The comparative Study of two recently developed A-scan devices: determination of central corneal thickness, anterior chamber depth and axial length

Department of Ophthalmology, Medical and Health Science Centre, University of Debrecen, Hungary.
Acta ophthalmologica (Impact Factor: 2.84). 03/2008; 86(1):45-8. DOI: 10.1111/j.1600-0420.2007.00994.x
Source: PubMed


The clinical use and comparison of two recently developed A-scan ultrasound devices.
The same investigator determined central corneal thickness (CCT), anterior chamber depth (ACD) and axial length (AL) with an OcuScan RxP (Alcon, Forth Worth, Texas, USA) and an AL-2000 (Tomey, Erlangen, Germany) ultrasound device in 80 eyes of 40 patients. The mean patient age was 63.72 years [standard deviation (SD) 18.92]. The patients did not suffer from any systemic or eye disease affecting the anterior and posterior segments of the eye, and their refractive error (spherical and astigmatic) did not exceed +/- 3.0 dioptres.
The value of the CCT was 541.55 (SD 34.97) microm with the OcuScan RxP, and 547.46 (SD 35.70) microm with the AL-2000 device (P < 0.001). With respect to the ACD and AL, significantly lower values were obtained with the AL-2000 instrument (P < 0.001). The ACD was 2.92 (SD 0.48) mm with the AL-2000 and 3.07 (SD 0.47) mm with the OcuScan RxP device. The AL was 22.67 (SD 0.84) mm with the AL-2000 and 22.81 (SD 0.87) mm with the OcuScan RxP instrument. However, a positive and significant correlation could be demonstrated between the devices (r = 0.88 CCT, r = 0.86 ACD and r = 0.91 AL; P < 0.001).
The instruments are reliable in clinical use; however, statistically significant differences were found between the devices. During patient follow-up, the devices cannot simply be used interchangeably.

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    • "The accuracy of biometric assessments (axial length, anterior chamber depth, lens thickness and central pachymetry) is a point of extreme importance for the evaluation of eye pathology, particularly when planning lens replacement surgery or other therapeutic procedures [1-3]. Currently, the eye specialist has several options for making such measurements [2]. "
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    ABSTRACT: To assess the reliability of the measurements obtained with the PalmScan, when compared with another standardized A-mode ultrasound device, and assess the consistency and correlation between the two methods. Transversal, descriptive, and comparative study. We recorded the axial length (AL), anterior chamber depth (ACD) and lens thickness (LT) obtained with two A-mode ultrasounds (PalmScan A2000 and Eye Cubed) using an immersion technique. We compared the measurements with a two-sample t-test. Agreement between the two devices was assessed with Bland-Altman plots and 95% limits of agreement. 70 eyes of 70 patients were enrolled in this study. The measurements with the Eye Cubed of AL and ACD were shorter than the measurements taken by the PalmScan. The differences were not statistically significant regarding AL (p < 0.4) but significant regarding ACD (p < 0.001). The highest agreement between the two devices was obtained during LT measurement. The PalmScan measurements were shorter, but not statistically significantly (p < 0.2). The values of AL and LT, obtained with both devices are not identical, but within the limits of agreement. The agreement is not affected by the magnitude of the ocular dimensions (but only between range of 20 mm to 27 mm of AL and 3.5 mm to 5.7 mm of LT). A correction of about 0.5 D could be considered if an intraocular lens is being calculated. However due to the large variability of the results, the authors recommend discretion in using this conversion factor, and to adjust the power of the intraocular lenses based upon the personal experience of the surgeon.
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    • "obtained in our study's control group correlate well with those described previously (Sohajda et al. 2008). A number of studies have demonstrated that CCT in full-term newborns is significantly greater than in adults (Ehlers et al. 1976; Autzen & Bjornstrom 1991). "
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