Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 7. Left eye, patient 2. Retroillumination image shows a well-centered IOL in the capsular bag.

capsular bag. For instance, for the 12-mm Morcher type 14 A capsular tension ring the diameter outside the eye is 14.5 mm, but it is 12 mm when inserted and perfectly round in the capsular bag. The haptic thickness varies according to the axial length of the eye: for emmetropic eyes the recommended thickness are 0.15–0.20 mm which makes the capsular tension ring very flexible and easy to implant (Tensiobag of Ioltech, Morcher capsular tension rings type 14 and 14C, Ophtec type PC275). For eyes with high myopia and great tendency toward capsule retraction the recommended thickness is 0.20 mm which makes the ring rigid enough to prevent shrinkage of anterior and posterior capsule (Morcher capsular tension ring type 14 A, Ophtec type PC276). In order to prevent posterior capsule opacification, rings 0.20 mm in thickness and 0.70 mm in width can be used (Ophtec types PC277-278). Finally, in the case of aniridia and iris colobom, special capsular tension rings with complete or partial iris diaphragm can be used for dimming the iris defect and provide relief of photophobia (Morcher types 94 G-L-S and 96 G-L-S for colobom; Morcher type 50C for aniridia).

Indications for capsular tension ring are: (1) weak zonules or subluxated cataracts; (2) intraoperative partial zonular rupture; (3) prevention of the anterior capsular contraction syndrome in eyes at high risk; (4) prevention of opacification of the posterior capsule; (5) aniridia or iris colobom, and (6) pediatric cataract to prevent fibrosis and IOL decentration (table 1). The most common indications for capsular tension rings are pseudoexfoliation syndrome, high myopia and subluxated lens including traumatic cataract with zonular dialysis and

Table 1. Indications for capsular tension ring implantation

Intraoperative zonular desinsertion Localized zonulolysis or weakness

Generalized zonular weakness demonstrated by iridodonesis and phacodonesis

Lens subluxation: Pseudoexfoliation, Marfan syndrome, Weill-Marchesani syndrome, homocystinuria

Traumatic zonular dialysis

Small capsulorhexis associated with poor mydriasis

Prevention or reposition of IOL decentration caused by zonular dehiscence Prevention of anterior capsule contraction syndrome: high myopia, pseudoexfoliation, retinosis pigmentaria, capsule contraction in the fellow eye

Prevention of opacification of the posterior capsule

Eyes at risk of photocoagulation or expected vitreoretinal surgery after cataract surgery Aniridia or iris colobom

Pediatric cataract surgery Intraocular measuring gauge

Marfan syndrome [2, 3, 6]. Other conditions associated with subluxated lens include homocystinuria and Weill-Marchesani syndrome [7]. Contraindications for the use of the capsular tension ring are: (1) capsule rupture with vitreous loss due to the possibility of posterior dislocation of the ring; (2) incomplete or instable capsulorhexis because of the risk of posterior tear when implanting the ring; (3) use of a plate-haptic IOL without fenestrations due to the risk of anterior dislocation because of the outward force of the ring, and (4) small eyes with very narrow angles for the increased possibility of angle closure [2].

In the case of zonular dialysis, when zonular weakness is noted preoperatively, the capsular tension ring should be inserted into the capsular bag after capsulorhexis and careful hydrodissection but before beginning phacoemulsification so that the bag maintains an endoskeleton once the lens is removed, preventing capsular bag collapse and vitreous herniation [3]. If an unsuspected zonular dehiscence occurs intraoperatively, the capsular ring can be implanted immediately to avoid further unzipping of the zonules and possible vitreous prolapse. When the capsular ring is used in order to prevent anterior capsule contraction syndrome or posterior capsule opacification, it is implanted just before implanting the IOL and after completing posterior capsule polishing.

The capsular ring can be implanted using an especially designed injector or with the aid of a forceps and a spatula (table 2). The capsular bag is expanded with viscoelastic and the ring is slipped into the incision and fed under the capsulorhexis with the aid of angulated forceps. It is important to introduce the leading edge of the ring under the anterior capsule to be able to rotate the ring and introduce it completely in the capsular bag. An instrument such as a buttonhole

Table 2. Actions of the capsular tension ring

Circular expansion of the capsular bag Increased centrifugal force to the zonula Stabilization of the capsular bag during the phacoemulsification

Inhibition of migration of lens epithelial cells Reduced risk of capsular fibrosis

Reduced risk of capsular shrinking

Stabilization of the IOL in the short and in the long term

spatula, Lester or Sinskey hook can be introduced through the side-port incision usually created at 2 o’clock and the ring can be gently pushed in a rotatory fashion against this instrument to avoid excessive pressure against the capsulorhexis edge. If a stop is noticed when the ring is rotated it is usually due to capsule pushing by the leading edge of the ring. In this situation, it is better to go back and introduce a small quantity of viscoelastic to expand the capsular bag in that area and then continue rotating the ring without pushing the capsular bag. The implantation of the ring is extremely easy provided that the capsular bag is full of viscoelastic.

Recently, Cionni and Osher [8] introduced the scleral fixation of the endocapsular ring in order to prevent further zonular disinsertion and future dislocation of the IOL in eyes with large zonular fiber loss, usually more than 150°. For the implantation of the Cionni’s ring a scleral incision of 1 mm is made opposite to the cataract incision and in the middle of the zonular dehiscence, coincident with the meridian where the zonules are considered to be intact, at 2 mm posterior to the limbus. Before implantation a double-armed 10/0 prolene suture is passed through the eyelet of the fixation hook of the ring. Viscoelastic is injected between the anterior capsule and the undersurface of the iris at the area of zonular weakness. Both needles are passed through the incision, entering the pupil and staying anterior to the anterior capsule are advanced posterior to the iris. The needles exit the eye through the ciliary sulcus and the previously created scleral incision, with or without the aid of a 25-gauge needle passed through the scleral incision. The needles should exit the globe 1 mm apart from each other. Before inserting the ring in the capsular bag it is important to make sure that the fixation hook courses into a plane anterior to the rest of the ring. The fixation hook should capture itself anterior to the capsulorhexis while the rest of the ring remains within the capsular bag. The ring should be rotated so that the hook reaches the axis where the fixation sutures exit the eye. When the hook is in the middle of the zonular dehiscence and anterior to the capsulorhexis edge, tension on the fixation sutures is applied so that centration of the lens is

Table 3. Signs of loose or broken zonules

Preoperative

Phacodonesis or iridodonesis

Lens center is not coincident with pupil center

Significative subluxation of the lens

Presence of vitreous in the anterior chamber

Iris bulging from vitreous

Very deep anterior chamber

Significative pseudoexfoliation of the lens

Intraoperative

Radial folds when puncturing the anterior capsule Excessive movement of the lens during capsulorhexis

Unusual movement of the lens during hydrodissection or hydrodelineation Difficulty for nuclear rotation

Excessive posterior displacement of the lens when starting irrigation Vitreous herniation around the lens

achieved. A temporary or permanent knot is made, the knot is buried and the suture is covered with conjunctiva.

Significant zonular dialysis makes phacoemulsification and cortical aspiration difficult even for the experienced surgeon (table 3). Hence, although endocapsular rings help to perform a safer surgery in the presence of zonular weakness, the use of such devices should only be considered in the case of surgeons familiar with the techniques employed in cataracts with loose zonules: bimanual capsulorhexis, low fluid-dynamics phacoemulsification, and use of viscoelastic to prevent vitreous prolapse and to assist in viscodissection and manipulation of the nucleus [6]. Of utmost importance is not to overpressurize the eye at any time during surgery, especially after peribulbar injection, after expansion with viscoelastic before capsulorhexis, and during phacoemulsification itself using excessively high bottle height. It is usually difficult to perforate the anterior capsule to begin the anterior capsulotomy, and radial folds are early signs of zonular weakness at this step. During the capsulotomy, special care is required not to unzip weakened fibers. Ideal capsulorhexis size is about 5.5 mm in these cases, because it leaves a relatively small amount of lens epithelial cells while maintaining the IOL into the bag. The capsular tension ring permits cortical cleaving hydrodissection and hydrodelineation, but the ring usually holds much of the cortex pressed up against the capsular fornices, requiring aditional force to remove the cortex.

Anterior capsule contraction syndrome consists on the shrinkage of the capsulorhexis opening from the proliferation and metaplasia of residual lens

epithelial cells which transform into myofibroblastic-like cells. A fibrous membrane extends from the inner and also from the outer surface of the anterior capsule to the IOL center, and when it contracts the anterior capsule is shrunken and the capsulorhexis opening is closed [9]. Postoperative capsular bag shrinkage may lead to IOL decentration or tilting, impairing visual acuity or causing monocular diplopia. Complete closure of the anterior capsule opening may also occur and consequently reduce visual acuity and increase the difficulty to explore or treat eventual diseases of the posterior segment of the eye [10–12]. Anterior capsule contraction is a relatively common finding in eyes with pseudoexfoliation and also in eyes with high myopia [13]. The weakness of the zonular apparatus has a major role in this progressive contraction of the anterior capsule opening, but also in these conditions a breakdown in the ocular-blood barrier has been reported which may increase inflammatory response and promote fibrous membrane formation [9,14]. Other risk factors for anterior capsule contraction include myotonic dystrophy [15], retinitis pigmentosa [16], history of uveitis and any other condition in which significative zonular weakness is present. The use of silicone IOL is associated with higher incidence of anterior capsule phimosis in comparison with other materials such as acrylic or PMMA IOLs [17]. In all these situations, the use of an endocapsular ring should be considered. There have been attempts to design loopless IOLs which exactly fit the capsular bag in order to prevent capsular bag shrinkage, but the large size of this kind of IOL requires a larger incision and may induce significant astigmatism [18]. Intraocular lenses with loop shapes that conform to that of the capsular bag are not successful in mantaining the circular contour of the bag [19], whereas animal studies have shown that the capsular tension ring maintains the round shape of the capsular bag both in vitro and in vivo, preventing excessive capsular shrinkage and fibrosis [20, 21]. Risk factors for anterior capsule contraction syndrome are additive, and progressive and even complete closure has been reported despite the use of a capsular tension ring [22, 23].

Posterior capsule opacification is the most common complication associated with decreased vision after uneventful cataract surgery. A capsular tension ring designed with a sharp cross section creates a discontinuous bend in the equatorial capsule. It has been demonstrated that lens epithelial cells do not migrate over an abruptly discontinuous bend in the posterior capsule, and hence an endocapsular ring with sharp cross section helps to prevent the opacification of the posterior capsule [24]. Increasing the width of the capsular tension to 0.7 mm and creation of a rectangular edge results in the so-called capsular bending ring [4]. This band-shaped, sharp-edged capsule bending ring prevents the anterior capsule from coming into contact with the posterior capsule, and so the epithelial cells underneath the anterior capsule do no undergo fibrous metaplasia, reducing the incidence of opacification of the posterior capsule. This kind

of endocapsular ring has been used successfully to enhance the safety of posterior chamber IOL implantation in pediatric cataract surgery, and to reduce capsule opacification in this population [5]. Rounded endocapsular rings on cross section may not have such an important impact in reducing capsular fibrosis [20, 24]. The capsular bending ring also inhibits lens epithelial cell migration based on the principle of compression inhibition: cell proliferation is prevented by mechanical compression [21]. An anterior circular capsulotomy slightly smaller than the optic diameter together with the use of a band-shaped, sharp-edged capsular tension ring decreases the incidence of fibrous metaplasia with fibrous strand and contracture of the posterior capsule, and also preserves the barrier effect of the IOL and the capsule after YAG laser capsulotomy. The capsular bending ring has been especially proposed for cases that need good fundus visualization for photocoagulation or expected vitreoretinal surgery after cataract surgery [4].

In summary, the capsular tension ring enhances the safety of phacoemulsification in the presence of zonular dialysis minimizing the stretching of the intact zonular fibers, facilitates IOL implantation, prevents IOL decentration and resists contraction of the capsular bag reducing the incidence of both anterior capsule contraction syndrome and secondary cataract. As a general rule, cataract surgery with small zonular dialysis can be performed using routine phacoemulsification technique although the use of a capsular tension ring is highly recommended. When the dehiscence is 90–120°, it is mandatory to insert an endocapsular ring to perform the phacoemulsification of the cataract safely. When faced with zonular dehiscences 120° the use of a scleral fixated capsular tension ring should be considered prior to the phacoemulsification. Anterior capsule contraction syndrome and posterior capsule opacification can be prevented with the use of the band-shaped, sharp-edged capsular bending ring, which may also facilitate cataract surgery in pediatric patients. The capsular tension ring together with the modified capsular bending ring enlarge the surgical options in cataract surgery.

References

1Sun R, Gimbel HV: In vitro evaluation of the efficacy of the capsular tension ring for managing zonular dialysis in cataract surgery. Ophthalmic Surg Lasers 1998;29:502–505.

2Fine IH, Hoffman RS: Phacoemulsification in the presence of pseudoexfoliation: Challenges and options. J Cataract Refract Surg 1997;23:160–165.

3Gimbel HV, Sun R, Heston JP: Management of zonular dialysis in phacoemulsification and IOL implantation using the capsular tension ring. Ophthalmic Surg Lasers 1997;28:273–281.

4Nishi O, Nishi K, Menapace R: Capsule-bending ring for the prevention of capsular opacification: A preliminary report. Ophthalmic Surg Lasers 1998;29:749–753.

5Dick HB, Schwenn O, Pfeiffer N: Implantation of the modified endocapsular bending ring in pediatric cataract surgery using a viscoadaptive viscoelastic agent. J Cataract Refract Surg 1999; 25:1432–1436.

6Cionni RJ, Osher RH: Endocapsular ring approach to the subluxed cataractous lens. J Cataract Refract Surg 1995;21:245–249.

7Groessl SA, Anderson CJ: Capsular tension ring in a patient with Weill-Marchesani syndrome. J Cataract Refract Surg 1998;24:1164–1165.

8Cionni RJ, Osher RH: Management of profound zonular dialysis or weakness with a new endocapsular ring designed for scleral fixation. J Cataract Refract Surg 1998;24:1299–1306.

9Kurosaka D, Ando I, Kato K, Oshima T, Kurosaka H, Yoshino M, Nagamoto T, Ando N: Fibrous membrane formation at the capsular margin in capsule contraction syndrome. J Cataract Refract Surg 1999;25:930–935.

10Hansen SO, Crandall AS, Olson RJ: Progressive constriction of the anterior capsular opening following intact capsulorhexis. J Cataract Refract Surg 1993;19:77–82.

11Davison JA: Capsule contraction syndrome. J Cataract Refract Surg 1993;19:582–589.

12Joo CK, Shin JA, Kim JH: Capsular opening contraction after continuous curvilinear capsulorhexis and intraocular lens implantation. J Cataract Refract Surg 1996;22:585–590.

13Hayashi H, Hayashi K, Nakao F, Hayashi F: Anterior capsule contraction and intraocular lens dislocation in eyes with pseudoexfoliation syndrome. Br J Ophthalmol 1998;82:1429–1432.

14Küchle M, Nguyen NX, Hannappel E, Naumann GO: The blood-aqueous barrier in eyes with pseudoexfoliation syndrome. Ophthalmic Res 1995;27(suppl 1):136–142.

15Newman DK: Severe capsulorhexis contracture after cataract surgery in myotonic dystrophy. J Cataract Refract Surg 1998;24:1410–1412.

16Hayashi K, Hayashi H, Matsuo K, Nakao F, Hayashi F: Anterior capsule contraction and intraocular lens dislocation after implant surgery in eyes with retinitis pigmentosa. Ophthalmology 1998; 105:1239–1243.

17Hayashi K, Hayashi H, Nakao F, Hayashi F: Reduction in the area of the anterior capsule opening after polymethylmethacrylate, silicone, and soft acrylic intraocular lens implantation. Am J Ophthalmol 1997;123:441–447.

18Tetz MR, O’Morchoe DJ, Gwin TD, Wilbrandt TH, Solomon KD, Hansen SO, Apple DJ: Posterior capsular opacification and intraocular lens decentration. II. Experimental findings on a prototype circular intraocular lens design. J Cataract Refract Surg 1988;14:614–623.

19Meur G: A new capsule supported intraocular lens. Ophthalmic Surg 1987;18:395–396.

20Nagamoto T, Bissen-Miyajima H: A ring to support the capsular bag after continuous curvilinear capsulorhexis. J Cataract Refract Surg 1994;20:417–420.

21Hara T, Hara T, Sakanishi K, Yamada Y: Efficacy of equator rings in an experimental rabbit study. Arch Ophthalmol 1995;113:1060–1065.

22Strenn K, Menapace R, Vass C: Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methylmethacrylate) capsule tension ring. J Cataract Refract Surg 1997;23: 1543–1547.

23Faschinger CW, Eckhardt M: Complete capsulorhexis opening occlusion despite capsular tension ring implantation. J Cataract Refract Surg 1999;25:1013–1015.

24Nishi O, Nishi K, Mano C, Ichihara M, Honda T: The inhibition of lens epithelial cell migration by a discontinuous capsular bend created by a band-shaped circular loop or a capsule-bending ring. Ophthalmic Surg Lasers 1998;29:119–125.

Prof. Dr. Gonzalo Muñoz, Instituto Oftalmológico de Alicante,

Universidad Miguel Hernández, Avenida de Denia 111, E-03015 Alicante (Spain) Tel. 34 902 333 344, Fax 34 965 260 530, E-Mail oftalio@ibm.net

Kohnen, T (ed): Modern Cataract Surgery.

Dev Ophthalmol. Basel, Karger, 2002, vol 34, pp 119–130

Optical Coherence Biometry

Wolfgang Haigis

University Eye Hospital, Würzburg, Germany

With optical coherence biometry (OCB), also termed partial coherence interferometry (PCI), laser interference biometry (LIB) or laser Doppler interferometry (LDI), an innovative optical method for measuring axial lengths has recently become available as a possible alternative to commonly applied ultrasound biometry. In the IOLMaster [7, 14, 18], introduced in autumn 1999 by Carl Zeiss Jena, this new distance-measuring technique is combined with a classical measurement setup to determine central corneal curvatures together with a slit image-based method to measure anterior chamber depths. All three measurements are noncontact procedures – easy to apply for the examiner and well acceptable for the patient. With these measurement facilities, all data necessary for the calculation of intraocular lenses is thus acquired by one stand-alone device. The system software allows IOL calculation with all popular formulas and includes databases for IOL and surgeon data.

The application of PCI to measuring human ocular dimensions dates back to the mid-1980s, when Vienna physicist Fercher [2] performed the first optical axial length measurement in vivo. Since autumn 1997, our laboratory (Biometry Department of the University Eye Hospital, Würzburg) has been involved in the development and transformation of this fascinating new technique into clinical applications [5, 7, 9, 13, 14].

Measurement Principle

In the IOLMaster, a laser diode is mounted in one arm of a Michelson interferometer setup (fig. 1). An infrared laser beam ( 780 nm) of short

ILM RPE

ALop

ALac

Fig. 2. Optical (ALop) and acoustical (ALac) axial lengths: different distances in different directions: ALac anterior corneal vertex to internal limiting membrane (ILM); ALop intersection of visual axis with anterior cornea to retinal pigment epithelium (RPE).

Furthermore, whereas an ultrasound axial length extends from the anterior corneal vertex to the inner limiting membrane (ILM), an optical axial length is confined by the retinal pigment epithelium, because this is where the dominant reflection usually originates [11]. Thus, optical (ALop) and acoustical (ALac) axial lengths are different distances from different directions. With RT denoting the retinal thickness we may write to a first approximation:

ALop ALac RT

Another difference stems from the fact that ultrasound allows simultaneous segmental measurements of the eye, not so – at least with the present IOLMaster hardware – optical coherence biometry. Although ACD and lens thickness measurements have been reported in the literature [1], these measurements were carried out separately and not simultaneously during axial length determination. This is due to the small amount of light returning from the obliquely intersected lens surfaces along the line of sight [1]. It may, however, well be that future PCI equipment will also offer this modality. Until then – equivalent to applying a mean velocity in ultrasound – a mean (group [17]) refractive index nPCI ( 1.3549 [11]) has to be used in order to translate the measured optical path length (OPL) into a geometrical eye length (ALop), i.e.:

ALop OPL/nPCI

Up to now, all clinical experience in IOL implantation and refractive outcome is built on ultrasound data. To make this vast experience available for