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J Ng 1 , S Velaedan 1 , W Wong 2 , L Thean 1

Comparison of Central Corneal Thickness Measurements with Handheld Ultrasound Pachymetry and Three Other Imaging Technologies. J Ng 1 , S Velaedan 1 , W Wong 2 , L Thean 1 1 Department of Ophthalmology, National University Health Systems 2 Singapore Eye Research Institute

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J Ng 1 , S Velaedan 1 , W Wong 2 , L Thean 1

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  1. Comparison of Central Corneal Thickness Measurements with Handheld Ultrasound Pachymetry and Three Other Imaging Technologies J Ng1, S Velaedan1, W Wong2, L Thean1 1 Department of Ophthalmology, National University Health Systems 2 Singapore Eye Research Institute The authors have no financial interest in the subject of matter in this poster.

  2. Introduction • Measurement of central corneal thickness (CCT) plays an important role1- 5 • Diagnostic assessment of corneal disorders • Therapeutic assessment in glaucoma • Significant parameter in refractive surgery • Ultrasound pachymetry has been long regarded as the gold standard • However, a number of new modalites have developed with recent times, including the Orbscan, Anterior Segment Optical Coherence Tomography (ASOCT), Ultrasound Biomicroscopy • Handheld devices such as the PalmScan could provide a portable alternative for CCT measurements

  3. Purpose • To compare the measurement of the central corneal thickness (CCT) by • PalmScan, a handheld portable ultrasound pachymetry • Sonomedultrasound pachymetry • Orbscan slit-imaging corneal topography and • Visante anterior segment optical coherence tomography PalmScan Sonomed Orbscan Visante

  4. Design and Methodology • Twenty-five normal subjects were recruited • Observational, cross sectional study • Each subject had CCT of both eyes measured by PalmScan, Sonomed, Visante and Orbscan • All measurements were performed by either one of two observers • Exclusion criteria: • Any previous intraocular surgery • Contact lens wear within the last 1 week • Active infection • Any known corneal pathologies (e.g. keratoconus, dystrophies) • Inability to cooperate • Inability to provide informed consent

  5. Results

  6. Results • Statistical evidence of difference in CCT readings obtained from 5 pair-wise comparisons of the Sonomed, PalmScan, Orbscan and ASOCT machines, except between Sonomed and PalmScan.

  7. Results • Graphical exploration of Bland Altman plots shows similar results, where both Sonomed & PalmScan has higher readings than Orbscan and ASOCT and there is no observed difference between Sonomed and Palmscan. Orbscan has the lowest readings. [Table 1]

  8. Results • Table 1: Bland Altman plots

  9. Discussion • Studies have been conducted extensively and concluded that ASOCT underestimated CCT compared to ultrasound pachymetry. This was demonstrated in our results as well.3 • Similarly, our study found that CCT measurements taken with ultrasound pachymetry, ASOCT and Orbscan are not directly interchangeable. This has been suggested to be a result of the different methodologies of the instruments.2,4 • The PalmScan, also a form of ultrasound pachymetry could potentially offer a more portable technology for measuring CCT. In our study, it is shown to be reliable and interchangeable with the Sonomed.

  10. Conclusion • PalmScan is reliable alternative for CCT measurements. • Although CCT measurements were well correlated amongst all 4 machines, the measurements should not be directly interchangeable in clinical practice except for possibly between the PalmScan and Sonomed.

  11. References • Li H, Leung CK, Wong L, Cheung CY, Pang CP, Weinreb RN, Lam DS. Comparative study of central corneal thickness measurement with slit-lamp optical coherence tomography and visante optical coherence tomography. Ophthalmology. 2008 May;115(5):796-801.e2. Epub 2007 Oct 4. • Zhao PS, Wong TY, Wong WL, Saw SM, Aung T. Comparison of central corneal thickness measurements by visante anterior segment optical coherence tomography with ultrasound pachymetry. Am J Ophthalmol. 2007 Jun;143(6):1047-9. • Li EY, Mohamed S, Leung CK, Rao SK, Cheng AC, Cheung CY, Lam DS. Agreement among 3 methods to measure corneal thickness: ultrasound pachymetry, Orbscan II, and Visante anterior segment optical coherence tomography. Ophthalmology. 2007 Oct;114(10):1842-7. Epub 2007 May 15. • Kim HY, Budenz DL, Lee PS, Feuer WJ, Barton K. Comparison of central corneal thickness using anterior segment optical coherence tomography vs ultrasound pachymetry. Am J Ophthalmol. 2008 Feb;145(2):228-232. Epub 2007 Dec 11. • Leung DY, Lam DK, Yeung BY, Lam DS. Comparison between central corneal thickness measurements by ultrasound pachymetry and optical coherence tomography. Clin Experiment Ophthalmol. 2006 Nov;34(8):751-4.

  12. Thank You!

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