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Editors Selection IGR 16-2
Anterior chamber depth
Comment by Tin Aung on:
16812 Comparison of different techniques of anterior chamber depth and keratometric measurements, Elbaz U; Barkana Y; Gerber Y et al., American Journal of Ophthalmology, 2007; 143: 48-53
Precise measurements of ocular dimensions have gained considerable importance with increasing numbers of cataract and keratorefractive surgeries. In particular, accurate biometry is vital in attaining the desired post-operative refractive outcome. ACD measurements are required in newer theoretical biometric formulas for intraocular lens (IOL) power calculations and implantation of phakic IOLs and newer accommodative IOLs. ACD is also important in glaucoma assessment, especially as a shallow ACD is regarded as a major risk factor for angle closure glaucoma.
The results obtained by ACD and keratometry may not be interchangeableNew non-contact devices have recently been introduced for anterior segment measurements. The Pentacam (Oculus, Wetzlar, Germany) is a type of Scheimpflug camera that images the anterior segment and can measure anterior chamber depth (ACD), lens thickness as well as corneal curvatures. The IOLMaster (Carl Zeiss Meditec, Jena, Germany) measures axial length, ACD and corneal curvatures. In this paper by Elbaz et al. (32) ACD measurements by Pentacam, IOLMaster and ultrasound were compared, as were keratometry measurements by Pentacam, IOLMaster and automated keratometry in 11 subjects (22 eyes). The authors found that for ACD measurements, IOLMaster and ultrasound were similar but Pentacam differed by about 0.1 mm. For keratometry, there was no difference between Pentacam and automated keratomery but Pentacam differed from IOLMaster by about -0.47 dioptre.
Optical measuring devices are to some extent operator independent and examiner subjectivity cannot be ignored, but the reproducibility of the measurements was not evaluated in the study. The paper provides useful information about the differences in measurements of these devices and reminds us to be aware of the different methodology and points of reference between the different instruments. For clinical applications such as ACD and keratometry, the authors suggest that results obtained by these instruments may not be interchangeable. However the differences found were small and thus unlikely to be clinically significant.
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