Intraoperative optical pachymetry in photorefractive keratectomy

Area of Science:

• Ophthalmology
• Refractive Surgery
• Ophthalmic Technology

Background:

• Accurate measurement of residual stromal bed (RSB) thickness is crucial for refractive surgery safety and efficacy.
• The integrated optical pachymeter in the WaveLight EX500 excimer laser is used for intraoperative measurements during photorefractive keratectomy (PRK).
• Understanding factors influencing pachymetry accuracy is essential for optimizing PRK outcomes.

Purpose of the Study:

• To evaluate the accuracy and reliability of the WaveLight EX500's optical pachymeter during PRK.
• To identify variables affecting the precision of intraoperative RSB measurements.
• To compare optical pachymetry readings with programmed RSB and long-term Scheimpflug measurements.

Main Methods:

• A retrospective chart review of 352 eyes undergoing PRK.
• Comparison of programmed RSB, post-ablation optical pachymetry, and 1-year Scheimpflug pachymetry (Pentacam).
• Analysis of variables including ablation time, preoperative/1-year spherical equivalent (SE), mitomycin-C use, OR conditions, and monovision.

Main Results:

• Optical pachymetry post-ablation significantly underestimated RSB thickness compared to programmed RSB (mean difference 27 μm) and 1-year Scheimpflug measurements (mean difference 24 μm).
• Preoperative SE (r=-0.36) and ablation time (r=0.30) correlated with differences between programmed and optical pachymetry RSB.
• Operating room temperature, humidity, and programmed monovision did not correlate with measurement discrepancies.

Conclusions:

• Intraoperative optical pachymetry during PRK tends to underpredict actual long-term RSB thickness.
• Increased ablation time for higher myopic corrections may contribute to underprediction, potentially due to temporary corneal drying.
• The findings highlight potential inaccuracies in intraoperative pachymetry, necessitating careful consideration in PRK planning and execution.