Iatrogenic ectasia
Ectasia after photoablation is the most feared complication of refractive surgery, because it occurs in an eye operated on electively. It results from biomechanical weakening pushed beyond the threshold where the cornea no longer holds its shape: a predisposed cornea, an over-aggressive procedure, most often both. The mechanism is the same as in keratoconus.
Prevention rests entirely on preoperative screening and respecting the limits. The Randleman score (ERSS) aggregates topography, residual bed, age, thickness, spherical equivalent; the PTA captures global biomechanical insult in one number. Add posterior-surface tomography and dynamic biomechanical assessment, which detect the formes frustes that Placido topography alone misses. Once established, management mirrors keratoconus: cross-linking to stabilise, intracorneal rings to regularise, lamellar keratoplasty as a last resort.
Faced with doubtful topography, a thin cornea or a PTA near 40%, the right decision is often to decline photoablation — or switch to a surface technique, or an intraocular solution. No refractive correction is worth an ectasia.
Comparative synthesis
The choice reduces to three axes: comfort/speed, respect for load-bearing tissue, complication profile.
| Surface (PRK) | LASIK | Lenticule (SMILE/SILK) | |
|---|---|---|---|
| Pain / recovery | +++ / slow | + / fast | + / fast |
| Biomechanical sparing | Excellent (no flap) | Reduced by flap | Theoretically good — not shown > LASIK |
| Dryness | Low | Marked | Theoretically lower — debated |
| Thin / borderline cornea | Suitable | Unfavourable | Intermediate |
| Signature pitfall | Haze | Flap, DLK, ectasia | Lenticule extraction |
| Range & follow-up | Moderate · long track record | Wide · long track record | Wide for myopia; astigmatism, hyperopia, presbyopia only for < 2 years → short follow-up |
These categories do not replace the examination: it is the patient's cornea — thickness, topography, biomechanics — that ultimately designates the technique. The surgeon's role is less to prefer a procedure than to recognise, for each eye, the one that corrects without weakening.
Publications & sources
- Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg. 1988. — ablation formula.
- Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008. — Ectasia Risk Score System.
- Santhiago MR, Smadja D, Gomes BF, et al. Percent tissue altered and post-LASIK ectasia in eyes with normal topography. Am J Ophthalmol. 2014.
- Santhiago MR, Smadja D, Wilson SE, et al. Role of percent tissue altered on ectasia after LASIK in suspicious topography. J Refract Surg. 2015.
- Dupps WJ, Wilson SE. Biomechanics and wound healing in the cornea. Exp Eye Res. 2006.
- Netto MV, Mohan RR, Wilson SE, et al. Wound healing in the cornea: haze and myofibroblasts.
- Sekundo W, Blum M, et al. Small incision lenticule extraction (SMILE): principles and results.
- Sachdev MS, Shetty R, Khamar P, et al. Safety and effectiveness of SILK using the ELITA femtosecond laser. Clin Ophthalmol. 2023.
- Chen L, Khamar P, Wang Y, Fu H, Shetty R. Higher-order aberrations after SILK (ELITA). Clin Ophthalmol. 2024.
- Reinstein DZ, Archer TJ, Randleman JB. Corneal biomechanics & preoperative selection in refractive surgery. J Refract Surg.
- Sonmez B, Maloney RK. Central toxic keratopathy: description of a syndrome. Am J Ophthalmol. 2007. — CTK vs DLK grade IV status debated.
- Linebarger EJ, Hardten DR, Lindstrom RL. Diffuse lamellar keratitis: diagnosis and management. J Cataract Refract Surg. 2000.
- Flach AJ. Corneal melts associated with topical NSAIDs. Trans Am Ophthalmol Soc. 2001.
Titles and years are given as pointers; exact wording, volumes and pages to be verified on PubMed before dissemination. Numerical values (depth/diopter, PTA thresholds, residual bed) are literature landmarks to recalibrate on each case's platform, nomogram and pachymetry.