Ординатура / Офтальмология / Английские материалы / Refractive Lens Surgery_Fine, Packer, Hoffman_2005

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There was a general tendency for the near performance of these patients to improve with time throughout the first year of clinical study. The reasons for this phenomenon are unknown. It is possible that the ciliary muscle slowly begins to function again after years of disuse. Another possible explanation is that a stiffer posterior capsule more effectively transfers force from the vitreous, allowing more movement of the optic.

Fig. 10.4. Spectacle use survey of FDA trial participants showed that 74% either did not wear spectacles, or wore them almost none of the time

S. J. Dell

The unusually small 4.5-mm optic initially sparked concerns among the clinical investigators that the Crystalens would create dysphotopsia in patients. The results of the trial demonstrated that this is not the case, and Crystalens patients generally report night vision comparable to standard IOLs. In a substudy examining pupil size under 0.04 Lux scotopic conditions, a questionnaire demonstrated minimal glare complaints despite average scotopic pupil sizes of 5.02 mm [8]. Studies of contrast sensitivity comparing the Crystalens to a traditional 6-mm Acrysof IOL have demonstrated comparable contrast sensitivity scores throughout the spatial frequency range [8].

Wavefront analysis has been used to demonstrate a refractive power change in Crystalens patients as they shift their gaze from near to distance fixation [9]. This is probably the most direct evidence of the accommodative abilities of these patients, although such measurements are a challenge to obtain given current wavefront aberrometry technology. Variations in pupil size, convergence during accommodation and lack of an accommodative target are just a few of the

Fig. 10.5. Ultrasound biomicroscopy showing anterior movement of the Crystalens in response to accommodation. (Courtesy of Miguel Angel Zato)

challenges associated with obtaining valid power change maps with wavefront aberrometry.

High-resolution ultrasound studies have also been performed, which demonstrate anterior movement of the Crystalens optic upon accommodation (Fig. 10.5). Additionally, in a study using immersion A-scan ultrasonography to examine the anterior chamber depth (ACD) in Crystalens patients upon paralysis of accommodation with a cycloplegic as compared to stimulation of accommodation with a miotic, the ACD decreased significantly [10]. Average forward movement of 0.84 mm was demonstrated in this study, which translated into 1.79 diopters of average monocular accommodation with the Crystalens (Fig. 10.6).

10.3Clinical Considerations

With an implant available that provides accommodation, what factors influence the decision to use the Crystalens in any given patient? One concern regarding the Crystalens, particularly in young patients, is the possibility that the lens could experience material fatigue, resulting in failure of the hinge over time. The lens has been subjected to biomechanical testing, which simulates the

many accommodative cycles likely to occur throughout the lifespan of a patient. In fact, the testing performed subjected the lens to much more vigorous movement than would ever be encountered physiologically. This testing indicates that the lens material will last without deterioration. Unlike acrylic, which has a tendency to crack under repeated stress, the flexibility of silicone is well suited to a moving hinge.

Another consideration relates to the use of the Crystalens in patients with very large pupils. While excellent scotopic results were achieved in the clinical trial, these patients had an average age of approximately 70 years. How will the lens perform in much younger patients with larger pupils? My own clinical impression is that Crystalens patients have no greater incidence of dysphotopsia than those with any other IOL, but I tend to proceed cautiously in patients with very large pupils. As we gain more experience with this lens, we will understand this issue more thoroughly.

Patients with diseased maculae and limited visual potential after lens surgery will probably not obtain sufficient benefit from the Crystalens to justify its use. Similarly, patients in whom the use of a silicone IOL is contraindicated are not candidates. FDA labeling of the Crystalens states that it should not be used in the presence of a posterior cap-

sule tear at the time of cataract surgery.An intact capsulorrhexis is required for placement of the lens. Due to the unpredictable capsular contraction possible in pseudoexfoliation patients, use of the Crystalens is probably not indicated in these cases as well.

Patients should be cautioned to expect halos from pupil dilation in the first week after surgery. During this period of cycloplegia, their near acuity will be quite poor. In fact, data from the clinical trial indicate that near acuity does not begin to improve significantly for several weeks. Patients should also be advised that the accommodative results tend to continue to improve throughout the first postoperative year. Additionally, in the FDA trial, bilateral implantations yielded better results than unilateral implantations.

One critical factor in the success of the Crystalens is its ability to perform well throughout the axial length range. Since the lens relies upon movement of the optic to produce its accommodative power change, one could infer that high-power lenses would perform better than low-power lenses. As an extreme example, an IOL with zero power could be moved an infinite distance with no effect on refractive power. When the accommodative function of the Crystalens was evaluated as a function of IOL power in the range included in the US clinical trial (16.5–27.5 D), the lens performed as well with low-power implantations as with high-power implantations. One possible explanation for this is that, although low-power implantations derive less refractive change for each millimeter of anterior lens motion, the lens–iris diaphragm configuration of these longer eyes allows for a greater anterior excursion of the lens upon ciliary body contraction. It remains to be seen what the lower-power limits will be for Crystalens implantation.

One could imagine a scenario where the IOL power used for any given eye could be ar-

tificially increased in a number of ways. Under one such scenario, a bioptics procedure could be performed in which a Crystalens power would be selected that would render the patient iatrogenically highly myopic,but a phakic IOL could be piggybacked in front of the Crystalens to return the patient to emmetropia. This may have the effect of boosting the potential accommodative amplitude to even higher levels.

Preservation of accommodation after YAG capsulotomy is another issue that has been thoroughly examined. Over 50 eyes in the US clinical trial have undergone YAG capsulotomy, and their accommodative abilities have remained undiminished by the YAG capsulotomy. Additionally, when patients who had undergone YAG were compared with those who had not undergone YAG who had clear capsules, there were no differences in accommodative abilities between the two groups. The incidence of YAG capsulotomy may be higher for the Crystalens than for some other intraocular lenses [11, 12]; however, many of these Crystalens patients underwent capsulotomy despite 20/20 best corrected distance vision. The reason for this is that very subtle posterior capsular fibrosis has an effect on near acuity prior to affecting distance acuity. The implication is that such patients would not receive a capsulotomy with a standard intraocular lens. Capsulotomy openings should be kept small, in the order of 3 mm or less, to avoid vitreous herniation around the optic.

Lastly, what assurances do we have that the accommodative effects of the Crystalens will persist? Three-year data are now available on the eyes from the US clinical trial,which show no degradation in accommodative performance over time (Fig. 10.7). Longer follow-up data are available from outside the US, which similarly indicate no degradation of the accommodative effect.

10.4Preoperative Considerations

Clinical success with the Crystalens requires achieving near emmetropia in a high percentage of patients. This is particularly true as many patients receive the lens in the context of refractive lens exchange. Precision biometry is essential to meet this goal. Accurate axial length determinations can be accomplished with immersion A-scan ultrasonography or laser interferometry using the IOL Master (Carl Zeiss Meditec, Jena, Germany); however, contact A-scan ultrasonography should be avoided as it is prone to compression errors with resulting underestimation of true axial length.

In the clinical trial, manual keratometry was used in all patients. The use of a manual keratometer is highly recommended, as automated keratometers lack the accuracy of manual readings. Topographically derived keratometry also lacks the accuracy of manual keratometry,and is therefore not recommended. Surgeons should take care to calibrate their keratometers regularly, as these instruments may periodically drift out of calibration.

Intraocular lens calculations should be performed with a modern IOL software program such as the Holladay II formula (Holladay Consulting, Inc., Bellaire, TX). The sur-

geon’s outcomes should be regularly tracked to monitor refractive accuracy.

For patients with corneal astigmatism, limbal relaxing incisions (LRI) are useful to reduce this component of the patient’s refractive error [13, 14]. Eliminating the spherical component of the refractive error without addressing the remaining corneal astigmatism will likely result in an unsatisfactory clinical outcome. LRIs may be performed at the time of Crystalens implantation, or at a later date after the astigmatic effects of the original surgery are known.

Patients seeking refractive lens exchange may have previously undergone keratorefractive surgery in years past. This is an issue of increasing significance. Prior keratorefractive surgery is not a contraindication to surgery with the Crystalens; however, such patients must be cautioned that the accuracy of biometry is reduced, and unexpected refractive errors may result.

10.5Surgical Considerations

The Crystalens is intended for placement in the capsular bag only, and a relatively small capsulorrhexis is required, typically in the range of 5.5 mm. This ensures that the extremely flexible plate haptics of the Crystal-

Fig. 10.8. Small capsulorrhexis helps ensure correct posterior vaulting of the Crystalens. A capsulorrhexis that is too large can allow anterior vaulting of the lens, while one that is too small complicates cortical removal and lens implantation, and tends to provoke an intense fibrotic reaction of the capsule

ens are posteriorly vaulted in the correct position (Fig. 10.8). A capsulorrhexis that is too large can allow anterior vaulting of the lens, while one that is too small can lead to an overly aggressive fibrotic response of the posterior capsule as many more anterior lens epithelial cells are left in place. Very small capsulorrhexes have the added disadvantages of complicating cortical removal and delivery of the trailing plate into the capsular bag. Additionally, a very small capsulorrhexis may dampen accommodative movement of the optic by trapping the Crystalens in a fibrotic cocoon formed by fusion of the anterior and posterior leaves of the capsule. Surprisingly, proper capsulorrhexis sizing has been one of the more challenging aspects of the first few cases of surgeons transitioning to this lens.

In general, the Crystalens provides excellent centration as a result of the polyimide loops at the termination of the plate haptics. Fixation of the polyimide loops occurs relatively early in the postoperative period and exchanging or repositioning the Crystalens can be difficult after approximately 4 weeks. The Crystalens cannot be dialed or rotated in a traditional fashion, as the four polyimide

Fig. 10.9. Crystalens that has become stuck in an anteriorly vaulted position due to a wound leak or sudden anterior chamber decompression. Striae are typically visible in the posterior capsule corresponding to the long axis of the lens. Surgical repositioning is required

loops engage the peripheral posterior capsule. However, the lens can easily be rotated by centripetally pulling on the optic and allowing it to rotate in short “jumps” with each such maneuver.

A watertight wound closure is essential with the Crystalens,as the implant is susceptible to a unique complication from a leaking wound. Standard IOLs may tolerate a wound leak with only transient shallowing of the anterior chamber, which re-deepens as the wound eventually seals. However, the architecture of the Crystalens creates a different situation. As a result of the extremely flexible plate haptics,a wound leak can allow the Crystalens to vault anteriorly, and the lens can become stuck in this position. This phenomenon requires surgical repositioning of the lens (Fig. 10.9). The Crystalens is designed to be implanted without folding. Typically, the lens can be implanted through an incision of approximately 3.2 mm as it auto-conforms to the incision tunnel architecture. As uniplanar clear corneal incisions are prone to leakage in the early postoperative period,their use is discouraged with the Crystalens [15, 16]. Miotics are not used at the time of surgery.

References

1.Coleman PJ (1986) On the hydraulic suspension theory of accommodation. Trans Am Ophthalmol Soc 84:846–868

2.Busacca A (1955) La physiologie du muscle ciliaire étudiée par la gonioscopie. Ann Ocul 188:1–21

3.Thornton S (1991) Accommodation in pseudophakia. In: Percival SPB (ed) Color atlas of lens implantation. Mosby, St Louis, pp 159–162

4.Kammann J, Cosmar E,Walden K (1998) Vitre- ous-stabilizing, single-piece, mini-loop, platehaptic silicone intraocular lens. J Cataract Refract Surg 24:98–106

5.Cumming JS, Ritter JA (1994) The measurement of vitreous cavity length and its comparison preand postoperatively. Eur J Implant Refract Surg 6:261–272

6.Steinert R, Aker BL, Trentacost DJ et al (1999) A prospective comparative study of the AMO ARRAY zonal-progressive multifocal silicone intraocular lens and a monofocal intraocular lens. Ophthalmology 106:1243–1255

7.Lindstrom RL (1993) Food and Drug Administration study update. One-year results from 671 patients with the 3 M multifocal intraocular lens. Ophthalmology 100:91–97

8.Dell SJ (2003) C&C vision AT-45 Crystalens. Paper presented at the American Society of Cataract and Refractive Surgery annual meeting; 10–16 Apr 2003, San Francisco, CA

9.Dick HB, Kaiser S (2002) Dynamic aberrometry during accommodation of phakic eyes and eyes with potentially accommodative intraocular lenses. Ophthalmologe 99:825–834

Chapter 10

10.Dell SJ (2004) Objective evidence of movement of the Crystalens IOL during accommodation. Paper presented at the American Society of Cataract and Refractive Surgery annual meeting; 1–5 May 2004, San Diego, CA

11.Davison JA (2004) Neodymium:YAG laser posterior capsulotomy after implantation of AcrySof intraocular lenses. J Cataract Refract Surg 30:1492–1500

12.Ando H, Ando N, Oshika T (2003) Cumulative probability of neodymium:YAG laser posterior capsulotomy after phacoemulsification.J Cataract Refract Surg 29:2148–2154

13.Packer M, Fine IH, Hoffman RS (2002) Refractive lens exchange with the array multifocal intraocular lens. J Cataract Refract Surg 28: 421–424

14.Bayramlar Hü, Daglioglu MC, Borazan M (2003) Limbal relaxing incisions for primary mixed astigmatism and mixed astigmatism after cataract surgery. J Cataract Refract Surg 29:723–728

15.Shingleton BJ, Wadhwani RA, O’Donoghue MW et al (2001) Evaluation of intraocular pressure in the immediate period after phacoemulsification. J Cataract Refract Surg 27: 524–527

16.McDonnell PJ, Taban M, Sarayba M, Rao B, Zhang J, Schiffman R, Chen Z (2003) Dynamic morphology of clear corneal cataract incisions. Ophthalmology 110:2342–2348

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11.1Introduction

Presbyopia remains one of the great unsolved challenges in ophthalmology. Ever since von Helmholtz [1], much research has been conducted concerning mechanisms of accommodation, presbyopia and potential solutions [2–8].

Despite excellent restoration of visual acuity and good biocompatibility of presently used posterior chamber intraocular lenses (PCIOL), there is no accommodation in pseudophakic eyes so that patients usually remain presbyopic after cataract surgery. Newer attempts surgically to correct or reduce presbyopia, including scleral expansion surgery, zonal photorefractive keratectomy, or implantation of corneal inlays, so far have achieved no or very limited success in solving the problem [9–11]. Multifocal intraocular lenses (IOLs) allow for improved uncorrected near vision, but at the cost of reduced contrast sensitivity and loss of image quality [12]. This problem has only partly been solved by the introduction of diffractive and bifocal PCIOL [13]. Therefore, in the past few years, there has been increased interest in the development of new IOL devices to achieve active, ciliary muscle-derived accommodation by optic shift principles without reducing image quality. Among these new IOLs, a new accommodative PCIOL (1CU, HumanOptics, Erlangen, Germany) has been designed after principles elaborated by K.D. Hanna. This PCIOL is intended to allow accommodation by anterior movement of the lens optic (optic shift) secondary to contraction of the ciliary muscle.

11.1.1 Definitions

In the literature, various terms such as accommodation, pseudo-accommodation and apparent accommodation are being used interchangeably with regard to pseudophakic eyes. We define pseudophakic accommoda-

N. X. Nguyen · A. Langenbucher · B. Seitz, et al.

tion as dynamic change of the refractive state of the pseudophakic eye caused by interactions between the contracting ciliary muscle and the zonules–capsular bag–IOL, resulting in change of refraction at near fixation. Furthermore, we define pseudophakic pseudoaccommodation (apparent accommodation) as static optical properties of the pseudophakic eye independent of the ciliary muscle, resulting in improved uncorrected near vision.

11.1.2Anatomy and Description of the 1CU Accommodative Intraocular Lens

Several studies using impedance cyclography, ultrasound biomicroscopy and magnetic resonance imaging have shown that the ciliary body retains much of its contractility in older patients [5–7]. Furthermore, modern technology allows refined finite element computer methods to simulate the changes of the ciliary body–zonular–lens apparatus during accommodation. Based on these models, the 1CU PCIOL was developed to allow transmission of the contracting forces of the ciliary body into anterior movement of the lens optic to achieve pseudophakic accommodation. This focus shift principle should allow a defined amount of accommodation, theoretically 1.6–1.9 D per 1-mm anterior movement of the PCIOL optic using the Gullstrand eye.

11.1.31CU Posterior Chamber Intraocular Lens

Based on concepts by K.D. Hanna and on finite element computer simulation models, a new acrylic hydrophilic foldable single-piece PCIOL has been designed and manufactured (Type 1CU, HumanOptics AG, Erlangen, Germany). The spherical optic has a diameter of 5.5 mm, with a total diameter of the PCIOL of 9.8 mm (Fig. 11.1). This PCIOL is intended to allow accommodation by anterior movement