Purpose: To report visual outcomes and corneal biomechanical changes after femtosecond-assisted Intacs SK implantation in keratoconic eyes.
Methods: This prospective interventional case series is comprised of 32 keratoconic eyes of 25 patients with mean age of 23.8 ± 5.4 years. Uncorrected (UDVA) and corrected (CDVA) distance visual acuity, refraction, manifest refraction spherical equivalent (MRSE), keratometry, central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF) were measured preoperatively, and 1, 3 and 6 months postoperatively.
Results: Mean UDVA improved from 0.81 ± 0.3 LogMAR preoperatively to 0.53 ± 0.2 LogMAR six months postoperatively (P < 0.001). At 6 months, MRSE was significantly reduced only in eyes with moderate KCN (mean change, +2.61 ± 0.54 diopter [D]; P< 0.001). A significant improvement in sphere (mean change, +1.92 ± 0.37 D; P< 0.001) and mean keratometry (mean change, -3.34 ± 0.47D; P< 0.001) were observed. CCT increased from 446.1 ± 38 μm preoperatively to 462.2 ± 50 μm at six months (P < .001). CRF decreased from 6.5 ± 1.6 mmHg to 5.9 ± 1.1 mmHg six months after surgery (P = 0.02). CDVA, refractive cylinder and CH did not change significantly (P = 0.48, 0.203 and 0.55, respectively). Linear regression analysis disclosed that a decrease in CCT and moderate KCN are associated with higher CRF (standardized B,-0.513 and 0.314;P= 0.004 and 0.024, respectively; Adjusted R square = 0.353).
Conclusion: Visual, refractive and keratometric indices remarkably improved in a parallel fashion. CRF was inversely associated with CCT. Changes in CRF represent the trend of changes in corneal biomechanics and thickness during the early postoperative months.
Keywords: Corneal Biomechanic; Corneal Hysteresis; Corneal Resistance Factor; Femtosecond Laser; Intacs SK; Intracorneal Ring Segment; Keratoconus.