To compare the measurements of posterior corneal
elevation above the best-fit sphere before and after photorefractive
keratectomy (PRK) using two different technologies—Scheimpflug imaging
using Pentacam (Oculus) and scanning slit combined with Placido imaging using
Orbscan II (Bausch & Lomb).
In a retrospective observational case series study, 60
eyes measured using Orbscan II and Pentacam before or after PRK were evaluated.
The data were analyzed as three groups: preoperative, early postoperative (from
1 to 3 months after surgery), and late postoperative (>3 months
postoperatively but not exceeding 1 year). Anterior chamber depth, posterior
best-fit float sphere, posterior central elevation (PCE) above the best-fit
sphere, and posterior maximum elevation (PME) above the best-fit sphere in the
6.0-mm zone were analyzed.
Posterior central elevation and PME values measured
using Orbscan II were greater than those measured using Pentacam
(P<.001). Anterior chamber depth values measured using Orbscan II
were smaller than those measured using Pentacam in all three groups
(P<.001). Using Orbscan II, PCE and PME values for the two
postoperative groups were greater than for the preoperative group. Using
Pentacam, the PCE values for the three groups were similar, and the PME values
for the preoperative and late postoperative groups were similar.
These findings indicate that Orbscan II measurements of
posterior corneal elevation before and after excimer laser refractive corneal
surgery may not be valid. Pentacam measurement showed no significant change in
posterior corneal elevation from before to after excimer laser corneal surgery.
[J Refract Surg. 2009;25:290-295.]
From the Institute of Vision Research, Department of
Ophthalmology, Yonsei University College of Medicine, Seoul (Sang W. Kim, E.K.
Kim, T. Kim); the Department of Ophthalmology, Soonchunhyang University College
of Medicine, Bucheon (Sun W. Kim); and Siloam Eye Hospital (Ha), Seoul, Korea.
The authors have no proprietary interest in the
materials presented herein.
Correspondence: Tae-im Kim, MD, Dept of Ophthalmology,
Yonsei University College of Medicine, Seodaemungu Sinchondong 134, Seoul,
Korea. Tel: 822 2228 3570; Fax: 822 312 0541; E-mail:
Received: September 5, 2007; Accepted: March 25, 2008
Posted online: June 13, 2008