Orbscan pachymetry: Implications of a repeated measures and diurnal variation analysis∗☆,
Section snippets
Instrumentation
The Orbscan system is a computerized corneal mapping device that obtains elevation information from both the anterior and posterior corneal surfaces. It uses a calibrated video and slit-beam system to noninvasively measure three-space points on the front and rear corneal surfaces. The three-space points are used to construct mathematical representations of the true topographic surfaces (i.e., maps of z [elevation] vs. x and y [horizontal and vertical coordinates]). Therefore, corneal thickness,
Results
A calibrated surface was repeatedly scanned to assess accuracy of the estimated anterior surface elevation model. Calibrated surface data were very accurate with the mean standard deviation (SD) of 12 repeated measures equal to 2 μm over the entire measured 7-mm diameter anterior surface map (range, 1.2 μm centrally to 3.2 μm peripherally). These measurements were taken four times from three different calibrated surfaces of spherical shape (37.5 D, 47.54 D, and 54.57 D).
Figure 2 illustrates the
Discussion
The accuracy of the surface maps of the calibrated standards yielded a mean SD of 2 μm (range, 1.2 μm centrally to 3.2 μm peripherally). Presuming similar accuracy for posterior maps, a simple mathematical addition of those errors would yield pachymetry SD values of greater than 2 μm but perhaps less than 8 μm for a constructed pachymetry map. This is in general agreement with the experimental data obtained: the apical measurements had a mean SD of 5 μm (range, 3–7 μm), and the mean SD for the
Acknowledgements
The authors thank Hospital Corpsman 3rd Class (HM3) George Meyer for his exceptional support services.
References (15)
- et al.
Postoperative change in the corneal thickness of the pseudophakic eyeamplified diurnal variation and consensual increase
J Cataract Refract Surg
(1987) - et al.
Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK study
Ophthalmology
(1986) - et al.
Diurnal variation in vision after radial keratotomy
Am J Ophthalmol
(1989) Effect of corneal hydration and intraocular pressure on keratometric power after experimental radial keratotomy
Ophthalmology
(1990)The location of the fluid pump in the cornea
J Physiol (Lond)
(1972)- et al.
Diurnal variation of corneal thickness in the cat
Invest Ophthalmol Vis Sci
(1985) - et al.
A clinical comparison of optical and ultrasonic pachometry
Acta Ophthalmol (Copenh)
(1991)
Cited by (169)
Influence of soft contact lens material on corneal warpage: prevalence and time to resolution
2018, Canadian Journal of OphthalmologyCorneal thickness differences between type 2 diabetes and non-diabetes subjects during preoperative laser surgery examination
2017, Journal of Diabetes and its ComplicationsComparison of dual rotating Scheimpflug-Placido, swept-source optical coherence tomography, and Placido-scanning-slit systems
2015, Journal of Cataract and Refractive SurgeryIntraobserver repeatability and interobserver reproducibility of corneal measurements in normal eyes using an optical coherence tomography-Placido disk device
2015, Journal of Cataract and Refractive SurgeryCitation Excerpt :This means that the maps were not done individually and that the OCT data map was built on the topography data map. The scan was performed under scotopic conditions using the standard anterior segment single-scan protocol, and all measurements were taken between 10:00 am and 4:00 pm to minimize the effect of diurnal variation on corneal thickness.14–16 The construction of the posterior corneal elevation and curvature was performed by the built-in system software.
Evaluation of corneal thickness using a Scheimpflug-Placido disk corneal analyzer and comparison with ultrasound pachymetry in eyes after laser in situ keratomileusis
2013, Journal of Cataract and Refractive SurgeryCitation Excerpt :The mean of the remaining 3 measurements was used to calculate the CCT. All measurements were taken between 10 am and 5 pm to minimize the diurnal effect of pachymetric measurements.22 All data were analyzed using SPSS for Windows software (version 13.0, SPSS, Inc.).
Comparison and repeatability of keratometric and corneal power measurements obtained by Orbscan II, Pentacam, and Galilei corneal tomography systems
2013, American Journal of Ophthalmology
- ☆
Supported by the Naval Health Research Center and the Naval Medical Center, San Diego.
- ∗
The authors have no financial interest in products cited in this article.
The views of the authors do not purport to reflect the positions of the Department of the Army, the Department of the Navy, or the Department of Defense.
Citation of a brand or trade name does not constitute endorsement of a product or service.