Collagen crosslinking may improve intrastromal corneal ring segments effects
March 1, 2010
Intrastromal corneal ring segments can improve visual and refractive outcomes in eyes with keratoconus by reshaping the cornea, but collagen crosslinking may have an additive effect as an enhancement and stabilizing procedure.
Ankara, Turkey-Intrastromal corneal ring segments (Intacs, Addition Technology) can improve visual and refractive outcomes in eyes with keratoconus by reshaping the cornea, but collagen crosslinking (CXL) may have an additive effect as an enhancement and stabilizing procedure.
Evidence suggests that the most effective sequence of procedures is placement of the intrastromal corneal segments (ICS) first and that the interval between the two steps should be short, perhaps during the same session, said Aylin Kilic (Ertan), MD.
Dr. Kilic also has investigated CXL with intracorneal riboflavin injection during the same session as implantation of the intrastromal rings to strengthen the corneal structure and prevent progression of keratoconus.
Intrastromal rings reshape the surface of the keratic eye, improving vision and postponing or preventing corneal transplantation in the majority of cases. However, they do not treat the underlying structural problem of weakened collagen and may not stop progression of keratoconus, said Dr. Kilic, chairwoman, Department of Cataract and Refractive Surgery, Kudret Eye Hospital, Ankara, Turkey.
CXL, on the other hand, may change corneal intensity, rigidity, and function but does not significantly alter corneal shape.
The use of intrastromal ring implantation with and without CXL was reported in 2007 (Chan, et al.). Dr. Kilic said that she uses the combination of CXL and intrastromal rings in most of her patients with keratoconus other than young individuals with early-stage disease and good visual acuity.
A study by Dr. Kilic and colleagues (Cornea. 2009;28:719-723) reported refractive and topographic results of transepithelial crosslinking treatment in eyes with ICS. CXL after placement of the intracorneal segments produced additional improvement in uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), sphere, cylinder, and keratometry. In this study of 15 patients, the mean interval between ICS and CXL was nearly 4 months.
The preoperative mean ± SD UCVA was 1.61 ± 1.23. Three months after implantation, the mean UCVA was 3.58 ± 2.29 (p > 0.05). Data obtained 2 months after CXL showed that the mean UCVA was 4.80 ± 2.0 (p > 0.05). BCVA results in the same eyes showed a change from the preoperative mean of 4.18 ± 2.09 to 6.54 ± 2.02 after ICS implantation (p > 0.05). After CXL, the mean BCVA was 7.27 ± 2.02 (p > 0.05).
Dr. Kilic also provided an analysis of the change in parameters after ring implantation and after CXL. The mean change in UCVA between post-ICS and pre-ICS was 1.90 ± 2.04, while the change between post-CXL and post-ICS was 1.22 ± 0.084 (p > 0.05). BCVA following ICS implantation was 2.02 ± 1.53, and the change between post-CXL and post-ICS was 0.77 ± 1.60 (p < 0.05).
In her research, Dr. Kilic has attempted to achieve a higher degree of riboflavin penetration into the stroma as well as greater safety and efficacy. She has developed a new method in which riboflavin is injected into a channel created by a femtosecond laser immediately before ICS implantation. Additional riboflavin is administered over a 30-minute period following the implantation (simultaneously with irradiation with ultraviolet-A [UV-A]), followed by CXL.
She conducted a study in which this technique was used in 15 keratoconic eyes versus 13 eyes in which ICS implantation was followed at least 6 months later by CXL.
In the first group, riboflavin was injected into the channel 30 minutes before UV-A irradiation, followed by additional instillation during UV-A irradiation. In group 2, riboflavin was instilled before and during UV-A irradiation without corneal injection in eyes with ICS.
More improvement in UCVA and BCVA (both, p < 0.05) was observed in the eyes that received the riboflavin injection along with ICS and CXL. Improvement in keratometry was also statistically significant in the riboflavin group (p < 0.05); although more improvement in cylinder and sphere occurred in the riboflavin-treated eyes, the difference was not statistically significant.
Commenting on these findings, Dr. Kilic said that an immediate change in corneal thickness occurs following ICS, riboflavin, and CXL.
"For CXL safety, we should have a corneal thickness of at least 400 μm. The general rule for endothelial safety is not to perform CXL when the thickness is less than that," Dr. Kilic said. "If we inject riboflavin into the corneal channel, we are creating corneal edema and thickening of the cornea immediately, conditions that are suitable for CXL. In addition, riboflavin injection in the channel provides channel visibility, easier segment implantation during the surgical maneuver, and more penetration of riboflavin into the corneal stroma."