Agreement of non-contact pachymetry after LASIK: comparison of combined scanning-slit Placido disc topography and specular microscopy

• Published in: Eye (London) Vol. 24; no. 6; pp. 1064 - 1070
• Main Authors: López-Miguel, A, Nieto, J C, Díez-Cuenca, M, Piñero, D P, Maldonado, M J
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2010; Nature Publishing Group
• Subjects: Biological and medical sciences; clinical-study; Cornea - anatomy & histology; Cornea - diagnostic imaging; Cornea - surgery; Corneal Topography - instrumentation; Corneal Topography - methods; Humans; Keratomileusis, Laser In Situ; Laboratory Medicine; Medical sciences; Medicine; Medicine & Public Health; Miscellaneous; Myopia - surgery; Ophthalmology; Pharmaceutical Sciences/Technology; Surgery; Surgical Oncology; Ultrasonography; Orbscan-II pachymetry; LASIK; central corneal thickness; specular microscopic pachymetry; Postoperative; Cornea; Keratomileusis; In situ; Pachymetry; Specular microscopy; Contact; Photorefractive keratectomy; Thickness; Agreement; Topography; Laser; Ophthalmology; Comparative study
• ISSN: 0950-222X; 1476-5454
• DOI: 10.1038/eye.2009.233

Purpose To assess the interchangeability of central corneal thickness (CCT) measurements between combined scanning-slit/Placido disc topography (Orbscan-II) and specular microscopy (Topcon SP-2000P) in patients who underwent laser in situ keratomileusis (LASIK) for myopia. Patients and methods We recruited 118 consecutive patients who underwent LASIK for myopia. The CCT was measured using Orbscan-II and Topcon SP-2000P randomly. Orbscan-II and Topcon SP-2000P CCT data were analysed using the paired-sample t -test and the limits of agreement (LoA) were calculated with the method described by Bland–Altman. Results The average CCT measurements by Orbscan-II and Topcon SP-2000P were 447.55±49.78  μ m and 461.38±35.35  μ m, respectively ( P <0.0001; mean difference, 13.83±22.31  μ m; 95% confidence interval, 9.77–17.09  μ m). The Bland–Altman plot showed an inverse association between the average and the difference between the devices: Topcon–Orbscan-II=174.23 –0.353 × Average ( P <0.01). The widths of the crude and regression-based 95% limits of agreement were 87.45 and 63.72  μ m, respectively. Conclusions Orbscan-II measurements of CCT after myopic LASIK were significantly lower than those obtained using Topcon SP-2000P. The limits of agreement between the two devices were too broad and, therefore, both pachymetric values cannot be used interchangeably. Further, the tendency towards comparably Orbscan-II readings in thinner corneas precludes that one technique can directly replace the other. This is important for the adequate medium- and long-term follow-up of the growing LASIK patient population.