Presbyopia / SPO - 4 - What has not progressed and future perspectives

4. What has not progressed and future perspectives

Fernando Soler Fernández (1) y Oscar Asís Vainer (2)

1 - Innova Ocular, Clínica Dr. Soler, Elche, España

2 - Perpetuo Socorro, Las Palmas, España

INTRODUCTION

When it comes to writing a work, an article, a chapter of a book, we are overwhelmed by a beautiful feeling of euphoria, of joy: we are going to share with our partners the fruit of our work. The effort dedicated to developing a certain technique, for example, will be rewarded by the satisfaction of considering that these small achievements may have contributed to the growth of this beloved specialty. That is not the case this time however since here we will devote ourselves to recapitulating failures. Failed professional and business acts that surely also required a lot of effort, work and huge investments. Hopefully these lines serve as recognition of these activities, as it is our humble intention to prevent them from being forgotten.

ACCOMMODATION

The cornea has a fixed dioptric power because, neither its shape nor its refractive index, change during the vision process. The crystalline lens is the optical component responsible for adjusting the focus for objects located at different distances. This phenomenon is called accommodation. From the point of view of optical engineering, the processes through which the eye focuses images in a range from far to near in the retina are well understood. However, when it comes to explaining the phenomenon of accommodation in vivo, the analogy of the human eye with optical instruments becomes more difficult. Equipment is manufactured with clear parallelisms with the eye, photo cameras, for example, that contain moving optical parts (lenses, mirrors, prisms) that together act to modify the focal length. The human eye is different, it has a deformable lens: the crystalline lens, which changes its dioptric power by varying its shape and refractive index, and thus accommodates. From the physiological point of view the process of accommodation is still a topic subject to discussion. At this point, it seems necessary, in order to better understand the different postulated surgical techniques, to refer to the different theories proposed on accommodation.

Helmholtz, described the crystalline capsule as a deformable bag, suspended by the zonular fibers. The relaxation-contraction of the zonules, as a result of the tension of the ciliary muscle is what produces the accommodation. This hypothesis dates back to 1855. The studies carried out a posteriori with more modern equipment allow the theory to be questioned. Koretz et al found that the insertion of the zonular fibers varies with age. With aging, this is moving towards the center of the capsule. As a result of this, they propose that presbyopia may be due to a geometric disorder, in which the prevailing cause would be the change in size and angular relationship between the lens and the zonule. Glasser et al., working with crystalline lenses in vitro, emphasize the importance of the hardening of the lens over the years, assigning to this fact the fundamental cause of presbyopia. Schachar et al. develop a theory about accommodation, opposite to that of Helmholtz and his likes. His argument is based on the fact, that the tension of the zonular fibers increases the accommodative power of the lens, rather than decreases it.

CLASSIFICATION

Procedures aimed at surgically correcting presbyopia have been applied in four structures of the eye: sclera, cornea, anterior chamber and lens.

1. Sclera

Relying on the theory of Schachar, a series of surgical techniques emerged in order to expand the scleral ring at the height of the ciliary body. These were developed in three different ways with their respective variations: incisions, implants and laser ablations.

1.1 incisions, anterior ciliary sclerotomy

Histologically, the crystalline lens is of ectodermal origin and grows throughout life, increasing its size in all dimensions. The sclera comes from the mesoderm and this means that it does not have the same evolution of the lens, that is, at some point it stops growing. This evolutionary disparity produces a gradual and progressive narrowing of the space between the equator of the lens and the ciliary body/sclera, with the consequent laxity of the zonular fibers (figure 1).

Based on the above, Fukasaku and Thornton propose their surgical technique for the correction of presbyopia, based on re-tensioning the zonular fibers (Figure 2).

It was originally described as eight radial incisions equidistant from the conjunctiva and the sclera on the ciliary body in each of the oblique quadrants. Subsequently, the technique evolved to two pure scleral incisions per quadrant in addition to limbal peritomies in the oblique quadrants.

The regression of the effect obtained due to the contraction of the wounds with both techniques, suggested the addition of a material to keep the incision open, thus the anterior ciliary sclerotomy was born with implantation of scleral expansion plugs, and the material chosen was silicone. Another author, William Jory, preferred titanium.

1.2. Implants

Regardless of the material and surgical equipment used, the scleral band implantation technique is similar.

Four scleral tunnels are practiced, one per quadrant at 2.75-3.25 mm of the limbus aided, as in this case, by the presby drive.

Once the tunnels are created, the segments are implanted inside. The most commonly employed, according to the original Schachar technique, were of PMMA.

Baykoff, chose to modify the architecture of the implant.

1.3 LASER

Based on the fact that all the previous techniques presented a regression of up to 90% after three to twelve months post-operatively, the LASER procedure for the regression of presbyopia arises. It was developed by Lin and Kadambi in collaboration with Surgi Light and Opti Vision. The application of two infrared LASER barriers per quadrant would produce an increase in the elasticity of the scleral ring in the ablated area.

2. Cornea

Different surgeries for the correction of presbyopia have been applied to the cornea, with the purpose of altering its curvature, modifying its asphericity, changing aberrometric patterns to the eye... We chose the ellipsis because we consider that this chapter has not yet been completed

The alternatives that have become outdated can be classified as: incisional, cicatricial and ablational.

2.1 Incisional

Possibly, the hexagonal keratotomy was one of the first interventions that were performed on the cornea, initially to correct hyperopia, and secondarily presbyopia. It consisted of making a series of straight incisions on the middle cornea that, when joined, formed a hexagon. With the contribution of the microkeratome, a very thick cut was attempted, more than 400 microns thick, which theoretically generated a controlled ectasia, which improved the near vision: hyperopic – presbyopic. As can be understood from the above, it produced very little reproducible treatments and unpredictable results.

2.2 Cicatricial

The thermal techniques so that the peripheral corneal collagen shrinks and as a result, the central cornea is incurred, with the consequent improvement of near vision, can be performed with or without laser. It is always a one-eye surgery, looking for monovision. Historically, two different types of lasers have been applied for this purpose: a contact diode, Rodenstock continuous wave pro-laser (Figure 10) and a non-contact YAG holmium by Sunrise Hyperion ltd (Figure 11).

Figura 10

Figure 11.

Because Refractec received some FDA approvals, conductive keratoplasty was probably the most popular collagen contraction procedure. Mendez introduced the radiofrequency as a non-ablative technique, without laser, with the purpose of generating a scar in the peripheral corneal stroma, causing a myopic central incursion of it (Figure 12).

This effect is achieved by introducing a conductive needle into the peripheral cornea that applies a temperature of 65-75 °C, which produces an intermediate denaturation of the collagen (Figure 13), with the consequent cinch effect.

2.3. Ablational

Presbyopia could not be left out of the revolution that the excimer LASER meant in the treatment of the different refractive defects of the eye. Vinciguerra devised a mask that allowed a crescent ablation in the lower cornea. Different authors, taking as a starting point the LASIK technique, performed a multifocal ablation of the cornea. Avalos carves in the stromal bed of a LASIK a bifocal treatment profile, leaving the myopic central area for near vision, same as Agarwal. In contrast, Ruiz leaves the central zone for distance.

3. Anterior chamber

Taking advantage of the experience he had with the anterior chamber IOLs for the correction of myopia Baikoff developed a similar lens, of angular support, foldable, bifocal, refractive, with the idea of treating presbyopia: gbr/vivarte.

Figure 14

4. Crystalline lens

The replacement of the presbyopic lens with a multifocal intraocular lens is the present. Being the current procedure, we will not abound in its treatment. Gone are some initially implanted prostheses, precursors of the current ones.

FUTURE PERSPECTIVES

Arduous task that of the futurologist. On the basis that the crystalline lens is one of the leading actors in the presbyopia scenario, this should not be left out of any future speculation.

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