Comparison of corneal thickness measurements using ultrasound and Orbscan slit-scanning topography in normal and post-LASIK eyes

Chakrabarti, H S; Craig, Jennifer P.; Brahma, Arun; Malik, Tahira Y; McGhee, Charles N J

doi:10.1016/s0886-3350(01)01089-6

Cited by 139 publications

(82 citation statements)

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“…Although the accuracy, precision, and repeatability of the Orbscan system has been accepted for use in research, it is recognized that it overestimates CCT compared to the more commonly used technique of ultrasound pachymetry. 10,31,32 The current study has taken this into account by applying the standard acoustic correction factor. 13 The repeatability of Orbscan pachymetry has been demonstrated to be approximately 2 mm 33 to 5 mm.…”

Section: Discussionmentioning

confidence: 99%

Identifying relationships between tomography-derived corneal thickness, curvature, and diameter and in vivo confocal microscopic assessment of the endothelium in healthy corneas of young adults

Patel

McGhee

2008

Eye

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Purpose Despite the importance of a healthy endothelial layer in anterior segment surgery, the possible influence of corneal parameters on endothelial cell density (ECD) has largely been ignored in the young adult eye. This study investigated the possible associations between corneal tomographic parameters and ECD values in young adults. Methods Subjects aged 21-30 years, with normal corneas were recruited. Mean ECD, mean cell area (MCA), coefficient of variation for cell area (COVA), and proportion of hexagonal cells were derived by in vivo confocal microscopy. The Orbscan II system was used to measure corneal parameters including: thickness, horizontal corneal diameter, corneal curvature, anterior and posterior elevation, and eccentricity. Results Sixty-two subjects (42 female, 20 male) were included (mean age 25±3 years). Overall mean ECD was 3169±309 cells/mm 2 with no differences between genders. Mean percentage of hexagonality was 53 ± 5%, male subjects (55%) had a higher percentage of hexagonal cells than female subjects (51%) (P ¼ 0.02). Central corneal thickness (CCT) was 529±43 lm. Central ECD was significantly correlated with CCT (Pearson's r ¼ 0.26, P ¼ 0.04). However, horizontal corneal diameter (r ¼ 0.19, P ¼ 0.14), anterior corneal curvature (r ¼ À0.07, P ¼ 0.6), and posterior corneal curvature (r ¼ À0.07, P ¼ 0.6) were not correlated with ECD or percentage of hexagonality. There was no statistically significant association between anterior chamber depth (3.6±0.3 mm) and ECD (r ¼ 0.15, P ¼ 0.3). Conclusion Corneal thickness is related to ECD in normal young adult eye, with lower ECD values identified in thinner corneas; however, corneal diameter and corneal curvature do not have a significant correlation with ECD.

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Section: Discussionmentioning

confidence: 99%

Identifying relationships between tomography-derived corneal thickness, curvature, and diameter and in vivo confocal microscopic assessment of the endothelium in healthy corneas of young adults

Patel

McGhee

2008

Eye

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“…The pachymetric values variation, observed in both patients groups, remained within the normal limits for the test (24)(25)(26) (Table 1).…”

Section: Discussionmentioning

confidence: 54%

Comparison of central corneal edema and visual recovery between liquefaction and conventional phacoemulsification in soft cataracts

Nakano¹,

Hida²,

Kara‐José³

et al. 2009

Rev. bras.oftalmol.

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Purpose:The aim of the present study is to assess central corneal edema and visual recovery after cataract surgery performed according to two technologies: conventional ultrasonic and liquefaction (Aqualase ® ). Methods: This is a prospective contralateral study in wich 20 patients with comparable preoperative conditions were submitted to cataract surgery were evaluated. Preoperative assessment involved complete ophthalmological examination and the study included patients with bilateral cataracts up to grade 2, according to the Lens Opacity Classification System II. The same cristaline fracture technique was used in all cases, and surgical procedures were performed by the same experienced surgeon, using two technologies: liquefaction or conventional phacoemulsification. Postoperative central corneal edema was measured by corneal optical pachymetry (Orbscan II ® ) on the 1 st , 3 rd , 7 th and 10 th postoperative days. Results: None of the 20 patients submitted to surgery was lost during the postoperative follow-up or excluded from the analysis. On the first postoperative, the visual acuity average was 0.031 logMAR in the Aqualase ® group and 0.043 logMAR in the conventional surgery group. No statistical difference was detected in the assessment of visual acuity throughout the postoperative period. Central corneal pachymetry varied from 543.93 + 34.69 preoperatively to 545.08 ± 25.67 on the last day of follow-up in the Aqualase ® group, and from 543.13 + 30.62 to 536.08 + 34.89 in the conventional technique group, without statistical significance. Conclusion: This study suggests that both techniques are equally effective for surgery on lenses with grade I or II cataract, and that they provide similar results in terms of visual recovery and central corneal edema.

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“…The normal healthy cornea is usually prolate, but after myopic LASIK the corneal curvature is altered and tends to become oblate. 2 The reconstruction algorithms, using lower order polynomials, which create elevation data in the Orbscan-II may be properly designed in a normal corneal surface, but they might be ineffective in a post-LASIK corneal surface. 2 The main limitation of the current study is that the reason for the variability between measurements showed a wide distribution between methods was not completely addressed, although it can be explained by the measurement repeatability of Orbscan-II being generally lower than that of Topcon NCSM in postmyopic LASIK patients.…”

Section: Discussionmentioning

confidence: 99%

“…2 The reconstruction algorithms, using lower order polynomials, which create elevation data in the Orbscan-II may be properly designed in a normal corneal surface, but they might be ineffective in a post-LASIK corneal surface. 2 The main limitation of the current study is that the reason for the variability between measurements showed a wide distribution between methods was not completely addressed, although it can be explained by the measurement repeatability of Orbscan-II being generally lower than that of Topcon NCSM in postmyopic LASIK patients. 35 In addition, this study included only patients who had undergone LASIK to treat myopia, and, therefore, the conclusions cannot be applied to patients with hyperopia, in whom the postoperative corneal shape is more prolate.…”

Section: Discussionmentioning

confidence: 99%

“…Accurate analysis of the corneal thickness is of paramount importance for assessing corneal disease and non-refractive and refractive surgical procedures. 1,2 Measurement errors could affect the preoperative assessment of candidates for primary and retreatment laser in situ keratomileusis (LASIK), [3][4][5][6] the intraocular lens (IOL) power calculations after LASIK, 7 and the contribution of the CCT to measurement of the intraocular pressure (IOP). 8 CCT can be measured using various techniques.…”

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confidence: 99%

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

López-Miguel

Nieto

Díez-Cuenca

et al. 2009

Eye

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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 lm and 461.38 ± 35.35 lm, respectively (Po0.0001; mean difference, 13.83±22.31 lm; 95% confidence interval, 9.77-17.09 lm). The Bland-Altman plot showed an inverse association between the average and the difference between the devices: TopconOrbscan-II ¼ 174.23 -0.353 Â Average (Po0.01). The widths of the crude and regression-based 95% limits of agreement were 87.45 and 63.72 lm, 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 longterm follow-up of the growing LASIK patient population.

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Comparison of corneal thickness measurements using ultrasound and Orbscan slit-scanning topography in normal and post-LASIK eyes

Cited by 139 publications

References 10 publications

Identifying relationships between tomography-derived corneal thickness, curvature, and diameter and in vivo confocal microscopic assessment of the endothelium in healthy corneas of young adults

Identifying relationships between tomography-derived corneal thickness, curvature, and diameter and in vivo confocal microscopic assessment of the endothelium in healthy corneas of young adults

Comparison of central corneal edema and visual recovery between liquefaction and conventional phacoemulsification in soft cataracts

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

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