Post-keratorefractive ectasia is one of the most serious complications of LASIK, PRK, and SMILE. It is characterized by progressive and eccentric thinning of the corneal stroma, accompanied by steepening of the anterior and posterior surfaces. It is irreversible and significantly reduces both uncorrected and spectacle-corrected visual acuity.
The overall incidence of postoperative ectasia is reported to be 0.02–0.6%. By procedure, it is 90 per 100,000 eyes for LASIK, 20 for PRK, and 11 for SMILE, with LASIK having approximately 4.5 times the incidence of PRK1). However, the follow-up period after SMILE approval is short, so the incidence may be underestimated1).
Corneal ectasia is thought to result from insufficient corneal thickness, worsening of pre-existing subclinical keratoconus, and postoperative manifestation of genetically determined ectasia1). Even in cases with identified risk factors, ectasia has been reported in individuals without any known risk factors, particularly in younger patients.
It is estimated that up to 6% of refractive surgery candidates have some form of subclinical ectatic disease, making improved preoperative screening essential.
Patients notice progressive myopia and astigmatism months to years after surgery. Initially correctable with glasses or contact lenses, but as it progresses, irregular astigmatism reduces corrected visual acuity. Increased higher-order aberrations, especially vertical coma, cause point light sources to appear with a downward tail.
Color-coded maps of corneal topography show localized steepening and asymmetric patterns 1). The following findings support the diagnosis.
Slit-lamp microscopy reveals findings similar to keratoconus. Characteristic features include Fleischer ring (iron deposition in the epithelium at the base of the cone), Vogt’s striae (folds in Descemet’s membrane), scarring at the corneal apex, and prominent corneal nerves 1). In advanced cases, acute corneal hydrops may occur due to rupture of Descemet’s membrane.
Note that due to the biomechanical weakening and thinning of the cornea associated with ectasia, Goldmann applanation tonometry may measure intraocular pressure lower than the actual value 1).
Postoperative ectasia is detected within 1 year in about 30% of cases and within 2 years in about 70%, but it may also develop several years later 2). Progression tends to be faster in younger patients, making long-term follow-up important.
The pathogenesis of corneal ectasia involves genetic, biochemical, and biomechanical factors 1). Specific risk factors for refractive surgery are as follows.
Corneal Parameters
Abnormal corneal topography: Including forme fruste keratoconus
Low preoperative corneal thickness: Less than 500 μm
Low residual stromal bed (RST): Less than 280 μm2)
High LT index: Maximum ablation thickness/CCT ratio > 28%2)
High PTA: Percent tissue altered > 40%
Patient Factors
Young age: Under 34 years. Progression in 77% of those aged 18 or younger3)
High myopia: Spherical equivalent > 8 D
History or family history of keratoconus
Eye rubbing habit1)
Comorbid atopic disease1)
The proposed risk scoring system assigns 0–4 points to each of the following five factors for comprehensive assessment1).
| Factor | High-Risk Criteria |
|---|---|
| Corneal topography pattern | Abnormal pattern |
| RST thickness | Low |
| Age | Young |
| Corneal thickness | Low |
| Myopia degree | High |
Logistic regression analysis identified “abnormal corneal topography” as the most important predictor. However, the clinical utility of this scoring system remains debated.
PTA = (flap thickness + ablation depth) / central corneal thickness. PTA ≥ 40% is strongly associated with ectasia development even in eyes with normal corneal topography. However, for SMILE/KLEx, since the cap maintains structural integrity, it is debated whether the same PTA threshold as LASIK should be applied 2). When cap thickness is included in the calculation for PTA > 40%, 31.9% of all eyes meet this criterion, but no postoperative ectasia was observed during follow-up of more than 3 years 2).
Corneal topography or RST alone does not exceed 70% sensitivity in predicting postoperative ectasia 2). Comprehensive evaluation using multimodal data is necessary 2).
Proposed biomechanical criteria for suspected ectasia include CBI (Corvis Biomechanical Index) > 0.5 and TBI (Tomographic and Biomechanical Index) > 0.29 2).
Down syndrome, connective tissue diseases (such as Ehlers-Danlos syndrome and osteogenesis imperfecta), obstructive sleep apnea, high BMI, and floppy eyelid syndrome have also been reported as risk factors 1).
Eye rubbing is the only lifestyle factor confirmed to be associated with progression, and behavioral modification guidance is recommended for all patients 1).
Placido disc-based corneal topography images the anterior corneal surface. It evaluates only about 60% of the corneal surface and lacks peripheral data, limiting its ability to detect pellucid marginal degeneration 1).
Scheimpflug cameras (such as Pentacam) and slit-scanning tomography enable three-dimensional evaluation of the cornea (anterior and posterior surfaces plus total corneal thickness map) 1). They expand diagnostic criteria for keratoconus, forme fruste keratoconus, and post-refractive ectasia, and are considered essential for proper screening of refractive surgery candidates 1).
Belin-Ambrósio Enhanced Ectasia Display (BAD): Software available on Pentacam that analyzes nine parameters to calculate the “D value” (BAD-D) 1). A BAD-D > 1.65 is the threshold for suspected ectasia 2). It is a multivariate index integrating anterior elevation, posterior elevation, and pachymetric data, and is useful for detecting forme fruste keratoconus 1).
In keratoconus, the epithelium over the thinned stroma undergoes compensatory remodeling, showing a “doughnut pattern” with central epithelial thinning and surrounding epithelial thickening 1). This can be accurately mapped using high-resolution AS-OCT or high-frequency ultrasound 1).
Provides high-resolution cross-sectional images of the cornea, angle, anterior chamber, and anterior lens 1). Pachymetric mapping is possible, and software for keratoconus detection is also available 1).
The 2015 international consensus defined “progression of ectasia” as consistent changes exceeding measurement noise in at least two of the following parameters.
In young patients (18 years or younger), progression on tomography has been reported in 77% of cases3), and it is recommended to shorten the examination interval and evaluate over time with the same device whenever possible.
| Parameter | Progression threshold |
|---|---|
| KMAX | +1.20 D or more3) |
| Posterior elevation | +24.3 μm or more3) |
| Thinnest corneal thickness | −30.5 μm or more3) |
Corneal topography (Placido disc) alone is insufficient. Three-dimensional evaluation of the anterior and posterior surfaces and corneal thickness using Scheimpflug tomography (e.g., Pentacam) is essential. Furthermore, a comprehensive assessment combining BAD-D calculation, epithelial thickness mapping with AS-OCT, and corneal biomechanical measurement (e.g., Corvis ST) is recommended.
When ectasia is confirmed, the treatment strategy has two main pillars: preventing progression and correcting visual function.
Corneal Cross-Linking (CXL): Recommended as the first-line treatment for confirmed progressive corneal ectasia 1)2). It promotes cross-linking of corneal collagen using riboflavin and ultraviolet irradiation to stabilize the corneal structure. There are standard, accelerated, and pocket methods 2). For patients at high risk of progression (e.g., prepubertal), early CXL is recommended without waiting for further vision loss 1).
Vision Correction: Glasses or contact lenses are the mainstay of treatment for most patients 1). In mild cases, soft contact lenses may be sufficient, but for high irregular astigmatism, rigid contact lenses are prescribed. Emphasis is placed on good centration and movement; if spherical lenses are not possible, multi-curve lenses can be selected.
Topography-Guided PRK + CXL: This approach simultaneously reduces corneal irregular astigmatism and stabilizes the structure in advanced ectasia. Planning methods such as the Athens protocol (Kanellopoulos) and the LYRA/San Diego protocol (Motwani) have been reported 4). In Motwani et al.’s cases, the LYRA/San Diego protocol improved uncorrected visual acuity to 20/20 and reduced higher-order aberrations (HOA RMS) from 1.642 to 0.920 4). However, evidence is still limited; it is recommended to perform this procedure with RSB > 350 μm, maximum ablation depth within 50–60 μm, and simultaneously with CXL 4).
Electron microscopy studies show Z-shaped breaks in Bowman’s layer. The epithelial layer extends posteriorly into Bowman’s layer, and collagen extends anteriorly into the epithelial layer. This fragmentation of Bowman’s layer is similar to that in keratoconus and is considered an early change leading to ectasia.
In the proposed pathophysiological model, the essence of ectasia is not primary collagen fiber insufficiency, but interlamellar biomechanical slippage caused by excimer laser destruction, followed by interfibrillar biomechanical slippage 2). Regardless of the presence or absence of ectasia after LASIK, corneal biomechanical stability deteriorates rapidly when RST falls below 280 μm 2), and when the LT index exceeds 28%, the rate of change in CH and CRF increases significantly 2).
Enzyme activity abnormalities and oxidative stress are involved in the pathogenesis of corneal ectasia 1). In keratoconus corneas, increased matrix metalloproteinases (MMPs) and decreased tissue inhibitors of metalloproteinases (TIMPs) are observed, leading to progressive matrix degradation 1). Inflammatory mediators such as IL-6, TNF-α, and mucosal pemphigoid-9 are increased in tears, promoting apoptosis of keratocytes 1). Although corneal ectasia has traditionally been classified as “non-inflammatory,” inflammation may directly or indirectly contribute to its pathogenesis and progression 1).
Connective tissue diseases with collagen abnormalities and hyperelasticity, such as Ehlers-Danlos syndrome, osteogenesis imperfecta, congenital hip dysplasia, nail-patella syndrome, and pseudoxanthoma elasticum, are associated with keratoconus 1). It is thought that patients with genetic predisposition develop ectasia when exposed to environmental secondary stimuli such as eye rubbing or iatrogenic thinning from refractive surgery 1).
In 2025, the first guidelines dedicated to Keratorefractive Lenticule Extraction (KLEx / SMILE-type) were published, following WHO guideline development procedures 2). They recommend RST ≥ 280 μm and LT index ≤ 28%, and state that RST < 250 μm is not acceptable even considering measurement error 2). Ultra-thin caps with cap thickness < 100 μm are not recommended 2). It was shown that biomechanical evaluation can complement the limitations of topography and RST 2).
A DNA test for corneal ectasia risk by Avellino Labs received FDA approval in 2021. It is expected as a screening tool for high-risk candidates for refractive surgery, but further validation is needed to establish its clinical utility and scope of application.
It has been shown that corneal topography or RST alone does not exceed 70% sensitivity in predicting postoperative ectasia 2). The future direction is multimodal evaluation integrating anterior and posterior corneal shape, pachymetry, epithelial thickness, and biomechanics, along with the development of automated screening using artificial intelligence.
Check the BAD-D value on Scheimpflug tomography and evaluate the presence of posterior elevation. It is also important to check for a “doughnut pattern” of central thinning and peripheral thickening on epithelial thickness mapping. CBI > 0.5 and TBI > 0.29 are biomechanical criteria for suspected ectasia. Also inquire about family history of keratoconus, atopy, and eye rubbing habits.
American Academy of Ophthalmology Corneal/External Disease Preferred Practice Pattern Panel. Corneal Ectasia Preferred Practice Pattern. San Francisco, CA: AAO; 2024.
Guideline Development Group. Evidence-Based Guidelines for Keratorefractive Lenticule Extraction Surgery. Ophthalmology. 2025;132(4):395-410.
Meyer JJ, Gokul A, Vellara HR, McGhee CNJ. Progression of keratoconus in children and adolescents. Br J Ophthalmol. 2023;107(2):176-180. doi:10.1136/bjophthalmol-2020-316481.
Motwani M, Agu E, Xu A, Yung M. Application of Surgical Protocols for the Treatment of Highly Irregular Astigmatism with Topographic Guided Ablation in a Case of Post-LASIK Ectasia. Int Med Case Rep J. 2025;18:91-98.
