Effect of Cone Location on Outcomes of Combined Topography-Guided PRK and Accelerated CXL
Purpose
To evaluate the effect of the keratoconus (KC) cone location on refractive, corneal aberrometric and biomechanical outcomes after combined topography-guided photorefractive keratectomy (T-PRK) and accelerated collagen crosslinking (ACXL).
Methods
T-PRK and ACXL using high intensity ultraviolet light was performed in KC eyes. Outcome parameters were assessed at baseline and 12 months after the procedures. Eyes with the cone located inside and outside the central 2 mm zone were classified as centered (C, n = 26) and decentered (DC, n = 12), respectively.
Results
The uncorrected distance visual acuity (UDVA) and best corrected distance visual acuity (BDVA) improved in both groups, more in the C (UDVA: p=0.01; BDVA: p<0.0001) than in the DC group (UDVA: p=0.03; BDVA: p=0.03). Similarly, sphere, cylinder, spherical equivalent, steep and flat K improved post-operatively more in the C than in the DC group (p<0.05). Total corneal aberrations root mean square (RMS), defocus and spherical aberration changed significantly (p<0.05) in the C group. In the DC group, the total RMS was the only variable with significant change. Interestingly, corneal hysteresis appeared to improve after treatment more in the DC (p=0.03 and 0.71 in the DC and C group, respectively). Corneal resistance factor also improved after treatment in both groups (p>0.05).
Conclusion
When combining T-PRK and ACXL, centered cones may provide better refractive and aberrometric outcomes than decentered ones. The cone location may be considered in patient-specific treatment planning.