VII. FEMTOSECOND LASER CAPSULORRHEXIS
Problems with capsulorrhexis size, circularity, and placement have been solved in large measure by femtosecond laser technology, although new problems have arisen. A femtosecond laser creates a tiny gas bubble at each location where it is fired. A cylinder pattern is applied at the desired diameter starting some distance inside the lens and finishing some distance anterior to the lens capsule, thereby compensating for any tilt of the lens relative to the laser interface. A small amount of tissue coagulation may also occur as strain gauge testing of capsulorrhexis strength demonstrates that openings made by femtosecond lasers withstand a greater amount of mechanical stretching than those made by continuous tear techniques (Figure 9-7).
Seldom is the anterior capsule freely floating in the anterior chamber after a femtosecond laser creates it. It is usually tethered to the anterior lens cortex. In some cases, there are “postage stamp” tags where the laser did not completely amputate the capsule. In some of these, the skip areas may be the result of the patient interface device. Rigid curved interfaces may cause endothelial folds that interfere with imaging and laser energy delivery. Even with liquid optic interfaces, skip lesions can develop if subtle corneal opacities block laser light delivery to a portion of the capsule. The surgeon should remove the amputated capsule cautiously. Tags can be resistant to tearing in the usual sense and radial run away tears may extend posteriorly.
Because femtosecond lasers facilitate the predictability of capsulorrhexis size and location, they may improve effective lens position calculations. Additionally, they may reduce the rate of posterior capsule opacification since 360-degree optic overlap of square edge lenses has been shown to reduce the posterior migration of lens epithelial cells. Lastly, they may enable the wide- spread adoption of accommodating lenses that are dependent on the geometry of the capsulorrhexis, such as the Synchrony dual optic intraocular lens (Visiogen, Abbott Medical Optics).
VIII. POSTERIOR CAPSULORRHEXIS
Posterior capsules in infants and children often cloud quickly after cataract surgery. Nd:YAG lasers that shoot straight down are not widely available for performing posterior capsulotomies on patients who are supine on an operating table. Therefore, many surgeons prefer to open the pediatric posterior capsule, and even perform a limited anterior vitrectomy, at the time of cataract surgery.
A posterior capsulorrhexis has all the advantages of an anterior capsulorrhexis. An IOL can be implanted in the capsular bag if there are well- constructed, continuous anterior and posterior capsulotomies. In addition to providing optimum long-term centration of the IOL, there is no chance of uveitis developing because of haptic erosion into vascular tissue in the ciliary sulcus.
Performing a good posterior capsulorrhexis is trickier than performing a good anterior capsulorrhexis because the capsular bag is floppy at the time it is done. There is no lens material to provide counter-traction. The technique for creating a posterior capsulorrhexis depends on whether a pars pla- navitrectomy was previously performed and whether a plaque is present on the capsule, but the basics are similar from case to case. A straight 30-gauge needle is used to puncture the capsule centrally, and viscoelastic is injected between the capsule and the anterior hyaloid, if it is still present. This causes the posterior capsule to dome forward. Capsulorrhexis forceps are then used to grasp the capsule and tear it in a circular fashion. The surgeon should attempt to tear the capsule tangentially, as is the case with the anterior capsule, but this can be difficult. The posterior capsulorrhexis should be kept relatively small initially because it tends to radialize. When a posterior capsule plaque is present, the surgeon should tear around the plaque if it is not too large. It is difficult to tear through a plaque. If a plaque extends beyond the diameter of the desired capsulorrhexis, I may use Vannas or retinal scissors to cut through it rather than tear around it.
I often perform a posterior capsulorrhexis if a patient has a history of a pars plana vitrectomy and develops a dense central posterior capsule plaque. In such eyes, there is little concern over vitreous loss and the plaque may impair visual recovery for a long time before a laser capsulotomy can be performed safely. Any remaining anterior cortical gel can be removed quickly after the posterior capsulorrhexis has been made. The risks of cystoid macular edema and retinal tear or detachment usually associated with inadvertent posterior capsule rupture should be relatively low in the setting of a previous pars planavitrectomy.
IX. OPTIC CAPTURE
It is possible to capture the optic of an IOL, if necessary, in a good capsulorrhexis.5 For instance, if the posterior capsule is completely blown open, the surgeon can place the haptics of the lens in the ciliary sulcus and capture the optic posteriorly through the capsulorrhexis. This might be desirable, for instance, if the diameter of the haptics on the IOL is insufficient for proper sulcus fixation. There are many ways to capture an optic. Both haptics can be placed in the ciliary sulcus and the optic can be pushed through both the anterior and posterior capsulorrhexis openings. This is often done in pe- diatric eyes to retard lens epithelial cell migration over the anterior hyaloid. Alternatively, the haptics can be placed inside the capsular bag and the optic can be captured anterior to the capsulorrhexis. In all cases, the capsulorrhexis must be smaller than the optic for the optic to remain captured. The primary benefit of optic capture is that it ensures centration of the optic when things are not perfect. A disadvantage is that the capsule opening tends to stretch in the direction in which the haptics insert into the optic and narrow in the other direction. The capsule opening then takes on an oval or marquise shape with a short diameter in one meridian that may cause glare symptoms at night.
X. CAPSULORRHEXIS IN BIMANUAL PHACOEMULSIFICATION
Standard capsulorrhexis forceps, especially Utrata forceps, are too large to manipulate through an incision that is less than 2-mm wide. Special capsulorrhexis forceps have been developed for smaller incisions such as those used in bimanual or sleeveless phacoemulsification. These instruments have a circular shaft and a spring-loaded mechanism that allows the user to pinch the handles at the proximal end of the device to open and close small forceps at the distal end. These forceps are elegant for making a capsulorrhexis through a sub 2-mm incision, but they are more difficult to use than standard capsulorrhexis forceps.
XI. CAPSULE STAINING
Good visualization is critical for performing each step of the capsulorrhexis. I use higher magnification and excellent focus to give the best visualization of the capsule. If the cortex is white or a nucleus is densely brunescent, staining the capsule will facilitate visualization. I find it useful to stain the capsule when I implant additional devices in the capsular bag such as Morcher artificial iris segments (Morcher GmbH). Trypan blue is the most common capsule dye in use at this time. Methylene blue should not be used, as it is toxic to the corneal endothelium. Indocyanine green does not stain the capsule as well as trypan blue.
Staining the anterior capsule is a simple procedure. A large air bubble is injected into the anterior chamber after the paracentesis is created and before OVD is injected. The capsule stain is injected through the air bubble onto the anterior lens surface. I find it helpful to rub or paint the dye into the capsule using the injection cannula; this increases the staining effect. Balanced salt solution is then injected to wash out most of the dye. OVD is injected next to increase the space available so that the capsulorrhexis can be performed in the usual fashion. The surgeon will note improved contrast between the capsule and underlying lens material once the capsule is punctured with the bent 30-gauge needle, making it easier to visualize the edge of the capsulorrhexis. The capsule will be a little more brittle as it is torn because of the trypan blue (Figure 9-8).
*Dikutip dari Buku Essentials of Cataract Surgery 2nd Ed, halaman 95-99