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

Figure 2-17. Mean decrease in refractive cylinder between toric IOL and ALRI.

Preoperative Refractive Cylinder

Figure 2-19. Preoperative versus postoperative refractive cylinder in the ALRI.

TORIC IOLS

We were part of a randomized prospective study that compared toric IOLs with anterior limbal corneal relaxing incisions for pre-existing corneal astigmatism. As an initial investigator for FDA approval for the STAAR Surgical (Monrovia, Calif ) UV-Absorbing Collamer toric implantable contact lens (TICL) for myopia and astigmatism, I felt it was important to compare this STAAR TICL with its competitive technique, the anterior limbal corneal relaxing incision. This clinical trial involved 60 patients randomized to receive either the STAAR toric IOL or an anterior limbal corneal relaxing incision to correct pre-existing corneal astigmatism. Healthy eyes with 1.00 to 3.50 D of corneal astigmatism, correctable with an implant having a spherical power range of +17.00 to 24.00 D (the lenses initially available), were included. We excluded patients whose white-to-white measurements were greater than 11.75 mm.

Figure 2-18. Preoperative versus postoperative refractive cylinder in the TIOL.

The surgical technique was a clear, self-sealing, temporal corneal incision measuring 2.65 to 3 mm. The cases randomized to receive the toric IOL received model AA4203T if they had a cylinder of +l.00 to +2.50 D and model AA4203TF for cylinder of greater than 2.50 to 3.50 D. At 2 to 4 months, follow-up was 100% for the toric IOLs and 97% for the anterior corneal relaxing incision patients. Preoperative mean refractive cylinder for the toric IOLs was 1.50 D and 1.70 D for the ALRI patients. The mean refractive cylinder at the last postoperative visit was 0.39 for the toric IOL patients and 0.35 for the anterior limbal corneal relaxing incision patients. The mean decrease in refractive cylinder was 1.10 D for the toric IOL compared with 1.40 D for the anterior limbal CRI patients (Figure 2-17). All cases except 1 had significant decrease in their refractive cylinder (Figure 2-18) and the same is true for the anterior limbal corneal relaxing incision (Figure 2-19). The mean decrease in keratometric cylinder for the toric group was surprising at only 0.01 D. Essentially no astigmatism was induced with the corneal incision. As expected, the anterior limbal CRI group had decreases in refractive and keratometric cylinder. The mean induced refractive cylinder in the toric cases was 1.60 D and in the ALRI cases was 1.50 D.

COMPLICATIONS

Three of 30 toric IOL cases had an axis rotation more than 30 degrees. These implants were shifted at slit lamp under topical anesthesia 10 to 14 days postoperative with a 30-gauge needle. The investigators discovered that trying to rotate the lens early in the postoperative period was ineffective because it shifted back to its original position. At 10 days the capsule begins to fibrose slightly, this allows the lens to remain where it is rotated. Eighty-three percent saw 20/40 or better uncorrected, but 14% of the toric IOL patients saw

Figure 2-22. The Canrobert "C" procedure.

20/20 or better uncorrected compared with 28% of the ALRI patients. Best-corrected visual acuity (BCVA) was 20/25 or better for 38% of the toric patients compared with 48% of the ALRI patients (Figure 2-20).

In 1999, when the study was completed, only 2 toric IOL powers were available: the STAAR model AA4203T corrected about 1.35 D and the STAAR model 4203TF, which corrected 2.35 D. CRIs, however, can correct a wide range of refractive errors. Since this study was completed, there have been a number of changes in the lenses, including an increase the length of the toric IOL to 10.8 mm. Now that this lens is not placed in eyes with a white-to-white longer than 11.75 mm, the malposition rate has fallen to approximately 1%. We expect future improvements to in the lens, including a stickier lens material such as collamer or acrylic lens material. Lenses made of these materials have an extremely low tendency to rotate.

Canrobert "C" Procedure Nomogram for Astigmatism

Figure for patients less than 40 years old.

Patients older than 40 years, increase optical zone by 0.5 mm.

*Please note that on 6-D "C" incisions, the 45° incision shifts 15° toward steep meridian.

T A B L E

2-4

One of the complications of astigmatic keratotomy is the “keratopyramis phenomenon” described by Dr. Canrobert Oliveira.15 This is especially evident in moderateto highcorneal astigmatism cases. The phenomenon is associated with a shifting of the plus axis of astigmatism to either side of the relaxing incision. It can usually be resolved by nonconnecting C-incisions 1-mm posterior and beside the CRI or anterior corneal relaxing incision (Figures 2-21, 2-22, and Table 2-4).

BIOPTICS

Bioptics is defined as a second, complementary refractive procedure and includes a variety of techniques. Excimer laser correction for residual refractive errors can be performed with

laser-assisted in-situ keratomileusis (LASIK), LASEK, or PRK following initial surgical procedures, including refractive lensectomy, refractive cataract surgery, and corneal transplantation. Some surgeons create a LASIK flap before cataract surgery or refractive lensectomy. Following the procedure, when the refraction has stabilized, the flap can be elevated and most residual refractive error corrected. The drawback is that this is a secondary LASIK flap manipulation with an increased epithelial ingrowth rate of about 5%. I prefer to create the flap when the surgical wound and refractive error are stabilized. I discourage this in sutured incisions and/or incisions larger than 4 mm.

Dr. Leonardo Akaishi pioneered using toric or nontoric STAAR implantable contact lenses (phakic posterior chamber IOL) to correct residual refractive errors following cataract surgery and IOL implantation in the bag. This technique is highly effective and can be done under topical anesthesia through a small sutureless corneal incision. These implantable contact lenses are stable and rarely rotate after they are positioned in the ciliary sulcus on the anterior surface of an IOL. We have not seen rotation of these lenses in more than 200 procedures for myopic correction.

CORNEAL REFRACTIVE

PROCEDURES

The most common bioptic corneal refractive procedures are LASIK and PRK. Before any bioptic corneal incision is created after the first operation, the refractive error and surgical incision must be stable and the patient must be well informed of the reasonable surgical options and risks. Also, the risk:benefit ratio should be favorable.

LASER-ASSISTED IN-SITU

KERATOMILEUSIS

In my hands, LASIK is safe as early as 1 month after the initial surgery. We perform a thorough preoperative examination and informed consent, insert temporary punctal plugs, and begin HydroEye, 1 capsule PO BID for at least the first month before surgery. After prepping but no draping, a Moria plated speculum is used to retract the lids. I use a modified CB Moria microkeratome to create the flap with a superior hinge. The flap is folded internal surface to internal so that if the laser does ablate the hinge, it will strike the edge of the epithelium on the flap.

I use my personalized nomogram and constantly adjust my nomogram based on monthly postoperative refractions. We continually upgrade our nomograms by following our patients using the Holladay software for analyzing outcomes.

I reposition the flap with minimal irrigation and use a Johnson flap compressor to squeeze excess fluid from the

interface. I dry the edges with a wet Merocel sponge and instill levofloxacin (Quixin, Santen, Japan). Patients are informed to keep their eyes closed until the slit lamp examination 30 to 60 minutes after surgery. The eye is shielded and the patient is discharged and instructed to rest until the next day.

The routine postoperative regimen is a shield for the first week; one HydroEye capsule PO BID for at least 1 month; levofloxacin, 1 drop TID for 4 days; fluorometholone (FML, Allergan, Irvine, Calif) or loteprednol (Lotemax, Bausch & Lomb, Rochester, NY) TID for 4 days; and frequent lubrication with preservative-free artificial tears.

SURFACE ABLATION

I rarely perform PRK or LASEK for a variety of reasons, one of which is that the modified manual CB Moria microkeratome provides flap thickness ranging from 80 to 120 µm. The flap depth varies with the speed of the turn. When chosen, PRK requires the same evaluation and informed consent as LASIK. I use the Amoils (Innovative Excimer Solutions, Canada) corneal brush to remove the epithelium, then ablate using the personalized nomogram. I place a high-water bandage contact lens along with Quixin and shield the eye. The patient is given pain medication and returns the following day.

LASER-ASSISTED EPITHELIAL

KERATOMILEUSIS

Although it has not earned widespread support, LASEK continues to gain popularity among refractive surgeons. There are several different methods of removing the epithelium before ablation, then replacing it after the refractive correction is made. Some surgeons peel the epithelium back after first loosening its attachments with a diluted alcohol solution. Another technique uses a device that captures the epithelium in a rolled pattern. At the end of the laser treatment, the epithelium is unfurled back over the treated corneal bed, straightened, and a bandage contact lens is applied.

RADIAL KERATOTOMY, LASER

THERMAL KERATOPLASTY,

CONDUCTIVE KERATOPLASTY,

AND INTRACORNEAL RINGS

Once well-known and popular worldwide, RK has become far less common. We now know that the procedure

can cause progressive hyperopia and tends to destabilize the cornea more than other more modern refractive techniques. Today it is rarely performed.

Some surgeons have reported varying degrees of success with laser TK for undercorrected hyperopic pseudophakes or overcorrected myopic pseudophakes.

Conductive TK is a newer technique which, in addition to being less expensive than other procedures, has the advantage of allowing the surgeon to place the TK needle on the flat axis and adjust astigmatism.

ICRs are another option to correct residual myopia, but its relatively high cost and lengthy operating time have made this a rarely used bioptics technique following lens extraction with IOL implantation.

I think the public is underinformed about the capabilities of refractive procedures following other anterior segment surgeries; I believe the ophthalmic community has a duty to educate our patients that many of the refractive errors created following cataract surgery, corneal transplantation, retinal detachment, and glaucoma procedures can be corrected. Residual refractive errors can be treated with excimer laser procedures, astigmatic keratotomy, piggyback IOLs, and phakic IOLs. This knowledge might lead to a large market of patients wanting to improve their functional vision, even if the procedure were not reimbursable.

Postoperative Regimen for Anterior Limbal Corneal Relaxing Incisions or Corneal Relaxing Incisions

Quixin 1 drop to operated eye TID for 10 days and stop.

Pred Forte QID for 7 days, BID for 7 days and stop.

Frequent lubrication with preservative-free artificial tears.

If combined case with cataract extraction and lens implant and either corneal relaxing incision or anterior limbal relaxing incisions:

Quixin TID for 10 days and stop

Pred Forte QID for 2 weeks, t.i.d. for a week, BID for a week, QID for a week and then stop.

Preservative-free artificial tears

(We avoid prostaglandin inhibitors with corneal incisions)

REFERENCES

1.Alio JL, de la Hoz F, Ruiz-Moreno JM, Salem TF. Cataract surgery in highly myopic eyes corrected by phakic anterior chamber angle-supported lenses. J Cataract Refract Surg. 2000;26(9):1303-11.

2.Artola A, Ayala MJ, Claramonte P, Perez-Santonja JJ, Alio JL. Photorefractive keratectomy for residual myopia after cataract surgery. J Cataract Refract Surg. 1999;25(11):1456-60.

3.Donoso R, Rodriguez A. Piggyback implantation using the AMO array multifocal intraocular lens. J Cataract Refract Surg. 2001;27(9):1506-10.

4.Gills JP, Van der Karr MA. Correcting high astigmatism with piggyback toric intraocular lens implantation. J Cataract Refract Surg. 2002;28(3):547-9.

5.Inoue T, Maeda N, Sasaki K, et al. Factors that influence the surgical effects of astigmatic keratotomy after cataract surgery. Ophthalmology. 2001;108(7):1269-74.

6.Mierdel P, Kaemmerer M, Krinke HE, Seiler T. Effects of photorefractive keratectomy and cataract surgery on ocular optical errors of higher order. Graefes Arch Clin Exp Ophthalmol. 1999;237(9):725-9.

7.Muller-Jensen K, Fischer P, Siepe U. Limbal relaxing incisions to correct astigmatism in clear corneal cataract surgery. J Refract Surg. 1999;15(5):586-9.

8.Patterson A, Kaye SB, O’Donnell NP. Comprehensive method of analyzing the results of photoastigmatic refractive keratectomy for the treatment of post-cataract myopic anisometropia. J Cataract Refract Surg. 2000;26(2):229-36.

9.Artola A, Ayala MJ, Claramonte P, Perez-Santonja JJ, Alio JL. Photorefractive keratectomy for residual myopia after cataract surgery. J Cataract Refract Surg. 1999;25(11):1456-60.

10.Muller-Jensen K, Fischer P, Siepe U. Limbal relaxing incisions to correct astigmatism in clear corneal cataract surgery. J Refract Surg. 1999;15(5):586-9.

11.Oshika T, Yoshitomi F, Fukuyama M, et al. Radial keratotomy to treat myopic refractive error after cataract surgery. J Cataract Refract Surg. 1999;25(1):50-5.

12.Oshika T, Shimazaki J, Yoshitomi F, et al. Arcuate keratotomy to treat corneal astigmatism after cataract surgery: a prospective evaluation of predictability and effectiveness. Ophthalmology. 1998;105(11):2012-6.

13.Budak K, Friedman NJ, Koch DD. Limbal relaxing incisions with cataract surgery. J Cataract Refract Surg. 1998;24(4):503- 8.

14.Troutman RC, Buzard KA. Corneal Astigmatism: Etiology, Prevention and Management. St. Louis, MO: CV Mosby; 1992.

15.Canrobert Oliveira R. The keratopyramis phenomenum and the Canrobert “C” procedure. Presented at the International Society of Refractive Keratoplasty 1993 Pre-American Academy of Ophthalmology meeting. Chicago, IL. November 12-13, 1993.

INTRODUCTION

Congenital cataracts offer a complex set of challenges to the ophthalmologist, which requires an understanding of children and the pediatric eye and dexterity in anterior segment surgery. The surgical decision-making process, surgical technique, and complications of surgery differ from the adult procedure.

Aspects of pediatric cataract surgery requiring special preoperative care include the difficulty of examining infants and children and the possibility of underlying systemic disease. The distinct tissue characteristics of the pediatric eye require special intraoperative techniques; structures are smaller, and there is greater elasticity of the tissue, particularly the sclera and the lens capsule, making capsulotomy more challenging. There is often more posterior vitreous pressure as compared with adults and the vitreous is more formed than adults. Congenital cataracts may involve the capsule itself with an attenuated posterior capsule, such as in posterior lentiglobus, or even preexisting defects in the posterior capsule. Dense fibrotic or vascular attachments predispose to vitreous hemorrhage, such as in persistent hyperplastic primary vitreous (PHPV). Pediatric patients are more prone to severe postoperative inflammation, secondary cataract membranes, and glau-

coma. Choice of IOL power is made difficult by the changing size and refractive power of the child's eye.

Equally important to the actual surgery is meticulous preoperative and postoperative care. A team approach may involve the child's pediatrician or a geneticist in the evaluation for associated systemic disease, and a pediatric ophthalmologist to assist in postoperative refraction, contact lens fitting, and management of associated amblyopia and strabismus.

Fortunately, because of advances in technique such as continuous curvilinear capsulorrhexis (CCC), posterior continuous curvilinear capsulorrhexis (PCCC), and posterior optic capture, and technologies such as high-viscosity viscoelastics, pharmacologically treated IOLs, and automated vitrectomy, the surgical management of pediatric cataracts is safer and more effective than ever before.

PREOPERATIVE EVALUATION

Careful preoperative assessment is especially important in children. Because many children with cataracts are preverbal or preliterate, determining the visual significance of the cataract may be difficult. While some cataracts, such as anterior polar cataracts, are rarely visually significant, any cataract

causing amblyopia that is not responding to treatment should be treated surgically. The elements of the physical examination are similar to those in the adult; however, the method of obtaining the information may be different in children.

Determining Visual Significance of Cataracts

Assessing the visual significance of cataracts involves determining both the visual acuity and the obscuration of the visual axis.

Determining the visual acuity in children age newborn to 3 months involves the assessment of fix and follow behavior, or photophobic response. After the onset of binocularity at age 3 to 5 months, the maintaining of fixation is compared between the 2 eyes to assess for amblyopia. In the absence of strabismus, a 10.00-D prism is placed base down to check for refixation movement on each eye, and compared between the 2 eyes.1 Preferential looking and spatial sweep visual evoked potentials are additional methods available for the evaluation of preverbal infants and toddlers.2 Children ages 3 and older should be able to perform some form of optotype testing, such as Allen Figures or the H, O, T, and V letter test (HOTV). Developmentally normal children over the age of 6 years can be tested by their ability to read Snellen figures.

The obscuration of the visual axis should be determined by evaluating the effect of the size and density of the opacity on the red reflex both with and without pupillary dilation. Some patients with small lenticular opacities may require a trial of amblyopia therapy prior to determining the necessity of surgery. For example, some children with unilateral cataracts respond to amblyopia therapy consisting of chronic dilation to see around the cataract and patching of the contralateral eye.3,4 Some surgeons use 3 mm as a rule of thumb for determining if the size of the opacity is visually significant in a preverbal child. Others use the retinoscopic reflex. If retinoscopy cannot be performed around the opacity, then it is likely to be visually significant.5 Merin and colleagues suggest that the density, rather than the size of the opacity, portends to a poor visual prognosis.6 Dilation with a cycloplegic agent should be performed with retinoscopy to assess refractive error. If a small opacity is accompanied by significant anisometropia, other capsular irregularities, or irregular astigmatism, these optical aberrations may be as amblyogenic as the lenticular opacity itself.

Physical Examination

An examination under sedation or general anesthesia should be performed for pediatric patients in whom adequate preoperative physical examination cannot be obtained in the office.

Many cataracts disrupt binocularity at an early age and cause strabismus.7 Strabismus should be evaluated preoperatively with cover testing wherever possible, although in cases of vision loss, Hirschberg or Krimsky light reflex tests may

be more appropriate. The rotations should be checked with ductions and versions, or vestibulo-ocular response.

Evaluation of the pupils for afferent pupillary defect will help to assess the possibility of posterior retinal or optic nerve malformations, which may affect the final visual prognosis.

The anterior segment evaluation should involve inspection for microphthalmia, as well as measurement of the corneal diameter with calipers. Slit lamp examination may be performed with a portable slit lamp in infants and toddlers, while many children ages 2 and older are able to sit at a slit lamp. The nature of the cataract should be determined with the slit lamp, such as anterior polar, nuclear, lamellar, or posterior lentiglobus. Smaller eyes with prominent ciliary processes may have persistent hyperplastic primary vitreous.

Biometry involving A-scan and keratometry is useful for determining intraocular lens power. In addition, preoperative keratometry values may be helpful for the fitting of contact lenses postoperatively in infants who will be left aphakic. Axial lengths may be followed to assess progressive axial myopia and/or aphakic glaucoma. In older children, these may be performed preoperatively in the clinic; however, in many infants and young children these are best performed under general anesthesia just prior to cataract surgery.

Intraocular pressure (IOP) should be measured to follow for the possibility of glaucoma. When determined under anesthesia, the pressure should be taken during masked induction as measurement too early in anesthesia may elevate IOP. Similarly, deep anesthesia may artificially lower IOP. Preoperative gonioscopy provides a baseline from which to follow the angle for developmental anomalies or the possibility of synechiae and aphakic or pseudophakic glaucoma in the future.

Evaluation of the posterior segment includes indirect ophthalmoscopy wherever possible. Often the posterior pole structures may be visualized around the opacity. When this is not possible, B-scan ultrasonography should be performed.

Preoperative Evaluation for Systemic Disease

Preoperative assessment should include appropriate history and laboratory evaluation to determine the possibility of underlying systemic disease. The differential diagnosis of bilateral cataracts includes genetic conditions, most commonly autosomal dominant hereditary cataracts, Down syndrome, or Lowe's syndrome. Infectious causes include intrauterine infection with toxoplasmosis, rubella, cytomegalovirus, or herpes simplex virus. Metabolic causes include galactosemia and galactokinase deficiency.

Many unilateral cataracts require no additional work-up; however, bilateral cataracts should receive consideration for systemic workup. In a large series of pediatric cataract patients, Lambert describes 50% of bilateral patients receiving a systemic diagnosis providing an etiology for the cataracts.8 Past medical history should include careful ques-

Figure 3-1. A bent 27-gauge needle or cystotome is used to create a can opener capsulotomy. (Reprinted with permission from J Cataract Refract Surg, 19, Gimbel HV, Willerscheidt AB, What to do with limited view: the intumescent cataract, 659, Copyright [1993], with permission from The American Society of Cataract and Refractive Surgery and the European Society of Cataract and Refractive Surgery.)

Figure 3-3. Electron microscopy showing a discontinuous capsular edge following vitrector capsulotomy. (Reprinted with permission from J Cataract Refract Surg, 25, Andeo LK, Wilson ME, Apple DJ, Elastic properties and scanning electron microscopic appearance of manual continuous curvilinear capsulorrhexis and vitrectorhexis in an animal model of pediatric cataract, 537-538, Copyright [1999], with permission from The American Society of Cataract and Refractive Surgery and the European Society of Cataract and Refractive Surgery.)

technologies such as diathermy and the fugo blade may offer additional means to safely perform capsulotomies in difficult pediatric cases.15,16

CAN-OPENER CAPSULORRHEXIS

After the instillation of viscoelastic, a cystotome is used to create small nicks in the capsule to form a can-opener capsulorrhexis. The capsular openings are then joined using the cystotome (Figure 3-1).

The elasticity of the pediatric capsule may make this difficult; therefore, the anterior vitrector is used to remove any capsular tags or remnants. In cases of white or liquified cataracts where visibility of the capsule is difficult, the vitrector could be used to complete, modify, or enlarge the capsular opening.

VITRECTOR CAPSULORRHEXIS

After the instillation of viscoelastic, an anterior vitrector is placed with the port directed downward toward the cap-

Figure 3-2. The vitrector is used to create an anterior capsular opening.

Figure 3-4. Electron microscopy showing continuous capsular edge following CCC. (Reprinted with permission from J Cataract Refract Surg, 25, Andeo LK, Wilson ME, Apple DJ, Elastic properties and scanning electron microscopic appearance of manual continuous curvilinear capsulorrhexis and vitrectorhexis in an animal model of pediatric cataract, 537-538, Copyright [1999], with permission from The American Society of Cataract and Refractive Surgery and the European Society of Cataract and Refractive Surgery.)

sule. The aspiration of the instrument is activated and the anterior capsule is engaged in the vitrector port.

The cutting function of the vitrector is then activated to create an opening in the anterior capsule. The vitrector is then used to enlarge the opening as desired (Figure 3-2).17

The elasticity of the pediatric capsule allows the serrated capsular edge to roll under and to create a round appearance, although at a microscopic level, it still appears discontinuous (Figures 3-3 and 3-4).18

CONTINUOUS CURVILINEAR CAPSULORRHEXIS

Indocyanine Green

In cases of poor capsular visibility such as white, opaque cataracts, ICG, or trypan blue may assist in visualization of the capsulorrhexis.19 ICG use has been described in pediatric patients.20 A small lake of balanced salt solution (BSS) is

Figure 3-5. The initial 2-mm capsular tear is located at the 3 o'clock position.

Figure 3-7. The tear is then directed 360 degrees.

instilled beneath the Healon GV or Healon 5 using a blunt 23-gauge cannula. The diameter and positioning of the BSS is geared to the size and positioning desired for the CCC. A syringe of dye is then prepared with a filter attached. A blunt cannula is used to add the dye to the pool of BSS. The tip of the cannula is used to gently distribute the dye throughout the BSS lake, stroking the capsular surface to stain the capsule in the location and diameter desired for the CCC. The viscoelastic acts as a barrier to protect the corneal endothelium from the dye. The dye is then removed by aspirating it through the cannula. If necessary, any viscoelastic that has been stained by dye is also removed or displaced to provide a clear view of the capsule.

CCC provides the advantage of the controlled creation of a stable, smooth-edged anterior capsular opening.21,22 A 27gauge needle with the tip bent or a cystotome is used to create a 2-mm anterior capsular tear at the 3-o'clock position (Figure 3-5).

Utrata forceps are used to grasp the capsule and direct the tear first superiorly toward the 12-o'clock position. (Figure 3-6).

The tear is then continued counterclockwise 360 degrees (Figure 3-7). The direction of pull may require greater tan-

Figure 3-6. Forceps are used to grasp the flap and tear superiorly towards the 12 o'clock position.

Figure 3-8. Vannas scissors are used to create a second snip if initiating the capsulorrhexis is difficult.

gential force than in adults and more frequent regrasping with the forceps may be needed because of the capsule elasticity and tendency for radial extension. The elasticity of the capsule often causes the capsulorrhexis opening to end up larger than intended. A shearing motion directed tangentially to the progressing tear often prevents too large of an opening or an extension peripherally.

The elasticity of the capsule may make beginning the capsulorrhexis difficult. After puncturing the lens with the cystotome, if the elasticity of the capsule prevents beginning a flap tear, use of Vannas scissors in a modification of the 2- stage capsulorrhexis may enhance the surgeon's ability to begin or enlarge the capsulorrhexis.23 This technique employs Vannas scissors to create a second snip in the initial capsular opening created by the cystotome or 27-gauge needle. It is important to close the blade of the scissors only partially to avoid creating a nick in the capsule at the end of the second snip. This initiates a controlled linear tear to enable additional manipulation of the capsulorrhexis (Figure 3-8).

Tissue displacement by the viscoelastic may affect the CCC centration and/or size. The space-occupying viscoelastic may inferiorly decenter the iris opening or the lens itself, making central placement of the CCC difficult. These

decentrations must be taken into account when the placement for the CCC is chosen. The size of the capsular opening should be 4 to 6 mm. Because of the stretching of ocular tissues by the highly viscous Healon GV or Healon 5, the size of the capsular opening may be overestimated. The size and placement of the CCC should be adjusted according to the surgeon's judgment of the amount of tissue displacement by the viscoelastic.

Removal of the Lens

Historically, because of the unique difficulties associated with soft pediatric cataracts, optical iridectomy, discission, and linear extraction were advocated. In 1960 Scheie popularized aspiration of pediatric and soft cataracts.24,25 Modifications of this aspiration technique made possible by technological advances continue to be used to the present day.

Recent technology makes several methods of aspiration possible. Either an ocutome, an infusion/aspiration (I/A) handpiece, a blunt cannula on a syringe, or a phacoemulsification handpiece may be used depending on the nature of the cataract, although because of the soft nature of the cataract ultrasound is rarely needed.26 Having a variety of techniques available allows for the creative response to the multitude of intraoperative conditions in pediatric patients.

Vitrectomy instruments may be optimal in cases where the cataract is associated with fibrotic membranes for which a cutting tool is needed in addition to aspiration. At times an microvitreoretinal (MVR) blade is necessary to dissect dense fibrotic membranes into ribbons small enough to be engaged by the vitrector mouthpiece. In addition, some pediatric cataracts may have an attenuated or absent posterior capsule. In these cases, having immediate vitrectomy capabilities available may aid in the controlled removal of lens material associated with vitreous prolapse through the posterior capsule opening without its loss into the vitreous. Use of the I/A handpiece or blunt cannula on a syringe may be optimal in cases where small and angled ports are necessary to remove cortex. Use of the phacoemulsification handpiece may be helpful in cases where the lens has hard, calcified portions or subcapsular plaques.27

Management of the Posterior Capsule

Postoperative opacification of the posterior capsule is common in children. It is the most important complication of pediatric cataracts because even a technically successful surgery may eventually be functionally unsuccessful if the visual axis does not remain clear for long-term amblyopia therapy. Many authors advocate a planned primary posterior capsular opening at the time of initial cataract surgery for all children under 6 years of age.28,29 Vitrectomy instrumentation has been used for this purpose; however, with recent advances in viscoelastics, PCCC has been described.30

Figure 3-9. Creation of the posterior capsular opening. (Reprinted with permission from J Cataract Refract Surg, 20, Gimbel HV, DeBroff BM, Posterior capsulorrhexis with optic capture: maintaining a clear visual axis after pediatric cataract surgery, 659, Copyright [1994], with permission from The American Society of Cataract and Refractive Surgery and the European Society of Cataract and Refractive Surgery.)

VITRECTOMY POSTERIOR CAPSULOTOMY

The posterior capsule may be removed from an anterior or posterior approach. For the anterior approach: After removal of the lens material, the ocutome is once again placed port side downward over the posterior capsule. The aspiration function is activated and the posterior capsule engaged. The cutting function is then activated and the posterior capsule penetrated. A thorough anterior vitrectomy is then performed through the posterior capsular opening to remove the vitreous face, and any scaffolding for fibrosis. The posterior capsule may be removed by a pars plana approach as well.

POSTERIOR CONTINUOUS CURVILINEAR

CAPSULORRHEXIS

PCCC provides the advantage of a smooth edge and controlled posterior capsular opening.31 The integrity of this smooth capsular opening makes posterior optic capture of the IOL possible.30,32,33 The advent of high-viscosity viscoelastic agents such as Healon GV or Healon 5 has made PCCC more technically facile in children by decreasing posterior vitreous pressure.

After removal of the lens material, high-viscosity viscoelastic such as Healon GV or Healon 5 is instilled both in front of and into the capsular bag. A cystotome or barbed, disposable 27-gauge needle is used to create an opening in the posterior capsule (Figure 3-9).

Healon GV or Healon 5 on a blunt 30-gauge cannula is then instilled behind the posterior capsule to create a plane between the posterior capsule and the vitreous face (Figure 3-10).

Failure to thus separate the posterior capsule and the vitreous face may result in rupture of the vitreous face and the uncontrolled extrusion of vitreous forward.

The needle is then used to hook, lift, and tear the capsule to create a triangular opening and capsular flap (Figure 3-11).