Minimizing postLASIK ectasia with maximized refractive technology

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Intracorneal ring surgery, when combined with an optical coherence tomography-guided femtosecond laser, will be a boon to centers providing high-volume LASIK and keratoconus treatment, relates one surgeon.

Dr. Tomita

By Minoru Tomita, MD, PhD, Special to Ophthalmology Times

As director of a very high-volume LASIK center-where surgeons have operated on more than 1 million patients and continue to perform 5,000 LASIK procedures a month-postLASIK ectasia is a significant concern of mine.

To minimize the occurrence of postLASIK ectasia, the approach in our center has been to focus on patient selection. Patients undergo a variety of thorough tests before surgery to exclude those with risk factors for postLASIK ectasia, such as high myopia, reduced preoperative corneal thickness, and asymmetrical corneal steepening. As a result, we have been able to reduce the incidence of ectasia after LASIK to about 1 in every 20,000 patients.

However, for those patients who do develop ectasia, our preferred mode of treatment includes use of an intracorneal ring segment (ICRS) (Kera­ring, Mediphacos). We also use the implant to treat patients who present with keratoconus.

About the device

The polymethyl methacrylate-based ICRS is designed for the treatment of ectatic corneal disorders, such as keratoconus and ectasia. Implanted within the cornea, the device is designed to correct corneal surface irregularities, improve uncorrected and best-corrected visual acuity, and reduce refractive errors by flattening the cornea.

The ICRS is available in a variety of shapes and sizes, allowing surgeons to customize the implant according to patients’ corneal parameters. The device comes in two optical zones of 5 and 6 mm (SI5 and SI6, respectively); five arc lengths of 90°, 120°, 160°, 210°, and 355°; and five thicknesses of 150, 200, 250, 300, and 350 µm. This affords physicians several combinations to match more closely with patients’ needs.

When the device was first made available, the main mode of implantation was mechanical dissection of the cornea with surgical instruments for creating the tunnel into which the ring was subsequently inserted.

Although manual tunnelling is an effective option, care needs to be taken when using this approach. Due to the number of steps involved in this manual technique, there can be a potential for complications, such as epithelial defects, perforation, and infectious keratitis, especially early in the learning curve.1

technology advances

The advent of femtosecond laser provided surgeons with a faster, less invasive, and more consistent means for tunnel creation.

The laser provides greater flexibility in making tunnels of multiple sizes and depths anywhere in the cornea with superior accuracy and quality.

However, through our experience we have learned that certain complications, such as endothelial perforation, still remain a concern. The main reason for the continuing incidence of this complication is surgeons’ inability to visualize the depth of the tunnel during its creation. Although this complication occurs at a rather low frequency-for instance, studies have reported frequencies of endothelial perforation of 0.6% to 1.7% during ICRS implantation2,3-at a high-volume center like ours small percentages still translate into large numbers of patients.

We have recently begun using an optical coherence tomography (OCT)-guided femtosecond laser (Z6, Ziemer Ophthalmic Systems) to implant the ICRS. This system allows surgeons to visualize the endothelium both before and during laser ablation, a feature that further minimizes the risk of endothelial perforation.

More specifically, the OCT component of the system lets surgeons confirm the integrity of the endothelium of the applanated cornea before making the tunnel and to view its depth in real time in the x- and y-axis windows.

The system also provides a visual plan of the intended tunnel. Tunnel creation can then be followed in real time through the appearance of bubbles.

Tunnel formation can also be confirmed by comparing images of the endothelium before and after ablation (bubbles will be absent before ablation, whereas they will be present after ablation).

Insertion of the corneal ring into the tunnel created with this system is very simple.

Case reports

Initial results with the OCT-guided femtosecond laser system have convinced us that ring implantation with this system can ameliorate ectasia while eliminating the occurrence of endothelial perforations.

Two case reports demonstrate the safety and efficacy of using the ring in combination with the OCT-guided system.

> The first patient is a 33-year-old woman with keratoconus in her left eye. Preoperative exams revealed good visual acuity-uncorrected distance visual acuity (UDVA) of 1.0 decimal and corrected distance visual acuity (CDVA) of 1.5 decimal. She had a Kmax of 46.60 D and a Kmean of 44.40 D.

> The second patient was a 22-year-old woman with ectasia in her left eye. She had UDVA of 0.15 decimal, CDVA 0.70 decimal, Kmax 49.10 D, and Kmean 42.00 D.

On account of the topographies, we decided to implant the device (SI5 Keraring) with an arc length of 160° and a thickness of 200 µm in both patients.

Although the patient with keratoconus showed a transient drop in UDVA and CDVA 1 day after surgery, she had complete restoration of her distance vision by 1 week postoperatively, achieving the same distance visual acuity as before surgery (Figure 1A and 1B).

The patient with ectasia, having gone into surgery with low visual acuity, showed a gradual improvement of UDVA and CDVA after surgery, with UDVA reaching 0.6 decimal and CDVA reaching 0.9 decimal 1 week after surgery (Figure 1A and 1B).

In terms of topography, the patient with keratoconus who had inferior temporal placement of the ring showed an improvement of 5.3 D a week after surgery (Figure 2A).

In the patient with ectasia, we implanted the ring inferiorly. At 1 week postoperatively she, too, showed a substantial improvement in K value of 6.5 D (Figure 2B).

The implantation procedure was simple and straightforward, and the patients’ corneal curvatures were improved.

In both cases, the ring was effective in improving visual acuity and keratometric readings. Furthermore, use of the OCT-guided system simplified the implantation of the ring and eliminated the risk of endothelial perforation.

Conclusion

The marriage between an established solution for keratoconus/ectasia-an ICRS and an OCT-guided femtosecond laser system for implantation-will simplify corneal ring surgery and make it safer in the future. This combination will be a boon to centers providing high-volume LASIK and keratoconus treatment.

References

1.  Ruckhofer J, et al. J Cataract Refract Surg. 2001;27:287–296.

2.  Coskunseven E, et al. Acta Ophthalmologica. 2011;89:54–57.

3.  Ferrer C, et al. J Cataract Refract Surg. 2010;36:970–977.

Minoru Tomita, MD, PhD

e: tomita@shinagawa-LASIK.com

Dr. Tomita is director of Shinagawa LASIK Centre, Japan.