Evaluation Of Corneal Biomechanical Changes After Intrastromal Corneal Ring Segment Implantation In Keratoconus Patients Using Corvis Oculus

To evaluate the effect of stromal tunnel creation and ICRS surgery on corneal biomechanical indices measured by Corvis ST.

This study was done at Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.

We recruited the patients with keratoconus who were candidates for ICRS implantation surgery between January 2019 and July 2020. Patients with any history of ocular diseases and surgery, connective tissue disorders, pregnancy or lactation were excluded. Central corneal thickness, IOP, inferior-superior steepening, and also biomechanical parameters which could be obtained by Oculus Corvis including HCDA, A1L & A2L, HR, A1V & A2V, HCPD, SP-A1, DA.ratio, ARTh, IR, and CBI were recorded before and 6 months after surgery. All patients underwent Keraring implantation by manual technique by the same surgeon.

In the total of 26 eyes, the mean preoperative UDVA and CDVA of patients were 0.85±0.65 and 0.57±0.53 which significantly improved postoperatively to 0.48 ± 0.2 and 0.27 ± 0.18, respectively. Kmax and I-S value reduced significantly with P values of 0.005 and 0.002, respectively. CCT and IOP did not change significantly. The results of analysis of biomechanical parameters revealed that most of the biomechanical parameters had no statistically significant changes, except 2 parameters. One of them was ARTh which decreased in patients from the mean of 161.49 ± 31.58 to 126.16 ± 41.64 after the surgery with a P-value of 0.001. The other one was HR which decreased significantly from the mean of 6.42 ± 1.13 to 6.00 ± 1.26 with a P-value of 0.022.

Our study showed improvements in vision and corneal regularity 6 months after surgery. Nevertheless, most of the corneal biomechanical parameters remained stable except ARTh and HR. Since the segment Kerarings are located in the midperiphery of the post-surgical corneas, increase in the thickness toward the corneal periphery and the increase in ARTh is well justified. The HR parameter was also increased. It is possible for the rings to play a confounding role in this parameter, although ruling out the ectatic progression is only possible by longer follow ups and serial HR measurements. Results indicate that ICRS have no significant effect on corneal biomechanics and crosslinking should be considered in progressive or young patients.