Intrastromal corneal ring segment helps correct high astigmatism after DALK

Physicians describe their surgical approach and outcomes from the first patients who underwent the technique.

Issue: September 25, 2016

ByAna Cruz Fourcade, MD

ByAdriana C. Lotfi, MD

ByCarlos H. Gordillo, MD

ByJuan C. Grandin, MD

Corneal transplantation has progressed significantly from full-thickness penetrating keratoplasty to selective corneal transplantation in which only the diseased portions of corneal tissue are replaced surgically with similar healthy donor tissue. This has revolutionized corneal transplantation because the healthy parts of the patient’s cornea are retained. When the endothelium is untouched surgically, this eliminates the possibility of endothelial graft rejection. The diseased portion of the cornea needs to be localized to the anterior regions of the patient’s cornea, such as in keratoconus, while the endothelium remains healthy.

When the corneal stroma is replaced almost fully or totally, as in deep anterior lamellar keratoplasty or total anterior lamellar keratoplasty, this requires corneal sutures to retain the donor corneal disc in place. The circular corneal wound along with the corneal sutures can introduce corneal astigmatism that can significantly alter the quality of postoperative vision in these procedures.

In this column, Drs. Grandin, Lotfi, Cruz Fourcade and Gordillo describe their surgical approach in reducing corneal astigmatism and improving quality of vision by using an intrastromal corneal ring segment and femtosecond laser following DALK. While this elegant surgical technique appears promising in the management of corneal astigmatism following DALK, larger patient numbers and longer follow-up are necessary to evaluate the overall long-term efficacy and reproducibility of this procedure.

Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor

The purpose of this study is to describe the surgical technique and first outcomes of Intraseg intrastromal corneal ring segment (ICR) implantation, assisted with IntraLase (Abbott Medical Optics), for reducing high astigmatism in patients with previous deep anterior lamellar keratoplasty. Ametropia due to high spherical or astigmatic error is the leading cause of low vision in patients with corneal grafts. After topography-guided, selective suture removal in DALK, there are many surgical options to correct a high degree of astigmatism. They include relaxing procedures such as transverse or arcuate keratotomy, wedge resection, repeat keratoplasty, phakic IOL implantation and excimer laser photoablation techniques. Several studies have reported the use of an ICR after penetrating keratoplasty. We are using the Intraseg ICR (Gamma Vision) to treat postoperative astigmatism after DALK, assisted with femtosecond laser. We will evaluate the improvement in uncorrected distance visual acuity, corrected distance visual acuity, refractive astigmatism and topographic changes.

Patients and methods

We included our first 22 patients who underwent ICR implantation assisted with IntraLase for reducing high astigmatism after DALK with 18 months of follow-up. Complete ophthalmological examination, corneal topography and anterior segment OCT were performed preoperatively and postoperatively at 1 day, 3 days, and 1, 3, 6, 12 and 18 months.

Figure 3. Anterior segment OCT of an ICR placed in DALK.

Figure 5. Example case of ICR in a previous DALK.

Figure 6. Example case of ICR in a previous DALK. Low- and high-power slit lamp photographs display the corneal ring segment.

Patient selection

We included cases with high astigmatism of more than 5 D after DALK, without sutures remaining in the graft. The requirement included that the visual system should have the potential to gain vision after the surgery. Corneal astigmatism after DALK is usually regular, in contrast to irregular astigmatism of keratoconus. The cornea should be clear, without opacities, scars or vascularization, and the endothelial cell density must be more than 1,000 cell/mm2. The ICR surgery was performed at least 1 year after the DALK procedure. The median time of placing an ICR in our patients was 32 months after DALK.

Ring segment selection

Using our own nomogram (Intraseg Smart nomogram, Gamma Vision) (Figure 1), ring segment diameter and thickness are selected based on various parameters such as corrected distance visual acuity, keratometry readings, type of astigmatism, corneal pachymetry, patient’s previous graft size and pupil diameter. Ring diameter is usually 5 mm with different options of arc length of 90°, 120°, 150° and 210° and thickness of 25-µm steps from 100 µm to 275 µm (Figure 2).

Surgical technique

After ring selection, parameters are set in the femtosecond laser, including tunnel inner diameter of 5.4 mm and outer diameter of 6 mm or 6.2 mm, which creates a circular tunnel and a single incision. Based on corneal pachymetry, the tunnel depth created for placing the ICR is set at 80% of the minimum corneal thickness. Preoperative eye drops include proparacaine hydrochloride 0.5%, lidocaine 4%, moxifloxacin 0.5% and pilocarpine hydrochloride 2%.

After the patient is positioned in the IntraLase bed, the eyelashes are covered with a plastic adhesive drape and the lid speculum is applied, the cornea is marked in the middle of the graft (coincident with the center of the pupil in cases of well-centered grafts). A disposable suction ring for the IntraLase is placed. The laser creates the tunnel and an incision of 1.2 mm length on the selected axis. The Intraseg ring segments are implanted and placed in the final position with the help of special forceps (Figures 3 and 4). At the end of the procedure, a silicone-hydrogel bandage contact lens is placed on the cornea, and topical moxifloxacin 0.5%, prednisolone acetate 1%, phenylephrine 0.12%, ketorolac tromethamine 0.5% and cyclopentolate hydrochloride 0.5% are instilled in the eye. Topical steroids, antibiotics and artificial tears are prescribed for 1 month after surgery.

Results

The mean logMAR uncorrected visual acuity changed from 1.2 ± 0.7 preoperatively to 0.9 ± 0.3, and corrected distance visual acuity changed from 0.5 ± 0.4 to 0.2 ± 0.4. Mean manifest cylinder changed from –5.1 ± 1.5 to –3.5 ± 1.9. Kmax decreased from 50 ± 1.8 to 48.1 ± 3.1, while Kmin only changed from 43 ± 2.5 to 43.5 ± 3.4. Simulated keratometry decreased from 7.4 ± 2.3 to 5 ± 2.9. No complications occurred during or after surgery. Figures 5 and 6 show an example case of ICR segments that were placed in a previous DALK case.

Conclusion

Femtosecond-assisted intrastromal corneal ring segment implantation is an efficient procedure for reducing high astigmatism after lamellar keratoplasty, improving uncorrected and corrected distance visual acuities, producing topographical changes with the regularization of astigmatism and decreasing manifest cylinder with the consequent improvement of visual acuity.

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For more information:
Juan Grandin, MD, from the Instituto Zaldivar, Cornea Department, Mendoza, Argentina, can be reached at email: cornea@institutozaldivar.com.
Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University at Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at email: tjcornea@gmail.com.

Disclosures: Grandin reports he is a medical consultant for Gamma Vision. John reports no relevant financial disclosures.