Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

chamber. After closing the chamber the IOL cannot be seen during monomanually advancing because of the metal-type rod. This sharp-edged rod needs an incision opening of 3.8–4.0 mm.

Single-Use Injectors for Three-Piece Silicone IOLs (EasyPack, EasySert, Mport)

The three-piece silicone IOL (SeeOn Edge 911A, Pharmacia) has to be positioned very exactly on a plane or the bottom of the injector chamber (EasyPack) covered with viscoelastic material. Special care has to be taken to position the haptics after closing the injector chamber. Another follow-up of injecting, first screwing and then pushing, facilitates a monomanual procedure. The IOL can be implanted directly into the capsular bag through a 3.4-mm incision.

The three-piece silicone IOL (PC 410, 415, 420, Ophtec) can be implanted monomanually. The IOL can open after leaving the rod without rotation of the injector, but the IOL opens quickly, nearly uncontrolled. The cartridge-based system (EasySert) can be implanted through a 3.2-mm incision.

The three-piece silicone IOL (Soflex 2, Bausch & Lomb) has to be positioned very exactly into the loading deck. After closing the drawer, the IOL is compressed M-like in the injector chamber. The leading haptic has to be pulled forward before the well-positioned plunger can push the IOL. With its M-like lens fold the IOL comes out on plane, there is no tumbling. The IOL can be implanted directly into the capsular bag through a 3.3-mm incision.

Discussion

Injector-based implantation devices appeared on the market in 1984. Mike Bartel [6] suggested a so-called ‘folder’ for foldable IOLs. Other injector systems like ‘Prodegy’ (Allergan) and ‘Disk Lens Injector’ (Geuder) disappeared from the market again. In the last 2 years some new single-use injectors have been introduced. But still most of the foldable three-piece IOLs are implanted with forceps although some disadvantages of the forceps implantation – manipulation of the IOL, touch of the conjunctiva, incision size to be enlarged – can be minimized with injector implantation. Most of the foldable one-piece silicone IOLs (C11, EasAcryl*1, Bausch & Lomb; AA-4203VF, Staar) are implanted with injectors. These systems are easy to load, the positioning of the IOL into the cartridge needs no extra manipulations and the injection of the IOL into the capsular bag is possible in a one-step delivery and very predictable.

Injectors and cartridges are different in dimensions and material. Thus they should only be used with that IOL they are developed for. The injectors can

be differentiated in respect to their function. Screwing injectors are to be used bimanually, the plunger must be screwed at its end and the injector itself often has to be rotated in the opposite direction. Injectors where the IOL only has to be pushed forward can be used monomanually, thus leaving the other hand free for a second instrument.

The tips of the plungers vary in respect to inner and outer diameters or form and the cartridges are adopted to the IOLs and to the plunger. The cartridges vary in respect to their bevel cutaway (aside – Allergan, down – Bausch & Lomb). Thus the cartridges can only be used with the injector belonging to the system and the specific IOL which is recommended for this system.

With some cartridge systems (Unfolder, Allergan), the plunger is not long enough. Thus the plunger has to be withdrawn before rotating the IOL into the capsular bag (two-step delivery). This problem has been solved with the Unfolder Silver T. Another cartridge system (Monarch, Alcon) allows the direct implantation of the IOL with moving the plunger only forward (one-step delivery). During this maneuver the surgeon has to be very careful not to touch the iris or ciliary body on the opposite site.

Injector systems with folding chamber (EasyPack, Mport, Passport II) track more attention to the positioning of the IOL into the chamber. Both haptics have to be positioned as pointed out (EasyPack, Pharmacia), the haptic has to be placed very exactly onto the plunger recess (Mport, Bausch & Lomb) or the plunger has to meet precisely the edge of the IOL optic (Passport).

Preparing and loading the injector system can be performed by the operating room staff. Thus the surgeon has only to take over the loaded injector. This can reduce the time of exposure to air of the IOL, thus reducing the possibility of adhesion of dust to the lens material.

Within all injector systems one still has to manipulate directly the IOL by forceps or other instruments. This is at least problematic for presbyopics, you cannot see it in a darkened operating room and you cannot manipulate it under the microscope without changing magnification and viewing angle. All IOL and/or injector producers should concentrate on efforts to minimize or to avoid such handlings with the IOL out of the package into the folding device. The best solution would be a closed system for the IOL from the package into the capsular bag.

Working with injectors, reproducibility of implantation, safety in respect to an unharmed IOL do need a learning process. Handling of the system has to be trained before working with it in a human eye. Thus one has to learn that each injector system has its own characteristics and using them varies. Injector systems give advantages in respect to IOL isolation from ocular surface bacteria and debris, reproducibility of geometry and smaller size for wound width, implantation through small capsulorhexis, implantation into the capsular bag

or sulcus with compromised capsular bag structures and prevention of crimping the haptics. Respecting recommendations for handling the injectors, the implantation with injector systems will be of benefit for the eye of the patient and for a well-controlled surgery.

References

1Dick B, Eisenmann D, Fabian E, Schwenn O: Refraktive Kataraktchirurgie mit multifokalen Intraokularlinsen. Berlin, Springer, 1999.

2Fabian E, Dick B: Injektor-Systeme für die Implantation von faltbaren Linsen. OphthalmoChirurgie 2000;12:43–52.

3Kohnen T, Lambert RJ, Koch DD: Incision sizes for foldable intraocular lenses. Ophthalmology 1997;104:1277–1286.

4Kohnen T, Koch DD: Experimental and clinical evaluation of incision size and shape following forceps and injector implantation of a three-piece high-refractive-index silicone intraocular lens. Graefes Arch Clin Exp Ophthalmol 1998;236:922–928.

5Mackool RJ, Russel RS: Effect of foldable intraocular lens insertion on incision width. J Cataract Refract Surg 1996;22:571–574.

6Mazzocco TR, Davidson BM: Insertion technique and clinical experience with silicone lenses; in Mazzocco TR (ed): Soft Implant Lenses in Cataract Surgery. Thorofare, Slack Inc, 1986.

7Olson R, Cameron R, Hovis T, Hunkeler J, Lindstrom R, Steinert R: Clinical evaluation of the Unfolder. J Cataract Refract Surg 1997;23:1284–1389.

8Steinert RF, Deacon J: Enlargement of incision width during phacoemulsification and folded intraocular lens implant surgery. Ophthalmology 1996;103:220–225.

Priv.-Doz. Dr. Ekkehard Fabian, IOL Injector Systems, AugenCentrum Rosenheim, Luitpoldhaus, Bahnhofstrasse 12, D–83022 Rosenheim (Germany)

Tel. 49 8031 389 500, Fax 49 8031 389 5038, E-Mail Dr.Fabian@AugenCentrum.de

projects were started. Both studies documented wound enlargement with insertion of selected silicone IOLs.

The purpose of this study was: (1) to develop a new mechanical caliper, which could easily measure incision sizes in clinical and experimental settings;

(2) to determine the smallest incision size required for insertion of a representative spectrum of foldable silicone, hydrophobic acrylic (soft acrylic) and hydrophilic acrylic (hydrogel) IOLs; and (3) to study wound stretching or incisional damage of both tight and appropriately sized incisions following forceps and injector insertion of foldable IOLs.

Patients, Material and Methods

Experimental Studies

The experimental studies were approved by the Institutional Review Board for Human Subject Research for Baylor College of Medicine and Affiliated Hospitals prior to commencement of the experiments. All experimental work was performed at the Cullen Eye Institute, Baylor College of Medicine, Houston, Tex., USA.

Subjects (Part A)

Sixty-nine fresh human cadaver eyes were obtained from several eye banks in the United States. The donors’ mean age was 81 years (range 69–102). Exclusion criteria were previous anterior segment pathology or intraocular surgery, which were confirmed by each eye bank’s protocol. The eyes were stored at 4–8°C until the experiments were performed and were grossly examined by us to confirm the absence of any anterior segment abnormality that might affect the outcome of this study. All surgeries were done within 48 h of death of the donors.

Subjects (Part B)

Ten fresh human cadaver eyes (6 for the incision size measurements, 4 for the scanning electron microscopy (SEM) evaluation) were obtained either from the Lions Eye Bank of Texas, Houston, Tex., USA or from the Central Florida Lions Eye Bank, Tampa, Fla., USA. The donors’ mean age was 79 years (range 68–93). Exclusion criteria were as described in Part A.

Preparation of the Globes

To thin the corneas, the eyes were placed for 20–30 min in hyperosmotic 15% dextran solution [2, 6, 39]. Corneal thickness between 500 and 650 m was confirmed using ultrasonic pachymetry (DGH 2000, DGH Technology, Frazer, Pa., USA) before the experiments were performed. The globes were fixated in an artificial eye holder, and a 23-gauge needle was passed through the optic nerve into the vitreous cavity. Infused balanced salt solution maintained the intraocular pressure, which was monitored with Schiotz tonometry to be between 10 and 20 mm Hg. To maintain corneal thinning until the eyes were used, a paracentesis was performed two clock hours away from the anticipated tunnel incision area, and 15% dextran solution was instilled to fill the anterior chamber.

Table 1. Characteristics of foldable IOLs (in 20.5 D) and their implantation devices

1Formerly called IOGEL 2000SM.

Foldable IOLs and Implantation Devices (Part A)

We wished to determine the smallest incision sizes permitting insertion and the actual incision size following insertion for eight different foldable IOLs, all with a power of 20.5 diopters (D). The foldable IOLs were 4 silicone (2 three-piece and 2 plate-haptic), 2 three-piece soft acrylic and 2 hydrogel (1 three-piece and 1 one-piece) IOL (table 1). In this experiment each IOL was inserted using implantation instrumentation that either was recommended by the IOL manufacturer or was commonly used by cataract surgeons (table 1).

Fig. 1. Forceps to implant the foldable silicone IOL Allergan SI40NB (Fine Universal Folder II, Rhein Medical), experimental study Part B.

Foldable IOLs and Implantation Devices (Part B)

The IOLs were model SI40NB™ (Allergan Medical Optics, Irvine, Calif., USA) with the following parameters: three-piece construction; 20.5-D, 6-mm silicone optics with a refractive index of 1.46; extruded PMMA haptics, and overall lens diameter of 13.0 mm. Further in the text the Allergan high-refractive silicone IOLs are described without the™ trademark sign. The implantation devices were either a forceps (Fine Universal Folder II, Rhein Medical) (fig. 1) or an injector (UNFOLDER™ AMO® PHACOFLEX II®, Allergan Medical Optics) (fig. 2). The UNFOLDER™ AMO® PHACOFLEX II® is further in the text called ‘Unfolder’. In the same eye, two insertions were performed on the horizontal meridian (determined by white-to-white measurements) through different incisions 180° apart, one with forceps, the other one with injector. The order of use of the implantation devices was determined in a randomized fashion.

Measurements

To make tunnel incisions of various sizes, stainless-steel, angled, bevel-up keratomes (A-OK Full Handle Slit Knives) were provided by Alcon. Several of the keratomes had to be custom manufactured for the studies. The widths of the keratome blades were 2.0, 2.25, 2.5, 2.75, 3.0, 3.2, 3.5, 3.7 and 4.0 mm. Preoperative measurement of the keratome widths revealed a deviation of 0.05 mm.

To measure the corneal tunnel dimensions, we modified an Osher internal incision caliper (K3-9012, Katena Products Inc., Denville, N.J., USA) by adding a screw mechanism to assure precise, stable positioning of the caliper arms (fig. 3). A vernier caliper with a digital display (Mitutoyo Corp., Tokyo, Japan) (fig. 3) was used to measure the actual external spread of the caliper arms (in hundredths of a millimeter); we did not use the gauge on the Osher caliper itself. In Part B, all incisions were also measured with a new caliper (Kohnen incision caliper, G-19136, Geuder, Heidelberg, Germany) (fig. 7–9), which was developed during this study for use in the clinical evaluation of incision size (see Results, Development of a New Caliper to Measure Incision Sizes).

Surgical Procedure

All procedures in the experimental studies were performed by one surgeon (T.K.) with the use of an operating microscope (Model Urban US-1, Storz, St. Louis, Mo., USA) in the Ophthalmic Microsurgical Laboratory, Baylor College of Medicine. The dextran solution in the anterior chamber was exchanged for a viscoelastic agent (Viscoat, Alcon, Ft. Worth, Tex., USA or Vitrax, Allergan Medical Optics). Using a diamond step-knife (Alcon), a groove 3.5 mm wide and 300 m deep was created at the limbus of the autopsy eye. To construct tunnel incisions of various sizes, we used stainless-steel, angled, bevel-up keratomes of different widths (2.75, 3.0, 3.2 and 3.5 mm) (A-OK Full Handle Slit Knives, Alcon). The keratomes were used to dissect rectangular corneal tunnel incisions with a radial length of

Fig. 3. Modified Osher internal caliper (below) and digital caliper (above) used to determine external and internal incision sizes.

width, the forceps were inserted until the tips extended no more than 0.5 mm into the incision (fig. 4b). For the measurements of internal incision width, the forceps were inserted until the tips were at or just central to the internal opening of the incision (fig. 4c).

The incision width was first approximated in a pilot study. For each foldable IOL, 1–3 fresh cadaver eyes (a total of 15 eyes which were not included in the 48 eyes of the experimental study Part A) received corneal tunnel incisions starting at a width of 2.25 mm, and IOL insertion was attempted. The incisions were enlarged by 0.2 or 0.25 mm using the metal keratomes until the IOL could readily be inserted with minimal resistance.

To determine the smallest incision size the cadaver eyes were randomized into 6 eyes for each of the eight different foldable IOLs tested in this study. The experiments with the 48 human cadaver eyes were started with incisions 0.5 mm smaller than the predetermined width obtained for each IOL model in the pilot study. Insertion was attempted with force, but in a way which still felt comfortable for the surgeon. The incisions were enlarged by 0.2 or 0.25 mm, depending on the keratome, until the IOL could be inserted. This incision is hereafter called ‘smallest possible pre-insertion incision’.

Before each insertion attempt and following the final insertion, the external and internal incision widths were determined with the above-described calipers (fig. 4b, c). The internal incision size was also measured from the endothelial side after the cornea had been removed from the globe (fig. 4d). Three measurements were taken, and the mean value was used for statistical analysis. The measured incision widths are abbreviated in the following text as:

(1) pre-insertion external preinext; (2) post-insertion external postinext; (3) pre-insertion internal preinint; (4) post-insertion internal postinint 1; (5) post-insertion internal after the cornea was removed postinint 2.

Determination of the Incision Sizes (Part B)

To determine the differences between incision sizes permitting insertion and actual incision sizes following insertion, all incisions were measured before and after insertion of the IOLs. As we had determined the minimal incision size for insertion of a similar IOL in the experimental study Part A (Allergan Medical Optics SI30NB), IOL implantation was first

a b

Fig. 4. Determination of the incision size for corneal tunnel incisions in a human autopsy eye. a External measurement of the tunnel length. b External measurement of the external wound width. c External measurement of the internal wound width (method A). d Internal measurement of the internal wound width after removal of the whole cornea following the IOL insertion (method B).

attempted through 2.75-mm incisions. The incisions were enlarged by 0.2 or 0.25 mm using the metal keratomes until the IOL could readily be inserted with minimal resistance. This incision is hereafter also called ‘smallest possible pre-insertion incision’.

Before each insertion attempt and following the final insertion, the external and internal incision widths were determined by inserting the caliper tips into the incision and then gently opening until modest tissue resistance was felt. Three measurements were taken, and the mean value was used for statistical analysis.

Determination of Tissue Damage Following IOL Implantation (Part A)

In a pilot study with two autopsy eyes, we implanted IOLs through the smallest possible incision and performed SEM of the endothelial surface of the incision. We found that insertion through a tight incision damaged corneal tissue more than a keratome incision alone. Therefore, each of four additional donor eyes received two corneal tunnel incisions adjacent to the limbus, 180° apart. One incision was created with a 3.0-mm keratome and the other with a 3.5-mm keratome. Two eyes each were implanted with a high-refractive-index