Presbyopia represents the most common refractive error, however, there is currently no established surgical treatment approach. Excimer laser surgery is a routine procedure to correct myopia, hyperopia, and astigmatism. Various presbyopic treatment strategies using the excimer lasers have also been brought forward. Beside monovision, the creation of a multifocal cornea represents an attractive option. This procedure is also called presby-LASIK.
Within this article, we will review several ablation profiles to form a multifocal cornea and summarize first clinical results. Presby-LASIK is a new and exciting strategy, with potential for future application.
Beginning at the age of 20 years, range of accommodation decreases, and by age 55 years, it is nearly completely lost.1 In 2004, in Germany alone, more than 15 million people were aged 65 years or older. This affects the relevance of presbyopia and costs for optical devices.2,3
The pathomechanism of presbyopia is not completely understood, however, it is likely that all components of accommodation are involved.4-7 Former treatment approaches—attempting to cure presbyopia by rejuvenation of accommodation—had only limited success, perhaps due to an insufficient understanding of the physiology of accommodation. Recently, presbyopia was also corrected by surgical enhancement of pseudoaccommodation.
ACCOMMODATION, PSEUDOACCOMMODATION
Accommodation leads to an increase of refractive power. As tension of the ciliary muscle causes the zonular fibers to relax, the curvature of anterior lens surface increases. Thus, refractive power of the lens increases (Figure 1).
The natural near vision reaction is called accommodative trias and consists of accommodation, convergence reaction, and miosis. Several studies have shown a change of corneal power due to accommodation.8-10 Accommodation should be distinguished from pseudoaccommodation. An increase in depth of field—not the change in refractive power—facilitates near vision. This is achieved by ocular aberrations (eg, astigmatism, spherical aberrations, higher-order aberrations) or miosis.11-13 Therefore, every eye has a potential for pseudoaccommodation, and reading ability may be restored with a relatively small correction of 1.00 D to 2.00 D.14 Unfortunately, the effect of pseudoaccommodation and accommodation cannot be distinguished by simple subjective measurements.15,16
TREATMENT OPTIONS
Below is a list of treatment options that have been used, and some that are still being used, for presbyopia correction.
Monovision. This is one of the first and simplest presbyopia treatments. The dominant eye is corrected for far vision, and the nondominant eye is corrected for near vision. This targeted anisometropia causes selective suppression of one retinal image; it is achieved with spectacles, contact lenses, IOLs, or refractive excimer laser surgery.3,17 Monovision may cause visual problems, due to a longer learning phase, reduced binocular vision, and steropsis.18,19 Also, driving ability may be limited.20,21
Corneal correction of refractive errors. Schiötz22 described the first corneal correction of refractive errors in 1885. Because of its initial lack of predictability, it was not pursued any further. In the 1930s and 1949, respectively, radial keratotomy23-25 and keratomileusis26 were introduced. Following much later, conductive keratoplasty and corneal inlays were developed.27
Excimer laser. In 1983, Trokel performed the first excimer laser treatment on a human cornea,28 and in 1988, PRK was performed to treat myopia.29 Pallikaris and Buratto30-32 described the first LASIK procedures by 1991. Since then, further developments in ablation procedures and the introduction of devices including the femtosecond laser helped advance excimer laser treatments. The treatment of refractive errors like myopia, hyperopia, and astigmatism by excimer laser represent established procedures. Correction of presbyopia is still at its infancy. The main goal cannot be to restore accommodation, but to allow people older than 45 years independence from reading spectacles.
Presby-LASIK. Presby-LASIK encompasses all strategies that shape a multifocal corneal surface with an excimer laser. First investigations by Moreira et al33 have been performed on plastic hemispheres, PMMA plates, and corneas. They developed different ablation profiles and techniques to shape a bifocal cornea. The most promising method was a myopic ablation from the periphery of 4.00 D, with a 6-mm diameter. Before reaching the central 3-mm zone, ablation was stopped, and the central 3-mm zone was untreated. Since these first trials, other studies identified appropriate ablation profiles for a multifocal cornea. In the following section, current presby-LASIK concepts are summarized.
TECHNIQUES
Presby-LASIK techniques aim at correcting possible refractive errors and shaping a corneal zone for near vision, not restoring true accommodation. In contrast to multifocal contacts or IOLs, an exact centration to the visual axis is possible.34 Contraindications are the same as for excimer laser surgery.
Various treatment strategies are distinguished. There are bi- and multifocal ablation profiles; the location of the single zone is variable. All procedures describe a temporary decrease in visual acuity after surgery. One possible profile is a bilateral inferior decentered ablation for near vision (Figure 2), where the transition zone is either cascade or progressive.35-37
Multifocal ablation profiles show annular zones. Far and near vision zones may be arranged from the periphery to the center, or vice versa. All new strategies include data from aberrometry into the calculation of ablation profile. Below are two techniques named by the way they correct the central zone.
Peripheral presby-LASIK. If the central zone is corrected for far vision, the procedure is named peripheral presby-LASIK (Figure 3). In Telandro's38 method, the progressive aspheric lens is shaped in the cornea—allowing far and near vision—with the EC-5000 Excimer Laser and Pseudoaccomodative Cornea calculator software (both manufactured by Nidek, Gamagori, Japan). After the multistep mulitfocal ablation, a peripheral myopic ring for near vision is created.
In this retrospective study with 83 hyperopic and 77 myopic eyes, patient age ranged from 18 years to 78 years. Three months after surgery, 72.5% of the hyperopia group and 66.7% of the myopia group were within ±0.50 D of emmetropia. One percent of hyperopic eyes lost two or more lines of BSCVA. All patients showed a binocular near UCVA of J3 or better. In hyperopic eyes, 35% could read J1 unaided for near vision, versus 41% of myopic eyes.
Central presby-LASIK. Ablation of a central zone for near vision is called central presby-LASIK (Figure 4). Here, the diameter of the central zone for near vision is chosen independently from pupil size to achieve an aspheric cornea with multifocal design.
In one multicenter study, 75 eyes of 43 hyperopic and presbyopic patients (age range, 47 years to 68 years) were treated with the Star S4-Wave Scan (Advanced Medical Optics, Inc./Visx, Santa Ana, California, and Santa Clara, California).39 Six months postoperative, all eyes (n=56) showed a monocular distance UCVA of 20/40 and a binocular distance UCVA of 20/25 or better. Ninety-three percent achieved a monocular near UCVA of J3 or better. One eye lost two or more lines of distance visual acuity, and two eyes lost two or more lines of near visual acuity after 12 months. A total of 82% of eyes were within ±0.5 D of emmetropia 12 months postoperative. Ninety-four percent of patients were satisfied or very satisfied with distance vision at daylight, and 80% were satisfied or very satisfied with near vision at bright light 12 months after surgery.
In a trial by Telandro,40 all enrolled eyes (225 hyperopic and 135 myopic) reached a binocular near UCVA of J3 or better 6 months after surgery. With a near addition of 1.00 D, most patients were able to read J1. Loss of distance BCVA was similar to monofocal LASIK treatment, and therefore acceptable. After 12 months, both groups showed stable results, where 84% of hyperopic and 74% of myopic eyes were located within ±0.50 D of target refraction.
This year, Alió and colleagues described the first open-label, prospective, noncomparative, interventional trial.33 They treated 50 eyes (25 presbyopic patients; age range, 51 years to 68 years) with the H.Eye.Tech excimer laser (Technovision, Munich, Germany, and Bausch & Lomb, Rochester, New York) and Presby-One software (Technovision). Preoperative distance BCVA was 20/25. All patients could read J2 or J3, with a preoperative addition of 1.50 D. The ablation profile created a 6-mm multifocal cornea.
First, a hyperopia treatment was performed over the entire diameter. At the central 3-mm zone, a hyperopia of 1.50 D remained. A 1.5-mm transition zone connected the peripheral ring of emmetropia with the central zone for near vision. The amplitude of accommodation improved from 1.43 ±0.52 D preoperatively to 2.12 ±0.64 D 6 months after surgery. Binocular distance UCVA increased from 0.39 ±0.19 to 0.97 ±0.14, and binocular near UCVA increased from 0.35 ±0.21 to 0.45 ±0.22. A majority of patients (64%) were within ±0.50 D of emmetropia 6 months after laser treatment. Then, a retreatment for far distance correction was performed in six eyes. The Holladay contrast acuity test showed a significant change in contrast sensitivity at 3, 6, 12, and 18 cycles/degree. Seven eyes lost two or more lines for distance BSCVA, and eight eyes lost two or more lines for near BSCVA. Seventy-six percent of patients reported a high degree of satisfaction six months after treatment; 72% were spectacle free at all distances.
Enlargement of depth of field. A multifocal effect of the cornea may also be achieved by superimposing a standard correction profile (Figure 5) with an increased Z (4.0). With this strategy, a monofocal ablation is performed to shift the spherical aberration into the plus range. This special aspheric shape could improve the depth of field and improve near vision. This method was developed for the MEL 80 excimer laser system (Carl Zeiss Meditec AG, Jena, Germany). There are no published data for this method thus far.
CONCLUSION AND OUTLOOK
An effective, safe, and reliable treatment option for presbyopia would represent a breakthrough. So far, all methods regarding the treatment of sclera, lens, or cornea have limitations regarding vision quality (eg, reduction in contrast sensitivity, halos, and glare). All approaches to restore accommodation capability have not yet achieved satisfactory result. Therefore, there is increasing interest in the enhancment of pseudoaccommodation.
During recent years, modeling a multifocal cornea have been developed as a novel approach. McDonnel et al41 described an improved near visual acuity after radial keratotomy. Several topographical analyses showed a multifocal cornea with zones of steepening and flattening.42-44 Moreira and his colleagues33 performed the first ablation to create a multifocal cornea in 1992. Over the course of the following years, various concepts were invented and studied in small case series. In 2003, first reports about presby-LASIK were published in peer-reviewed journals.34 Despite encouraging initial clinical results, various questions are unsolved. There are no long-term results, and most trials include hyperopic patients. Presby-LASIK was often performed on relatively young patients, with no or little presbyopia (fewer than 2.00 D). It is unknown whether or not a retreatment is needed later. Safety issues including impairment of contrast sensitivity and unwanted optical aberrations with appearance of glare and halos should be addressed in future studies.
K.A. Becker, MD, is from the Department of Ophthalmology, University of Bonn, in Germany. Dr. Becker states that he has no financial interest in the products or companies mentioned. He may be reached at telephone: +49 228 2875505; fax: +49 228 2875603; or klio.becker@ukb.uni-bonn.de.
F.G. Holz, MD, is from the Department of Ophthalmology, University of Bonn, in Germany. Dr. Holz states that he has no financial interest in the products or companies mentioned. He may be reached at telephone: +49 228 2875505; fax: +49 228 2875603.
Up Front | Jan 2007
Presby-LASIK and the State of Presbyopia Correction
One new corneal approach to treat presbyopia is with the excimer laser.
K.A. Becker, MD, and F.G. Holz, MD
