Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

three-piece silicone IOL (Allergan SI-30NB) of 20.5 D using a Fine Universal II folder and with a plate-haptic silicone IOL (Staar AA-4203) of 20.5 D using a Microstaar injector.

Following IOL insertion, the corneas were removed from the globes, immediately immersed in Optisol GS (Chiron IntraOptics, Irvine, Calif., USA), stored over ice, and shipped by overnight express service to the National Vision Research Institute Laboratory, San Diego, Calif., USA. Upon receipt, the corneas were washed in 0.1 M cacodylate buffer, placed in 1/2 Karnovsky’s fixative for 8 h, and subsequently rewashed in buffer. Each cornea was then dissected into two pieces, postfixed in 2% osmium tetroxide for 2 h, and dehydrated in a graded series of ethanol. The tissue pieces were placed in 100% acetone and subjected to critical-point drying (Samdri-750, Tsoumis, Rockville, Md., USA). The dried specimens were mounted on viewing stubs, coated on their endothelial surface with a gold-palladium alloy to a depth of approximately 9 m, viewed in a Hitachi S-520 scanning electron microscope (Hitachi Ltd, Tokyo, Japan), and photographed with a Polaroid Type 55 PositiveNegative 4 5 instant sheet film (Polaroid, Cambridge, Mass., USA).

Determination of Tissue Damage Following IOL Implantation (Part B)

SEM of the endothelial surface of the cornea was used to assess tissue damage. Each of four donor eyes received two corneal tunnel incisions at the 3 and 9 o’clock position adjacent to the limbus. In two eyes, both incisions were created with a 3.0-mm keratome and in the other two eyes with a 3.2-mm keratome. In each of the four eyes, one IOL was inserted with the Fine forceps and one with the Unfolder.

Following IOL insertion, the corneas were removed from the globes and were then processed as described in Part A.

Clinical Studies

All clinical work was performed at the Department of Ophthalmology, Johann Wolfgang Goethe University, Frankfurt am Main, Germany.

Patients (Part A)

In 12 consecutive cataract procedures (patients’ age 69.7 years, range 54–89 years), Allergan Medical Optics SI40NB IOLs of 18.0–24.5 D were implanted in a randomized fashion using the forceps or injector as described in the experimental study Part B (fig. 1, 2) and the incision sizes were determined intraoperatively using the newly developed incision caliper (Kohnen incision caliper, G-19136, Geuder, Heidelberg, Germany; figures 7–9; see Results, Development of a New Caliper to Measure Incision Sizes). Six eyes were implanted with each insertion method.

Patients (Part B)

In a prospective, randomized study, incision sizes were evaluated for 5.5-mm total optic foldable IOLs. Forty cataract cases were included in this study. The mean age of the patients was 67.3 years (range 55–86). All eyes had no previous intraocular surgery or anterior segment pathology. Three different 5.5-mm total optic 3-piece foldable IOLs were used, two silicone IOLs (Pharmacia CeeOn 912, Allergan SI55NB), and one hydrophobic acrylic IOL (Alcon MA30BA). The refractive optic of the IOLs were different: 5.5 mm for the Pharmacia

Fig. 5. 5.5-mm total optic foldable IOLs made of silicone and hydrophobic acrylic material. a Silicone IOL Pharmacia CeeOn 912. b Hydrophobic acrylic IOL Alcon Acrysof MA30BA. c Silicone IOL Allergan SI55NB.

Table 2. Characteristics of the 5.5-mm total optic 3-piece foldable IOLs

CeeOn 912 and the Alcon Acrysof MA30BA, 5.0 mm for the Allergan SI55NB IOL. Characteristics of the three foldable IOLs are shown in figure 5 and reported in table 2. The inclusion criteria into this study were IOL power between 20 and 30 D (table 3). From each IOL type, 10 lenses of different dioptric power were implanted using different implantation forceps (table 3, fig. 6). Additionally, 10 Allergan SI55NB IOLs were implanted with the AMO Unfolder injector (fig. 2).

Table 3. Dioptric range of the implanted 5.5-mm total optic 3-piece foldable IOLs and their implantation devices

Surgical Procedure

All operations were performed by one surgeon (T.K.) using posterior chamber phacoemulsification through a temporal posterior limbal corneal tunnel incision under topical anesthesia. First, using a 0.7-mm steel knife, two paracenteses were performed ca. two clock hours on either side of the incision, and the aqueous humor was replaced with hyaluronic acid (either with Healon® or Healon® GV, Pharmacia, Uppsala, Sweden). There was no specific indication for the two different viscoelastic substances. A 500- m deep groove was made at the peripheral vascular arcade of the temporal cornea with a preset three-cut diamond step

knife. Using a 3.0-mm clear-corneal diamond keratome (for forceps implantation of the Pharmacia CeeOn 912, the Alcon Acrysof MA30BA, and the Allergan SI40NB and SI55NB and injector implantation of the Allergan SI40NB using the AMO Unfolder) or a 2.5-mm metal keratome (for the injector implantation of the Allergan SI55NB using the AMO Unfolder), a rectangular limbal corneal tunnel incision with a radial length just under 2.0 mm was incised. Following continuous curvilinear capsulorhexis and multilamellar hydrodissection, the nucleus was emulsified with an in situ four-quadrant phacofracture technique. The cortical material was removed using a small-port bimanual irrigation/aspiration system (Koch/Kohnen bimanual A/I system, G-22100/1, Geuder) through the two-side port incisions, and the posterior capsule was vacuumed on a low aspiration setting. The viscoelastic agent (either Healon® or Healon® GV, Pharmacia) was reinjected to deepen the anterior chamber and to inflate the capsular bag. Using forceps or injector, implantation of the 3-piece foldable intraocular lenses was first attempted without enlargement. If this failed, a minimal enlargement of the incision was performed with the diamond or metal keratome. Following comfortable IOL implantation into the capsular bag, residual viscoelastic substance was removed with the bimanual tips, and the anterior chamber was deepened by injecting balanced salt solution (BSS®, Alcon Surgical Inc., Ft. Worth, Tex., USA) through a side-port opening. The wound was checked for leakage and if it was found not to be watertight, the stroma of the corneal tunnel incision was hydrated. All incisions were left sutureless.

Determination of the Incision Sizes

In each surgical case, the incision size was measured once at four different time points using the newly developed incision caliper (G-19136, Geuder) (see Results, Development of a New Caliper to Measure Incision Sizes): (a) after performing the limbal corneal tunnel incision; (b) following phacoemulsification; (c) before IOL implantation (which was equivalent to the previous measurement if the wound did not need to be enlarged, but was greater when further enlargement was necessary); and (d) after IOL implantation.

The predicted incision sizes for the three different 5.5-mm total optic 3-piece foldable IOLs and the different implantation devices were predetermined for each IOL/insertion device combination in five cataract procedures before the beginning of the clinical study. According to the prefindings either a clear-corneal diamond keratome (for forceps implantation of the Pharmacia CeeOn 912, the Alcon MA30BA, and the Allergan SI40NB and SI55NB) or a 2.5-mm metal keratome (for the injector implantation of the Allergan SI40NB and SI55NB using the Unfolder) was used in the main study. To maintain the incision size of 2.5–2.6 mm during the phaco procedure (for the injector implantation of the Allergan SI55NB using the Unfolder) a smaller phaco-tip (Mini-Mega-Ultrasonic-Tip, G-24070, Geuder) was necessary. For the other procedures with an initial incision width of approximately 3.0 mm, a regular phaco-tip (Mega-Ultrasonic-Tip, G-24055, Geuder) was used.

Statistical Analysis

To determine if there was a significant effect of various IOL materials and designs and inserting foldable IOLs with injector or forceps, incision size measurements were assessed using one-way analysis of variance (ANOVA). When the ANOVA indicated that there was statistical significance (p 0.05), the Tukey-Kramer multiple comparison test was used to detect significant differences between the means (p 0.05). Both statistical analyses were performed with SAS software (JMP, SAS Institute, Inc., Cary, N.C., USA) [35].

0.1-mm steps

2 4

3.5

9

Fig. 7. The caliper for small-incision cataract surgery can be sterilized, is suitable for intraoperative use, and is available in two ranges: 1.0–6.0 and 2.0–4.0 mm.

Fig. 8. Design specifications of the caliper screw (range 1.0–6.0 mm).

Fig. 9. Sketch of the small-incision caliper screw (range 2.0–4.0 mm) which shows the 0.1-mm measurement steps. The arrows indicate the motion of the screw. In this position, the caliper would measure an incision size of 3.5 mm.

Results

Development of a New Caliper to Measure Incision Sizes

To measure incision sizes in clinical and experimental settings, a new mechanical caliper was developed (Kohnen incision caliper, G-19136, Geuder). The metal caliper is made out of two arms with fine tips (fig. 7). The length and

Table 4. Comparison of internal incision sizes by two different methods1

1One-way analysis of variance did not show statistically significant difference between the external and internal measurement of the internal incision size (p 0.07).

2Measurement performed with globe intact.

3Measurement performed following removal of cornea.

angulation of the tips allow external and internal measurements of tunnel incisions. A screw connects the two arms of the caliper in the middle of the device (fig. 8). The instrument measures distances in the range of 1–6 mm in 0.1-mm steps. The device is produced for two ranges, 2–4 and 1–6 mm (fig. 8, 9). The thread of the screw is covered with a layer of silicone to allow inadvertent locking.

Experimental Studies

Incision Sizes (Part A)

There was no significant difference between the two methods of measuring post-insertional internal incision size (table 4). Therefore, calculations were performed using the numbers obtained from method A (postinint 1), in which the post-insertional internal incision was measured from outside. In addition, although there were slight differences between the external and internal incision widths, the ANOVA indicated no statistically significant differences between those two measurements (table 5). Therefore, the mean of these two measurements was used to calculate the absolute and percentage enlargement (fig. 10, table 5).

Pre-insertion incision widths ranged from 2.9–3.7 mm and increased to 3.2–3.8 mm following IOL insertion (table 5). Incisions enlarged after insertion in each case, ranging from 3.5 to 10.3% (mean 5.9%) for the lenses inserted with forceps and 10.6 to 11.2% (mean 10.9%) for those inserted with injectors. However, there was no statistically significant difference in the percentage enlargement among the different IOLs.

Table 5. External and internal incision sizes for foldable IOLs measured in 48 cadaver eyes (6 per IOL)

Statistically, there were three incision size classes for both the preand postinsertional assessments (table 6). The largest incisions were associated with the Alcon MA60BM and IOLAB LI41U lenses. The incisions required for insertion of hydrogel lenses (Alcon SH30BC and Storz H60M) were intermediate in size, though the Alcon SH30BH post-insertion incisions were comparable to those of the group with the smallest post-insertion incisions. The smallest incisions were associated with the remaining four lenses, which were not statistically different from each other, even though two were inserted with injectors (Chiron C10UB, Staar AA-4203) and two with forceps (Allergan SI-30NB, Alcon MA30BA).

Fig. 10. Incision sizes (average of external and internal measurements) in 48 autopsy eyes undergoing insertion of eight different foldable IOLs (6 eyes per IOL), experimental study Part A.

Table 6. Statistical grouping1 of the preand postoperative incision size measurements

1Using the Tukey-Kramer test; incision sizes with the same letter in each column are not significantly different. A, D, G, J smallest incision; B, E, H, K intermediate incision; C, F, I, L largest incision.

Incision Sizes (Part B)

The mean external and internal tunnel widths for the smallest possible incision before IOL insertion were 3.05 and 3.02 mm with the forceps and 3.06 and 3.01 mm with the Unfolder, respectively (table 7). Following implantation, the mean external and internal incisional widths were 3.33 and 3.33 mm with

Table 7. External and internal incision sizes for implantation of SI-40NB IOLs using forceps (Fine Universal Folder II) and injector (Unfolder) (6 implantations per device)

the forceps and 3.32 and 3.33 mm with the Unfolder. The differences between the external and internal incision widths were negligible, and the ANOVA indicated no statistically significant differences between those two measurements (table 7). Therefore, the mean of these two measurements was used to calculate the absolute and percentage enlargement. The comparison of the incision sizes before and after IOL insertion between the two devices were not statistically significant different. The enlargement following IOL insertion through the smallest possible incision was 9.0% when using the forceps and 8.8% when using the Unfolder. The incision enlargements were not statistically significant different between the forceps and injector groups.

SEM Study of the Incisions (Part A)

The results of the SEM analysis of the morphology of the endothelial surface of the incisions in the six specimens (with and without IOL implantation) can be summarized as follows: (1) Insertion through a tight incision damaged corneal tissue more than a keratome incision alone. (2) Tearing of Descemet’s membrane and corneal stroma appeared at the lateral borders of the smaller, tight incisions following IOL insertion (fig. 11 vs. 12 and fig. 13 vs. 14).

(3) There was some herniation of corneal stromal tissue into the anterior chamber in the 3.0-mm incisions following IOL insertion, and this appeared to be more extensive in corneas implanted with the injector insertion device than with the forceps (fig. 11, 12). The corneal stroma appeared to retain some memory of the shape of the injector after it had been withdrawn from the incision (fig. 11A). This persistent tissue distortion was also noted with inspection of the tighter incisions intraoperatively with the surgical microscope (fig. 15).

Fig. 11. 3.0-mm corneal tunnel incision in a cadaver-eye cornea following plate-haptic IOL (Staar AA-4203) insertion with a cartridge/injector system. The limbus is in the upper left-hand side of the photographs (E endothelium). a The low magnification gives an overview of the shape of the incision. Descemet’s membrane appears to be torn at the inferior border of the incision. Stromal collagen has herniated into the anterior chamber, mainly along the upper border of the incision. Both lateral margins show evidence of tearing and disruption of Descemet’s membrane. SEM. Orig. magn. 45. b The higher magnification of the right lateral border demonstrates the tearing of the incision. SEM. Orig. magn. 180.

Fig. 12. 3.5-mm corneal tunnel incision in a cadaver-eye cornea (same as in figure 4) following plate-haptic IOL (Staar AA-4203) insertion with a cartridge/injector system. The limbus is again in the upper left-hand side of the photographs (E endothelium). a The overview of the incision shows bulging of stromal tissue in the upper part of the incision. The cut edge of Descemet’s membrane is smooth and continuous and the lateral borders show little if any evidence of tearing. SEM. Orig. magn. 45. b The higher magnification of the left edge demonstrates almost no tearing of the incision. SEM. Orig. magn. 180.