Resumen de Influence of stromal surface humidity in intraoperative ultrasound pachymetry during LASIK

Rafael Bilbao Calabuig, Valentín Jiménez Mateo Sidrón, Fernando J. Gómez Sanz

• PURPOSE: To investigate the influence of surface stromal humidity in intraoperative ultrasound pachymetry during LASIK.

  SETTING: Clínica Baviera, Instituto Oftalmologico Europeo, Madrid, Spain.

  DESIGN: Evaluation of diagnostic test or technology.

  METHODS: In this prospective study, 267 consecutive eyes were operated by 2 experienced surgeons: after the corneal flap was cut with the Moria LSK-One microkeratome, it was lifted and the degree of stromal surface humidity was evaluated on a subjective scale; we then measured stromal bed thickness with ultrasonic pachymetry before and after drying the stromal surface with a Weck-cel sponge. Flap thickness was calculated taking into account preoperative pachymetry. Statistical analysis was performed using the paired Student t-test to evaluate the difference between wet and dry stromal bed pachymetry, and a multivariate regression analysis of this difference with several clinical parameters was made.

  RESULTS: Mean flap thickness before drying was 93 ± 15 μm, and after drying 102 ± 15 μm. The mean difference between wet and dried stromal bed pachymetry was 8.8 ± 5.5 μm (P<0.001). This difference was not associated with the surgeon, preoperative pachymetry or keratometry, flap thickness, suction ring or right or left eye. The only variable showing a significant influence to explain the difference found between wet and dry measurements was stromal bed humidity (P<0.05).

  CONCLUSIONS: When performing intraoperative LASIK ultrasonic pachymetry, the actual stromal thickness should be considered to be around 10 microns less than the thickness measured without drying. In case of thin preoperative pachymetry, large ablations or a very wet stromal surface, drying the surface before pachymetry could improve the safety of the procedure