Ординатура / Офтальмология / Английские материалы / Phakic Intraocular Lenses_Hardten, Lindstrom, Davis_2004

Figure 8-5. Preoperative keratoconus is a contraindication for LASIK.

6 months, is a contraindication for any refractive procedure. A preoperative scotopic pupil size greater than 7.0 mm can increase the risk of postoperative night halos after both phakic IOLs and LASIK and may require operative adjustments to avoid this complication. Any active corneal or ocular disease should be treated and stabilized prior to refractive surgery. If a preoperative opacity is noted in the crystalline lens, refractive lensectomy/cataract surgery may be the preferred procedure. Patients that have a BCVA of 20/40 or less in one eye should be considered carefully. A reduction in BCVA to less than 20/40 in their previously “good” eyes could result in the loss of an unrestricted driver’s license.

LASIK is contraindicated for patients with corneal pathology such as forme fruste keratoconus (Figure 8-5), as it can exacerbate corneal ectasia. If the amount of corneal thickness is inadequate and the complete LASIK correction can’t be performed, phakic IOLs are often a better option. LASIK requires a healthy corneal epithelium to avoid postoperative epithelial defects with prolonged visual recovery, postoperative pain, interface keratitis, and epithelial ingrowth.

Phakic IOLs are contraindicated in patients with a shallow anterior chamber (depth less than 2.8 mm) as the insertion and manipulation of the phakic IOL becomes extremely difficult. Phakic IOL implantation has been associated with an endothelial cell loss of 5% to 10%14 (Figure 8-6); therefore, any signs of corneal endothelial weakness, such as guttata or a reduction in the endothelial cell count less than 2000 cells/mm, should be approached with caution. A past ocular history of anterior uveitis is a relative contraindication for phakic IOLs, as any anterior segment manipulation could cause reactivation of the inflammation. Presbyopic patients may be better candidates for refractive lensectomy, as this can restore reading ability if a multifocal lens is used, provide early correction of a cataract, and achieve excellent visual outcomes.

Figure 8-6. Iris-claw phakic IOLs have been associated with a progressive loss of endothelial cells (adapted from Menezo JL, Cisneros AL, Rodriguez-Salvador V. Endothelial study of iris-claw phakic lens: four year follow-up. J Cataract Refract Surg. 1998;24(8):1039-1049).

PREOPERATIVE ASSESSMENT

Both phakic IOLs and LASIK involve a detailed preoperative assessment. The past ocular history should ideally be unremarkable. The ocular exam should indicate healthy eyes without evidence of cataracts. Cycloplegic and several noncycloplegic refractions are performed to evaluate the stability of the refractive error and the contribution of accommodation. Only patients who have stable prescriptions are candidates for a refractive procedure as performed by either method. For both phakic IOLs and LASIK, topography is required to identify irregular astigmatism and forme fruste keratoconus. For LASIK, these conditions are a contraindication for surgery. These conditions do not preclude phakic IOL surgery but do preclude LASIK as an enhancement procedure following phakic IOL insertion. Pupil testing is performed in dim light with an infrared pupillometer. Pupils 8 mm or greater in diameter could be associated with postoperative glare with either procedure.

LASIK outcomes can be affected by certain pre-existing ocular conditions that should be sought preoperatively. Anterior basement membrane dystrophy should be identified. The presence of dry eyes should be determined by preoperative questioning and Schirmer testing. Patients with dry eyes preoperatively can be expected to have exacerbation of their symptoms after LASIK and may benefit from the preoperative placement of punctal plugs. Corneal thickness measurements should be obtained by Orbscan or ultrasonic pachymetry to determine the limitations of the excimer ablation. The Orbscan is also helpful in identifying preoperative posterior corneal ectasia, which has been suspected as a precursor of keratoconus (Figure 8-7).15

Figure 8-7. Preoperative posterior corneal ectasia, as demonstrated by greater than 50 m of elevation on the posterior float map, is a contraindication for LASIK.

With phakic IOLs, the healing of the cornea after the procedure is limited, therefore the risks are different. However, most of the same tests listed above for LASIK are performed in phakic IOL candidates, as it is usually unclear during the initial preoperative assessment which procedure will be recommended. Patients with corneal guttata or suspicious endothelial pathology may not be good candidates for phakic IOLs due to potential endothelial cell loss. Patients with less than a 2.8-mm anterior chamber depth do not have adequate room to allow the phakic IOL to be inserted atraumatically. Finally, phakic IOLs sit close to the crystalline lens and, therefore, the lens should carefully be evaluated for a cataract. If there is a cataract present preoperatively, a refractive lensectomy is preferable because a phakic IOL may induce further cataract changes. Phakic IOL patients are often high myopes and, therefore, need to have a careful peripheral retinal evaluation to ensure that no holes or other retinal pathology are present that could result in postoperative retinal detachment.16

PREOPERATIVE CONSENT

The preoperative consent form is essential in any refractive procedure. This should ideally be given to the patient prior to the procedure so that he or she has time to review it. The consent form for refractive procedures should include the risks of the procedure and the options for surgery. Patients should understand that they might not achieve a perfect outcome.

The key differences between the consent forms for phakic IOLs and LASIK relate to the nature of the procedures. LASIK is generally performed as a simultaneous bilateral procedure and, hence, the consent should address the

Figure 8-8. Retroillumination demonstrates two superior iridotomies performed prior to the ICL implantation.

potential risk of bilateral surgery versus unilateral surgery. Most complications of LASIK result from the creation of the corneal flap or the excimer laser ablation of the cornea.

Phakic IOLs are implanted as a unilateral procedure due to the rare risk of endophthalmitis and the precedent set by cataract surgery. Consent forms need to be signed before each procedure. The patient should be made aware of the risk and symptoms of endophthalmitis so that they can seek prompt medical attention, if necessary. Furthermore, phakic IOL patients should understand that they will often have residual sphere and cylinder after the phakic IOL procedure and, therefore, may require a LASIK enhancement in order to achieve the best outcome. In the United States, the consent form should indicate that phakic IOLs are considered investigational, as none of the phakic IOLs have currently been approved by the FDA. The ICL requires two peripheral iridotomies to be performed prior to the ICL implantation, so an additional consent is required to describe the risks of this procedure (Figure 8-8).

PREOPERATIVE PREPARATION

The preparation of patients for LASIK differs from the preparation of patients for phakic IOLs. LASIK patients need to have careful protection of their corneal epithelium to ensure that they do not develop epithelial defects. LASIK patients should receive a minimal number of preoperative drops in order to reduce the risk of toxic keratopathy and epithelial defects. If patients do require dilation for LASIK on the LADARVision laser (Alcon Surgical, Fort Worth, Tex), it should be done with sponges that are soaked in the mydriatic drops and then placed under the lower lid to avoid corneal toxicity.

With phakic IOLs, dilation is required if a posterior chamber IOL, such as the ICL, is being used. For the irisclaw or the anterior chamber phakic IOL, pupillary constriction may be used. In either case, corneal toxicity is not a major concern. If topical anesthesia is used, it should be generously applied preoperatively in order to ensure there is good penetration of the cornea so that the corneal incision and the iris manipulation are pain free.

72 Chapter 8

Figure 8-9. Insertion of the ICL is done through a self-sealing 3-mm clear corneal incision.

SURGICAL TECHNIQUES

The surgical technique for LASIK involves topical anesthesia, the keratectomy, and the excimer laser ablation. It can be performed on both eyes in approximately 10 minutes. LASIK can be performed as a simultaneous bilateral procedure, as it is extraocular with a low risk of endophthalmitis. All other LASIK complications are not considered interdependent events between eyes except corneal infection, which has been reported bilaterally.17 LASIK is not generally performed as a true sterile procedure. The microkeratome and instruments are autoclaved for each procedure and sterile disposable instruments are used. However, strict sterile technique with a sterile operating room is rarely used.

Phakic IOL implantation involves the creation of a small peripheral corneal incision under anesthesia, implantation of the phakic IOL with viscoelastic control, positioning the phakic IOL, removal of the viscoelastic, and possible suturing of the incision (Figure 8-9). The procedure is more technically challenging when compared to LASIK because bimanual manipulation is required in the anterior chamber. Phakic IOLs are performed unilaterally with a sterile technique due to the increased risk of endophthalmitis.

POSTOPERATIVE COURSE

LASIK patients often have slightly blurred vision immediately postoperatively but can see well 4 to 5 hours after the procedure. A mild dry eye sensation is experienced for a few hours after LASIK, followed by a rapid resolution. The following day, LASIK patients usually have excellent vision. However, over the next several months, there may be some regression of effect and LASIK patients may require an enhancement procedure. Visual quality usually improves over the first several weeks. LASIK patients experience a neurotrophic cornea after LASIK due to the severed corneal nerves from the flap creation.18 This creates a temporary dry eye that generally resolves within a few weeks but can

last several months. LASIK patients are given a topical steroid and antibiotic to use postoperatively for several days. They are also given ocular lubricants to use for the first postoperative month as the neurotrophic cornea recovers.

Phakic IOL patients have rapid improvement of their vision after IOL implantation. A mild foreign body sensation may be experienced after the anesthetic wears off and the corneal incision heals. There is no regression of effect as there is no corneal healing required. Phakic IOL patients may still require an enhancement procedure because of residual spherical or cylindrical error from the original phakic IOL implantation. There are few associated neurotrophic changes after phakic IOL implantation. It is important to check the intraocular pressure after phakic IOL implantation, as retained viscoelastic can cause an increase in intraocular pressure immediately after the procedure. The pressure after phakic IOL implantation should be checked at 1 hour, 4 hours, and 1 day postoperatively. Phakic IOL patients use topical steroid and antibiotic drops on a tapering schedule for 4 weeks. Topical lubrication is generally not mandatory.

ENHANCEMENT PROCEDURES

Enhancement procedures are often required for both LASIK and phakic IOL procedures. For LASIK, there is variable healing of the cornea, which can require an enhancement to be performed. Enhancements occur at a rate of approximately 1% per D of correction, with the rate varying between 5% to 20% between surgeons and lasers. The timing of the LASIK enhancement depends on the amount of the original LASIK correction. Generally, enhancements should be delayed 1 month for each spherical equivalent of correction, although most enhancements are practically performed between 3 and 6 months.

Enhancements are also required for phakic IOLs. Phakic IOLs are excellent at correcting spherical refractive error; however, they are generally only accurate within 1 D. This means that patients will often have some residual spherical correction. Patients may also have residual astigmatism that was not corrected by the phakic IOL unless a toric phakic IOL was used. In more than 250 ICLs procedures that the author has performed, approximately 50% of them had returned for LASIK in order to achieve the best uncorrected vision (Figure 8-10). All of the LASIK enhancements have been performed without complications from the previous corneal incision or from movement of the ICL. These enhancements have been performed as soon as 1 month after the ICL implantation.

RESULTS AND QUALITY OF VISION

The quality of the vision after refractive surgery can be evaluated in several ways. The percentage of eyes achieving 20/20 or 20/40 vision and those that fall between

Figure 8-10. The two corneal incisions of a bioptics procedure. The most peripheral straight vertical incision is used for the ICL insertion. The rounder central incision, the LASIK flap.

0.50 and 1.00 D of emmetropia are the standard measures of success. The percentage of lost BCVA is also a measure of the safety of the procedure. The safety index is the ratio of the postoperative BCVA to the preoperative BCVA. The stability of the refractive change is a measure of the long-term outcome of the refractive result. Recently, wavefront testing has allowed the quality of vision to be evaluated objectively.

Most of the reports of refractive procedures focus on one procedure and one technique. Reports of LASIK for low myopia19 and high myopia,20 NuVita phakic IOL,21 Artisan phakic IOL,22 and the ICL23 are compared in Table 8-2. It should be noted that the phakic IOLs were all performed in high myopes in these studies. Because phakic IOLs do not involve corneal healing postoperatively, the results for phakic IOLs for the correction of low myopia could be expected to be similar except that they do not correct corneal astigmatism. Studies of the results of bioptics with the ICL24 and the Artisan25 demonstrate the results of treating all residual astigmatism and sphere with LASIK. It should be noted that the UCVA results are dramatically better for low myopia treated with LASIK. However, the predictability of the different refractive procedures is similar, particularly when LASIK is performed as an enhancement procedure. Few of the procedures had a loss of two or more lines of BCVA and all showed a large percentage of gain of BCVA, particularly when a LASIK enhancement procedure after phakic IOL implantation was performed.

Recently, studies have compared the results of phakic IOLs and LASIK for the treatment of high myopia. The results of the Artisan were compared with the results of LASIK for treatment of high myopia in 25 patients.26 At the 1-year follow-up, 24% of LASIK and 20% of Artisan eyes achieved at least 20/25 UCVA. The predictability was with 1.00 D in 64% of the LASIK eyes and 60% of the Artisan eyes. The safety index for LASIK was 0.99 and 1.12 for the Artisan. There was no significant difference between the groups in the amount of anterior chamber flare, endothelial cell loss, and contrast sensitivity at 1 year. The subjective visual acuity was better in the Artisan group. In another comparison study of 90 eyes with high myopia27 treated with these two modalities at 1 year, the UCVA of 20/20 and 20/40 was 20.9 and 88.4%,

and 12.2 and 58.5% in the LASIK and the Artisan group, respectively. No Artisan eyes and 12.2% of LASIK eyes lost two or more lines of BCVA. More patients in the LASIK group complained of glare. The quality of the vision after Artisan implantation was preferred in 72.2% of patients.

Vukich has recently compared data of 559 LASIK eyes with 210 ICL eyes for the treatment of myopia of 8 to 12 D.28 At 1 year, 20/20 UCVA and 20/20 BCVA were achieved by 36% and 82% of LASIK vs 52% and 90% of the ICL eyes, respectively. Predictability was within 0.50 D at 1 year in 57% of LASIK eyes and 69% of ICL eyes. The LASIK eyes showed an average regression from -0.06 D at 1 week to -0.51 D at 1 year, while the ICL group had no regression (Figure 8-11). At 1 year, the loss and gain of one line of BCVA was 11% and 29% for the LASIK group and 6% and 49% for the ICL group (Figure 8-12). Wavefront testing of 10 eyes in each group at least 6 month postoperatively found coma of 0.46 and 0.22 m and spherical aberration of 0.39 and 0.13 m for LASIK and ICL, respectively.

COMPLICATIONS

Phakic IOLs and LASIK share some of the same risks. Both procedures can result in postoperative glare if the scotopic pupil size is larger than the optical zone of the laser treatment or the phakic IOL optic.29 Infection can rarely occur with both procedures. BCVA can be lost and enhancement procedures are often required for both procedures.

The complication rate with LASIK is low for major complications. Perforation of the cornea is the most serious LASIK complication but it has rarely been reported. Other serious LASIK complications are flap related. A recent retrospective study evaluated the intraoperative flap complications in 84,771 cases of LASIK with the ACS or the Hansatome.30 The rate of all flap complications was 0.302%, partial flaps 0.099%, buttonholes 0.07% (Figure 8-13), thin or irregular flaps 0.087%, and free flaps 0.012%. The incidence of postoperative flap displacement should be less than 1/1000, although an incidence of over 1% has been reported.31 A recent review of the world literature found that 41 LASIK infections have been reported to date.32 In a study of 2873 eyes, 19 eyes (0.66%) developed post-LASIK kerectasia.33

Minor LASIK complications occur with greater frequency. A recent study evaluating the risk factors for intraoperative epithelial defects during LASIK found an incidence of 9.7% in 247 eyes.34 Diffuse lamellar keratitis is estimated to occur in 1:200 to 1:500 cases but may occur in sequential patients (outbreaks) at a specific location (Figure 8-14). In a study of 3786 eyes, significant epithelial ingrowth occurred in 0.9% of primary LASIK cases and 1.7% of enhancement cases (Figure 8-15).35 A study of

Table 8-2

IOLS

PHAKIC

LASIKAND

OFESULTS R

77 56 83 14 1.3

22

8.57

4.5

84

20 alet

myopiaLASIK—high Zaldivar

47.8 40 65.5 36.2 11.1

NR

12.5

24

68

21 alet

Baïkoff

NuVita IOL

12.1 40.9 56.7 67.2 NR 0

14.7

35

67

22 alet

Landesz

Artisan IOL

68 44 69 36 0.8

2

13.4

11

124

23 alet

Zaldivar

ICL

Figure 8-11. Stability of the refractive result after LASIK and the ICL. The regression of the average refractive error after LASIK contrasts with the stable result of the average ICL error (courtesy of John Vukich).

Figure 8-13. Central button-hole with a “skip” pattern over the central cornea.

Figure 8-12. Changes in the BCVA after LASIK and phakic IOLs. Phakic IOLs demonstrate a greater improvement in BCVA and less of a loss of BCVA (courtesy of John Vukich).

Figure 8-14. Central intracorneal striae and haze associated with grade 4 diffuse lamellar keratitis.

Figure 8-16. Central corneal island with dramatic central steepening on topography. This is generally associated with residual myopia, diplopia, and a loss of BCVA.

Figure 8-15. Grade two epithelial ingrowth after LASIK extending 2 mm from the flap edge.

236 LASIK eyes treated for mild to moderate myopia found that while mild to moderate glare was reported by 10% of patients at the 6 month follow-up, there was no

significant increase in marked or severe glare or halos.36 The incidence of decentrations of 0.5 mm or more has been found to occur in 20.8% of eyes after PRK.37 Dry eye symptoms are increased in all patients after LASIK but become problematic in only a small number of patients. LASIK flap striae occur in approximately 1/300 cases. Central islands after LASIK38 are less common with the advent of scanning excimer lasers (Figure 8-16).

Figure 8-17. Anterior subcapsular cataract 1 year after ICL implantation demonstrated by retroillumination through a dilated pupil.

Complications for phakic IOLs depend on the type of lens implanted (Table 8-3) and have been reported at a greater frequency than the major LASIK complications. The NuVita anterior chamber phakic IOLs were found at a 2-year follow-up of 21 eyes to be associated with pupil ovalization (40%), endothelial cell loss (15.2%), moderate glare (20%), IOL rotation more than 15 degrees (14.2%),

and chronic flare and ocular hypertension (4.8%).39 The Artisan iris-claw IOL is associated with endothelial decompensation (10.9% at 3 years),40 and rarely inflammation,41 dislocation,42 and cataracts.43 The ICL has been associated with anterior subcapsular cataracts (2.9% to 12.6%) (Figures 8-17 and 8-18),44 endothelial cell loss (12.3% at 4 years),45 peripheral anterior synechiae (Figure 8-19),46 angle closure glaucoma (Figure 8-20),47 elevated IOP at 3 months,48 pigment dispersion,49 and retinal detachment.50

FUTURE DEVELOPMENTS

Customized wavefront LASIK is a rapidly evolving field that allows the excimer laser ablation pattern to be tailored to the wavefront error of each eye (Figure 8-21). Custom LASIK has been found to have even better outcomes of UCVA, BCVA, and reduction in the wavefront error. This promises to be an exciting and evolving extension of LASIK over the next 10 years.

While phakic IOLs are growing in popularity, they continue to be used mainly for the high myopic and hyperopic corrections in patients who are not LASIK candidates or have presbyopia. The recent introduction of

Figure 8-18. Anterior subcapsular cataract 1 year after ICL implantation on direct illumination through an undilated pupil.

Figure 8-20. Pupillary block glaucoma 1 year after ICL insertion. Note the dilated pupil and transillumination of the iris, indicating areas of early atrophy.

toric phakic IOLs should expand the range of correction for phakic IOLs and reduce the enhancement rate. While two of the phakic IOLs are now foldable, smaller sutureless incisions will be possible once this is possible with the other phakic IOLs. Refinement of the phakic IOL procedures and the implantation techniques will further improve the results. Phakic IOLs may soon be designed to incorporate wavefront correction as well. All of these improvements may extend the range of correction of phakic IOLs to lower levels of myopia and hyperopia in the future.

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