the patient’s primary physician, the surgeon, a governmental agency, and a third-party payer. The decision, thus, is determined not only by technological findings and expectations but also by a “holistic” evaluation of the impact of such a decision on that person’s life, as defined by that society.

Lenticular Malposition

Subluxation and dislocation of the lens are different degrees of the same phenomenon and result from dysfunction of the zonule. The zonule may be defective as a result of congenital malformation, total or partial agenesis, or a hereditary metabolic disorder, such as Marfan’s syndrome. Chronic inflammation and pseudoexfoliation have been shown to be associated with a weakness in the zonular fibers or their attachments. Ocular trauma is an obvious cause.

Partial subluxation, in the absence of associated sequelae, may not be visually significant and may not be an indication for lensectomy. Similarly, complete dislocation of an intact lens into the inferior vitreous may be a quiescent event in the absence of inflammation and may simply produce a state of refractive aphakia, correctable nonsurgically with a spectacle or contact lens or surgically with intraocular lens (IOL) implantation. Partial subluxation to the extent that the equator of the lens is visible in the midsized pupil is usually visually significant, causing glare, fluctuating vision, and monocular diplopia. This symptom complex would qualify for lens surgery.

Lenticular Malformation

These conditions of abnormal lens development are congenital. They may be genetic, hereditary, or the result of intrauterine infection or trauma. These conditions include lens coloboma, lenticonus, lentiglobus, and spherophakia, as well as varieties of congenital cataract. Partial iris coloboma or total aniridia, whether congenital, traumatic, or surgical, may be an indication for lens surgery to improve visual function or for cosmesis. The availability of aniridia IOLs ( Fig. 42-1 ) and opaque endocapsular rings ( Figs. 42-2 and 42-3 ) offers great improvements for such patients.

The indications for surgery depend on the degree to which the specific malformation interferes with vision or the integrity of the involved eye. Such abnormalities may be associated with amblyopia. Early detection and surgical intervention should be incorporated with a plan for amblyopia therapy.

 

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Figure 42-1 Aniridia intraocular lens with opaque peripheral “pseudoiris.” (Courtesy of Morcher, GMBh, Germany.)

Lens-Induced Ocular Inflammation

Certain specific prerequisites are necessary for phacoanaphylactic endophthalmitis to occur: the first is an immunologically mature and competent host; the second is a physical or chemical disruption of the lens capsule. Removal of the lens protein that is perceived to be foreign to the organism may be curative. This is one form of ocular inflammation for which surgery is the appropriate treatment.

Lens-Induced Glaucoma

Phacolytic glaucoma is not associated with a physical or chemical disruption of the lens capsule. Denatured lens protein leaks out through an intact capsule and is engulfed by macrophages. The macrophages then occlude an open angle. As with the lens-induced inflammatory syndromes, removal of the offending organelle, the lens, is usually curative, obviating the need for other forms of medical or surgical pressure management.

Postoperative Retained Lenticular Material

Retained remnants of nucleus following extracapsular surgery, particularly phacoemulsification, may cause ocular inflammation, ocular hypertension, cystoid macular edema, and corneal edema. Small remnants may inadvertently be left in the anterior chamber angle or posterior to the iris in the ciliary sulcus. A few days of observation and medical management with corticosteroids, cycloplegics, beta blockers and nonsteroidal anti-inflammatories may aid in controlling the inflammation and hypertension while phagocytosis occurs. However, significantly decreased visual acuity or elevated intraocular pressure may be an indication for surgical intervention.

Small fragments of nucleus in aqueous are usually hydrated after a few days and are easily aspirated with a cannula through a paracentesis incision. Larger fragments in the vitreous have been observed to cause either no reaction or significant vitreitis. Those that cause no reaction may be completely embedded in, and surrounded by, formed vitreous and act as though they are insulated from uveal tissue. Others appear to be exposed to the uvea and incite an inflammatory reaction. These are also easily removed but usually require pars plana vitrectomy.

Retained remnants of cortex are a rare indication for surgical intervention, as small amounts of residual cortex appear to be

 

 

Figure 42-2 Aniridia endocapsular ring. (Courtesy of Morcher, GMBh, Germany.)

 

 

Figure 42-3 Iris coloboma endocapsular ring. (Courtesy of Morcher, GMBh, Germany.)

phagocytosed in a matter of weeks. Occasionally, however, a large wedge of adherent cortex may remain, either unintentionally or intentionally, and may cause excessive and prolonged postoperative inflammation, hypertension, and, if in the pupillary space, visual symptoms. These would be indications for surgical aspiration.

Some posterior subcapsular opacities are extremely adherent to the central posterior capsule and may be resistant to removal by vacuuming, polishing, curetting, or with forceps. The surgeon may then elect to perform primary posterior capsulorrhexis or to defer definitive primary treatment, for fear of disrupting the adjacent vitreous face, in favor of secondary postoperative yttrium-aluminum-garnet (YAG) laser posterior capsulectomy.

Postoperative Capsular Opacification

The prevention of capsular opacification following extracapsular extraction techniques is currently undergoing intense investigation.

 

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Primary techniques at the time of lens extraction, such as simple mechanical polishing and curetting, vacuuming, and even vacuuming with ultrasound, have been espoused. Hypothermic destruction of lens epithelial cells has been attempted with the use of a cryoprobe.[12] Physiological osmotic cell destruction was tried with simple sterile distilled water. [13] Currently, pharmacological agents are being studied,[14] including steroidal and nonsteroidal[15] anti-inflammatory agents,[16] as well as antimetabolites[17] and immunological agents, specifically monoclonal antibodies.[18]

It appears, however, with current lens removal technology, that it is virtually impossible to surgically remove all living lens epithelial cells from the inner surface of the remaining lens capsule, especially from the capsular fornix. It also appears that following extracapsular surgery, lens epithelial cells become mobile, diapedetic, and that they try to adopt three new functions: (1) repairing the rent created in the anterior capsule, (2) encapsulating the foreign body (IOL), and (3) replacing the removed natural crystalline lens with a new natural crystalline lens.

The first mission of the lens epithelial cells, repairing the rent in the anterior capsule, can result in the fibrotic phimotic contraction of the anterior capsular opening, in some cases resulting in successful complete closure ( Fig. 42-4 ). This rare phenomenon, facilitated by a small initial surgical capsulectomy and by hydrophilic polymethyl methacrylate (PMMA) and silicone, results in obstruction of vision requiring correction with YAG laser. Fibrous metaplasia of the lens epithelial cells occurs when they come in contact with what they perceive to be foreign material, particularly hydrophobic IOL optics such as PMMA and silicone. These, therefore, are considered “nonbiocompatible” and often result in a white, fibrous opacification of the anterior capsule weeks after surgery ( Fig. 42-5 ) that may preclude easy visualization of the peripheral retina. In contrast, hydrophilic IOL materials, such as poly-hydroxy-ethyl-methacrylate and collagen-copolymer, appear to be perceived as natural substances and do not cause the fibrous metaplastic response that the hydrophobic materials do. These, therefore, are considered more “biocompatible.”

The third mission of remaining lens epithelial cells is to multiply rapidly in an attempt to fill the newly voided capsular space with a new, functional, natural crystalline lens. This rapid recrudescence of mitotic activity, lens epithelial cell hyperplasia, is engendered by the physical loss of contiguity of previously adjacent cells, which were removed at surgery, causing a loss of cellular contact inhibition. Without the proper embryonically created template, these now migratory lens epithelial cells can do no

 

 

Figure 42-4 Virtual complete closure of capsulorrhexis over a PMMA implant. (Courtesy of John Shepherd, M.D., Las Vegas, Nevada.)

better than to multiply in an uncontrollable and disorderly fashion and form optically disrupting epithelial “pearls” ( Fig. 42-6 ). Symptomatic posterior capsular opacification by such a process may be an indication for either a secondary surgical posterior capsulectomy or capsulotomy or a YAG laser posterior capsulectomy. If surgical intervention is indicated, such as for IOL exchange or secondary “piggyback” IOL implementation, then simple vacuuming of the posterior capsule may remove soft epithelial pearls.

REFRACTIVE INDICATIONS FOR LENS SURGERY

The refractive indications for lens surgery include all the classic well-known refractive states of the “healthy” eye, which is why this new indication for lens surgery has been somewhat controversial. There may be no true histopathology to most of these eyes; however, some, such as those with extreme axial myopia, may be at risk for true pathology following surgical intervention. In addition, the historical development of spectacles and contact lenses, having long antedated the development of modern lens surgery, created a mind-set among many that “inborn errors of refraction” are not diseases and are therefore not conditions to be treated with medicine or surgery, especially if such treatment

 

 

Figure 42-5 Fibrosis of the anterior capsule. A “nonbiocompatible” reaction of lens epithelial cells (LECs) to hydrophobic intraocular lens materials.

 

 

Figure 42-6 Posterior capsular opacification by lens epithelial cell hyperplasia.

 

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might unnecessarily endanger an eye or expose an otherwise “healthy” eye to undue risk. Although there may be merit to that argument, it is a concept that is rapidly losing popularity. Whether prudent or not, the global anterior segment ophthalmic surgical community has embarked on a new and enticing endeavor—rendering the human population emmetropic. The process began as an idea before its time in the 1950s, with the failed attempts of Sato at endothelial radial keratotomy and Barraquer and others at phakic anterior chamber IOL implantation.[18] The ophthalmic surgical “technolution” (technical revolution) that ensued over the following decades led to renewed interest in the surgical correction of refractive errors 30 years later in the 1980s, this time as an idea whose time had come. Refinements in ocular anesthesia, incision technology, lensectomy techniques, ophthalmic visco-surgical device (OVD) tissue protection, and IOL manufacturing and implantation allowed the successful return of the concept of intraocular correction of refractive errors, including both clear lensectomy and phakic implantation. All this, combined with the multitude of new keratorefractive procedures, has actually led to the development of a new, bona fide ophthalmic surgical subspecialty, that of refractive surgery.

As may be observed in Box 42-2 , almost all the operable tissues and spaces of the eye have come under investigation as locations for refractive surgical modulation: corneal epithelial surface, corneal stroma, corneal endothelial surface, anterior chamber, iris, pupil, posterior chamber, lens, and sclera. The

 

 

REFRACTIVE SURGERY

 

I.

Cornea

 

A.

Incisional keratotomy

 

1.

Radial (RK)

 

2.

Tangential astigmatic (AK)

 

B.

Laser thermal keratoplasty (LTK)

 

C.

Radiofrequency conductive keratoplasty (CK)

 

D.

Laser surface ablation (PRK)

 

E.

Subepithelial laser ablation (LASEK)

 

F.

Lamellar keratotomy/keratectomy

 

1.

Keratomileusis

 

2.

Keratophakia

 

3.

Automated lamellar keratectomy (ALK)

 

4.

Laser stromal ablation (LASIK)

 

G.

Intrastromal corneal inlays

 

1.

PMMA rings (Intacs)

 

2.

Hydrogel discs

 

3.

Gel injection

 

H.

Surface tissue onlays

 

1.

Epikeratophakia

 

2.

Epitheliokeratomileusis

 

II.

Lens

 

A.

Clear lensectomy without IOL (aphakia)

 

B.

Clear lensectomy with monofocal or toric IOL (pseudophakia)

 

C.

Clear lensectomy with multiple monofocal IOLs (polypseudophakia)

 

D.

Clear lensectomy with multifocal IOL

 

E.

Clear lensectomy with accommodative IOL

 

III.

Phakic IOL implantation

 

A.

Anterior chamber

 

1.

Angle fixation (Baikoff, Kelman)

 

2.

Iris fixation (Worst-Fechner, Singh)

 

3.

Scleral fixation (Maggi)

 

B.

Posterior chamber

 

1.

Pupillary fixation (Fyodorov)

 

2.

Zonular fixation (Fyodorov)

 

3.

Sulcus fixation (Fyodorov)

 

IV.

Sclera

 

A.

Posterior homograft scleroplasty

 

B.

Scleral expansion/implantation (Schachar)

 

C.

Radial incisional sclerotomy (Thornton-Fukasaku)

 

 

 

lens therefore assumes its role among the others as a popular location for surgical refractive modulation for those who prefer a familiar procedure that spares the cornea and saves the economic expense of an excimer laser. Those who decry the lenticular approach emphasize all the potential intraoperative and postoperative complications attendant with invasive intraocular procedures.

Despite the controversy, clear lens replacement stands as a viable procedure today for both myopia and hyperopia and has begun to be included in the surgical treatment of astigmatism and presbyopia. Toric IOLs are now available for the intraocular correction of astigmatism ( Fig. 42-7 ). Multifocal IOLs represent some of the first attempts at the intraocular correction of presbyopia ( Fig. 42-8 ). Other attempts at the development of a truly accommodative pseudophakos have included the intracapsular injection of liquid silicone [19] [20] [21] and the intracapsular placement of high-water-content poly-HEMA lenses, a liquid silicone-filled intracapsular balloon[22] [23] ( Fig. 42-9 ), multiple IOLs (polypseudophakia)[24] [25] ( Figs. 42-10 and 42-11 ), and flexible plate–haptic foldable accommodative IOLs.

 

 

Figure 42-7 Foldable silicone plate–haptic toric intraocular lens. (Courtesy of STAAR Surgical, Monrovia, California.)

 

 

Figure 42-8 Foldable silicone multifocal intraocular lens. (Courtesy of Advanced Medical Optics, Inc.)

 

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Figure 42-9 Accommodative inflatable silicone intracapsular balloon. (Courtesy O. Nishi, M.D., Osaka, Japan.)

 

 

Figure 42-10 Polypseudophakia. Two silicone plate–haptic intraocular lenses in the capsular bag.

 

 

Figure 42-11 Accommodative PMMA polypseudophakic intraocular lens. (Courtesy of T. Hara.)

INDICATIONS FOR DIFFERENT LENS SURGERY TECHNIQUES

Surgery affecting the human lens can be organized historically by chronology of development ( Table 42-1 ) or divided into four major categories by technique ( Box 42-3 ):

• Lens repositioning

• Lens removal

• Lens replacement

• Lens enhancement

Lens repositioning, traditionally known as “couching,” is perhaps the oldest form of lens surgery and is still in use in some

 

TABLE 42-1 — HISTORY OF CATARACT SURGERY TECHNIQUES

Year

Technique

Place

Surgeon

800

Couching

India

Unknown

1015

Needle aspiration

Iraq

Unknown

1100

Needle aspiration

Syria

Unknown

1500

Couching

Europe

Unknown

1745

ECCE inferior incision

France

Daviel

1753

ICCE by thumb expression

England

Sharp

1860

ECCE superior incision

Germany

von Graefe

1880

ICCE by muscle-hook zonulysis and lens tumble

India

Smith

1900

ICCE by capsule forceps

Germany

Verhoeff

 

 

 

Kalt

1940

ICCE by capsule suction erysiphake

Europe

Stoewer I. Barraquer

1949

ECCE with posterior chamber IOL and operating microscope

England

Ridley

1951

Anterior chamber IOLs

Italy

Strampelli

 

 

Germany

Dannheim

1957

ICCE by enzyme zonulysis

Spain

J. Barraquer

1961

ICCE by capsule cryoadhesion

Poland

Krawicz

1967

ECCE by phacoemulsification

United States

Kelman

 

 

 

J. Shock

1975

Iris-pupil supported IOLs

Netherlands

Binkhorst

 

 

 

Worst

1984

Foldable IOLs

United States

Mazzocco

 

 

South Africa

Epstein

ECCE, Extracapsular cataract extraction; ICCE, intracapsular cataract extraction; IOL, intraocular lens.

 

 

third-world countries today. In stark contrast, at the other end of the historical spectrum is the most recent category of lens surgery, that of lens functional enhancement. These new investigational techniques involve surgical procedures designed to enhance accommodation in the presbyopic eye.

The indications for a particular lens surgery technique may be determined by several factors ( Box 42-4 ). Different medical conditions or pathological states of the eye and the lens may favor one technique over another. In some countries, the availability of equipment, as well as the level of training of the surgeon, may be factors that dictate technique. Certain countries have governmental agencies, professional organizations, academic institutions, insurance payers, or surgical facilities that regulate and control the types of surgical techniques surgeons may perform. For the purpose of this text, however, only specific medical or pathological conditions of the eye are discussed as factors determining the choice of surgical technique.

Couching

This is the oldest technique of lens surgery; it has been performed for more than 1000 years and is still in use today in some underdeveloped countries. The original method was an extracapsular technique that involved the placement of a sharp needle through the sclera at the pars plana, behind the iris, until the tip of the needle was visible in the pupil in front of the lens. The anterior capsule was then scratched open with the needle tip, and the nucleus was pushed inferiorly until the pupillary space appeared clear. This early extracapsular technique, which was being performed long before the development of topical anti-inflammatory medications, was associated with inflammation, secondary glaucoma, posterior synechiae, pupillary block, Soemmerring’s rings, and capsular opacification, not to mention

 

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LENS SURGERY TECHNIQUES

 

I.

Lens repositioning (“couching”)

 

A.

Extracapsular

 

B.

Intracapsular

 

1.

Physical (instrumental) zonulysis

 

2.

Pharmacological (enzymatic) zonulysis

 

II.

Lens removal

 

A.

Total (intracapsular)

 

1.

Capsule forceps

 

2.

Suction erysiphake

 

3.

Cryoextraction

 

B.

Partial (extracapsular)

 

1.

Anterior capsulotomy/capsulectomy

 

a.

Discontinuous

 

b.

Continuous (capsulorrhexis)

 

c.

Linear

 

2.

Nucleus removal

 

a.

Assembled delivery (large incision)

 

1.

Expression (“push”)

 

2.

Extraction (“pull”)

 

b.

Disassembled extraction

 

1.

Phacosection

 

2.

Phacoemulsification-aspiration

 

a.

Ultrasound

 

b.

Laser

 

c.

Water jet

 

d.

Impeller

 

3.

Cortex removal

 

a.

Irrigation

 

b.

Aspiration

 

III.

Lens replacement (intraocular lens implantation)

 

A.

Locations

 

1.

Anterior chamber

 

a.

Angle fixation

 

b.

Iris fixation

 

2.

Pupil

 

3.

Posterior chamber

 

a.

Iris fixation (sutured)

 

b.

Ciliary sulcus (sutured or unsutured)

 

4.

Lens capsule

 

a.

Anterior capsule

 

1.

Haptic sulcus/optic bag

 

2.

Optic posterior chamber/haptic bag

 

b.

Intracapsular (“bag-bag”)

 

c.

Posterior capsule (haptic bag/optic Berger’s space)

 

5.

Pars plana (sutured)

 

B.

Optic materials

 

1.

Hydrophobic

 

a.

PMMA

 

b.

Silicone

 

c.

Acrylic

 

2.

Hydrophilic

 

a.

Poly-HEMA

 

b.

Acrylic

 

c.

Collagen-copolymer

 

C.

Optic types

 

1.

Monofocal

 

a.

Spherical

 

1.

Plus

 

2.

Minus

 

b.

Toric

 

c.

Telescopic

 

d.

Prismatic

 

2.

Multifocal

 

3.

Accommodative

 

IV.

Lens enhancement: reversal of presbyopia by scleral expansion

 

A.

Ciliary cerclage

 

B.

Radial anterior ciliary sclerotomy

 

 

 

endophthalmitis. Considering current technology, there may be no indications for extracapsular couching today.

Intracapsular couching, however, is another matter. This procedure was (and still is) performed without anesthesia with the patient in the sitting position, sometimes outdoors. However,

 

 

LENS REMOVAL TECHNIQUES: OCULAR INDICATIONS

 

I.

Intracapsular extraction

 

A.

Zonular absence/dialysis

 

B.

Lens subluxation

 

C.

Lens dislocation

 

II.

Nuclear delivery

 

A.

Status of cornea

 

1.

Low endothelial cell count

 

2.

Guttate dystrophy

 

B.

Status of cataract

 

1.

Brunescent nuclear sclerosis

 

2.

Cataracta nigra

 

C.

Torn posterior capsule during phacoemulsification

 

D.

Zonulodialysis

 

III.

Phacosection

 

A.

Same corneal, cataract, and capsular indications as nuclear delivery

 

B.

Astigmatism management

 

IV.

Phacoemulsification

 

A.

Status of cornea

 

1.

Normal endothelial cell count

 

2.

No guttate dystrophy

 

B.

Status of cataract

 

1.

Immature nuclear sclerosis

 

2.

Cortical or subcapsular cataract

 

C.

Astigmatism management

 

 

 

couching can also be performed safely under an operating microscope in a matter of minutes following enzymatic zonulysis with a-chymotrypsin. Unlike the exposed nucleus and cortex in the extracapsular method, the intact, encapsulated, dislocated crystalline lens in the intracapsular method is immunologically inert. The low skill level required and the low cost of this simple, safe, fast, and effective procedure make it an attractive alternative for economically disadvantaged third-world countries, which harbor a large majority of the world’s estimated 18 million cataract blind.

Intracapsular Extraction

The intracapsular method of lens removal has not been the procedure of choice in industrialized nations since the development of modern extracapsular techniques in the late 1970s, primarily because of lower rates of postoperative posterior segment complications such as hemorrhage, vitreous loss, retinal detachment, and cystoid macular edema. Current indications for planned intracapsular extraction, therefore, are related to intraocular conditions that preclude safe and successful extracapsular surgery. The absence or lysis of a significant number of zonular fibers, which may occur as an isolated congenital anomaly or as a result of Marfan’s syndrome, pseudoexfoliation, trauma, or following pars plana surgery, may be an indication for intracapsular extraction. Significant subluxation or dislocation of the lens may leave no other option except for removal of the lens in its capsule.

Traditionally, intracapsular extraction involved removal of the complete intact lens through a large incision measuring 11–16?mm. Later, implantation of a PMMA IOL, either primarily or secondarily, rendered these eyes pseudophakic, with both procedures requiring sutures. A more modern small incision intracapsular technique is one in which the capsule, cortex, and nucleus are all removed by phacoemulsification through a 3?mm scleral incision, followed by PMMA anterior chamber IOL implantation through a 5–6?mm scleral incision and no sutures. This rare technique may be of particular value in eyes that demonstrate no zonular support upon introduction of the phacoemulsification tip. In addition, a foldable silicone IOL can be implanted through the small incision and sutured to the posterior surface of the iris or to the sclera.

 

322

Nuclear Delivery

This technique became popular in the 1980s as surgeons, who had been performing long incision intracapsular extraction and anterior chamber implantation, desired the benefits derived from an intact posterior capsule and posterior chamber implantation. The technique persists today and is performed in great numbers, particularly in Asian countries, where the more advanced small incision techniques of phacoemulsification and foldable lens implantation are not yet available. In Europe, Japan, and the United States, where phacoemulsification and foldable lens implantation are widely standard, the only ocular indication for planned nuclear delivery may be an advanced nucleus that is too hard to be emulsified safely. Corneas at risk for developing irreversible edema, such as those with low endothelial cell counts or guttate dystrophy, may be relative indications for nuclear delivery. However, small incision lens surgery in the presence of high-risk corneas remains a viable option, particularly when highly retentive dispersive ophthalmic visco-surgical devices are used in combination with endolenticular or intercapsular phacoemulsification.

Another indication for nuclear delivery is the occurrence of a tear in the posterior capsule during phacoemulsification. Although it may be possible to continue to emulsify the nucleus over ophthalmic visco-surgical device or over a lens glide (Michelson technique), a large capsular tear with presentation of vitreous may preclude safe emulsification, necessitating incision enlargement and nuclear delivery.

Phacosection

These techniques involve delivering the nucleus not as a single intact unit in one step through a large incision, but in parts through a small incision. The nucleus may be separated concentrically, delivering the smallest endonucleus separately from outer layers of epinucleus. This technique may be performed through a 7–8?mm sutureless scleral incision using side-port irrigation through a chamber maintainer to hydroexpress the nuclear components, which delaminate as they pass through the incision. This has been called the “mini-nuc” technique. [26]

True intraocular phacosection involves bisecting or trisecting the nucleus by instrumentation, achieving geometrical nuclear division in the anterior chamber. The small sections may then be removed linearly with forceps through incisions as small as 3–4?mm.[27]

The indications for phacosection techniques are the same as those for intact nuclear delivery, as a manual extracapsular technique, with the addition of astigmatism management. Unlike long incision, single-stage nuclear delivery, small incision phacosection may induce no change in astigmatism, particularly if a foldable lens is used and all is accomplished through a 3?mm scleral incision.

Phacoemulsification

This technique of nucleus removal has been performed through incisions ranging from 3.2?mm down to less than 1.0?mm. Combined with foldable lens implantation, the major advantage of phacoemulsification is the small incision. Current techniques are using self-sealing, sutureless scleral and clear corneal incisions measuring 2.3–3.2?mm. These incisions should be astigmatically neutral. Corneal incisions can be moved centrally from the limbus and can be grooved as two-plane, two-stage incisions, allowing the reduction of preexisting astigmatism, especially when used in combination with astigmatic keratotomy.[28] Therefore, the presence of corneal cylinder is an indication for phacoemulsification and foldable lens implantation, just as is the absence of corneal cylinder.

The status of both the nucleus and the cornea factors into the decision whether to perform phacoemulsification. It has been observed that with certain phacoemulsification techniques, the longer the duration of ultrasound, the greater the loss of endothelial cells ( Fig. 42-12 ). In addition, the closer the emulsification process is to the cornea, the more cells are lost ( Table 42-2 ), and corneas with guttatae lose more cells than normal corneas do ( Table 42-3 ). Therefore, the degree of nuclear sclerosis and the health of the cornea are indications for protective ophthalmic visco-surgical devices and for phacoemulsification as far away from the cornea as possible. When phacoemulsification was originally performed in the anterior chamber and in the iris plane, high-risk corneas and dense nuclei were considered contraindications, and nuclear delivery was recommended. However, long ultrasound times have been shown to be well tolerated when the ultrasonic energy is confined to the capsular bag. Newer emulsification techniques, such as phaco chop [29] and high vacuum, have also been shown to greatly reduce ultrasound times, providing further protection to the cornea ( Box 42-5 ). Newer modalities of nuclear emulsification not involving ultrasound include sonic mode (Staar Wave), with axial movements of the tip reduced from 40,000 to 400 cycles per second; neodymium:YAG laser [30] [31] [32] [33] [34] ; erbium:YAG laser [35] [36] [37] ; pulsed water jet; “plasma blade” molecular bond disruption; impeller aspiration-emulsification; and others.

Lens Capsule Surgery

When capsulectomy was first conceived, it was performed in discontinuous fashion, either as multiple punctures (“can-opener”) with a bent needle or cystotome or as triangular (Kelman) or square (Gills) capsulectomies facilitated with scissors ( Fig. 42-13 ). Discontinuous openings, being weak, allow easy dislocation of the nucleus anteriorly for either delivery or emulsification. However, they are also prone to developing multiple radial anterior tears out to the equator, with possible extension around to the posterior capsule.[38] Postoperatively, they have a high rate of posterior synechia formation and anterior IOL loop dislocation.[39] Plate-haptic lenses are contraindicated in the presence of a discontinuous anterior capsular opening, as they have also been shown to dislocate anteriorly postoperatively. There is, therefore, rarely a current indication for a discontinuous capsulectomy, except possibly in the case of advanced nuclear sclerosis with absence of a red reflex and nonavailability of a biological capsule stain, such as trypan blue or indocyanine green.

Continuous curvilinear capsulectomy (CCC), also known as capsulorrhexis, [40] is much more desirable than previous discontinuous methods. The continuous anterior capsular opening is stronger and more resistant to radial tearing than are discontinuous

 

 

Figure 42-12 Endothelial cell loss in relation to (1) scleral versus corneal incision phacoemulsification and (2) duration of ultrasound.

 

323

openings.[41] The continuous anterior capsulectomy of the appropriate size and shape has also been shown to retain IOL haptics of all designs and materials within the capsular bag postoperatively virtually 100% of the time. A circular opening of 4–5?mm also readily retains the nucleus for in situ or endolenticular emulsification techniques. Larger openings of 6–7?mm allow nuclear prolapse for intact delivery, phacosection, or anterior chamber emulsification. Continuous openings that are too small may contract postoperatively due to fibrous metaplasia of LECs (see Figs. 42-4 and 42-5 ), obstructing not only the patient’s vision but also the doctor’s view, precluding examination and treatment of fundus disorders. YAG laser anterior capsulectomy would then be indicated, just as posterior capsulectomy is indicated for posterior capsular opacification. The ideal continuous anterior capsular opening is 1.0?mm smaller than the diameter of the lens optic to be implanted.

The capsular contents may also be removed through a linear capsulotomy rather than a capsulectomy. Both discontinuous and continuous linear capsulotomy techniques have been employed for nuclear delivery[42] and emulsification.[43] The advantage of these intercapsular techniques, if the anterior capsule is left intact during surgery, is protection of the cornea. Leaving the anterior capsule in place also offers the postoperative possibility of total encapsulation of an accommodative pseudophakos. The implantation of a pliable refractive material into a complete, intact lens capsule may establish the potential for pseudophakic accommodation.

Animal experimental trials were begun in the early 1980s, first by Schanzlin’s group, who evacuated the capsular contents through a 3?mm linear capsulotomy and injected liquid silicone in rabbit eyes.[44] These procedures worked surgically; however, the resultant optical power of the liquid injectable material could not be controlled, the anterior capsules became opacified by white fibrosis in a few weeks, and accommodative function was not determined. In the late 1980s, Nishi et al.[23] developed a

 

TABLE 42-2 — ENDOTHELIAL CELL LOSS IN PHACOEMULSIFICATION

 

Percent Cell Loss

Anterior chamber

20

Posterior chamber

14

Phaco-in-situ in the capsular bag

7

Intact anterior capsule (intercapsular phacoemulsification)

4

 

 

 

 

Figure 42-13 Anterior capsulectomy shapes used for extracapsular cataract surgery. (Courtesy of Adanced Medical Optics, Inc.)

liquid silicone-filled intracapsular balloon and placed it in monkey eyes. The power of the IOL was now controllable, and Scheimpflug photography demonstrated 6D of apparent accommodation. Also in the late 1980s, the first potentially accommodating IOLs were placed in human eyes; they were 66% water, poly-HEMA “full-size” expandable IOLs.[45] Unfortunately, none of these first human subjects, approximately 46 in number, demonstrated accommodation. A more recent design is that of a flexible hinged plate–haptic silicone IOL.

Although there may be major surgical and clinical advantages to leaving most of the lens capsule in the eye, there are also disadvantages with present materials and techniques. The posterior capsule can opacify as a result of lens epithelial cell hyperplasia (see Fig. 42-6 ), and the anterior capsule can opacify as a result of lens epithelial cell fibrous metaplasia (see Fig. 42-5 ). In addition, excessive fibrosis can result in contraction of the entire capsule with deformation of the IOL haptics, decentration of the IOL optic, and zonular dialysis with capsular bag subluxation or dislocation. Efforts to prevent unwanted postoperative lens epithelial cell activity have included primary posterior capsulotomy, primary posterior capsulectomy,[46] and methods of mechanically cleaning the capsule, including vacuuming, vacuuming with ultrasound, curettage, and cryosurgery ( Box 42-6 ).[47] Attempts at pharmacologically disabling the lens epithelial cell have included hypotonic hydrolavage, antiprostaglandins,[15] [16] antimetabolites,[17] and immunosuppressors.[18] These techniques are currently under investigation. In addition, newer IOL materials that are hydrophilic, such as poly-HEMA, acrylic, and collagen-copolymer, appear to stimulate very low levels of lens epithelial hyperplasia and almost no fibrous metaplasia. The possibility of using hydrophilic IOLs as drug delivery systems is also very attractive. However, the most recent clinical advancement that has been demonstrated to reduce the incidence of posterior capsular opacification is the use of IOL optics with “square” posterior edges ( Fig. 42-14 ). These are manufactured in acrylic (Alcon,

 

TABLE 42-3 — ENDOTHELIAL CELL LOSS FOLLOWING PHACOEMULSIFICATION IN EYES WITH NORMAL CORNEAS VERSUS EYES WITH DISEASED CORNEAS

 

Percent Cell Loss

Normal cornea

7

Guttatae

14

 

 

 

 

 

PHACOEMULSIFICATION TECHNIQUES

 

I.

Location

 

A.

Anterior chamber (Kelman, Brown)

 

B.

Iris plane (Kratz)

 

C.

Posterior chamber (supracapsular) (Maloney)

 

D.

Capsule (endolenticular, in situ)

 

1.

Anterior capsulectomy (Sinskey)

 

2.

Anterior capsulotomy (intercapsular) (Hara)

 

II.

Techniques

 

A.

Carousel

 

B.

Chip-and-flip (Fine)

 

C.

Phacofracture

 

1.

Divide-and-conquer (Gimbel)

 

2.

Four-quadrant pregrooved (Shepherd)

 

3.

Nonstop chop (Nagahara)

 

4.

Stop-and-chop (Koch)

 

5.

Double chop (Kammann)

 

 

 

 

324

 

 

Figure 42-14 Acrylic intraocular lens optic, Sensar® AR40e, with rounded anterior edge and squared posterior edge. (Courtesy of AMO.)

 

 

 

LENS EPITHELIAL CELL SURGERY

 

I.

Primary procedures

 

A.

Mechanical

 

1.

Capsular polishing

 

2.

Capsular vacuuming

 

3.

Capsular vacuuming with ultrasound

 

4.

Capsular curettage

 

5.

Capsular cryo

 

B.

Pharmacological

 

1.

Hypotonic hydrolavage

 

2.

Antimetabolites

 

3.

Antiprostaglandins

 

C.

Immunological

 

1.

Monoclonal antibodies

 

D.

Prophylactic posterior capsulotomy/capsulectomy (CCC)

 

II.

Secondary procedures

 

A.

Invasive

 

1.

Capsulotomy/capsulectomy (CCC)

 

2.

Curettage

 

3.

Vacuuming

 

B.

Noninvasive

 

1.

Nd:YAG laser capsulotomy/capsulectomy

 

 

 

AcrySof MA60AC and AMO, Sensar AR40e) and in silicone (AMO, ClariflexBand Pharmacia C911). The square edge has been shown to be a physical barrier to the central posterior migration of LECs.[23]

Zonular Surgery

The preceding discussion of the surgical management of the lens capsule concentrated on endocapsular techniques and management of the viable LECs on the interior surface of the lens capsule. The discussion would be incomplete if it did not address a significant, difficult, new area of capsular surgery that deals with an abnormality of the exterior capsule—management of the weak or partially absent zonule.

In most cases, the goal of this type of lens surgery is the same as that for eyes without a compromised zonule: to remove the contents of the capsular bag though a CCC and replace the contents with a foldable IOL. However, in these cases, the goal is extended to include performing the surgery without further compromising the zonule, without disrupting the vitreous, without jeopardizing the long-term integrity of the capsulozonular apparatus, and, if possible, to recircularize and recenter a subluxed capsule.

To accomplish these surgical goals and avoid a long incision, intracapsular extraction, vitrectomy, and anterior chamber IOL, several modifications to the standard procedure are planned for eyes with compromised zonules. In these eyes, there is some

 

 

Figure 42-15 Complete closed, circular, foldable silicone endocapsular ring. (Courtesy of T. Hara.)

zonular support to the capsule (partial zonular absence), enough of a circumference of attached fibers to support CCC and implantation of an endocapsular ring. If only a small percentage of the zonule is attached, or if the zonule is completely absent, intracapsular extraction with anterior chamber IOL or sutured posterior chamber IOL may be the only technique available.

Endocapsular rings were originally conceived in Japan, not for the purpose of supporting the zonule, but for the purpose of placing pressure on the equatorial LECs to prevent posterior capsular opacification. Two models were manufactured in the early 1990s. A completely closed circular model, made of silicone for foldability and implantability through a 3?mm incision, was designed by Hara ( Fig. 42-15 ), and an open PMMA model was designed by Nagamoto. It was subsequently demonstrated in clinical trials and by phase-contrast videography of living LECs (Nagamoto and Bissen-Miyajima) that the presence of a ring in the capsular equator had no effect on the viability and migratory activity of LECs. Witchell et al. in Germany also designed an open PMMA ring for the purpose of supporting capsules with compromised zonules ( Fig. 42-16 ), and Cionni (Cincinnati, Ohio) designed modifications to the PMMA capsule tension rings (CTRs) to allow them to be sutured to the eye wall,[48] thus creating a synthetic “pseudozonule” attached to an intracapsular skeletal supporting apparatus ( Fig. 42-17 ). When surgery on such eyes is planned, if OVD is to be used for the CCC, care must be taken not to overinflate the eye, especially with a dispersive OVD, as this may stress or further tear zonular fibers. A CCC can usually be performed and should be large. This facilitates hydrodissection and allows for the possibility of nuclear hydro- or viscoexpression. Complete hydrodissection is essential so that nuclear manipulations place no stress on the remaining zonular fibers. Similarly, expressing the nucleus through the large CCC into the supracapsular space, the pupillary plane, or the anterior chamber allows for nuclear emulsification safely away from the zonulocapsular apparatus.

If the zonule is weak or absent in only a limited meridional arc such that there is no decentration or subluxation of the capsule, a simple CTR can be implanted. These simple rings can be implanted with forceps or by injection with a special instrument (Geuder) and can be implanted at any stage in the surgical procedure:

• After hydrodissection, before phacoemulsification

• During phacoemulsification

• After phacoemulsification, before cortical aspiration

• During cortical aspiration

• After cortical aspiration, before IOL implantation

If there is capsular subluxation, a Cionni CTR may be implanted; ideally, the ring is sutured to the sclera in the meridian that is the

 

325

 

 

Figure 42-16 Open PMMA endocapsular ring. (Courtesy of Morcher, GMBh, Germany.)

 

 

Figure 42-17 Cionni-modified endocapsular ring for suturing to sclera to create a pseudozonule. (Courtesy of Morcher, GMBh, Germany.)

center of the arc of zonular absence. The ring will recentralize the capsule, and the suture will recentralize the capsule and will re-elevate a posteriorly tilted capsule to the zonular plane.

Another modification to the routine technique is that of lowering the infusion bottle to a level that provides the slowest stream of irrigation beyond a drip, such that the phacotip is cooled and the chamber is maintained, but excessive volume with posterior displacement of the lens is avoided. The Cionni ring type of sutured skeletal support of the capsule is often strong enough to support careful endocapsular phacoemulsification techniques. Chopping performed with equicentripetal forces places no lateral stress on the zonule.

When choosing an IOL, it would be ideal to implant a material that induces no fibrous metaplasia of the LECs and a design that blocks the formation of central posterior capsular opacification. Therefore, PMMA and silicone are not ideal materials for these eyes. Among those currently available, the IOL of choice is one with an acrylic optic and a square posterior edge. Two such models are available, the Alcon AcrySof MA60AC and the AMO Sensar AR40e (see Fig. 42-14 ). Additionally, these hydrophobic acrylics unfold in a very slow, controlled fashion that produces zero stress on the capsule or zonule.

Surgery for Presbyopia

These new and experimental procedures are designed to enhance lens function; that is, they are performed to improve the amplitude of accommodation in a presbyopic eye. These procedures are intended for purely presbyopic noncataractous eyes with no lenticular pathology other than the normal physiological middle-aged loss of accommodative function.

Although one could theoretically make a case for clear lens replacement with an accommodative pseudophakos, it has never been conclusively demonstrated that loss of elasticity of the lens is the sole or even the major cause of presbyopia—in fact, more to the contrary. Changes have been shown to occur in the area of insertion of the zonular fibers, as well as in the configuration of the ciliary muscle. With only this limited knowledge, the present procedures represent the first attempts at the surgical correction of presbyopia by altering the ciliary architecture. Scleral expansion over the ciliary muscle by implantation of four circumferential PMMA rods or by radial sclerotomy, restoring tension to the flaccid zonular fibers, has been shown in early clinical studies to have mixed success at restoring some accommodative power to the ciliary-zonule-lens mechanism.

 

 

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14. Inan UU, Ozturk F, Kaynak S, et al. Prevention of posterior capsule opacification by intraoperative single-dose pharmacologic agents. J Cataract Refract Surg. 2001;27:1079–87.

 

15. Nishi O, Nishi K, Yamada Y, Mizumoto Y. Effect of indomethacin-coated posterior chamber intraocular lenses on post-operative inflammation and posterior capsular opacification, J Cataract Refract Surg. 1995;21:574–8.

 

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17. Power WJ, Neylav D, Collum LMT. Daunomycin as an inhibitor of human lens epithelial cell proliferation in culture. J Cataract Refract Surg. 1994;20:287–90.

 

18. Goins KM, Optiz JR, Fulcher SFA, et al. Inhibition of proliferating lens epithelium with antitransferrin receptor immunotoxin. J Cataract Refract Surg. 1994;20: 513–5.

 

19. Gindi JJ, Wan WL, Schanzlin DJ. Endocapsular cataract surgery. I. Surgical technique. Cataract. 1985;2(5):6–10.

 

20. Haefliger E, Parel J-M, Fantes F, et al. Accommodation of an endocapsular silicone lens (Phaco-ersatz) in the non-human primate. Ophthalmology. 1987;94(5): 471–7.

 

21. Haefliger E, Parel J-M. Accommodation of an endocapsular silicone lens (Phaco-ersatz) in the aging rhesus money. J Refract Corneal Surg. 1994;10:550.

 

22. Nishi O. Refilling the lens of the rabbit eye after endocapsular cataract surgery. Folia Ophthalmol Jpn. 1987;38:1615–8.

 

23. Nishi O, Hara T, Hayashi F, et al. Further development of experimental techniques for refilling the lens of animal eyes with a balloon. J Cataract Refract Surg. 1989;15:584–8.

 

24. Hara T, Hara T, Yasuda A, Yamada Y. Accommodative intraocular lens with spring action. Part 1. Design and placement in an excised animal eye. Ophthalmic Surg. 1990;21:128–33.

 

25. Hara T, Hara T, Yasuda A, et al. Accommodative intraocular lens with spring action. Part 2. Fixation in the living rabbit. Ophthalmic Surg. 1992;23:632–5.

 

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27. McIntyre DJ. Cataract surgery: techniques, complications and management. In: Steinert RF, ed. Phacosection cataract surgery. Philadelphia: WB Saunders; 1995:119–22.

 

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29. Koch PS, Katzen LE. Stop and chop phacoemulsification. J Cataract Refrac Surg. 1994;20:566–70.

 

30. Dodick JM, Christiansen J. Experimental studies on the development and propagation of shock waves created by the interaction of short Nd:YAG laser pulses with a titanium target. J Cataract Refract Surg. 1991;17:794–7.

 

31. Grabner G, Alzner E. Dodick laser phacolysis: thermal effects. J Cataract Refract Surg. 1999;25:800–3.

 

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34. Kanellopoulos AJ: Laser cataract surgery: a prospective clinical evaluation of 1000 consecutive laser cataract procedures using the Dodick photolysis Nd:YAG system. Ophthalmology. 2001;108:649–55.

 

35. Neubaur CC, Stevens S. Erbium:YAG laser cataract removal: role of fiber-optic delivery system. J Cataract Refract Surg. 1999;25:514–20.

 

36. Hoh H, Fischer E. Pilot study on erbium laser phacoemulsification. Ophthalmology. 2001;107:1053–62.

 

37. Duran SD, Zato M. Erbium:YAG laser emulsification of the cataractous lens. J Cataract Refract Surg. 2001;27:1025–32.

 

38. Assia E, Apple D, Barden O, et al. An experimental study comparing various anterior capsulectomy techniques. Arch Ophthalmol. 1991;109:642–7.

 

39. Apple D, Park S, Merkley K, et al. Posterior chamber intraocular lenses in a series of 75 autopsy eyes. Part I. Loop location. J Cataract Refract Surg. 1986;12:358–62.

 

40. Gimbel HV, Neuhann T. Development, advantages, and methods of the continuous circular capsulorrhexis technique. J Cataract Refract Surg. 1990;16:31–7.

 

41. Assia E, Apple D, Tsai J, Lim E. The elastic properties of the lens capsule in capsulorrhexis. Am J Ophthalmol. 1991;111:628–32.

 

42. Galand A. A simple method of implantation within the capsular bag. Am Intra-ocular Implant Soc J. 1983;9:330–2.

 

43. Hara T, Hara T. Intraocular implantation in an almost completely retained capsular bag with a 4.5 to 5.0 millimeter linear dumbbell opening in the human eye. Ophthalmic Surg. 1992;23:545–50.

 

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47. Hara T, Hara T. Observations on lens epithelial cells and their removal in anterior capsule specimens. Arch Ophthalmol. 1988;106:1683–7.

 

48. Ahmed II, Crandall AS. Ab externo scleral fixation of the Cionni modified capsular tension ring. J Cataract Refract Surg. 2001;207:977–81.

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