Screening For Post Laser Vision Correction Ectasia Risk: Are We Doing It Right?

To analyze the preoperative tomographic and biomechanical data of patients submitted to laser vision correction (LVC) - photorefractive keratectomy (PRK) and femtosecond laser-assisted in-situ keratomileusis (fLASIK) - for the correction of myopia and/or astigmatism and to evaluate their pre and 6 months’ postoperative ectasia risk.

Refractive Surgery Unit of the Ophthalmology Department of Centro Hospitalar Universitário de Santo António, Oporto, Portugal.

Retrospective study including patients submitted to fLASIK and PRK in our center, between November 2020 and December 2021. A total of 266 eyes from 138 patients were included: fLASIK (n=182) and PRK (n=84). Corneal tomography was evaluated through Scheimpflug tomography (Pentacam HR, Oculus) and biomechanical evaluation was made using Corvis ST (Oculus). Along with parameters like minimum pachymetry, IHD, ARTmax, BAD-D, Corvis Biomechanical Index (CBI) and Tomographic Biomechanical Index (TBI), the risk of preoperative ectasia was assessed using the Percent Tissue Altered (PTA) and an artificial intelligence tool (Brain Cornea). Six months after surgery, besides refractive outcomes evaluation, the CBI-LVC was also evaluated.

Preoperatively, PRK eyes presented lower minimum pachymetry (531,3±15,9 vs 567,1±23,9 fLASIK, p<0,001) and ARTmax (408,9±48,95 vs 487,3±64,99 fLASIK, p<0,001), and higher BAD-D (1,01±0,41 vs 0,59±0,39 fLASIK, p<0,001), CBI (0,30±0,18 vs 0,10±0,10 fLASIK, p<0,001) and TBI (0,14±0,13 vs 0,08±0,11 fLASIK, p=0,001). Brain Cornea (fLASIK: 10,6±16,1, PRK: 3,2±5,3 p<0,001) and PTA (fLASIK: 0,30±0,04, PRK: 0,18±0,05 p<0,001) were significantly higher in fLASIK eyes. No eyes exhibited a PTA >0,4. Six months after surgery, CBI-LVC was <0,2 in all eyes and did not differ significantly between groups (fLASIK: 0,01±0,09, PRK: 0,03±0,13 p=0,322). Also, eyes with higher preoperative risk of ectasia did not show different values in CBI-LVC.

Our study shows that preoperative screening favored the choice for PRK in cases of thinner corneas or eyes with suspicious ectasia risk features. Overall, the preoperative ectasia risk of our sample was low and at the 6-month follow-up visit, the corneal ectasia risk as measured by CBI-LVC was residual in both groups. To further support these findings, an increased sample size, along with a longer postoperative follow-up period would be desired.