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Today's Practice | Jan 2014

Noninvasive Thermal Laser Keratoplasty

With Opti-K, there is no neural adaptation period.

In recent years, various surgical methods—both corneal and lens-based—have been proposed to treat presbyopia. Yet, still, the most common presbyopia-correcting strategy is monovision. When applied on the cornea, monovision is achieved either with LASEK or LASIK. In these procedures, the dominant eye undergoes a full correction and the nondominant eye undergoes undercorrection for myopia or overcorrection for hyperopia. In lens-based monovision, patients are fitted with monofocal IOLs to achieve partial compensation for their presbyopic symptoms. With this strategy, we aim for emmetropia in the dominant eye and myopia (-0.75 to 1.75 D) in the nondominant eye.

POPULAR STRATEGIES

In my experience, women tolerate monovision better than men, as they tend to be less disturbed by its negative effects on far vision and stereopsis, are more interested in achieving excellent near vision, and are aesthetically motivated to lose their reading glasses.

Monovision is just one surgical strategy, however. Other approaches to presbyopia correction include a wide range of presbyopia ablation profiles using technologies developed by manufacturers including Bausch + Lomb Technolas, Alcon (WaveLight), and Schwind eye-tech-solutions; multifocal and accommodating IOLs; and corneal inlay technologies.

A NONINVASIVE PROCEDURE

Another approach to presbyopia correction is optimal keratoplasty (Opti-K), a noninvasive thermal laser keratoplasty (LTK) technique performed with the Opti-K System (NTK Enterprises, Inc.). Opti-K aims to temporarily reduce symptoms of presbyopia, improve near visual acuity, and correct low to moderate hyperopia by reshaping the cornea. This is achieved through changing the structure and properties of the extracellular matrix by means of laser thermal modification.

In comparison with conductive keratoplasty, in which the corneal epithelium and basement membrane are severed, Opti-K does not cause epithelial damage or associated discomfort.

Treatment is performed with a continuous-wave thulium fiber laser (1.93 μm wavelength) with a sapphire applanation window. The corneal absorption coefficient is 110 cm-1, and the average absorption depth is 90 μm. For a 500-μm thick cornea, 0.4% of the incident light penetrates the corneal endothelium.

The procedure begins after a single drop of proparacaine is applied to the corneal surface. The cornea is applanated by an illuminated suction cone (Figure 1), and a sapphire window with a crosshair reticle is used to center it over the pupil (Figure 2). With suction applied, laser light is delivered through 16 optical fibers (Figure 3) and guided into the central cone of the suction ring. With the fibers secured into position with magnets, the laser is activated, and 16 laser beams are applied to the cornea for 2.5 seconds, producing a treatment pattern of 16 spots in two concentric circles (6.0 and 7.2 mm in diameter). At the end of the procedure, a drop of bromfenac is applied, and no antibiotics, bandage contact lens, or anesthetic drops are used.

The corneal topographic change induced by Opti-K resembles an eight-leaf rosette of alternating steep and flat sectors, and the result is corneal multifocality (Figure 4). Because the rosette extends from the center of the cornea to its periphery, this multifocality is independent of pupil size.

Treatment does not abrade the cornea, and the sapphire window acts as a heat sink, protecting the epithelium from thermal damage. Any induced opacifications fade over time, and irradiated stromal tissue appears to return to its pretreatment condition. This is a temporary but repeatable procedure for the treatment of presbyopia and hyperopia.

PRELIMINARY RESULTS

I have performed bilateral Opti-K in four presbyopic patients with low hyperopia. A video of the second procedure I performed can be viewed at eyetube.net/?v=fukoz.

In the four patients I have treated to date, the mean preoperative spherical equivalent for distance was 1.30 D, sphere ranged from 0.00 to 1.75 D, and astigmatism ranged from 0.00 to -0.75 D. The reading addition in these patients ranged from 2.25 to 3.00 D.

Immediately after the procedure, all patients achieved near UCVAs between 1.00 and 1.25. At 1 week, the near UCVA remained unchanged, the mean distance UCVA was 0.6, and the mean BCVA was 1.0 with an average correction of -1.25 D. At 1 month, all patients had a near UCVA of 1.0 and a distance UCVA of 0.6, and at 3 months the near UCVA and BCVA were both 0.8. By 6 months, the distance and near UCVAs were 0.8 and 0.7, respectively.

Two patients were satisfied with their near visual acuity at each examination, and regression did not begin until after 6 months. Both opted to undergo a second treatment at 1 year.

One other patient with high hyperopia was overcorrected for distance in the first 3 months. She complained about difficulties driving but was satisfied with her near vision. The fourth patient was satisfied in the early months but asked for a longer-lasting procedure, and thus I performed clear lens exchange at 5 months postoperative.

CONCLUSION

When compared with other methods of presbyopia correction, bilateral Opti-K treatment potentially has several advantages, including a fast procedure time and no need for special surgical skills or long periods of patient cooperation. This treatment does not affect stereopsis and, therefore, avoids the neural adaptation process associated with multifocal techniques.

Opti-K is an option for patients with slight hyperopia and presbyopia who are between the ages of 40 and 55 years and do not want to undergo clear lens exchange. All patients must understand the temporary nature of the operation and be open to subsequent applications or alternative treatments.

In my opinion, it may be possible to create a longer-lasting effect with Opti-K by inducing a slight overcorrection in near vision in the nondominant eye. This would create a slight myopic monovision to improve near vision in the nondominant eye and would avoid overcorrection of distance vision in the first few months, as occurred with the patient described above.

Magda Rau, MD, is the Head of the Augenklinik Cham and Refractive Privatklinik-Dr. Rau, Cham, Germany, and Eye Centre Prag, Czech Republic and a Visiting Professor at the Bulgarian- American Eye Institute ProLight. Dr. Rau is a member of the CRST Europe Editorial Board. She states that she has no financial interest in the products or companies mentioned. She may be reached at tel: +49 9971 861076; e-mail: info@augenklinik-cham.de.

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