Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 13. 3.0-mm corneal tunnel incision in a cadaver-eye cornea following forceps insertion of a high-refractive-index three-piece silicone IOL (Allergan SI-30NB). The limbus is in the upper left-hand side of the photograph (E endothelium). Unlike the two previous incisions (fig. 12, 13), the extent of stromal herniation into the anterior chamber is minimal, but there is evidence of tearing of the lateral borders of the incision (arrows). SEM. Orig. magn. 45.

Fig. 14. 3.5-mm corneal tunnel incision in a cadaver-eye cornea (same as in figure 14) following forceps insertion of a high-refractive-index three-piece silicone (Allergan SI-30NB). The limbus is in the upper left-hand side of the photograph (E endothelium). There is some mild herniation of corneal tissue into the anterior chamber, but the lateral edges of the incision are sharply defined, suggesting that corneal tearing is absent in this tissue. SEM. Orig. magn. 45.

Fig. 15. Appearance of an incision after forceful insertion of a plate-haptic IOL using an injector.

SEM Study of the Incisions (Part B)

3.0- vs. 3.2-mm incisions: For forceps and injector insertion, the 3.0-mm incisions revealed more tearing of the lateral incision borders and Descemet’s membrane than the 3.2-mm incisions (fig. 16). In all four specimens, there was bulging or herniation of intrastromal tissue into the anterior chamber; this was much more pronounced in the 3.0-mm than in the 3.2-mm incisions.

Forceps vs. injector: Comparing the forceps and injector groups, there was no difference in the morphology of the incisions.

Clinical Studies

Part A

In 12 consecutive cataract procedures, the incision sizes before and after IOL implantation were 3.23 ( 0.10 SD) mm (range 3.1–3.4) and 3.36 ( 0.06) mm (range 3.3–3.4) with the forceps and 3.12 ( 0.08) mm (range 3.0–3.2) and 3.22 ( 0.10) mm (range 3.1–3.3) with the injector, respectively (table 8). The incision sizes for forceps and injector groups were statistically significant different before (p 0.005) and after implantation (p 0.05); however, the incision enlargement (comparison of incision sizes before and after IOL insertion) was not statistically significant for the two devices.

Part B

In the 40 cataract procedures the tunnel width (in mm) preand postimplantation was 3.32 ( 0.06) and 3.42 ( 0.06) for the Pharmacia CeeOn 912 using Nichamin implantation forceps, 3.28 ( 0.09) and 3.42 ( 0.09) for the

Fig. 16. SEM study of endothelial surface of corneal tunnel incisions of cadaver eyes following insertion of SI40NB IOLs. The limbus is in the upper left-hand side of the photographs. Orig. magn. 45. a 3.0-mm corneal tunnel incision after insertion with forceps. b 3.2-mm corneal tunnel incision after insertion with forceps. c 3.0-mm corneal tunnel incision after insertion with injector. d 3.2-mm corneal tunnel incision after insertion with injector. a, c 3.0-mm incisions: Descemet’s membrane appears to be torn at the borders of the incision. Stromal collagen has herniated into the anterior chamber and the lateral margins show evidence of tearing. The morphology of the incisions is similar after either forceps or injector implantation. b, d 3.2-mm incisions: The borders of Descemet’s membrane are smooth and continuous, and the lateral borders show minimal if any evidence of tearing. The appearance of the incisions is similar after either forceps or injector implantation.

Table 8. Incision sizes measured during 12 cataract procedures using forceps (Fine Universal Folder II) and injector (Unfolder) insertions of SI-40NB IOL (6 implantations per device)

Alcon Acrysof MA30BA using Buratto implanation forceps, 3.0 ( 0.07) and 3.1 ( 0.05) for the Allergan SI55NB using a Fine Universal II Folder, and 2.66 ( 0.08) and 2.81 ( 0.11) for the Allergan SI55NB using the AMO Unfolder, respectively (table 9).

The incision sizes before and after IOL implantation were statistically significantly different for the groups (table 10). The enlargement (comparison of incision sizes before and after IOL implantation) was very similar in all four study subgroups with a calculated value of 3–5% (table 9).

The incision sizes for the Pharmacia CeeOn 912 and the Alcon MA30BA were not statistically significant different before and after implantation (table 10). However, these two IOLs were statistically significant different in preand postimplantation incision size to the Allergan SI55NB IOL implantations. Additionally, the Allergan SI55NB implantation with the AMO Unfolder was associated with statistically significant smaller incision sizes than implantation with the Fine Universal II Folder (tables 9, 10). It should be mentioned that the average dioptric power in this study was the highest in the MA30BA group and lowest in the SI55NB Unfolder group (table 3).

Discussion

Development of a New Caliper to Measure Incision Sizes

In a recent clinical study the incision sizes of cataract wounds were measured with several devices. Steinert and Deacon [38] used incision gauges to verify the incision size. Such gauges require in most cases several measurements and can slightly enlarge the wound. Mackool [19] used an Osher internal caliper, whose accuracy had been verified against a standard steel millimeter ruler. This caliper has an incremental scale of 0.5 mm, and therefore requires

Table 9. Incision sizes measured during 40 cataract procedures using forceps and injector implantation of 5.5-mm total optic 3-piece IOLs (10 implantations per IOL and device)

Pre Preimplantation; Post Postimplantation.

1Using the Tukey-Kramer test; incision sizes with the same letter in each column are not significantly different.

some estimation of the measurement on the part of the observer. In the experimental studies of our investigations, we have used a modified Osher and vernier calipers to precisely study the incision dimensions with an accuracy of 0.01 mm. This modified Osher caliper also measures with an accuracy of 0.5-mm steps and therefore requires a vernier caliper for more precise values. Unfortunately, this method is too time consuming for clinical studies, and therefore this new device was developed.

The practicability of the new instrument was evaluated in the clinical part of this research project for forceps and injector implantation of 3-piece high- refractive-index silicone IOLs (Part A) and for 5.5-mm total optic foldable IOLs (Part B). In Part A, the measurements were first performed with the modified Osher and vernier calipers and were then repeated with the new device. An accuracy of 0.1 mm was found. An advantage of this device compared to incision guages [38] and the modified Osher caliper/vernier caliper system is that only one maneuver is necessary to determine the incision size. With the appropriate surgical experience, enlargement of the incision can be avoided. However, only an optically driven measuring device could totally eliminate the ocular tissue with the forcep tips which might enlarge the tunnel dimensions.

For currently used small-incision cataract techniques and available foldable IOLs the new caliper should be preferably used with a measurement range of 2–4 mm (fig. 9).

In summary, this new caliper facilitated easy and atraumatic intraoperative measurement of incision sizes for small-incision surgery with an accuracy of 0.1 mm.

Experimental Studies

We believe that there are three major conclusions to be derived from the experimental study Part A:

First, implantation of foldable IOLs through the smallest possible corneal tunnel incision enlarges the wound. This increase in wound size is accompanied by tearing or disruption of corneal stromal tissue and Descemet’s membrane, whereas appropriately sized incisions show minimal if any insertional tissue damage (fig. 11–14). The clinical impact of this tissue injury is uncertain, but it is our clinical impression that stretched incisions are less likely to be self-sealing and more often require a suture in order to achieve wound closure.

Second, this study demonstrates that there are statistically significant differences in incision sizes required for implantation of various foldable IOL/inserter combinations. Following implantation of the 8 foldable IOLs, actual incision sizes ranged from 3.2 to 3.8 mm (experimental study Part A). Three categories of final incision sizes were found: (1) 3.2–3.4 mm: Allergan SI-30NB, Chiron C10UB, Staar AA-4203, Alcon MA30BA, and Alcon SH30BC; (2) 3.5 mm:

Table 11. Relationship between actual IOL optic diameter and mean postoperative incision size (calculated for a 20.5-D IOL)

Storz H60M; and (3) 3.8 mm: IOLAB LI41U and Alcon MA60BM. Comparing the two three-piece silicone IOLs (IOLAB LI41U and Allergan SI-30NB), the latter, with its high-refractive-index silicone and a smaller refractive optic size (5.3 vs. 6.0 mm), could be implanted through a smaller incision. Although both plate-haptic silicone IOLs tested in this study have a lower refractive index than the two three-piece silicone IOLs (1.41 vs. 1.43/1.46), our data suggest that the use of an injector reduces the incision size required for implantation of these IOLs (clinical study Part A). The soft acrylic IOLs have the highest refractive index of all tested lenses and therefore have the smallest central thickness. The larger incision sizes found for the 6-mm optic acrylic IOL (Alcon MA60BM) compared to most of the other 6-mm optic IOLs suggests that soft acrylic IOL material is not as compressible or pliable as silicone or hydrogel material.

There was no clear correlation between optic size and post-insertional incision size. The ratio of millimeters of IOL optic diameter per millimeter of incision was highest for the high-refractive-index silicone IOL and the two plate-haptic IOLs, and lowest for the IOLs that needed a 3.8-mm incision for insertion (table 11). For several IOLs the actual refractive part of the IOL is smaller than the total diameter of the IOL optic. Therefore, another way to evaluate required incision sizes is to calculate the ratio of millimeters of refractive optic diameter per millimeter of incision; this analysis shows a different ordering of the IOLs (table 12).

Third, the study suggests that, when implanting IOLs through the smallest possible incisions, there may be qualitative differences in the induced tissue changes depending upon whether forceps or injectors are used. Although these conclusions are only drawn based on two different IOLs (Allergan SI-30NB, Staar AA-4203) and two different implantation devices (Universal Fine II Folder and Microstaar injector) in 6 fresh human cadaver eyes, the SEM images

Table 12. Relationship between refractive IOL optic diameter and mean postoperative incision size (calculated for a 20.5-D IOL)

suggest that the increase in incision size following injector implantation is associated with greater tissue damage and that the corneal stroma appears to retain some memory of the shape of an injector. There was also a trend toward greater quantitative enlargement of incisions following the use of injectors (10.9% for injectors vs. 5.9% for forceps).

We recognize that there are limitations to the cadaver eye model for studying incision sizes following cataract surgery, but clinical studies have already shown comparable results between in vivo and in vitro surgery [19]. Recently, Steinert and Deacon [38] examined intraoperative cataract wound size and demonstrated that the incision enlarges at each step of the procedure – after entry with a keratome, after phacoemulsification and after IOL implantation. For clear corneal tunnel incisions, they found that the final incision sizes for high-refractive-index three-piece and plate-haptic silicone IOLs were 3.31 and 3.34 mm, respectively. They concluded from their study that irreversible incision stretching or tearing occurs, rather than reversible elastic incision deformation. Our laboratory, measurements and SEM evaluation indicate that the distortion seen during insertion of foldable IOLs through tight incisions is accompanied by wound enlargement and damage to corneal structures. We conclude, therefore, that the cornea’s capacity for true elastic deformation is limited and that the cornea is injured by excessive stretching.

In the experimental study Part B, additional information was obtained for forceps and injector implantation:

First, the study again demonstrated that IOL insertion through an excessively tight incision can damage corneal structures (fig. 4). In Part A we had evaluated by SEM the difference between 3.0- and 3.5-mm incisions for a high-refractive- index silicone IOL (Allergan Medical Optics SI30NB) and found tearing in the

smaller incision. In the study Part B the tighter incisions (3.0-mm) again showed greater disruption of corneal tissue than the larger incisions (3.2-mm).

Second, in our study, the occurrence of corneal damage was more dependent on the incision size before implantation than on the implantation device. Either the forceps or the injector caused comparable tissue damage if the incisions were too small.

Third, the experimental evaluation revealed that insertion of this IOL through a tight incision tears and/or deforms corneal tissue and thereby enlarges the wound by ca. 9%. The enlargement of the incision in the clinical investigation (Part A) was only 3.2 and 4.0%. In the experimental study, incisions were enlarged in 0.25/0.2-mm increments until smooth insertion was possible. In the clinical study Part A, a 3-mm wound was also enlarged minimally, but in a less controlled manner using a diamond knife. This may explain for the greater preinsertion wound width in the clinical series, and thus for the reduced amount of wound enlargement. One further possible explanation for this disparity is that, compared to living tissue, cadaver eye tissue sustains greater tearing or deformation from the incisional enlargement required to implant the IOL. This may therefore indicate a modest limitation of the cadaver eye model for studying incision sizes. However, another potential explanation for the differential incisional enlargement might be the type of blades used. In the cadaver eyes, the incisions were made with steel knives, whereas in the clinical study a diamond knife was used. Radner et al. [32] recently showed that the IOL implantation through 3.0-mm clear corneal incisions made with steel keratomes produced corneal trauma that was considerably more severe than implantation through 3.2-mm wide steel blade incisions or 3.0-mm diamond incisions. Another study by this group [31] demonstrated that cutting corneal tissue with diamond tips caused less tissue damage than expanding the incisions with blunt caliper tips. Thus the smaller amount of incisional enlargement in the clinical arm of our study Part A might be simply due to the use of the diamond knife. Additional clinical study will be required to verify this hypothesis.

Clinical Studies

The silicone IOL used in clinical study Part A allows the smallest possible incisions currently achievable for three-piece, 6-mm optic IOLs. Olson et al. [26] recently found in a clinical evaluation of the Unfolder that the new injector provided a controlled IOL implantation through incisions ranging from 2.7 to 3.2 mm in width. In their study, the incision sizes increased as a result of IOL implantation, with widths ranging from 2.9 to 3.3 mm. Their results are comparable to the incision sizes determined in our current investigation. In our clinical study and Olson’s evaluation, the incision sizes using the injector were

smaller than those required for forceps implantation with this IOL (table 8). We suspect that additional refinement of the design of injector systems might further reduce the incision size required for IOL implantation; however, the amount of reduction is not likely to exceed 0.5 mm with the current IOL design, since the IOL itself comprises the majority of material introduced into the wound when using the Unfolder.

Most of the IOLs studied in previous [24, 26, 38] and in our investigations were 6-mm total optic IOLs. Recently, 5.5-mm total optic foldable IOLs have been available, with one reason being a predicted decrease in postinsertion incision size. In the current investigation (clinical study Part B), incision sizes of 2.8–3.4 mm were found for 5.5-mm total optic 3-piece foldable IOLs. This is a decrease in the range of incision sizes compared to the 3.1–3.9 mm in studies investigating 6-mm IOLs [24–26, 38].

The incision sizes for 5.5-mm total optic IOLs obtained in other studies are comparable to the findings of the current investigation. For example, incision sizes for the Alcon Acrysof MA30BA were as follows: 3.38 0.10 mm in the experimental study Part A, 3.4 0.13 mm in a clinical study [25], and 3.42 0.09 mm in the current clinical investigation. The results from these experimental and clinical investigations were quite similar.

Beside our studies (experimental study Parts A B) several studies have recently shown that the wound progressively enlarges during the various steps of small-incision cataract surgery [19, 31–33, 38]. It was found that implantation of foldable IOLs through the smallest possible corneal tunnel incision enlarged the wound, and this enlargement was accompanied by tearing or disruption of corneal stromal tissue and Descemet’s membrane, whereas appropriately sized incisions showed minimal if any insertional tissue damage. When implanting IOLs through the smallest possible incisions, a qualitative differences in induced tissue changes was seen, depending upon whether forceps or injectors were used. All investigators observed that the smallest possible incision enlarged during the implantation process. Sufficient enlargement of the wound before IOL implantation is therefore recommended.

To investigate the impact of an implantation device the SI55NB IOL was implanted with an injector (AMO UNFOLDER Implantation Systems) and with forceps especially designed for this IOL (Fine Universal II Folder). A statistical difference was found for the incision sizes before and after IOL implantation (table 9). A difference between forceps and injector implantation was also found for 6-mm optic high-refractive-index silicone IOLs (Allergan SI30NB, SI40NB) in our experimetal study Part B and in another previous study [26]. The smallest incision sizes associated with using forceps were 3.31 mm [38], 3.36 mm (table 8) and 3.32 mm [24], whereas with the Unfolder the incison sizes were 3.21 mm (table 8) and 3.1 mm [26].