Review
`
`Advances in cataract surgery
`
`Expert Rev. Ophthalmol. 8(5), 447–456 (2013)
`
`Majed Alkharashi,
`Walter J Stark and
`Yassine J Daoud*
`The Wilmer Eye Institute, Johns Hopkins
`University, Maumenee 327,
`600 North Wolfe Street, Baltimore,
`MD 21287, USA
`*Author for correspondence:
`Tel.: +1 410 910 2330
`Fax: +1 410 910 2393
`ydaoud1@jhmi.edu
`
`Recent advances in cataract surgery have increased the safety and efficacy of this common
`procedure. Cataract surgery has evolved from ‘couching’ with sub-optimal
`results to
`phacoemulsification with excellent results. Introduction of the femtosecond laser into cataract
`surgery may further the safety and predictability of this procedure. In addition, innovations in
`intraocular lens material have enabled the surgery to be done through a small incision with
`quicker recovery and more predictable refractive outcome. New intraocular lens design
`technologies have helped patients minimize their need for glasses at most distances. Further,
`invention of ophthalmic viscosurgical devices reduced the risk of endothelial decompensation
`and corneal edema. These innovations have transformed the goal of cataract surgery from
`purely visual rehabilitation to a refractive procedure as well.
`
`KEYWORDS: cataract surgery (cid:129) femtosecond laser (cid:129) intraocular lens (cid:129) ophthalmic viscosurgical devices
`
`Cataract is a leading cause of blindness world-
`wide and cataract surgery is one of the most
`frequently
`performed
`operations
`in
`the
`world. Cataracts affect more than 20 million
`Americans older
`than 40 years. By 2020,
`more than 30 million Americans will have vis-
`ually significant cataract and 9.5 million are
`expected to have pseudophakia or aphakia [1].
`Advancements
`in phacoemulsification and
`intraocular lens (IOL) technology have ushered
`in a new era of cataract surgery. Innovations
`in IOL design and phacoemulsification instru-
`mentation have potentiated improved surgical
`outcomes,
`reduced perioperative morbidity
`and increased likelihood of spectacle independ-
`ence. As a result, surgeons are attaining unpre-
`cedented safety, efficiency and precision. The
`breakthrough of new technology is paralleled
`by patients’ heightened expectations from cata-
`ract surgery. In this new era, many patients
`arrive to their appointment well-researched
`and prepared with anticipation of exceptional
`postoperative visual acuity, both near and
`distance, without correction [2].
`
`History
`The first record of cataract being surgically
`treated is from 600 B.C. by Susruta of India [3].
`Cataracts were surgically addressed by couch-
`ing. Basically the surgeon would insert a long
`instrument posterior to the limbus and push
`the lens into the vitreous cavity, thus clearing
`the visual axis of the dense lens. Complication
`rate was high at that time, but it would change
`
`the patient’s life by giving him some ambula-
`tory vision and self-dependence. Couching is
`‘healers’
`still performed by some traditional
`in some parts of Africa, the Middle East and
`few other parts of the world. 33.3% of patients
`who undergo traditional couching end up
`with no light perception vision [4]. It is likely
`that outcomes of couching would have been
`worse in ancient
`times when there was no
`recourse to modern antibiotics for endophthal-
`mitis or treatments for glaucoma. The concept
`of cataract extraction rather than pushing the
`lens inside the eye was introduced by Ammar
`in Choice of Eye Diseases written in
`Ibn Ali
`Egypt in the 10th century. Ibn Ali invented the
`hollow needle and oral suction device, for the
`purpose of cataract extraction:
`“Then I constructed the hollow needle, but
`I did not operate with it on anybody at all,
`before I came to Tiberias. There came a man
`for an operation who told me: Do as you like
`with me, only I cannot lie on my back. Then
`I operated on him with the hollow needle and
`extracted the cataract; and he saw immediately
`and did not need to lie, but slept as he liked.
`Only I bandaged his eye for seven days. With
`this needle nobody preceded me. I have done
`many operations with it in Egypt [5].”
`As one would expect, this technique would
`not work on dense cataract and couching
`remained the widely performed surgery to treat
`cataract for many decades [3].
`ophthalmologist,
`In
`1747,
`a French
`Jacques Daviel, was
`the first
`to perform
`
`www.expert-reviews.com
`
`10.1586/17469899.2013.840238
`
`Ó 2013 Informa UK Ltd
`
`ISSN 1746-9899
`
`447
`
`Downloaded by [Deborah Maglione] at 09:25 16 October 2015
`
`SENJU EXHIBIT 2052
`INNOPHARMA v. SENJU
`IPR2015-00903
`
`Page 1 of 10
`
`

`
`Review Alkharashi, Stark & Daoud
`
`extracapsular cataract extraction through a large corneal
`incision. Then, he would incise the anterior capsule and
`express the nucleus. Because of the incomplete removal of
`the cortex, chronic inflammation with glaucoma and secon-
`dary capsular opacification would lead to unsatisfactory out-
`come. Thus, the procedure was not widely accepted at that
`time and surgeons tried to remove the lens as a whole with
`the capsular bag. In 1753, Samuel Sharp was among the
`first to successfully perform intracapsular cataract extraction
`(ICCE) through limbal
`incision using pressure from his
`thumb.
`Lens expression technique was improved over many years
`by using different approaches. In 1957, Joaquin Barraquer
`used a-chymotrypsin to dissolve the zonules to facilitate lens
`removal. However, glaucoma and clogging the trabecular
`meshwork with zonule fibers remnant was one of the many
`complications of the technique. Cryoprobe was first intro-
`duced in 1961 by Tadeusz Krwawicz to remove the lens by
`forming iceball and lessen the risk of capsular rupture. ICCE
`was a very successful operation compared to couching and
`early ECCE. However, the rate of potentially blinding com-
`plications was 5% apart
`from aphakia related habitation
`problems [6].
`introduction of operating microscopes during
`The gradual
`the 1970s offered better intraocular visibility and ability to
`safely place multiple corneal sutures. In addition, it had the
`advantages of leaving the posterior capsule intact which reduced
`the risk of potentially blinding complications (e.g., vitreous loss
`or retinal detachment). It also allowed posterior chamber lens
`implantation.
`introduced in 1967 by Dr.
`Phacoemulsification was
`Charles Kelman. Since then,
`there has been significant
`improvement
`in fluidics, energy delivery, efficiency and
`most important, safety of this procedure. Currently, phacoe-
`mulsification is the standard of care for cataract extraction
`in the western world. The major advantage of phacoemulsi-
`fication is that it reduced the morbidity from cataract sur-
`gery by reducing the incision size with subsequent faster
`recovery and decreased risk of complications
`including
`endophthalmitis.
`A major advance in cataract surgery was the invention of
`an intraocular lens that can be implanted to replace the
`extracted cataractous lens. Casaamata is believed to be the
`first
`surgeon to implant an intraocular
`lens
`(IOL)
`in
`1795 [7]. The idea of IOL implantation was revived by Har-
`old Ridley. Ridley inserted an artificial lens in the form of
`polymethyl-methacrylate (PMMA) in 1949 [7,8]. However,
`the idea of PMMA IOL did not gain popularity due to mis-
`calculation of the postoperative refraction. The cause of this
`miscalculation was later discovered to be due to the differ-
`ence in the refractive index of PMMA material in air vs in
`fluid inside the eye. Another drawback of the PMMA lenses
`is that they were rigid and could not be folded which neces-
`sitated large corneal incisions to insert such lenses. Subse-
`quent IOLs made of acrylic and silicone, were flexible and
`
`folded and inserted through a
`could be
`smaller incision.
`
`significantly
`
`Ophthalmic viscosurgical devices
`Healon (sodium hyaluronate 1%, Abbott Medical Optics Inc.
`Santa Ana, CA, USA) was the first ophthalmic viscosurgical
`device (OVD) to be introduced in 1979. Since then, a number
`of OVDs have been manufactured with varying composition
`and rheologic behavior. OVDs have variety of uses in ophthal-
`mic surgery which could be summarized in space creation,
`tissue stabilization and corneal endothelial cell protection [9].
`OVDs used to be classified as either dispersive or cohesive.
`Dispersive OVDs (e.g., Viscoat, Alcon. Fort Worth, TX,
`USA) are low in viscosity and molecular mass, have short
`molecular chain length and require longer aspiration time for
`complete removal. Typically, dispersives remain in the eye during
`phacoemulsification to protect the endothelium from turbulent
`flow.
`Cohesive OVDs (e.g., Healon, Abbott Medical Optics Inc.)
`are typically more viscous; have a higher molecular mass,
`possess longer chains, result in excellent space maintenance and
`are easy to remove. Thus, cohesives are used to expand the
`capsular bag for intraocular lens insertion at the end of cataract
`surgery.
`The introduction of Healon5 (sodium hyaluronate 2.3%) in
`1998 heralded a new class of OVDs termed viscoadaptive [10].
`Viscoadaptives (e.g., Healon5 and DisCoVisc, Alcon.) behave
`similar to superviscous cohesives under low shear stress. With
`change in fluid dynamics, the viscoadaptives fracture freeing
`pieces to float around in the balanced salt solution. This bipha-
`sic nature has resulted in viscoadaptives being referred to as
`pseudodispersive in ophthalmic surgery because they are well
`retained in the
`anterior
`segment
`similar
`to dispersive
`OVDs [11].
`OVDs have led to dramatic improvement in the safety of
`cataract surgery and minimized damage to the ocular structures
`that used to occur previously as a result of cataract surgery.
`Indeed, OVDs are of the most important advances in cataract
`surgery.
`
`Intraoperative floppy iris syndrome
`Intraoperative floppy iris syndrome (IFIS) typically occurs in
`patients receiving a-1 blocker. Features of IFIS include poor
`pupil dilation; progressive intraoperative pupillary miosis, iris
`prolapse and floppy iris. To decrease the risk of complications,
`few peri- and intraoperative interventions have been successfully
`attempted. Pre-operatively, using atropine drops for few days is
`recommended [12]. Intraoperatively, short and posterior corneal
`wound construction should be avoided. Intracameral preserva-
`tive free epinephrine may be utilized and adding preservative
`free epinephrine to a 500 ml BSS irrigation bottle is recom-
`mended (off-label). There should be a low threshold for
`using pupillary dilation devices. Because of the ability to place
`an iris retractor subincisionally, we prefer iris retractors to pupil
`expansion rings in IFIS cases with poor pupil dilation. Manual
`
`448
`
`Expert Rev. Ophthalmol. 8(5), (2013)
`
`Downloaded by [Deborah Maglione] at 09:25 16 October 2015
`
`Page 2 of 10
`
`

`
`Advances in cataract surgery Review
`
`pupillary dilation and stretching should be avoided, so is over-
`filling and overly pressurizing the chamber with OVD. Some
`OVD should be removed by pressing on the wound before
`performing hydrodissection. Low fluidic parameters should be
`utilized, and suturing the main corneal incision to avoid iris
`prolapse in case of leaky wound. Arshinoff described modified
`soft-shell and ultimate soft-shell
`technique (SST-USST) for
`IFIS [13] which relies solely upon OVDs for iris stabilization by
`using Viscoat (Alcon.) and Healon5 (Abbott Medical Optics
`Inc.) to add a semi-rigid OVD roof to stabilize the iris and
`cause some viscomydriasis. Chang et al., reported that the use
`of preoperative atropine followed by intraoperative Healon5,
`iris retractors and pupil expansion rings resulted in excellent
`surgical outcome [14].
`Viscoat may be useful in compartmentalization especially in
`cases of localized weakness of the zonules (e.g., trauma). The
`reverse soft shell technique (packing Viscoat in a region of
`broken zonules followed by placing cohesive OVD over it to
`prevent vitreous from prolapsing) can be used in case of poste-
`rior capsule rapture to cover and stabilize the tear. Viscoat can
`also partition residual
`lenticular material from the prolapsed
`vitreous. In July 2012, Healon EndoCoat was approved by
`the US FDA as a dispersive OVD.
`
`Capsular staining
`The advent of capsular staining has improved the safety of cata-
`ract surgery by allowing enhanced visualization. Indications
`for capsular staining include cases with a poor red reflex as in
`mature or white cataracts, opalescent cortical material, dense pos-
`terior subcapsular opacification, vitreous hemorrhage, or corneal
`opacity. In addition, staining is also useful for pediatric cataract
`extraction and for surgeons learning new intraoperative techni-
`ques requiring good visualization of the anterior capsule. Numer-
`ous
`intraocular dyes have been reported in the literature
`including indocyanine green (ICG), fluorescein, crystal violet,
`gentian violet and brilliant blue G (BBG) [15]. However, only try-
`pan blue is FDA approved as an adjunct to cataract surgery [16].
`
`Intraocular lenses
`advances have
`technological
`significant
`In recent
`years,
`improved our understanding of the aberrations of the normal
`human eye as well as the human eye that has been altered by
`refractive surgery. New corneal
`imaging techniques such as
`Scheimpflug imaging, placido-disk videokeratography and ante-
`rior segment optical coherence tomography have enhanced our
`understanding of the shape and functionality of the human
`cornea. These instruments have shown that the normal cornea
`is flatter in the central 2 mm, with steepening from 2-4 mm,
`and, then, flattening again beyond 4 mm. This correlates well
`with the fact that the spherical aberration value is not a con-
`stant throughout the cornea, but rather varies as one moves
`radially from the center of the cornea [101]. Further,
`in the
`young human eye, the positive spherical aberration introduced
`by the cornea is partially corrected by the negative spherical
`[17]. However
`aberration introduced by the crystalline lens
`
`changes that occur in the lens with age cause the positive spher-
`ical aberration of the lens to increase [18]. Thus, the aberration
`compensation is gradually lost, leading to an increase in total
`ocular aberrations. This,
`in turn,
`leads to a corresponding
`loss in optical and visual quality, reduction of scotopic contrast
`sensitivity and increase in optical side effects such as glare and
`haloes [19,20].
`This new understanding of ocular optics and aberrations has
`led to the development of new aspheric IOLs to neutralize the
`positive corneal spherical aberration and improve visual qual-
`ity [21]. This may be due to the improvement in contrast
`sensitivity and improved retinal image [22,23]. However, caution
`must be exercised in using aspheric IOLs in patients at risk of
`decentration (e.g., pseudoexfoliation and trauma) as this may
`induce further higher order aberrations [24]. Aspheric IOL should
`also be avoided in eyes that had hyperopic LASIK treatment as
`this might increase the negative spherical aberration of the eye.
`
`Intraocular lenses for presbyopia correction
`Presbyopia remains one of the most challenging optical prob-
`lems in cataract and refractive surgery. Different approaches
`to treat presbyopia have been studied in recent years. These
`include scleral remodeling (scleral expansion and sclerotomy
`techniques) [25]; corneal procedures (presbyLASIK [26], corneal
`inlays [27] and conductive keratoplasty [28]); and monovision
`[28]. Each of
`techniques
`these techniques has
`limitations,
`advantages
`and disadvantages. There has been increasing
`interest in correcting presbyopia at the time of cataract surgery
`by using presbyopia-correcting IOLs. The two major presbyopia-
`correcting IOL designs are the accommodating and the multi-
`focal IOLs.
`The first presbyopia-correcting IOL to be FDA-approved
`was the Array (Advanced Medical Optics, Santa Ana, CA, USA
`and USA) in 1997. The Array is a refractive multifocal lens
`with five progressive concentric zones on its anterior surface.
`Zones one, three and five are distance-dominant, whereas zones
`two and four are near-dominant. In some of the first studies,
`72% of the eyes implanted with the Array could see both 20/
`40 for distance and J3 for near compared with 48% with a
`monofocal lens [29].
`In 2005, the FDA approved two new multifocal designs, the
`refractive Rezoom IOL (Advanced Medical Optics, Inc.) and
`1
`(Alcon Laboratories, Inc.).
`the diffractive Acrysof Restor IOL
`The Rezoom represents new engineering of the Array platform,
`including a hydrophobic acrylic material and a shift of the
`zonal progression. Aspheric transitions between the zones offer
`intermediate vision. The near-dominant zones provide +3.50 D
`of add power at the IOL’s plane for near vision, yielding
`approximately +2.57 D of add power in the spectacle plane.
`The Rezoom has been shown to provide spectacle independ-
`ence in 93.4, 92.6 and 81.4% for distance, intermediate and
`near vision, respectively [102]. The major drawbacks of
`the
`Rezoom are its moderate dependence on spectacles for near
`tasks and the increased incidence of photic phenomena com-
`pared to other multifocal lenses [30].
`
`www.expert-reviews.com
`
`449
`
`Downloaded by [Deborah Maglione] at 09:25 16 October 2015
`
`Page 3 of 10
`
`

`
`Review Alkharashi, Stark & Daoud
`
`1
`1
`IOL employs a central 3.6 mm dif-
`ReSTOR
`The AcrySof
`fractive zone. This area comprises 12 concentric steps of gradu-
`ally decreasing (1.3-0.2 microns) heights, the farther from the
`center. These steps allocate energy based on lighting conditions
`and activity to create a range of vision. The ReSTOR has been
`shown to yield high rates of spectacle freedom with uncorrected
`distance visual acuity of 20/30 or better in 93.8% eyes and an
`uncorrected near visual acuity of 20/30 or better in 75.0% of
`eyes [31,32]. Glare and halos have been reported as the main com-
`plication of this type of lens. Moderate glare was reported by
`21.3% of the patients compared to 7.1% for a monofocal IOL.
`In 2007, the FDA approved the aspheric version of the
`ReSTOR (AcrySof IQ ReSTOR), which has a negative aspher-
`icity, while maintaining its apodization, diffractive and refrac-
`tive components. The AcrySof IQ ReSTOR IOL + 3.0 D
`(SN6AD1) incorporates a +3.0 diopter correction at the lentic-
`ular plane (˜+2.5 D at the spectacle plane). It also has nine
`concentric steps (three less steps than the original IOL) farther
`apart
`to improve intermediate vision over the AcrySof IQ
`ReSTOR IOL +4.0 D (SN6AD3), with similar near and dis-
`tance visual acuity. Halos and glare are still common com-
`plaints of patients
`implanted with these
`lenses. Patients
`implanted with the SN6AD1 noticed more glare and patients
`[33,34]. The
`implanted with SN6AD3 noticed more halos
`ReSTOR Toric is the newest addition to this lens design. It
`provides a single platform to correct astigmatism and improve
`near and intermediate vision. This lens is currently available in
`Europe
`and Canada, but
`is not
`yet
`available
`in the
`United States.
`In 2009, another diffractive IOL was approved, the Tecnis
`multifocal (Advanced Medical Optics, Inc. Santa Ana, Califor-
`nia). The newer version is a single-piece acrylic (ZMB00) and
`has a full diffractive posterior surface that makes it pupil inde-
`pendent. It has an aspheric anterior surface with +4 D near
`add (+3.0 D at the spectacle plane). A retrospective study on
`the earlier version of this IOL found an uncorrected distance
`visual acuity of 20/30 in 85% of eyes and an uncorrected near
`visual acuity of J1 in 93.7% of 2500 eyes, 3 years postopera-
`tively [35]. Glare and halos were reported as severe by 6.1 and
`2.12% of patients, respectively.
`Multifocal lenses have the persistent drawback of the poten-
`tial for patients to see glare or halos for few weeks or months
`following surgery. Indeed, it has been shown that multifocal
`lenses have greater incidence of glare and halos than monofocal
`IOLs [36]. However, it has been shown that glare and halos
`symptoms decrease as most people learn to disregard them
`with time [37]. Another drawback of multifocal IOLs is the
`potential
`for decreased contrast sensitivity especially in dim
`lights. However, contrast
`sensitivity with multifocal
`IOLs
`improves over time and may approximate the levels found with
`lenses by 6 months postoperatively [38].
`spherical monofocal
`Patient selection for multifocal IOL is critical. Patients with
`high expectations, or those with significant astigmatism, ocular
`surface disease (e.g., epithelial basement membrane disease and
`severe dry eye), zonular weakness (e.g., pseudoexfoliation ) or
`
`patients with retinal diseases (e.g., macular degeneration and
`epiretinal membrane) may not be good candidates.
`
`Accommodating lenses
`The Crystalens (Bausch & Lomb, Aliso Viejo, CA, USA) is the
`only FDA approved ‘accommodating’ lens to correct presbyo-
`pia in patients with cataracts. The Crystalens has undergone
`several modifications since the original model (AT-45). It has
`silicone optic and two flexible, hinged plate haptics. The latest
`models (HD and AO) have a central 1.5 mm blended bispheric
`optical zone to enhance near vision [39]. The Crystalens has
`been shown to have better uncorrected near visual acuity than
`a monofocal lens [39]. Although it was thought that the Crysta-
`lens mode of action is through accommodation, several studies
`have failed to demonstrate a significant accommodative shift.
`Indeed, the Crystalens have been shown to have poorer uncor-
`rected near visual acuity than the multifocal lenses. Thus, many
`Crystalens surgeons may aim for -0.50 D to -0.75 D of myo-
`pia in the nondominant eye to induce ‘mini-monovision’ in
`their patients [40-42]. Another drawback of the Crystalens has
`been issues with tilting and decentration of the lens caused by
`capsular contraction and fibrosis [43]. On the other hand, there
`are less complains of glare and halos from Crystalens than
`from the multifocal lenses. Thus, Crystalens is a good option
`for patients who are willing to accept some compromise in
`near vision but have a low threshold for glare and halos that
`may be present with multifocal lenses [44].
`One of the new accommodating lenses currently undergoing
`FDA trials is the Synchrony accommodating IOL (Abbot Medi-
`cal Optics, Abbott Park, IL, USA). The Synchrony IOL consists
`of a foldable, single piece, dual-optic system. A spring haptic
`joins the high plus anterior optic to a minus powered posterior
`optic [45]. During attempted distance vision, the two optics are
`close together. Near vision is achieved by attempted accommo-
`dation with subsequent decrease in capsular bag and zonular
`tension. This in turn moves the front optic forward and changes
`the focal point to intermediate or near vision. In a small pro-
`spective study, the Synchrony lens was shown to have equivalent
`uncorrected-distance and uncorrected- near visual acuity to the
`ReSTOR lens while providing better uncorrected-intermediate
`visual acuity and less halos and glare [46].
`Another promising technology is the three-piece Light Adjust-
`able Lens (Calhoun Vision Inc., Pasadena, CA, USA) made of a
`photosensitive silicone material. Within two weeks post-opera-
`tively, the residual refractive error could be corrected by shining
`an ultraviolet light on the IOL through a dilated pupil to change
`the shape of the lens. The Light Adjustable Lens corrects sphero-
`cylindrical errors as well as presbyopia by creating a small near
`zone add according to the pupil diameter [47-49].
`
`Implantable miniature telescope
`In July 2010, the FDA approved the Implantable miniature tele-
`scope TM (IMT, VisionCare Ophthalmic Technologies
`Inc.,
`Saratoga, CA, USA). The implantable miniature telescope
`(IMT) is a system which magnifies objects to improve vision
`
`450
`
`Expert Rev. Ophthalmol. 8(5), (2013)
`
`Downloaded by [Deborah Maglione] at 09:25 16 October 2015
`
`Page 4 of 10
`
`

`
`Advances in cataract surgery Review
`
`in patients with end-stage age-related macular degeneration
`(AMD).
`It
`is
`indicated for monocular
`implantation in
`patients with stable, but severe to profound vision impair-
`ment (best corrected distance visual acuity 20/160-20/800)
`caused by bilateral central scotomas associated with end-stage
`age-related macular degeneration, a visually significant cata-
`ract and who achieve at least a 5-letter improvement on the
`visual acuity chart using a trial external telescope. Two mod-
`els are available: one with 2.2-times magnification and the
`other with 2.7-times magnification. The device’s glass cylin-
`der housing the micro-optics is 4.4 mm long and 3.6 mm in
`diameter. The rigid haptic loops are 13.5 mm in diameter.
`The device is placed in the capsular bag while the anterior
`aspect protrudes
`through the pupil by 0.1-0.5 mm. The
`prosthesis projects an enlarged image of the patient’s central
`visual
`field onto the retina;
`thus reducing the size of
`the
`scotoma relative to the objects in the central field of vision.
`The implanted eye sees 20-24 wide field of view due to the
`enlarged image projection.
`The IMT has shown promise with 59.5% of 173 IMT-
`implanted eyes gaining three lines or more of BCVA compared
`to 10.3% of 174 fellow control eyes (p < 0.0001) after 2 years
`of follow-up. Meanwhile, 0.6% of 173 telescope-implanted eyes
`lost three lines or more compared to 7.5% of 174 fellow con-
`trol eyes (p = 0.0013). Two cases of corneal edema in IMT-
`implanted eyes required grafts between 9 and 12 months [50].
`There were no cases of corneal decompensation between 1 and
`2 years after
`surgery. The mean endothelial cell density
`stabilized after the first year through the second year [51].
`
`Zonules-supporting devices
`The anterior approach of removing a cataract with significant
`zonular weakness used to be ICCE until endocapsular devices
`were introduced in 1991 [52,53]. The capsular tension ring
`(CTR) is made of polymethyl-methacrylate (PMMA) material
`and has an oval-shaped cross section with eyelets at both free
`ends. The diameter of CTR is larger than that of the capsular
`bag and comes in different sizes. The CTR expands the capsu-
`lar bag and redistributes the forces, providing equal distribution
`of support over the remaining zonules [54]. At minimum, over-
`lap of the end terminals is needed to provide complete circum-
`ferential support. CTR is indicated when there is evidence of
`severe, but localized zonular dialysis (<4 h) or mild degree of
`generalized zonular weakness [54]. The CTR can be inserted
`manually with forceps or with injectors into the capsule bag
`before or after lens extraction.
`The CTR has intra- as well as post-operative advantages. By
`expanding the bag, it reduces the risk of further zonular dam-
`age. Also, it minimizes the risk of potentially aspirating the bag
`during the surgery. Post-operatively, CTR reduces the risk of
`IOL decentration and tilting [55]. It offers the advantage of pre-
`venting capsule wrinkling and facilitate recentering a mildly
`subluxed capsular bag. Further, it may decrease the prevalence
`of posterior capsule opacification or the incidence of capsular
`phimosis [56].
`
`insufficiency and a
`When there is a profound zonular
`severely subluxed capsular bag, a standard CTR may not supply
`enough intraoperative and postoperative support to maintain
`the desired orientation of the capsular bag. To deal with these
`problems, scleral-fixated devices such as the modified CTR
`(M-CTR) or the capsular tension segment (CTS) must be
`used [57]. Iris chafing from the fixation eyelet and chronic uvei-
`tis could occur with small capsulorhexis, thus an adequate size
`capsulorhexis (5.5 mm) should be performed [54].
`
`Correction of astigmatism during cataract surgery
`Corneal astigmatism can be measured by multiple techniques
`including manual keratometry, autokeratometry, optical biome-
`tery and corneal
`topography. Topographic measurement of
`corneal astigmatism is currently the standard of care. Corneal
`topographic measurements identify irregular astigmatism that
`may limit optimum results.
`Management of corneal astigmatism at the time of cataract
`surgery is an area of increasing importance and active research.
`Several approaches to correct corneal astigmatism have been suc-
`cessfully tried. These include main corneal incision-placement on
`the steep axis of the cornea, single or paired peripheral corneal
`relaxing incisions (PCRIs) and/or toric IOL implantation. Cor-
`neal incisions do not change the spherical equivalent power of
`the cornea enough to affect IOL power calculations. Because of
`the coupling effect, they flatten the meridian where they are
`placed and steepen the meridian 90˚ away.
`For corneal astigmatism <1 D, placing the main corneal inci-
`sion on the steep axis could be performed. With 1-1.5 D of
`astigmatism, peripheral corneal relaxing incisions may be uti-
`lized. Toric IOL is used for >1.5 D of astigmatism [58].
`
`On axis corneal incision
`A full thickness corneal incision for cataract surgery flattens the
`cornea in the meridian of the incision and therefore can reduce
`preexisting astigmatism. The incision is made on the steep axis of
`astigmatism. This is a good approach for correcting small amounts
`of against-the-rule astigmatism with a temporal incision.
`
`Peripheral corneal relaxing incisions
`Peripheral corneal relaxing incisions (PCRIs) are called limbal
`relaxing incisions (LRIs) in older literature, but this term is inac-
`curate because the limbus is not incised. The incisions reduce cor-
`neal astigmatism by flattening the cornea in the steep meridian
`and steepening the cornea in the flat meridian. PCRIs are useful
`for treating 1-1.5 D of regular corneal astigmatism when implant-
`ing non toric IOLs. Beyond 1.5 D, the risks associated with PCRI
`use begin to outweigh the potential benefits compared with toric
`IOLs. To achieve consistent incision depth, PCRIs should be per-
`formed at the beginning of surgery before altering the intraocular
`pressure. Unwanted under corrections may occur if relaxing inci-
`sions are made after a globe is penetrated [59]. Also, the axis mark-
`ing should be placed while the patient is in the upright position
`to prevent axis misalignment due to cyclorotation of the eye in
`the supine position. An axis misalignment of LRI of just 5˚ results
`
`www.expert-reviews.com
`
`451
`
`Downloaded by [Deborah Maglione] at 09:25 16 October 2015
`
`Page 5 of 10
`
`

`
`Review Alkharashi, Stark & Daoud
`
`in a 17% reduction in effect [60]. Because of risk of corneal perfo-
`ration or inducing higher order aberrations, PCRIs should be
`avoided on corneas with ectasia [58].
`PCRIs could be performed by laser during femtosecond
`laser-assisted cataract surgery with more precision of depth, axis
`and length. Also, the epithelium could be left intact to be
`opened postoperatively if needed.
`
`Toric IOL
`The first toric IOL available in the US market was the STAAR
`toric IOL (STAAR Surgical Co, Monrovia, CA, USA). The
`first version of STAAR toric IOL was approved by the FDA in
`1998. The overall haptic diameter was 10.8 mm. The STAAR
`toric IOL suffered from early postoperative rotational instabil-
`ity, particularly when implanted in large myopic eyes [61]. The
`newer version has longer haptic length (11.2 mm) and has
`been shown to be more stable than the older version. However,
`limited [62,63]. The
`widespread acceptance and usage was
`STAAR toric power at the IOL plane for both models is 2 and
`3.5 D, corresponding to 1.4 and 2.3 D at the corneal plane.
`In 2005, the one-piece acrylic Acrysof Toric IOL (Alcon
`Laboratories Inc., Fort Worth, TX, USA) was granted approval
`by the FDA. The lens has excellent rotational stability, with
`less than 4˚ of rotation at 1 year [64]. Poll et al., showed that
`eyes with astigmatism ‡2.26 D that were implanted with a
`toric lens implant were more likely to achieve 20/40 UDVA
`compared to PCRIs [65].
`Subsequent Acrysof Toric lenses can correct up to 4.11 D of
`astigmatism at the corneal plane. Visser et al. evaluated the
`effectiveness of Acrysof Toric SN6AT6 to SN6AT9 model
`IOLs to correct cylinder powers ranges from 2.50 to 4.50 D.
`They found that these IOLs were safe and effective at correct-
`ing astigmatism in eyes with >2.25 D of corneal astigma-
`tism [66]. The use of toric IOLs is controversial in eyes with
`irregular astigmatism, higher order aberrations, or zonular
`weakness [67]. Postoperative IOL rotation significantly decreases
`the effectiveness of toric IOLs. There is a 3.3% loss of astig-
`matic correction for every 1˚ of off-axis rotation. Patients with
`long axial lengths have a higher risk of postoperative toric lens
`rotation [68].
`
`Femtosecond laser-assisted cataract surgery
`Since the introduction of the Nd:YAG laser in the treatment of
`posterior capsular opacity,
`laser technology has proven to be
`safe and effective for the treatment of many ophthalmic dis-
`eases. Indeed, laser-assisted eye surgery has proven to be safer
`and superior to surgical-instrument-assisted eye surgery. A good
`example of this is the outcome of femtosecond lase