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Post-refractive surgery corneal ectasia is a rare but serious complication. Although ablative corneal surgery (such as PRK, LASIK, or guided surface surgery) is generally very safe, some eyes may experience structural weakening of the cornea over time, leading to ectasia.
Key aspects of this are outlined below: incidence, risk factors, clinical presentation, optical and surgical management, and prognosis.
Incidence and Safety of Ablative Surgery
Post-refractive ectasia is a rare complication. For example, in eyes without detectable risk factors, the estimated rates are:
PRK: 0.020% per 100,000 eyes
LASIK: 0.090% per 100,000 eyes
SMILE: 0.011% per 100,000 eyes
In general, most ablative corneal surgeries are performed without serious complications and with good visual outcomes.
However, ectasia, when it occurs, tends to behave more aggressively, with more rapid progression than in primary ectasia (such as idiopathic keratoconus).
Risk Factors for Post-Ablative Ectasia
Several predisposing factors increase the likelihood of ectasia occurring after refractive surgery:
Decreased corneal thickness before surgery (thin cornea).
Low residual stromal bed (RSB) thickness (<300 µm approx.).
High ablation depth (>75 µm).
High percentage of tissue altered (PTA) (>40%).
Young age at the time of surgery.
High degree of preoperative myopia or astigmatism.
Suspicious corneal topography or subtle irregularities (forme fruste of keratoconus) that may have gone undetected.
It is worth noting that studies have shown that in approximately 30% of cases of post-ablative ectasia, no clear prior risk is identified.
Clinical Behavior and Presentation
Post-ablative ectasia usually progresses more rapidly than normal spontaneous ectasia.
Initial symptoms may include:
Progressive decrease in visual acuity.
Need for higher-power optical correction (more myopia or astigmatism).
Visual distortions, irregular blurred vision.
Progression can begin several months after surgery, or even years later.
In studies, the average interval from surgery to ectasia diagnosis was ~73 months (about 6 years), although with great variability.
Urgency of Performing Cross-Linking (CXL)
To halt the progression of corneal thinning and deformation, it is essential to perform corneal cross-linking (CXL) as soon as possible once active ectasia is detected.
CXL strengthens the corneal matrix by forming additional bonds between collagen fibers, which helps stabilize the cornea.
Even with cross-linking, some eyes may continue to progress if the ectasia is very advanced.
CXL has been shown to be an effective measure to halt progression in multiple cases.
Optical Correction Options
To improve vision in eyes with refractive ectasia, the following optical strategies can be used:
Rigid gas permeable (RGP) lenses: These are one of the most widely used options for correcting corneal irregularities and achieving good visual acuity.
Piggyback system: a soft lens underneath and a rigid lens on top, combining comfort and visual quality.
Scleral lenses: These allow for comfortable fitting in highly irregular corneas and offer good visual quality, especially in advanced cases.
In cases where these modalities are not sufficient, intrastromal corneal segments (ICRS, "rings") can be considered, which modify corneal curvature and promote morphological regularization.
These options are often combined with cross-linking treatment to simultaneously stabilize the ectasia and improve vision.
Surgical Therapy and Corneal Transplantation in Severe Cases
In very severe or aggressive cases (scarring, extreme thinning, rapid progression despite CXL), a corneal transplant (PKP or lamellar) may be required as a salvage option.
In some combined cases, hybrid techniques can be used: cross-linking + ICRS + guided ablation, before transplantation.
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