Ординатура / Офтальмология / Английские материалы / Hyperopia and Presbyopia_Tsubota, Boxer Wachler, Azar_2003

cornea, enabling optimization of both near and distance vision through a range of optical zones. These studies offered the theoretical basis for refractive surgery to treat presbyopia using a multifocal corneal approach. The multifocal approach espouses the concept of pseudoaccomodation, or the ability to process multiple simultaneous images at the retina

(3).

Anschutz performed studies with photorefractive keratectomy (PRK) on polymethyl methacrylate (PMMA) lenses and porcine eyes to intentionally create multifocal corneal surfaces. A sectoral near zone as part of a concentric zone for distance was favored. He subsequently applied the models in clinical trials testing the effectiveness of PRK in treating myopia-presbyopia and hyperopia-presbyopia, described below (4). In addition, Moreira et al. investigated several modalities for achieving a multifocal surface (5). Four configurations of ablation were compared: monofocal ablation, two concentric ablations, two ablations with the smaller diameter ablation decentered inferiorly, and a single progressive ablation. The group concluded that a corneal surface with multiple refractive powers could be achieved in PMMA hemispheres and blocks, as well as, in rabbit corneas. They believed that the single progressive ablation would be the most effective, created with an iris diaphragm initially fully open to 6 mm and progressively closing until 3 mm, leaving a central zone with the preoperative refractive power (5). This technique would theoretically function in concert with pupillary miosis during near accommodation to decrease the percentage of light rays traversing the flattened zone of the cornea. Thus, degradation of the retinal image as a result of the multifocal lens effect may be reduced.

C. TECHNIQUES

In March 1999, Anschutz began human clinical trials of multifocal PRK to treat myopiapresbyopia. A 193-nm Aesculap-Meditec laser was used with an iris diaphragm to bifocally sculpt the cornea (4). The investigation involved two techniques for creating zones for near and distance vision: (1) an inferior pie-shaped sectoral near zone within a concentric distance zone and (2) a central near zone within a concentric distance zone. Both techniques involved an initial circular ablation of 2 or 3 D less than the myopic baseline refraction. For technique 1, this was followed by a second ablation to the full myopic correction using a sectoral template. Technique 2 used a central nonrotating template in a similar fashion. Figure 1 demonstrates the two techniques.

In treating hyperopia-myopia, Anschutz investigated the technique of an inferior sectoral steepening of the cornea, to create active myopization for near vision (4). For the initial hyperopic PRK ablation, a spiral eye mask (or double-heart mask) was used along with a rotating spiral template to correct for the complete hyperopic refraction. Next, a nonrotating presbyopic template with an oval aperture was inserted for the second ablation, to create an inferior sectoral zone of an additional 2.0 to 3.0 D presbyopic correction (Fig. 2).

The hyperopia-myopia study also included a subgroup of emmetropic presbyopes. Their ablations were performed with the hyperopic spiral mask and an oval template, to create an inferior zone of steepening (3.0 D) within a transition zone of 0.5 D (4). The configuration is similar to the inferior sectoral ablation for near vision shown in Figure 1.

Figure 3 PRK for presbyopia; inferior semilunar zone of ablation. (Adapted from Ref. 6.)

Thus, the superior pole of the ablated area served as the optical zone for near vision. Figure 3 shows the ablation zone.

Multifocal laser-assisted in situ keratomileusis (LASIK) has also been employed to treat hyperopia-presbyopia. Bauerberg used a 193-nm Coherent/Schwind Keratom 2 excimer laser with an 8.2-mm-diameter, 160- m-thickness corneal flap (7). Ablation depth was calculated by adding 10% to the preoperative spherical equivalent. A centrally located ablation was tested as well as an inferiorly decentered ablation (by 1 mm).

D. RESULTS

The myopia-presbyopia PRK study by Anschutz involved 46 eyes of 23 patients with follow-up of 2 1⁄2 to 3 years (4). The preoperative refractions ranged from 2.0 to 12.0 D; patients were divided into three groups: group 1 ( 2.0 to 6.0 D), group 2 ( 6.25 to 10.0 D), and group 3 ( 10.25 to 15.0 D). The goal was a presbyopic correction of 2.0 to 4.0 D. At 30 months, group 1 had a mean regression of 0.75 D, with an uncorrected near visual acuity (VA) of 20/22, which was three lines better than for the monofocally treated eyes. Group 2 had a mean regression of 1.5 D and an uncorrected near VA of 20/25. Group 3 had a mean regression of 4.0 D, with uncorrected near VA only 1 1⁄2 lines better than with monofocal ablation. Overall, greater regression occurred with greater preoperative myopic refraction, and multifocal PRK results were identical to those of monofocal PRK in patients with preoperative refraction greater than 6.0 D. In terms of postoperative complications, the investigators found 2 cases of loss of best corrected VA due to decentration; 1 case of wound-healing difficulties; and 2 cases of diminished near VA due to pupil sizes less than 2 mm. Glare and halo effects were also present in patients for only the first 6 months postoperatively. In addition, 20% of patients experienced “ghost pictures” and double contours for the initial 3 to 4 months postoperatively. Frequent complaints of monocular diplopia occurred in patients who received a central near zone ablation.

A total of 18 eyes with follow-up of 16 to 20 months were studied by Anschutz for PRK treatment of hyperopia-presbyopia. At 18 months, patients with preoperative refractions of 1.0 to 4.75 D showed a mean regression of 1.5 D and a mean near

The Bauerberg LASIK study for hyperopia-presbyopia involved 16 eyes of 8 patients (8 eyes with centered ablation and 8 eyes with off-center ablation) with maximum followup of 22 months (7). Preoperative refractions ranged from 2.0 to 6.0 D. At 12 months, the off-centered ablation eyes achieved uncorrected near VA of 20/30 or better with no loss of Snellen lines. The centered ablation eyes had uncorrected near VA of 20/40 or better with two eyes experiencing loss of 1 Snellen line. No glare was reported; however, 2 eyes had induced astigmatism. Subjectively, 6 patients preferred the eccentric inferior ablation for near vision, while 2 noticed no difference.

A summary of results is presented in Table 1.

E. CONCLUSIONS

The multifocal corneal approach to treating presbyopia remains experimental, although the technology and techniques of multifocal corneal sculpting have been well investigated. The four studies reviewed had the drawback of low patient numbers; however, follow-up time was considerably meaningful. A most important reason for studies of greater magnitude is the need to delineate the incidence of postoperative side effects such as glare, halos, ghost images, and monocular diplopia. The reviewed studies reported that symptoms such as halos, glare, and ghost images were present for a short period of time in the limited patient groups. The presence of these symptoms was perhaps due to a temporary transition period during which wound healing and adjustment to multifocal images occurred. Stability of the presbyopic corrections and their relationship with the natural progression of presbyopia should also be followed long-term.

Each of the studies revealed certain limitations for presbyopic multifocal refractive surgery as well as benefits for particular techniques. For myopia-presbyopia, Anschutz concluded that their inferior sectoral near zone is appropriate for patients with pupils greater than 2 mm diameter (4). Additionally, for patients with pupils larger than 3 mm, the central near zone may be advantageous in the case of dominant near vision, particularly in the presence of high myopia ( 10.0 D). The investigators also concluded that current multifocal hyperopia-presbyopia PRK is effective only for patients with a baseline refraction of less than 5.0 D due to the high degree of regression and the small optical zone for those with refractions greater than 5.0 D (4). Anschutz cites a need for improvement of the transition zone and aspherical reprofiling of the cornea in addition to simplifying the technique to require only one template.

Vinciguerra et al. found that the zonal presbyopic correction was effective for pupils up to 6 mm (6). Advantages of their technique include a pupillary center with intact epithelium acting as a protective shield against decentration during photoablation and the need for a very superficial (10 to 15 m) and small ablation zone. Because only 15% of the light entering a 3 mm pupil traverses the treated zone, contrast sensitivity was not significantly reduced. Nevertheless, Vinciguerra notes that the technique requires extreme precision to avoid erroneously aligned ablation and suboptimal presbyopic correction. In addition, for pupils greater than 6 mm, the technique may lead to an inadequate presbyopic correction.

LASIK for presbyopia was shown to have stable postoperative results with minimal recovery time and complications in a small study by Bauerberg (7). However, he notes that longer follow-up is needed. He concluded that the preferred orientation of the presbyopic ablation should be inferior off-center. It may be worth considering the implications that an asymmetrical corneal contour has for flap orientation and healing. To our knowl-

edge, no studies have been undertaken to compare multifocal PRK and LASIK in the treatment of presbyopia.

Last, pupillary size appears to play a significant role in the effectiveness of multifocal refractive surgery, as shown by the aforementioned studies. Another aspect that may require investigation is the positioning of a individual’s upper and lower lid margins with respect to the treated zone during distance and near vision. Could a raised lower lid position cover up a zone of inferior corneal steepening such that the presbyopic correction has no benefit? Conversely, could the same positioning protect the patient’s vision from visual distortion by covering up a rough transition zone?

REFERENCES

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2.Maguire LJ, Bourne WM. A multifocal lens effect as a complication of radial keratotomy. Refract Corneal Surg 1989; 6:394–399.

3.Talamo J, Krueger R eds. The Excimer Manual. Boston: Little, Brown, 1997:106.

4.Anschutz T. Laser correction of hyperopia and presbyopia. Int Ophthalmol Clin 1994; 34(4): 107–137.

5.Moreira H, Garbus JJ, Fasano A, Lee M, Clapham TN, McDonnell PJ. Multifocal corneal topographic changes with excimer laser photorefractive keratectomy. Arch Ophthalmol 1992; 110(7):994–999.

6.Vinciguerra P, Nizzola GM, Bailo G, Nizzola F, Ascari A, Epstein D. Excimer laser photorefractive keratectomy for presbyopia: 24-month follow-up in three eyes. J Refract Surg 1998; 14(1): 31–37.

7.Bauerberg JM. Centered vs. inferior off-center ablation to correct hyperopia and presbyopia. J Refract Surg 1999; 15(1):66–69.