Mifflin MD, Mortensen XM. Intraoperative optical pachymetry in photorefractive keratectomy.
J Cataract Refract Surg 2019;
45:495-500. [PMID:
30819562 DOI:
10.1016/j.jcrs.2018.11.033]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 11/24/2018] [Accepted: 11/28/2018] [Indexed: 11/30/2022]
Abstract
PURPOSE
To study the effect of variables on the accuracy and reliability of the optical pachymeter built into the WaveLight EX500 excimer laser during photorefractive keratectomy (PRK).
SETTING
John A. Moran Eye Center, University of Utah, Salt Lake City, USA.
DESIGN
Retrospective case series.
METHODS
A chart review of 352 eyes (181 patients) that had excimer laser PRK was performed. Programmed excimer laser residual stromal bed (RSB) measurements, optical pachymeter measurements after ablation, and Scheimpflug pachymetry measurements (Pentacam) at the 1-year follow-up were compared. Variables included ablation time, preoperative spherical equivalent (SE), 1-year SE, mitomycin-C use, operating room temperature and humidity, and programmed monovision.
RESULTS
The mean programmed RSB was 27 μm greater than the optical pachymetry post-ablation measurement (P < .001). Of patients with a 1-year follow-up, the 1-year Scheimpflug pachymetry RSB was 24 μm greater than the optical pachymetry post-ablation RSB (P < .001). Comparison of the programmed RSB with the optical pachymetry post-ablation RSB showed that the preoperative SE and ablation time had a Pearson correlation coefficient of -0.36 and 0.30, respectively (P < .001). There was no correlation between operating room temperature, humidity, or programmed monovision with these differences.
CONCLUSIONS
The RSB post-ablation values measured by optical pachymetry during PRK were significantly lower than the programmed excimer laser RSB value and 1-year Scheimpflug pachymetry RSB value. Intraoperative pachymetry during PRK underpredicted the actual long-term RSB thickness. The greater temporary drying effect associated with increased ablation time in higher myopic corrections might have caused this error.
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