Ординатура / Офтальмология / Английские материалы / Mastering theTechniques of Lens Based Refractive Surgery (Phakic IOLs)_Garg, Alio, Dementiev_2005

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44.M Alberti. PRK and Lasik Versus Intraocular Contact Lenses for High Myopia Correction. ASCRS annual meeting 199t,april. Boston,USA.

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Lens in Phakic, highly myopic eyes. AAO annual meeting 1998 New Orleans, USA.

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Matteo Piovella

Faberizio I Camesasca

Barbara Kusa

(Italy)

INTRODUCTION

Currently, phakic IOLs represent an interesting solution for high-myopia patients. Several new models of improved anterior and posterior chamber IOLs are available. Refractive surgeons, initially using phakic IOLs as a possible solution for myopia of 10.00 D and higher, are now beginning to consider them as an alternative to LASIK and LASEK even for lower degree of myopia.1-5

However, long-term occurrence of complication remains worrisome. Due to previous experience with early models in the early 1990s, widespread approval of phakic IOLs safety is still limited. Furthermore, maybe unconsciously, the cataract surgeon relates the anterior chamber IOL to a stressful situation in which, due to complications with the capsule, an IOL cannot be implanted in the bag. The anterior chamber IOL, soon proved to be a worst anatomical and technical solution than the posterior chamber IOL, and did not undergo the same technical evolution.

CLINICAL EXPERIENCE WITH VIVARTE

Our experience on anterior chamber phakic IOLs is based on a two-year follow-up study on VivarteTM, a recently introduced foldable phakic IOL. VivarteTM features onepiece foldable hydrophilic acrylic optic, semi-flexible, rigid PMMA haptics with smooth, soft hydrophilic acrylic feet (Fig. 9.1). We implanted VivarteTM in 33 eyes of 20 patients. Demographic and preoperative data are reported in Table 9.1. Table 9.2 list patient selection criteria. Preoperatively, all patients underwent complete ophthalmological examination, including careful peripheral fundus examination, endothelial cell counts

Figure 9.1: VivarteTM IOL.

Table 9.1: Demographic and preoperative data

Legenda. SE : spherical equivalent; SD: standard deviation

Table 9.2: Patient selection criteria

•Age: younger than 50 y.o.

•Good general health

•Minimal anterior chamber depth 3.2 mm

•Endothelial cell counts greater than 2500/mm2

•Open anterior chamber angle

•No cataract

•No angle hyperpigmentation

•No vessels in the angle

•No eccentrical pupil

Table 9.3: Intraoperative data

of 13.2 ± 3.0 mmHg. Initial eye size selection was performed with corneal white-to-white (acceptable range: 10.5–12.0 mm), and limbus white-to-white (acceptable range: 11.00 – 12.50 mm) measurements. White- to-white distance was measured preoperatively with IOLMaster (Carl Zeiss Meditech AG, Jena, Germany) and intraoperatively with a surgical sizer.

Informed consent was obtained from all patients. Intraoperative data is reported in Table 9.3. Myosis was induced with 2 percent pilocarpine eyedrops, and after topical anesthesia with 2 percent lidocaine eyedrops, a 2.5 mm corneal incision was performed, superiorly in 8 eyes (Fig. 9.2), and temporally in 26 (Figs 9.3A and B) eyes. Healon GV (Pharmacia & Upjohn, Uppsala, Sweden) was injected. Intraoperative measurement of anterior chamber width was performed with surgical sizer. Acceptable width for implantation ranged from 11.5 to 13.00 mm. Incision size was then enlarged to 3.75 mm, and a folded Vivarteâ IOL was implanted. Three models of IOL width were available at the time of surgery (120/125/130), fitting three different ranges of anterior chamber width. Viscoelastic was removed by

B

Figures 9.3A and B: Bilateral IOL implantation through temporal incision, right (A) and left eye (B). Note that the optichaptic junction is superior in the right eye, inferior in the left eye

irrigation/aspiration. No iridectomy was performed, and vancomycin (0.1 ml at 100 mg/ml) was injected in the anterior chamber. Postoperative therapy consisted of tobramycin-desamethazone association eyedrops, TRID for two weeks.

All patients were evaluated at days 1, 7, 30, 90, 180, 360 and 720 with complete ophthalmological examination, endothelial cell counts and aberrometric evaluation. Statistical evaluation was performed with Student’s t test for independent samples.

Mean follow-up period was of 731 ± 49 days. Final UCVA was 0.6 ± 0.3, BSCVA 0.9 ± 0.2 with –0.9

± 0.8 D SE. BSCVA increased significantly (p =.003). Figure 9.4 presents the percentage of lines of visual acuity

gained at 720 day postoperatively. No eye lost any line of best spectacle-corrected visual acuity. Safety index was 1.26. Intraocular pressure was unchanged, with a mean postoperative value of 13.4 ± 2.9 (n.s.).

Endothelial cell counts during all follow up are shown in Table 9.4. Intraand postoperative complications are reported in Table 9.5. ECC showed a 6.86 percent reduction at two years as compared with respect to preoperative values. Pupil ovalization, considered even when small in amount, was observed in 7 eyes (20.5%) at a mean postoperative time of 127 ± 106 days. Figure 9.5 shows one of these cases, with progressive reduction in pupil ovalization with time. Ovalized pupils showed a mean horizontal diameter of 6.6 ± 1.6 mm, and a mean vertical diameter of 4.4 ± 1.4 mm. To decrease ovalization in one case the IOL was rotated of 15° at nine months postoperatively. Figure 9.6 shows an iris fluorescein angiogram of this case before IOL rotation, with no sign of blood-iris barrier breakdown.

Table 9.4: Endothelial cell counts (cells/mm2)

Table 9.5: Intraand postoperative complications

•Intraoperative IOL exchange: n=2 (5.8 %)

•Difficult IOL insertion: n=1 (2.9%)

•Decentered IOL: n=1 (2.9%)

•Anterior capsule scratch n=1 (2.9%)

•Corneal edema:

•Day 1: n=1 (2.9%)

•Day 7: n=1 (2.9%)

•Pupil ovalization

•n=7 (20,5%)

•Severe ECC reduction: n=2 (5.8 %)

In one patient, that had received a bilateral implant, we noticed 1+ Tyndall and a sudden ECC reduction at eight months in both eyes, resistant to therapy. We decided to remove the IOLs, respectively, 14 and 19 months postoperatively, after which the ECC became stable in both eyes (Fig. 9.7).

Decentration was almost invariably related to insufficient lens size (Fig. 9.8).

1 month PO

Figure 9.6: Iris fluorescein angiography of a case with ovalized pupil, late phases. Note absence of blood-iris barrier breakdown

Patient satisfaction was evaluated at 720 days with a written questionnaire, and all patients were satisfied with the results of surgery. In particular, the twenty-

6 months PO

eight patients actively driving a car reported an better night vision than with respect to spectacles or contact lenses.

Table 9.6 reports aberrometric data. The two most visually impairing aberrations, coma and spherical aberration RMS were significantly decreased, while high order RMS values were unchanged.

WHY A FOLDABLE ANTERIOR CHAMBER

PHAKIC IOL ?

Presently, which are the criteria for phakic IOL selection? An anterior chamber IOL will definitively not induce cataract, differently from PC IOLs. The most troublesome aspect with an anterior chamber IOL is proper sizing,

hopefully improving in the future thanks to newly available devices. Recently, advances in surgical techniques, as well as technologic development in IOL design and production, have brought back to the ophthalmic scene the use of phakic IOLs for the correction of ocular refractive errors. Phakic IOLs offer several well-defined advantage over corneal refactive surgery.3 The amount of correctable myopia is well beyond those achievable with LASIK of LASEK. No longterm corneal curvature change is induced, and thus there is no increase in optical aberrations. The procedure is reversible.

The VivarteTM phakic IOL is an evolution of Baikoff’s anterior chamber IOLs, based on the Kelman’s Multiflex anterior chamber aphakic IOL, featuring several technical improvements aimed at reducing endothelial cell decrease and angle damage. An exciting feature of VivarteTM is its flexibility, allowing easy insertion through a 3.5 mm incision.

PATIENT AND EYE SELECTION

Careful preoperative patient evaluation remains mandatory, and eyes with less-than-optimal features must be considered with great attention before proceeding to anterior chamber phakic IOL implantation. Selection criteria are now much tighter than two years ago. Anterior chamber width and depth, as well as endothelial cell counts, are delicate parameters that must be evaluated both with slit-lamp examination and with sophisticated instruments. The main goal in implanting an anterior chamber phakic IOL is to determine the proper IOL size. Presently, there is no univocal method for the determination of anterior chamber diameter and width, and the existing ones have precision limits. The white-to-white method requires high precision and can not be performed at the slit-lamp. The amount of error may reach 1 mm, even using the IOLMaster. Finally, the relationship between white-to-white and anterior chamber diameter may not be reliable. Presently, intraoperative measurement with the caliper is the most reliable method for anterior chamber width determination. In the future, promising results may come

from the application to the anterior segment of instruments like the OCT. When in doubt, always insert the smaller IOL model, i.e. with an anterior chamber width measurement of 12.75, implant a 12.50 model. An excessively large IOL will induce pupil ovalization, while an inappropriately small IOL will simply rotate (Figs 9.8 and 9.9).

An interesting point of view takes into account the constant ocular dynamics related to accommodation, that may alter anterior chamber depth thus reducing the distance between the anterior chamber phakic IOL and the endothelium. Anterior chamber depth measurement with ultrasound may be imprecise if you push on the cornea with the probe, while determination with the IOLMaster device may be influenced by inaccurate focusing. Thus, if 3.2 mm is the minimal anterior chamber depth recommended for a –7.00 D to –13.00 D Vivarte implantation, the surgeon should be happy to find and anterior chamber depth of 3.3 or more.

COMMENTS ON SURGICAL TECHNIQUE

The logical approach to a successful phakic IOL surgery has as a main target an appropriate IOL sizing. We recommend to start with defining and marking the corneal apex. Initially, a superior approach was suggested for the Vivarte™, but we presently are pleased with a temporal approach, thus exploiting the widest corneal diameter. The whole surgery can be performed under topical anesthesia, avoiding the risks related to needle anesthesia. Initial incision can be performed with a 2.5 mm scalpel, to be widened up to 3.5 for IOL insertion.

Surgery is being performed under topical anesthesia, thus keeping the anterior chamber expanded is essential, and a heavily cohesive viscoelastic such as Healon GV is mandatory. At this point the anterior chamber sizer is introduced for final control, and the previously defined center of cornea provides confirmation of adequate anterior chamber width determination. The incision is now widened up to 3.5 mm.

We do not perform and iridectomy, because the junction between the optical portion and the haptics of

Figure 9.9: A case with normal, round pupil and haptics correctly placed in the angle

the Vivarte™ IOL is shaped so as to perform a valvelike motion in the case of pupillary block. The IOL is folded and inserted, the two-feet haptic first, with extreme care to prevent engagement of the pupillary rim. Once the optic is in the center of the anterior chamber the holding forceps can be released, for a controlled unfolding. Using a hook and extreme care, the two-feet haptic is then positioned, with the feet in the angle, inserting more viscoelastic if necessary. Now the singlefoot haptic can be inserted, guided with the hook, with a forward push and then a delicate down motion to position the foot in the angle under the corneal tunnel. At this point, the three feet are carefully checked with the hook, looking for iris chafe. A dentist mirror can be useful for this purpose.

Cohesive viscoelastic is carefully removed with I/A, after having checked setting and that the tubing is filled with BSS and no air bubble is present. The BSS bottle is kept low, to provide a low flux. Anterior chamber expansion due to a high-volume flux would induce pain. A well-built tunnel will require no suture.

COMPLICATIONS

Long-term complications of anterior and posterior chamber IOLs for the correction of high myopia are a well-known problem. Brauweiler et al, after discouraging the use of “Fyodorov” 094M-1 silicone posterior chamber IOLs because of high incidence of cataract formation, recommended evaluation of long-term results of a relatively large number of patients to ascertain the feasibility of this surgical approach.6 In the early 1990s, the available types of anterior and posterior chamber IOLs showed several complications, among which endothelial cell reduction, pupil ovalization and retinal detachment.7-9 More recently, pupillary block, intraocular pressure increase, and endophthalmitis and have been reported.3,10,11

The potential for damage to the anterior segment structures, especially the corneal endothelium, is one of the main problems with anterior chamber IOLs, specifically with angle-supported ones.2

IOL positioning with respect to iris and corneal endothelium is important. Endothelial touch will lead

to endothelial cell loss. If the haptic foot is not positioned in the angle, but in the cornea or is inserted in the iris, it will cause iritis, with fibrosis involving iris and haptic. An interesting feature of the materials used for the VivarteTM is haptic flexibility as well as the soft acrylic material covering of the haptic feet, designed to reduce angle damage as well as the risk of incarceration or feet protrusion in the angle. One of the two loops features a double feet, the other, the last one to be inserted in the anterior chamber, a single foot. This technical solution is aimed at solving problems observed with IOLs like the ORC, whose haptic progressively eroded the anterior chamber angle. Pertaining fibrotic reaction with incarceration of the IOL feet, in the two cases that we explanted due to progressively reducing EC counts, we never found, more than one year after surgery, fibrotic reaction incarcerating the Vivarte’s feet.

Comparing reported frequencies of pupil ovalization is difficult, because of the lack of uniformity in the threshold for defining a pupil oval. All our ovalizations were along the axis of the single-foot haptic, and in no case the ovalization reached the optic margins. Reported percentages range from 6.08 percent for ovalization reaching the optic edge, to 46.1 percent, when even slight pupil alteration is considered.3, 4 We may thus consider our 20.5 percent, that includes any amount of pupil deformation, within acceptable limits.

In the case in which we rotated of 15° the IOL nine months postoperatively, Vivarte™ showed no angular or iris sinechiae and could rotate freely with minimal trauma to the ocular structures. We performed iris fluorescein angiogram before IOL rotation, and no breakdown of the blood-iris barrier was observed (Fig. 9.6).

In our results, endothelial cell loss at one year was comparable or slightly higher than that reported in the literature, however always not statistically significant when compared to preoperative situation.3, 4 In one patient of our study, endothelial cell counts decreased bilaterally suddenly eight months after IOL implantation, together with indolent uveitis, resistant to therapy at eight months after surgery, requiring eventually requiring IOL removal in both eyes. Therefore, we recommend mandatory sixmonth endothelial cell counts postoperatively.

We did not observe cataract development, a major cause of explantation for IOL in the long-term study by Alio et al, or retinal detachment.3, 5, 7 Patient satisfaction at one year was encouraging, with particular improvement of the night-driving conditions. Aberrometric examination did not show increase of one of the most sight-threatening aberrations, spherical aberration, suggesting a scarce modification in total ocular aberrations induced by this procedure. The only aberration that showed a 50 percent increase was coma.

We caution against the possibility of anterior chamber size alteration during accommodation, vigorous eye rubbing, or peculiar sleep positions. Finally, we recommend to perform all relevant ocular measurement preoperatively, i.e. corneal pachimetry, biometry, IOLMaster. This because Vivarte™ may hamper precise biometric measurements for posterior chamber IOL determination when AC phakic IOL removal, with subsequent cataract removal and PC IOL implantation are planned.

CONCLUSIONS

With the information we have available at this point of follow-up, we recommend anterior chamber phakic IOL implantation only after careful patient selection, including accurate peripheral retinal evaluation, as well as endothelial cell counts, anterior chamber and angle examination. Presently, regular ocular examinations, including endothelial cell counts every six months postoperatively appear mandatory.

Two years postoperatively, VivarteTM phakic IOL provided safe and satisfactory correction for highly myopic eyes. All complications could be successfully managed. We are continuing accurate follow up of these patients, to detect possible future complications.

REFERENCES

1.US. Food and drug administration clinical trial of the implantable contact lens for moderate to high myopia. The implantable contact lens in treatment of myopia (ITM) study group. Ophthalmology 2003; 110:255-66.

2.Munoz G, Alio JL, Montes-Mico R, Belda JI Anglesupported phakic intraocular lenses followed by laserassisted in situ keratomileusis for the correction of high myopia. Am J Ophthalmol 2003;136:490-9.