Percent tissue altered and corneal ectasia

Area of Science:

• Ophthalmology
• Corneal Surgery
• Refractive Surgery Outcomes

Background:

• Ectasia is a serious complication following laser in-situ keratomileusis (LASIK).
• Accurate risk assessment is crucial for patient safety in refractive surgery.
• Existing metrics may not fully capture ectasia risk.

Purpose of the Study:

• To review the association of percentage tissue altered (PTA) with post-LASIK ectasia.
• To analyze the components of PTA and their influence on ectasia.
• To evaluate PTA's role in eyes with normal and suspicious corneal topography.

Main Methods:

• Review of studies investigating the percentage tissue altered (PTA) metric.
• Analysis of PTA formula: (flap thickness + ablation depth) / preoperative central corneal thickness.
• Comparison of PTA's predictive capability against individual variables and patient age.

Main Results:

• A robust relationship exists between high PTA and ectasia risk in eyes with normal preoperative topography.
• PTA ≥40% demonstrated the highest odds ratio and predictive capability for ectasia.
• Even low PTA values were sufficient to induce ectasia in eyes with suspicious topography.

Conclusions:

• The novel metric, percentage tissue altered (PTA), is a valuable tool for screening refractive surgery candidates.
• Patients with normal topography and PTA ≥40% are at higher risk for post-LASIK ectasia.
• PTA should be considered in the risk assessment for LASIK, especially in eyes with concerning topography.