We have recently seen an increased use of anterior-segment optical coherence tomography (AS-OCT) during surgical procedures such as Descemet-stripping automated endothelial keratoplasty and femtosecond LASIK.1 High-resolution AS-OCT can also be advantageous, both intra- and postoperatively, for implantation of intrastromal corneal ring segments (ICRSs) in keratoconic eyes.
When a patient presents with keratoconus, I perform a complete ophthalmic examination including topography and pachymetry. I also use the Ocular Response Analyzer (Reichert) to determine if corneal hysteresis is low, which raises the suspicion of keratoconus or corneal ectatic disorders. If, based on these findings, the patient is a suitable candidate for ICRS implantation, such as if he or she is spectacle and/or contact lens intolerant, I discuss the procedure and its potential results with the patient. It is essential to have a thorough discussion with each patient to understand what he or she wants and expects from the procedure.
In a recent study,2 I performed ICRS (Keraring; Mediphacos) implantation in 17 eyes of 13 patients with keratoconus, creating the corneal stromal tunnel with a femtosecond laser and then implanting the ring segment. AS-OCT was performed at postoperative month 3 (Figure 1). My colleagues and I measured the distance from the apex of the triangular cross-section of the ICRS to the anterior corneal surface and the distances from two basal corners to the posterior corneal surface (Figure 2). We determined that high-resolution AS-OCT was a rapid, convenient, and valuable technique in the follow-up of patients implanted with ICRSs.
Additionally, AS-OCT is helpful if there is an abnormality or a ring-related complication, as it enables the surgeon to determine the exact position of the ICRS. We know that sometimes these ICRSs may extrude through the cornea; using AS-OCT, we can determine if it is staying in same level in the cornea or if it is getting shallower or deeper.
It is likely that AS-OCT will continue to be used more frequently, and perhaps in the future it will be built into femtosecond lasers, as is being done in laser systems for cataract surgery. This would enable the surgeon to determine where he or she is creating the tunnels during ICRS implantation.
Pearls for ICRS Implantation
No. 1: Invest in a good AS-OCT system, as this device is especially helpful in corneal surgeries. We can exactly see how deep we implant ICRSs, and AS-OCT monitoring during follow-up exams over several postoperative years may be beneficial.
No. 2: The cornea is a delicate tissue that must be respected, as it cannot regenerate itself. When we perform any operation on the cornea, we must check repeatedly to ensure that we do not produce any harmful results.
No. 3: Perform ICRS implantation only in patients who will achieve the best results. Sometimes the patient desires an ICRS, but if I do not think he or she will benefit from the procedure, I will not implant it.
No. 4: ICRS implantation may be used to delay a second corneal transplantation. I treated a patient who worked with microscopes in a microbiology laboratory. She had undergone corneal transplantation in one eye, and she was contact lens intolerant in the other eye; she could not use the microscope. I informed her that ICRS implantation would not be a lifelong solution but that it could be used to postpone the second corneal transplantation. She underwent ICRS implantation and was able to use the microscope for several years. During subsequent penetrating keratoplasty in the second eye, I first explanted the ICRS and then performed the corneal transplantation; the patient is now happy with both eyes.
Raciha Beril Küçümen, MD, practices in the Department of Ophthalmology, Yeditepe University Eye Hospital, Istanbul, Turkey. Dr. Küçümen states that she has no financial interest in the products or companies mentioned. She may be reached at e-mail: email@example.com.
- Kucumen RB, Dinc UA, Yenerel NM, Gorgun E, Alimgil ML. Immediate evaluation of the flaps created by femtosecond laser using anterior segment optical coherence tomography. Ophthalmic Surg Lasers Imaging. 2009;40(3):251-254.
- Gorgun E, Kucumen RB, Yenerel NM, Ciftci F. Assessment of intrastromal corneal ring segment position with anterior segment optical coherence tomography. Ophthalmic Surg Lasers Imaging. 2012;43(3):214-221.