PURPOSE
To compare measurements of ultrasound, Scheimpflug, and
optical coherence pachymetric techniques to describe ablated depth after myopic
astigmatic corneal laser refractive surgery and achieved refractive correction.
METHODS
Ninety-six myopic astigmatism treatments using LASIK or
LASEK in 58 patients with 3-month follow-up were retrospectively analyzed. In
all cases, standard examinations, pre-/postoperative corneal topography, ocular
aberrometry, and pachymetry were performed. SCHWIND Custom Ablation Manager
(CAM) software and the ESIRIS laser were used for planning treatments and
performing ablations. Outcomes were evaluated in terms of predictability,
safety, and wavefront aberration. Pachymetry was taken before treatment
(ultrasound [DGH Pachette 2], Scheimpflug [Oculus Pentacam HR], and optical
coherence pachymetry [OCP] [Heidelberg-Engineering OCP]), after lifting the
flap (Pachette 2, OCP), immediately after finishing ablation (Pachette 2, OCP),
and at 3-month follow-up (Pachette 2, Pentacam HR).
RESULTS
At 3 months, 87 (91%) of eyes achieved 20/20 UCVA, and 89
(93%) of eyes were within ±0.50 diopters (D). Postoperative mean
spherical equivalent refraction was –0.15±0.30 D. Best
spectacle-corrected visual acuity improved in 30 (31%) of eyes. Differential
pachymetry correlated to intended central ablation depth for all techniques:
r2=0.60, P<.0001, slope 0.81 for ultrasound;
r2=0.75, P<.0001, slope 0.97 for Scheimpflug; and
r2=0.76, P<.0001, slope 1.03 for OCP. Relative
differential pachymetry correlated only marginally to achieved refractive
correction for ultrasound and OCP.
CONCLUSIONS
Differential pachymetry is a metric useful for describing
intended central ablation depth but not for achieved refractive correction. The
rotating Scheimpflug technique offers the best estimation (closest slope to 1)
and OCP offers the best correlation (closest r2 to 1) for describing
intended central ablation depth achieved. The three techniques give different
measurements for ablation depth, with OCP being substantially different from
ultrasound and Scheimpflug. Only borderline correlations were obtained for
achieved refractive correction with ultrasound and OCP. [J Refract
Surg. 2009;25:699-708.]
doi:10.3928/1081597X-20090707-04
AUTHORS
From Muscat Eye Laser Center, Muscat, Oman (Arbelaez,
Vidal); Grupo de Investigación de Cirugía Refractiva y Calidad de
Visión, Instituto de Oftalmobiología Aplicada, University of
Valladolid, Valladolid, Spain (Arba Mosquera); and SCHWIND eye-tech-solutions,
Kleinostheim, Germany (Arba Mosquera).
Mr Arba Mosquera is an employee of SCHWIND
eye-tech-solutions (Kleinostheim, Germany). The remaining authors have no
proprietary interest in the materials presented herein.
Correspondence: Maria Clara Arbelaez, MD, Muscat Eye Laser
Center, PO Box 938, PC 117, Muscat, Oman. Tel: 96 824 691 414; Fax: 96 824 601
212; E-mail: drmaria@omantel.net.om
Received: January 8, 2008; Accepted: July 29, 2008
Posted online: September 15, 2008
