Ординатура / Офтальмология / Английские материалы / Master Techniques in Cataract and Refractive Surgery_Hampton Roy, Arzabe_2004

Figure 6-5. Svyatoslav Fyodorov, Moscow 1981. (Courtesy of Richard J. Knox.)

the corneal apex), what shape, what length, and what depth. These decisions are based on how much cylinder is present, as determined by keratometry; at what axis, as determined by topography; at what depth, as determined by pachymetry (or empirically); and according to the patient’s age. The older the patient, the greater is the effect of incisional keratotomy.

In addition, what effect will the phacoemulsification incision have on the corneal curvature? Can the phacoemulsification incision be used to reduce preexisting astigmatism?11 A scleral-pocket incision (SPI), being farther from the cornea, has less effect on altering corneal curvature than do limbal and clear corneal incisions (CCI). In addition, the shape of the scleral incision also determines its effect on corneal curvature (Figure 6-12). A curved limbus-parallel SPI will cause more flattening at that meridian than a straight incision; and the frown12 or suspension-bridge13 curved SPI has even less effect and may be astigmatically neutral. However, either a straight or a limbus-parallel SPI, because each flattens the cornea at the meridian of placement, can be used to reduce up to approximately 2.00 D of astigmatism, depending on the patient’s age. An even greater effect can be obtained with a clear-corneal incision. Using CCIs on-axis to reduce astigmatism was popularized by Gills.14

The clear-corneal phaco incision can be constructed in two ways, and each can have a slightly different effect on corneal curvature.12 If the CCI is made as a 3.2-mm, 1-step single-plane stab incision (Figure 6-13), it will flatten the cornea usually no more than 0.37 D, and only in that hemimeridian. If a 2-step, biplane, grooved CCI is made (Figure 6-14), the vertical groove can act as an LRI and cause more flattening, up to about 1.25 D, depending on the patient’s age. Additionally, the length of the limbal arc groove and the depth are variables. The length may be up to 12 mm, according to some LRI nomograms. The depth may vary from 300 µm to 600 µm, as suggested by Langerman.16 The deeper the groove, the more flattening of the adjacent cornea (Figure 6-15).

Figure 6-6. Diagram of typical 8-incision RK combined with straight tangential (“T cuts”) AK for incisional correction of myopia with with-the-rule astigmatism.

Both the phacoemulsification incision and an AK or LRI can be used in combination to reduce higher degrees of corneal astigmatism. For example, a moderate degree of against-the-rule (ATR) astigmatism may be corrected with a temporal grooved CCI combined with a nasal AK or LRI. Performing lens surgery with this combination of incisions, a grooved CCI and an opposing AK or LRI, has been called keratolenticuloplasty by Kershner.17,18

Instrumentation for incisional keratotomy progressed through the years as the technology advanced. In the beginning, straight incisions were made with razor blade fragments held in special in instruments called blade holders. The amount of blade exposure was measured on a metal ruler (Figure 6-16). Metal blades are manufactured today with blade exposures preset at the factory determined by a metal footplate or guard (Oasis Medical, Glendora, Calif). They can be used for on-corneal AK or for the limbal groove of a CCI. Terry designed a metal-blade astigmatome (Oasis) (Figure 6-17), which has 1 or 2 metal blades set at fixed exposures designed to make reproducible accurate AKs by manual rotation of the trephine-like astigmatome (Figure 6- 18). For those with an unlimited surgical equipment budget, Rhein manufactures an automated suction trephine designed by Jorg Krumeich in Germany16 called the guided trephine system (GTS) (Figures 6-19 and 6-20). This vacuum trephine was originally designed for penetrating keratoplasty for front-cutting of both the donor and host corneal buttons. The instrument works like a LASIK microkeratome, obtaining purchase by vacuum-suction and using a rotating blade system. Another precise instrument for arcuate keratotomy is the Hanna arcitome (Moria, France)19,20 (Figure 6-21), which has diamond blades and the ability for the blades to translate forward and backward for incision redeepening.

Many surgeons performing CCI phacoemulsification today use diamond blades for their incisions and diamond blades for their AKs or LRIs. It has become the preference of this surgeon to perform on-corneal straight-T 3-mm AKs using the Feaster diamond blade (Rhein, Tampa, Fla)

Figure 6-12. Limbus-parallel (left), straight (center), “frown” (right) scleral incisions.

Figure 6-13. Single-plane 1-step clear-corneal incision with diamond blade. (Courtesy of Grabow.)

Figure 6-14. Groove LRI with guarded diamond blade as first step of 2-step biplane CCI. (Courtesy of Grabow.)

Figure 6-16. Setting metal blade exposure on metal gauge for incisional keratotomy as performed in the 1970’s and 1980’s.

Figure 6-18. Nomograms for correcting for WTR and ATR corneal astigmatism using the Terry astigmatome.

Figure 6-15. Flattening effect of temporal CCI as observed as the dark blue zone in the 1-day postoperative topography.

Figure 6-17. Terry astigmatome for metal-blade arcuate astigmatic keratotomy. (Courtesy of Oasis.)

Figure 6-19. Krumeich Guided Trephine System (GTS) for vacuum astigmatic keratotomy and lamellar keratectomy. (Courtesy of Rhein.)

Figure 6-20. View of suctioning ports of Krumeich Guided Trephine System. (Courtesy of Rhein.)

Figure 6-22. Feaster 3 mm diamond AK blade (Courtesy of Rhein) for straight T-cut astigmatic keratotomy.

Figure 6-21. Hannah Arcitome for diamond-blade astigmatic keratotomy.

(Figure 6-22). This blade was designed by Fred Feaster and is 3 mm long and designed to be used by indentation rather than translation. It is not infrequently observed with translating keratotomy that an epithelial flap or abrasion may occur due to the toxic effects of topical medication, weak epithelial-basement membrane attachment, and/or the age of the typical cataract patient. The accuracy of free-hand arcuate keratotomy may also not be as consistent and reproducible as with the fixed-length indentation system. With every AK being 3 mm long, the length of the AK is no longer a factor in the surgical plan to reduce astigmatism. The optical zone, the axis, the number of AK incisions, and the blade exposure remain as factors to be determined. From personal experience, this surgeon has established a table of Feaster blade exposure settings related to optical zone sizes (Figure 6- 23). Because indentation keratotomy pushes stroma ahead of the blade, incisions may be shallower than expected for the same exposure of a translating blade. Therefore, the empiric blade exposures for each optical zone are greater than would be used for translational keratotomy.

The Feaster system includes a Mendez axis gauge and optical zone markers (Figure 6-24). In addition, a Thornton

Figure 6-23. Feaster diamond blade settings for straight 3-mm astigmatic keratotomy. (Courtesy of Grabow.)

ring is available to stabilize the globe and create a more firm cornea during indentation keratotomy. The Feaster blade is then placed on the epithelial mark and rocked back-and- forth, heel-to-toe, allowing the blade to cut through Bowman’s and stroma full-depth to the footplate (Figure 6- 25). The blade is then simply withdrawn and the perfectly straight linear 3-mm AK can be observed without disturbance of the overlying epithelium. These AKs are usually performed at the beginning of surgery, before any incisions into the anterior chamber. In this way, the eye is more firm and there is no chance of the indentation pressure causing a wound leak or flat chamber. However, some surgeons prefer to perform AK at the end of the phacoemulsification procedure, either with viscoelastic still in the eye, or with the eye temporarily inflated to a firm IOP.

Figure 6-24. Mendez gauge and optical zone marker for Feaster diamond blade astigmatic keratotomy. (Courtesy of Rhein.)

Figure 6-26. Three-piece PMMA toric IOL with 5.5- x 6.5-mm optic and 13.0-mm polypropylene haptics implanted by Shimizu (Nidek, Japan).

INTRAOCULAR CORRECTION

OF ASTIGMATISM

The use of an intraocular lens (IOL) to correct a refractive error was first conceived and performed, as we know, for aphakia by Harold Ridley in England in 1949.22 These first rigid PMMA lenses, and their subsequent foldable successors, were spherical models able to correct only the spherical component of refractive errors. In 1986, spherical phakic IOLs made their re-entry into the surgical arena,23.24 after initial failure in the 1950’s.25-30 In the early 1990’s toric aphakic IOL implantation began on 2 continents. In Japan, Kimiya Shimizu31 began implantation with a 3-piece PMMA loop-haptic toric aphakic IOL manufactured by Nidek (Figure 6-26). This 3-piece loop-haptic design was shown to have rotated off axis 20 degrees or more in 30% of eyes. Shimizu later implanted a series of 1-piece loop-haptic all PMMA toric IOLs (Figure 6-27). Now, in the first decade of the new millennium, toric phakic IOL implantation has

Figure 6-25. Feaster diamond blade indentation astigmatic keratotomy. (Courtesy of Grabow.)

Figure 6-27. One-piece PMMA toric IOL with 5.25-mm optic and 12.5-mm haptics implanted by Shimizu (Nidek, Japan).

begun, both with the Artisan iris-fixated lens (Ophtec, the Netherlands) and with the ICL (implantable contact lens [STAAR, Monrovia, Calif]) in the posterior chamber, first performed in Europe by Tobias Neuhann of Munich and in North America by Howard Gimbel32 of Calgary.

In the same time period, the first foldable silicone toric IOLs were implanted in a STAAR Surgical FDA clinical trial. The first prototype lens to be studied, the STAAR AA4203T,33 was a 1-piece plate-haptic TIOL with small 0.3 mm haptic fenestrations (Figure 6-28). This model was 10.8 mm in diagonal length and had a 2.25-D toric correction on 1 optic surface. The side of the optic with the toric correction was marked at the optic haptic junction with alignment marks and was designed to be placed anteriorly. The alignment marks were also used at surgery to aid the surgeon in aligning the long axis of the IOL with the steep axis of corneal curvature. They were also useful in allowing the surgeon to evaluate the IOL axis postoperatively. The 2.25 D of front-surface toric correction were shown to correct approximately 1.25 D of refractive cylinder at the spectacle plane. This length plate-haptic toric showed a rate of 8% off-axis

Figure 6-28. First-generation 1-piece silicone platehaptic toric IOL with 0.03-mm haptic fenestrations (STAAR AA4203T).

Figure 6-30. Anterior dislocation of one haptic of platehaptic IOL. (Courtesy of Grabow.)

Figure 6-32. Subluxation of a plate-haptic IOL through unstable opening in posterior capsule. (Courtesy of Grabow.)

rotation of 30 degrees or greater. A subsequent model is now manufactured that is 11.2 mm long (STAAR AA4203TL) that is also available with 3.50 D of toric correction that corrects 2.25 to 3.00 of refractive cylinder. The longer length is designed to reduce the rate of off-axis rotation. In addition, the newer models have larger 1.15-mm haptic fenestrations

Figure 6-29. Second-generation 1-piece silicone platehaptic toric IOL with 1.15-mm haptic fenestrations (STAAR AA4203TF).

Figure 6-31. Short-axis decentration of a plate-haptic IOL. (Courtesy of Grabow.)

(Figure 6-29), designed to allow fibrotic fusion of the anterior and posterior lens capsules to prevent late post-YAG- capsulotomy IOL dislocation.

The technique of aphakic toric IOL implantation involves removing the lens nucleus and cortex through a small incision, usually 3.2 mm or less, and through an anterior continuous curvilinear capsulorrhexis (CCC) of 5.5 mm or less. It is not recommended to implant a plate haptic silicone IOL through an anterior CCC that is not continuous because late capsular fibrosis can cause anterior dislocation of one haptic (Figure 6-30) with subsequent optic decentration along the long axis of the IOL. Anterior CCC openings that are greater than the optic 6.0-mm diameter can allow anterior-posterior capsular fusion lateral to one side of the optic, which can result in optic decentration along the short axis of the IOL (Figure 6-31). It is also not recommended to implant a plate-haptic IOL in an eye with an unstable opening in the posterior capsule as subluxation (Figure 6-32) or posterior dislocation (Figure 6-33) may occur; a stable posterior CCC may be implanted.

The steep corneal axis may be marked prior to surgery in several ways. Some surgeons use a sterile gentian violet marking pen to mark the limbus, either using a reticle in a slit

Figure 6-33. Total posterior dislocation of a plate-haptic IOL through unstable opening in posterior capsule.

Figure 6-35. Removal of viscoelastic from the capsular bag with the irrigation-aspiration tip behind the platehaptic IOL. (Courtesy of Grabow.)

lamp or using a Mendez gauge. Some surgeons prefer to mark the vertical meridian and the steep meridian, or just the vertical meridian and then use a Mendez gauge at the time of implantation to align the IOL with the steep axis. Some surgeons prefer to mark the peripheral cornea with a cautery after topical anesthesia as the gentian violet marks may wash away with copious corneal irrigation.

The STAAR toric IOL is injected into the capsular bag in one step (Figure 6-34). The IOL is then rotated so that the long axis is approximately 90 degrees to the phacoemulsification incision to allow removal of viscoelastic from the capsular bag, behind the IOL (Figure 6-35). The IOL is then rotated to the steep corneal axis with the I/A tip.

High degrees of astigmatism may require combinations of procedures. An eye may require both corneal modulation, with AKs or LRIs and toric IOL implantation. Gills34 has recently demonstrated the use of 2 STAAR toric IOLs sutured together for piggyback toric IOL implantation. Hans-Reinhardt Koch in Germany designed a primary bitoric piggyback IOL system (Figure 6-36) in which the apposing optic surfaces are planar and the non-apposed optic

Figure 6-34. Injection of a plate-haptic silicone IOL. (Courtesy of Grabow.)

Figure 6-36. Piggyback bitoric PMMA IOL system for postoperative cylinder power and axis adjustment. (Courtesy of H-R Koch, Germany.)

surfaces are toric. The haptics are complete 360-degree circles allowing for the postoperative adjustment of cylinder and axis by the rotation of the anterior IOL. The initial prototypes of these IOLs were 1-piece PMMA requiring 6.5-mm incisions. Another company in Germany, Dr. Schmidt Intraocularlinsen, manufactures a PMMA toric IOL in sphere powers of -3 to +30 and toric powers of +1 to +12 for very high degrees of astigmatism.

Recently, Alex Hatsis in New York performed a combination of procedures he called trioptics. He placed a STAAR toric IOL in the bag (monoptic); an AMO (Santa Ana, Calif) Array multifocal IOL in the sulcus (bioptics); and then, as a second procedure, LASIK (trioptics) to fine-tune the refractive result.

TORIC IOL OFF-AXIS ROTATION

The plate-haptic toric IOLs are fixed-length IOLs without the expansile properties of longer loop-haptic IOLs. Therefore, if one is shorter than the diameter of the newly