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Refractive Surgery | Jul 2010

The Dawn of Presby-LASIK

There are specific indications for this presbyopia-correcting treatment.

Presby-LASIK is the name given to the surgical correction of presbyopia with an excimer laser ablation. It includes all types of excimer surgery, from surface ablation to femtosecond LASIK. Several ablation profiles for presby-LASIK have been described, but the two most important are central treatment for near vision and central treatment for distance. In the central near vision treatment, the ablation profile creates a distance vision zone in the periphery of the cornea and a near vision zone in the center of the cornea. The opposite is true in central distance vision treatments, in which the central cornea is ablated for distance vision and the periphery for near. In both circumstances, the final product is the creation of a multifocal cornea.

INDICATIONS FOR PRESBY-LASIK
Generally, presby-LASIK is indicated for any patient with presbyopia whose cornea meets the criteria for laser vision correction. Before suggesting presby-LASIK as a treatment option, the surgeon must ensure that the patient's corneal and biomechanical properties are well suited for excimer laser surgery. Several specific indications for this surgery must be considered:

  • Presby-LASIK is better suited for young presbyopes (40–55 years of age) whose crystalline lens is still transparent and in whom intraocular surgery may be too risky. These patients usually have large pupils, which can produce unwanted side effects and symptoms if a multifocal IOL is implanted. On the contrary, the multifocal cornea works better in big pupils.
  • When presbyopia and astigmatism are both present, presby-LASIK is indicated over any other type of correction. Astigmatism correction is more accurate with excimer laser ablation compared with toric IOLs or corneal incisions.1
  • Presby-LASIK is also indicated in eyes in which a monofocal IOL was previously implanted. This surgeryz not only corrects any existing refractive defect but also adds multifocality to the cornea, helping the patient to decrease spectacle dependence for near vision.2
  • Any potential refractive surgery patient over the age of 40 years who has a clear lens, regardless of the refractive defect, should be considered for presby-LASIK. This strategy avoids the onset of presbyopic problems with near vision. This is particularly true in myopic patients over the age of 40 years, who usually have excellent near vision that could be damaged by myopic correction with the laser.

CONTRAINDICATIONS
Contraindications can be divided into relative and definitive. Relative contraindications include:

  • Extreme refractive defects such as high myopia, high hyperopia, or some forms of oblique astigmatism.
  • Corneas that have previously undergone surgery such as incisional surgery. This type of surgery can still be performed in these eyes provided the optical zone is sufficiently sufficiently large and there is no irregular astigmatism.
  • Patients over the age of 65 years, who are naturally at risk for developing a cataract. An IOL must be considered in these patients.
Definitive contraindications include:
  • Any cornea that does not qualify for excimer laser surgery, such as thin corneas and those with signs of keratoconus.
  • Previous corneal surgery, particularly incisional surgery, resulting in a small optical zone or irregular astigmatism.
  • Eyes with ocular diseases such as maculopathy or cataract.

ADVANTAGES AND DISADVANTAGES
Advantages.
Presby-LASIK is not a new technique for the general ophthalmologist, and therefore the pre- and postoperative processes are familiar. Additionally, patients are accustomed to this type of procedure because refractive surgeons have been practicing excimer laser surgery for 25 years. Another advantage is that the complication rate is low,3-5 and complications are manageable without leaving permanent visual damage. Because it is completely extraocular surgery, there is no risk of permanent visual damage. In fact, presby- LASIK is completely reversible, which is probably its greatest advantage. A wavefront-guided ablation can erase the multifocality of the cornea and return it to its previous state. Lastly, presby-LASIK is repeatable, provided the cornea meets the parameters of excimer laser surgery in terms of biomechanical properties. This makes presby-LASIK well suited for repeated treatment in advancing presbyopia.

Disadvantages. The main disadvantage of presby- LASIK is the temporal nature of this procedure as a surgical correction of presbyopia. Because presbyopia is progressive, it is reasonable to expect a decreased surgical effect over time. This procedure also has high technology requirements and a demanding surgical technique. When it is performed as an intrastromal ablation procedure, larger flaps than those used in standard LASIK and other femtosecond-assisted surgeries are required. One must be sure that no aberrations are induced by these larger flaps, such as by wrinkles or folds.

The preoperative examination must be flawless, and patients must be informed that presby-LASIK can produce the same visual symptoms as multifocal IOLs, such as halos and glare at night, decreased contrast sensitivity, and possibly blurred distance vision. However, patients can be told that contrast sensitivity should return to normal levels after 3 to 6 months. When a cataract develops, the presence of this multifocal cornea can make IOL power calculation difficult. However, new programs using elevation topography are being developed to overcome this difficulty. In any case, miscalculation can be corrected with a wavefront ablation that erases multifocality and allows the power of the IOL to predominate.6

CONCLUSION
Presby-LASIK is a safe and effective alternative for the surgical correction of presbyopia. It is better suited for young presbyopes in whom the risk for intraocular surgery is high. It is also indicated in the presence of other refractive defects, particularly astigmatism. The greatest advantage of this procedure is that it can be reversed, for which I use CustomVue (Abbott Medical Optics Inc., Santa Ana, California) corneal ablation.7

Gustavo Tamayo, MD, practices at the Bogotá Laser Refractive Institute, Bogotá, Colombia. He states that he is a consultant to Abbott Medical Optics Inc., and is a paid consultant to Moria. He may be reached at e-mail: gtvotmy@telecorp.net.

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