Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 17. Injector systems (AMO® UNFOLDER Implantation System) for implantation of the Allergan three-piece high- refractive-index silicone IOLs: Comparison of the SI55NB and SI40NB cartridge tips side by side showing a difference in orifice and tip shaft (see Discussion).

The Unfolder cartridges for implantation of the Allergan SI40NB and SI55NB three-piece high-refractive-index silicone IOLs are shown in figure 17. Different cartridges and metal injectors are used for the IOLs. The differences in the injectors are: (1) The SI55NB orifice and tip shaft are 0.127 mm smaller relative to both the inside and outside diameters. (2) The SI55NB tip shaft has a more gradual taper at the distal end, making it slightly more parallel until about half way down the tip. Other than that, they are identical. The distal orifices are round while the proximal ends are more elliptical, with the transition gradually occurring throughout the tip. The slight changes of the tips for the Allergan SI40NB and SI55NB three-piece high-refractive-index silicone IOLs and the different diameters of the IOL (5.5 vs. 6 mm) allowed a decrease in incision size of ca. 0.4 mm (3.2–2.8 mm).

Another factor which influences incision size is dioptric power of the IOL [24]. We only used in the clinical study Part B IOLs with a dioptric power of 20 D and higher, because we feel that the 5.5-mm total optic IOLs are too small for myopic eyes. This is even more problematic with IOLs which only have a refractive optic of 5.0 mm like the Allergan SI55NB. Also the IOLs were only implanted in eyes with smaller pupils to prevent optic edge glare [11]. Additionally the capsulorhexis size was always smaller than the overall optic to cover the IOL body with anterior capsule. The groups were too small to perform a statistical analysis to correlate IOL power and incision size. With respect to the slight differences found in the study of Moreno-Montañés [24], a larger number of cases need to be investigated to show a real difference for different IOL powers.

From the clinical study Part B of 5.5-mm total optic foldable IOLs, several conclusions can be drawn:

(1) The average incison size for 5.5-mm total optic 3-piece foldable IOLs (2.8–3.4 mm) is smaller than for 6-mm total optic 3-piece foldable IOLs (3.1–3.9 mm) [24–26, 38].

Table 13. Relationship between actual (total) IOL optic diameter and mean postimplantation incision size

Table 14. Relationship between refractive (effective) IOL optic diameter and mean postimplantation incision size

(2)The incision width of 2.81 mm after IOL implantation of the Allergan SI55NB using an Unfolder is the smallest postimplantation incision currently documented in the peer-reviewed literature.

(3)For the same lens model, incision size associated with the implantation using an injector is less than using forceps.

(4)There is no clear correlation between the refractive index of the IOL material and post-insertional incision size. Although the high-refractive-index silicone IOL (refractive index of 1.46) showed a smaller incision size than the Pharmacia silicone IOL with a refractive index of 1.43, the incision size for the high-refractive-index (1.55) hydrophobic acrylic IOL was equal to the Pharmacia silicone IOL with a refractive index of 1.43.

(5)The ratio of millimeters of total IOL optic diameter per millimeter of incision was highest for the high-refractive-index silicone IOL implanted with the AMO Unfolder injector (table 13).

(6)However, another way to evaluate required incision sizes is to calculate the ratio of millimeters of refractive optic diameter per millimeter of incision, because the actual refractive part of the IOL can be smaller than the total diameter of the IOL optic. This analysis shows a different ordering of the IOLs (table 14).

The implantation of all three IOLs using the forceps shows the same results; the high-refractive-index silicone IOL implanted with the Unfolder still provides the best ratio (table 14).

Conclusions

Numerous clinical studies have reported incision sizes following cataract extraction and IOL implantation [3, 4, 12, 14, 18, 20, 22, 23, 28, 30, 37], but the actual incision sizes postoperatively were not measured. Since these measurements are the basis for further evaluation of the procedures (e.g., calculation of induced astigmatism or corneal topographical changes), determination of the true postoperative incision size is important before its impact on other variables can be accurately assessed.

Our studies demonstrate that incisions enlarge following foldable IOL insertion through the smallest pre-insertional incision. Incision sizes following insertion of foldable IOLs ranged from 2.8 to 3.8 mm. The results of these studies can assist surgeons in choosing an adequate incision size for atraumatic implantation of foldable IOLs through self-sealing tunnel incisions. To determine the correct incision size in clinical studies, the incision width must be carefully measured following IOL implantation.

Acknowledgments

The author would like to thank Douglas D. Koch, MD, Cullen Eye Institute, Baylor College of Medicine, Houston, Tex., USA, Richard J. Lambert, PhD, DVM, Alcon Laboratories, Inc, Ft. Worth, Tex., USA, and Jim Deacon, PhD, Allergan Medical Optics, Irvine, Calif., USA, for their help in designing and performing the study, Robert W. Lambert, PhD, and Perry S. Binder, MD, National Vision Research Institute, San Diego, Calif., USA, for the scanning electron microscopy studies and Alexander S. Kogan, Baylor College of Medicine, Houston, Tex., USA, and Rolf Palme, Department of Ophthalmology, Johann Wolfgang Goethe University, Frankfurt am Main, Germany, for the photography artwork.

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Priv.-Doz. Dr. med. Thomas Kohnen, Department of Ophthalmology, Johann Wolfgang Goethe University, Theodor-Stern-Kai 7, D–60590 Frankfurt am Main (Germany)

Tel. 49 69 6301 6739, Fax 49 69 6301 3893, E-Mail Kohnen@em.uni-frankfurt.de

Fig. 1. Allergan SI40 (high-refractive silicone IOL, 6-mm optic, PMMA haptics). a Overview. b Scheimpflug slit image.

Fig. 2. Pharmacia CeeOn 911A (high-refractive silicone IOL, 6-mm optic, polyvinylidene fluoride haptics). a Overview. b Scheimpflug slit image.

Fig. 3. Alcon AcrySof MA60BM (hydrophobic acrylic IOL, 6-mm optic, PMMA haptics). a Overview. b Scheimpflug slit image.

Table 1. Demographics of the examined patients

3-piece hydrophobic acrylic IOL with PMMA haptics (n 5). All IOLs had an optic diameter of 6.0 mm and C-loop haptic design.

The postoperative IOL position was measured 6 and 12 months after surgery using a rotating digital charge-coupled device Scheimpflug camera connected with a personal computer (EAS-1000, Nidek Co., Gamagori, Japan) that allowed digital processing of the obtained images. After maximal pupil dilation, two Scheimpflug slitlamp images of each IOL were taken at slit angles of 90 and 180°. The anterior and posterior surfaces of the cornea and the IOL were marked on the computer monitor to determine the visual axis of the eye and the optical axis of the IOL. The tilt of the IOL optic axis compared to the visual axis, the distance between the IOL vortex and the visual axis and the anterior chamber depth (ACD) were calculated. The differences among the three groups and the periodic changes in each group were compared by single-factor analysis of variance. Differences with a p value 0.05 were considered statistically significant.

Results

The amount of decentration of the three IOLs is shown in table 2. No statistical significance could be detected. Table 3 shows the degree of optic tilt. Although the Alcon AcrySof IOL showed slightly less tilt than the others, the differences between the IOLs were not statistically significant. Table 4 shows the ACD in the three groups. As for the other two parameters, a statistically significant difference was not detectable.

Discussion

Scheimpflug photography of IOLs has been performed mainly for two purposes: (1) Biometrical assessment of lens position (tilt and decentration) and positional stability (changes in lens position over time). (2) Monitoring of posterior capsule opacification (PCO) (light scattering from the posterior lens capsule).

Table 2. Amount of decentration (mm) of the examined IOLs 6 and 12 months after surgery (mean SD)

Table 3. Amount of IOL tilt (degrees) 6 and 12 months after surgery (mean SD)

Table 4. Anterior chamber depth (mm) in the examined eyes 6 and 12 months after surgery (mean SD)

Various types of anterior and posterior chamber IOLs have been developed for correction of aphakia and, more recently, as phakic implants to correct refractive errors. By the use of foldable IOLs, it has become possible to significantly reduce the incision size for IOL implantation [17]. Therefore, foldable IOLs have become increasingly popular among cataract surgeons [22]. The major advantages of the reduced incision size are faster visual rehabilitation and minimized induced astigmatism. With high-refractive silicone lenses, incision sizes 3 mm can be achieved [16]. Postoperative complications and refractive changes due to lens tilt and displacement have been reported [5, 18, 20].

An IOL decentration of 1.0 mm or an optic tilt of 5° have been considered to cause clinically significant impairment of visual quality [9]. Earlier studies reported tilt and decentration as main complications of foldable IOLs in comparison to rigid PMMA IOLs [1, 5].

There is a variety of methods to determine tilt and decentration of IOLs and to measure changes in postoperative IOL position [2, 18, 19, 27]. The Scheimpflug photography as applied by Sasaki et al. [29] has been proven to be a valuable tool for in vivo measurements. Optic tilt and decentration are calculated as deviation of the optic axis of the IOL from the optic axis of the eye (selected as the connecting line between the center of the anterior surface curvature and the geometrical center of the pupil) from two Scheimpflug slit images taken at angles of 180 and 90°. This method has been incorporated in the software of the EAS-1000 anterior eye segment analysis system from Nidek that was released in 1991 [28]. For this reason, almost all studies that involve Scheimpflug photography of IOLs were performed using this imaging system.

Several studies have been conducted using this technique. Hayashi et al. [11] compared tilt and decentration between one-piece and three-piece PMMA IOLs and found no significant differences regarding the optic tilt but better centration in the one-piece IOL than in the three-piece IOL with flexible haptics. Another study of the same authors, however, revealed no significant differences in tilt and decentration between rigid PMMA IOLs and silicone and acrylic soft IOLs [9]. The same group compared tilt and decentration in one-piece PMMA IOLs that were either scleral-suture fixated, sulcus-fixated or implanted in the capsular bag and found a significantly higher degree of dislocation in the suturefixated group [13]. Wang et al. [32] examined the positional changes of PMMA and silicone IOLs after phacoemulsification and in-the-bag implantation and found no differences in postoperative stability.

Our comparison of two silicone and one acrylic foldable IOLs likewise detected no significant differences for tilt and decentration and confirmed the previous findings. Hayashi and co-workers [8, 10, 12] conducted several studies about IOL stability in eyes with abnormal preoperative conditions and found increased tilt and decentration of the IOL in eyes with pseudoexfoliation, glaucoma and retinitis pigmentosa. Yang et al. [33] detected no significant differences in postoperative IOL position between eyes with primary angle-closure glaucoma and a normal control group.

A conclusion that can be drawn from these results is that the postoperative stability of modern IOLs depends not as much on the IOL material and design as on the surgical technique applied (in-the-bag, sulcus-fixated, scleral-suture fixated) and on the preoperative pathologies of the operated eye (glaucoma, pseudoexfoliation, retinitis pigmentosa).