Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 1. Screenshots of a sequence of the eyemetrics analysis of white-to-white measurement.

The eyemetrics subprogram of the Orbscan software provides an autodetection of the pupillary margin as well as the limbus, thus creating the white-to-white measures. We evaluated 26 eyes of 13 healthy volunteers with the Orbscan system (System Orbscan I, Orbtek Inc., Salt Lake City, Utah, USA).

Figure 1 demonstrates the steps of how the calibrated video image is processed for corneal diameter measurements. Two control measures were done using a ruler with micrometer scale (MM) and the millimeter scale of a Goldmann perimeter (GP).

Results

The average corneal diameter was 12.01 0.35 mm with the Orbscan, 11.97 0.35 mm control MM and 11.93 0.35 mm control GP (fig. 2).

Fig. 2. Mean values and standard deviation of corneal diameter measurements. There are virtually no differences.

Corneal diameter (mm) (Orbscan)

Fig. 3. Correlation: corneal diameter Orbscan versus micrometer ruler measurement. Good correlation with a coefficient of determination of 0.859.

Spearmann rank order correlation was r 0.91 (p 0.0001) Orbscan vs. control MM and 0.93 (p 0.0001) Orbscan vs. control GP. Linear regression analysis revealed a coefficient of determination ( square of correlation coefficient) of 0.87 Orbscan vs. control MM and 0.93 Orbscan vs. control GP, as well as 0.84 control MM vs. control GP (fig. 3–5).

Figure 6 represents problematic cases. In one picture the video image is blurred and not aligned because of eye and lid movement. In the other picture the image is too dark and contrast detection is quite difficult.

Fig. 4. Correlation: corneal diameter Orbscan versus Goldmann measurement. Good correlation with a coefficient of determination of 0.936.

Fig. 5. Correlation: micrometer ruler measurement versus Goldmann measurement. Good correlation with a coefficient of determination of 0.842.

Discussion

The Orbscan topography system offers a white-to-white measurement of the horizontal corneal diameter with its implemented eyemetrics program. Measurements show very accurate and reproducible data. Compared to two control

Fig. 6. Problematic image analysis. Left: the video image is blurred and not aligned because of eye and lid movement; right: the image is too dark and contrast detection is quite difficult.

measurements there were very good correlations and coefficients of determination. The mean values were virtually identical.

A disadvantage of the system is that the accuracy depends on the quality of the captured video image. This image is automatically drawn from the images that were accessed during the slit scanning process of the cornea. There is no possibility to switch images in the program. If the image is blurred or distorted due to eye or lid movements, the analysis does not work properly.

Nevertheless, this system offers a complete workup on a refractive patient to give also additional information such as the white-to-white data and anterior chamber depth when planning phakic IOLs. Sizing of phakic anterior chamber lenses can be planned directly and not during surgery. This applies of course also to conventional anterior chamber lenses for secondary implantation or for planned intracapsular cataract surgery.

References

1Arne JL, Lesueur LC: Phakic posterior chamber lenses for high myopia: Functional and anatomical outcomes. J Cataract Refract Surg 2000;26:369–374.

2Assetto V, Benedetti S, Pesando P: Collamer intraocular contact lens to correct high myopia. J Cataract Refract Surg 1996;22:551–556.

3Auffarth GU, Biazid Y, Tetz MR, Völcker HE: Measuring anterior chamber depth with the Orbscan topography system: A reliability study. J Cataract Refract Surg 1997;23:1351–1355.

4Auffarth GU, Wang Li, Völcker HE: Keratoconus evaluation using the Orbscan topography system. J Cataract Refract Surg 2000;26:222–228.

5Auffarth GU, Wesendahl TA, Apple DJ: Are there any indications for clinical use of anterior chamber intraocular lenses (AC IOLs) in the 1990s? An analysis of 4,104 explanted AC IOLs. Ophthalmology 1994;101:1913–1922.

6Fechner PU, Haigis W, Wichmann W: Posterior chamber myopia lenses in phakic eyes. J Cataract Refract Surg 1996;22:178–824.

7Kaya V, Kevser MA, Yilmaz OF: Phakic posterior chamber plate intraocular lenses for high myopia. J Refract Surg 1999;15:580–585.

8Marinho A, Neves MC, Pinto MC, Vaz F: Posterior chamber silicone phakic intraocular lens. J Refract Surg 1997;13:219–222.

9Perez-Santonja JJ, Bueno JL, Zato MA: Surgical correction of high myopia in phakic eyes with Worst-Fechner myopia intraocular lenses. J Refract Surg 1997;13:268–281.

10Saragoussi JJ, Puech M, Assouline M, Berges O, Renard G, PouliquenYJ: Ultrasound biomicroscopy of Baikoff anterior chamber phakic intraocular lenses. J Refract Surg 1997;13:135–141.

11Trindade F, Pereira F, Cronemberger S: Ultrasound biomicroscopic imaging of posterior chamber phakic intraocular lens. J Refract Surg 1998;14:497–503.

12Trindade F, Pereira F: Exchange of a posterior chamber phakic intraocular lens in a highly myopic eye. J Cataract Refract Surg 2000;26:773–776.

13Zaldivar R, Davidorf JM, Oscherow S: Posterior chamber phakic intraocular lens for myopia of –8 to –19 diopters. J Refract Surg 1998;14:294–305.

Gerd U. Auffarth, MD, Department of Ophthalmology, Ruprecht Karls University of Heidelberg, Im Neuenheimer Feld 400, D–69120 Heidelberg (Germany)

Tel. 49 6221 566 631, Fax 49 6221 561 726, E-Mail gerd_auffarth@med.uni-heidelberg.de

Fig. 1. Cartridge-based reusable injectors (from left to right): Lens Injector Set (Duckworth & Kent), Monarch (Alcon), Microserter (Bausch & Lomb), Sensar (Allergan), Unfolder (Allergan) and Unfolder T (Allergan).

Fig. 2. Single-use injectors (from left to right): EasySert (Pharmacia), EasyPack (Ophtec), Staar, Staar and Mport (Bausch & Lomb).

The tips of this central cylinder vary in respect to the diameter and to the overall design. The tip itself is made of metal, plastic or covered with a silicone sleeve. This depends on the diameter of the cartridge or the folding chamber and on the resistance of the IOL. The resistance of folding the IOL again depends on whether the process of folding and advancing the IOL is separated or not. The cartridge-based systems fold the IOL by closing the cartridge. This reduces the force needed to advance the IOL within the cartridge. The folding chamberbased systems exert more force on the IOL by folding and advancing the IOL in one step.

The cartridges vary in inner and outer diameters, in material and in round, oval or hexagonal tip designs. This influences the unfolding of the IOL and the incision width. The characteristics of different injector systems (alphabetically listed by the name of the company) are described below:

Alcon

The ‘Monarch’ is provided for the Acrysoft 5.5-mm IOL. This system uses a flat, not foldable, single-use cartridge to be completely filled with viscoelastic material. The IOL is placed within the cartridge and the leading haptic is stretched forward whereas the trailing haptic points out of the cartridge. The handpiece plunger must meet the edge of the IOL optic. Bimanual screwing of the plunger folds the lens and rotating of the injector delivers the IOL by slow release into the capsular bag.

Allergan

The ‘Unfolder’ handpieces and cartridges of the silver series are provided for silicone lenses with 6.0-mm optics (SI30, SI40, SA40) and the gold series for silicone lenses with 5.5-mm optics (SI55). These systems use flat, foldable, single-use cartridges to be filled with a small amount of viscoelastic material and single-use silicone soft-tip sheath. Proper positioning of the IOL is indicated on the right wing of the cartridge. The bimanual implantation procedure by screwing the plunger and rotating the unfolder facilitates controlled unfolding of the IOLs and safe, direct placement into the capsular bag.

The ‘Sensar’unfolder handpiece and cartridge is provided for acrylic lenses (AR40). The foldable, single-use cartridge indicates on the left wing of the cartridge, how to position the IOL underfilled with viscoelastic material. The bimanual implantation procedure by screwing the plunger and rotating the unfolder facilitates very slow unfolding and rotating of the IOL into the capsular bag.

Bausch & Lomb

The ‘Microserter’ handpiece and cartridge is provided for silicone (LI40) and for acrylic (EasAcryl) lenses. Different foldable, single-use cartridges have to be used with viscoelastic material for the specific IOL. Very slow screwing of the plunger bimanually advances the IOL; positioning into and centration within the capsular bag sometimes has to be done with a push-pull instrument.

The ‘Passport’ made for implantation for silicone lenses with plate haptic (C11) or with polyimide haptics is a single-use injector. The folding chamber is placed in front of the unit. After exact positioning of the IOL and closing of the folding chamber the tip of the injector has to meet the IOL optic very exactly.

The ‘Mport’ as a one-piece, single-use instrument with loading deck, folding chamber and injector is provided for silicone lenses (Soflex 2). By closing the loading deck the IOL is

folded in an M-like shape, advancing the plunger pushes the IOL forward, direct, monomanual implantation without rotation into the capsular bag is possible.

Duckworth & Kent

The ‘Lens Injector Set’ with injector, forceps and loading plate, which can be resterilized, is a one-piece instrument completely made of metal. Different models are provided for acrylic or silicone IOLs. This is an injector not produced and not delivered by an IOL company. After positioning the IOL into the injector chamber and closing it, the IOL is folded by pushing the plunger forward.

Ophtec

The ‘EasyPack’ as a one-piece, single-use injector with cartridge is provided for silicone lenses (PC410). The IOL is placed in the cartridge, filled with viscoelastic material, rolled into the cartridge and pushed by the plunger; the IOL is inserted monomanually into the capsular back.

Pharmacia

The ‘EasySert’ as a one-piece, single-use injector with integrated cartridge is provided for silicone lenses (SeeOn Edge). After exact positioning the IOL and closing the folding chamber, the three-faceted plunger has to push the IOL to roll and to inject it simultaneously. First the plunger has to be screwed bimanually and second it has to be pushed monomanually.

Results

Cartridge-Injector Systems for IOLs with Plate Haptics (Microserter, Passport II)

This type of IOL (silicone: C11, Bausch & Lomb, AA-4203VF, Staar; acrylic: EasAcryl*1, Bausch & Lomb) can be easily positioned into the cartridge of the Microsert (bimanual) injector or into the Passport II (monomanual). There is no need for rotation of the Passport II itself. The implantation of this IOL into the capsular bag is better controlled with the injector than with forceps; with higher diopters of the IOL, unfolding is also somewhat uncontrolled with the injector, advancing of the IOL performed by folding and injecting through a 2.5-mm incision.

Cartridge-Injector Systems for Three-Piece Silicone IOLs (Microserter, EasyPack)

These silicone IOLs (Soflex, Bausch & Lomb; PC140, Ophtec) can be implanted monomanually with pushing injectors (EasyPack) and bimanually with screwing injectors (Microserter). Positioning of the IOL into the rods of the cartridge has to be controlled, the haptics have to be set in the right direction (leading haptic forward, trailing haptic backwards out of the cartridge) thus

making the whole loading procedure more demanding. Insertion of the IOL is facilitated because the injector does not have to be rotated.

Cartridge System for Three-Piece Silicone IOLs (Unfolder, Unfolder Silver/Gold, Unfold Silver T)

These silicone IOLs with high index of refraction (SI40, SI55, SA40, Allergan) have to be implanted bimanually with a screwing injector. The bevel cutaway of the cartridge has to point to the left, the leading haptic is positioned into the bag, the injector itself is rotated counterclockwise, whereas the plunger is rotated clockwise during implantation of the silicone-covered tip. One has to rewind the rod to engage the trailing loop with the rod to place it also into the capsular bag. At the end of the learning curve for the bimanual counterrotating implantation process, this is the most controlled release of a silicone IOL into the capsular bag. The IOL can even be retracted when it is half way out of the rod. The Unfolder Silver T has wider threads to make the delivery of the IOL easier and to synchronize the rhythm of rotating the unfolder and injecting the IOL into the capsular bag. The implantation can be accomplished through 3.2-mm (silver series) or 2.9-mm (gold series) incisions.

Cartridge System for Three-Piece Acrylic IOLs (Unfolder Sapphire)

This acrylic IOL (AR40, Allergan) has to be implanted with the screwing ‘Unfolder Sapphire’injector. Exact positioning of the IOL into the cartridge before folding is important. A slightly higher resistance with a less enrolled acrylic IOL has to be regarded. The IOL is released out of the rod very controlled because the unfolding of the IOL is slow. The IOL can be rotated with the unfolder for complete, direct positioning into the capsular bag. Bimanual counterrotating implantation has to be understood for safe delivery. In contrast to the silicone IOL unfolder, the plunger may not be retracted during the injection process to avoid damage of the haptic. The implantation can be accomplished through a 3.4-mm incision.

Cartridge System for Three-Piece Acrylic IOL (Monarch)

This acrylic IOL (Acrysoft 5.5 mm, Alcon) has to be implanted bimanually with the screwing Monarch injector. Exact positioning of the IOL into the cartridge before injecting is important. The cartridge has to be completely filled with viscoelastic material. The tip of the plunger has to meet the edge of the optic to advance the IOL, otherwise it will glide over the IOL. The implantation can be accomplished through a 3.4-mm incision.

Injector Set for Three-Piece Acrylic IOL (Lens Injector Set DK 7705-1)

This system is delivered for different IOLs (acrylic and silicone three-piece). The loading plate and the forceps facilitate the placing of the IOL into the IOL