Characterization of Corneal Biomechanics Using CORVIS ST Device in Different Grades of Myopia in a Sample of Middle Eastern Ethnicity

Purpose

To characterize corneal biomechanical properties using the CORVIS-ST device in myopic individuals.

Methods

This prospective cross-sectional study included patients with myopia. Our study included 154 eyes of 154 myopic patients aged between 18 and 40 years, with stable refraction for at least 2 years. A full ophthalmological examination and corneal tomography were performed using a Pentacam HR device. Corneal biomechanical parameters were assessed using the CORVIS-ST device in mild, moderate, severe, and extreme myopia groups.

Results

Statistically significant differences were observed in the DA ratio (p = 0.033), SP-A (p=0.009), CBI (p=0.041), SSI (p=0.000), and Peak distance (p = 0.032). In correlation with different Corvis ST biomechanical variables, SE was found to be correlated with DA ratio(r=-0.191, p=0.018), SP-A(r=0.199, p=0.013) and SSI(r=-0.336, p=0.000), while in multiple regression analysis, SE was found to be independently correlated with SSI and peak distance(p=0.036,0.038 respectively) while the grade of myopia was found to be independently correlated with SP-A(p=0.034).

Conclusion

SSI, Peak distance, and SP-A were independently related to SE and myopia grade, confirming the hypothesis that eyes with higher myopia are more deformable and less stress resistant.

Simultaneous intratunnel cross-linking with intrastromal corneal ring segment implantation versus simultaneous epithelium-off cross-linking with intrastromal corneal ring segment implantation for keratoconus management

Purpose

The purpose of this study is to compare the efficacy of intratunnel cross-linking combined with intrastromal corneal ring segment (ICRS) implantation versus combined epithelium-off (epi-off) cross-linking and ICRS implantation for the management of keratoconus.

Methods

Our study included 20 eyes of 12 patients with moderate-to-severe keratoconus. Group A included 10 eyes that underwent simultaneous ICRS implantation with intratunnel cross-linking. Group B included 10 eyes that underwent simultaneous ICRS implantation with epi-off cross-linking. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest sphere and cylinder, mean and maximum keratometric readings, corneal thickness at pachy apex and thinnest location, as well as corneal hysteresis (CH) and corneal resistance factor (CRF) were compared preoperatively and at 6 months postoperatively.

Results

The mean UDVA and CDVA improved significantly in both groups with a statistically nonsignificant difference between the groups (P=0.798 and 0.126, respectively). The manifest cylinder decreased significantly in both groups, while the manifest sphere decreased significantly in Group A but nonsignificantly in Group B with a statistically nonsignificant difference between the groups (P=0.773 and 0.111, respectively). Both techniques led to significant flattening of the cornea and a significant decrease of K_m and K_max with a statistically nonsignificant difference between the groups (P=0.312 and 0.857, respectively). There was a statistically significant decrease in CH in both groups postoperatively; however, there was a statistically nonsignificant increase in CRF after both techniques with a statistically nonsignificant difference between the groups in the mean change of CH and CRF (P=0.633 and 0.313, respectively). No intraoperative or postoperative complications were observed in both groups.

Conclusion

Both techniques improved the visual and refractive outcomes in cases of moderate and severe keratoconus with no statistically significant difference between the groups; however, simultaneous intratunnel cross-linking and ICRS implantation showed early visual rehabilitation due to the absence of epithelial defect.

Femtosecond laser-assisted implantation of complete versus incomplete rings for keratoconus treatment

Purpose

To compare complete versus incomplete ring implantation for keratoconus correction.

Methods

We investigated 25 eyes of keratoconic patients, of which 15 had femtosecond-assisted MyoRing corneal implantation (Group 1) and 10 had femtosecond-assisted Keraring segments (Group 2). Uncorrected distance visual acuity (UCVA), best corrected distance visual acuity (BCVA), mean K (K_m), sphere, topographic cylinder, and corneal asphericity value (Q-value) were measured in all eyes preoperatively and at 4 weeks postoperatively (1 month).

Results

In Group 1, the K_m change was −6.15±2.16 D, with a mean change in sphere of 4.45±2.18 D and a mean change in refractive cylinder of 2.32±3 D. UCVA change was −0.57±0.273 logarithm of the minimum angle of resolution (LogMAR), BCVA change was −0.2±0.27 (LogMAR), and the Q-value change was 0.43±2.6. In Group 2, the K_m change was −3.15±1.68 D, UCVA change was −0.48±0.37 (LogMAR), BCVA change was −0.09±0.15 (LogMAR), and the Q-value change was 0.5±0.21. Changes in the means did not significantly differ between groups, except for the K_m change, which was significantly greater in Group 1 than in Group 2 (P=0.05).

Conclusion

Both complete ring and ring segment implantation are effective for improving corneal and visual parameters in keratoconus. Complete ring implantation may have a greater flattening effect on the anterior corneal surface.