Enhanced Screening for Ectasia Risk prior to Laser Vision Correction

Abstract

Aim: To prospectively review current understanding and future trends of screening for keratectasia risk prior refractive laser vision correction (LVC).Background: Progressive keratectasia is an uncommon but severe complication of LVC. Preoperative ectatic corneal disease is the most important risk factor. Screening for subclinical ectasia relies on proper interpretation of advanced diagnostic technologies, including front surface corneal topography, three-dimensional tomography, and biomechanical assessments.Summary: Studies involving eyes with normal and stable corneas, compared to eyes with frank ectatic diseases and to eyes with normal topography from patients with very asymmetric ectasia, allow for developing advanced methods and testing its sensitivity. However, the ideal study populations for testing the sensitivity and specificity of ectasia risk assessments are respectively the preoperative of cases that developed ectasia and the ones with stable outcomes after LVC. Young age and low thickness are surrogates of corneal biomechanics, which may be replaced as risk factors by direct measurements. Keratectasia may also occur due to the surgical impact on corneal structure or due to significant trauma postoperatively. Percentage tissue altered higher than 40% is a more sensitive para meter than a fixed value for minimal residual stromal bed of 250 µm. However, the biomechanical impact from surgery is related to the region and number of lamellae that are severed, so that flap thickness and geometry should play a more relevant role, which is in agreement with finite element simulations. Arti ficial intelligence methods allow for combining parameters, which significantly enhance the accuracy for detecting ectasia risk. Conclusion:An enhanced screening approach for preventing keratectasia should consider both preoperative patient-related data and procedure-related parameters to individually characterize ectasia susceptibility or predisposition.Clinical Significance: Keratectasia is an uncommon, however, severe complication of LVC. Although prevention is the best strategy, an individualized enhanced ectasia screening approach for ectasia risk assessment prior to LVC procedures should integrate patient-related (individual ectasia susceptibility) and procedure-related parameters (biomechanical impact).

Short term changes in corneal stress-strain index and other corneal biomechanical parameters post-laser in situ keratomileusis

“…Previous studies have reported an increase in CBI in eyes with ectasia. [ 13 23 ] However, the newer software allows an automatic assessment of the biomechanical stability post-laser vision correction using a new metric called CBI- Laser Vision Correction (LVC). CBI-LVC estimates the risk for ectasia after laser vision correction.…”

Influence of tomographic and biomechanical corneal indexes on myopic refractive surgery indications: A multicenter study

“…To establish the risk of ectasia or subclinical keratoconus diagnosis, cut-off points were set for tomographic and biomechanical index. Based on Belin and Ambrósio 19 (for BAD), Vinciguerra et al 10 (for CBI) and Ambrósio et al 11 (for TBI), indexes were set on 1.2, 0.2 and 0.16, respectively.…”

“…Soft contact lens wearers were advised not to use them at least 7 days before preoperative assessment and hard contact lens wearers a longer period of 15 days prior to examinations, (10) anterior chamber depth (ACD) from endothelium ≥ 2.8 mm (11) endothelium cell density (ECD) ≥ 2000 cells/mm 2 . Exclusion criteria were: (12) hyperopia, (13) eye diseases, such as glaucoma and cataracts, (14) progressive corneal diseases, such as keratoconus or the presumed keratoconus and pellucid marginal degeneration (Topographical Keratoconus Classification ≥ 1), (15) ocular surface diseases, (16) signs of retinal vascular pathology, (17) immunodeficient patients or those diagnosed with connective tissue diseases, (18) pregnant or breastfeeding patients, (19) patients with known sensitivity to the drugs used in LVC or pIOL surgery, (20) patients with eye muscle disorders such as strabismus or nystagmus, or any other disorder that affects ocular fixation and ( 21) patients without visibility or with amblyopia in the other eye.…”

First Clinical Impressions on the Integrated Corneal Tomography and Corneal Deformation with Scheimpflug Imaging

“…14 Candidates for refractive surgery often have no to mild topographic changes that may progress to corneal ectasia after laser refractive surgery. 15 Scheimpflug corneal tomography is effective in detecting moderate to severe changes of the anterior corneal surface but has lower sensitivity in mild ectasia or fruste keratoconus.…”