Wide-Range Calibration of Corneal Backscatter Analysis by In Vivo Confocal Microscopy

T. Hillenaar, V.A.D.P. Sicam, K.A. Vermeer, B. Braaf, L. Remeijer, R.H.H. Cals, J.F. de Boer

Research output: Contribution to JournalArticleAcademicpeer-review


PURPOSE. To report intra- and interinstrument calibration methods for corneal backscatter analysis by in vivo confocal microscopy. METHODS. Applicability of two reference standards was evaluated for corneal backscatter calibration. Repeated measurements of four concentrations of AMCO Clear (GFS Chemicals, Inc., Powell, OH) suspension and three transparencies (26%, 49%, and 65%) of polymethylmethacrylate (PMMA) slabs were performed to assess image intensity acquisition in a wide backscatter range. Intra- and intersession repeatability and lot-to-lot variation were determined for both standards. The effect of light intensity (LI) variation on image intensity acquisition was evaluated by examination of PMMA slabs with nonreference (60% and 80%) and reference (72%) LIs. Both reference standards were implemented in the protocol. Intrainstrument calibration was verified by measuring three normal corneas with 60%, 72%, and 80% LIs. Interinstrument calibration was tested by measuring PMMA slabs on a second, similar confocal microscope. RESULTS. AMCO Clear was used to express image intensity in absolute scatter units (SU), whereas the 49% transparent PMMA slab showed best repeatability, without image saturation, to adjust for LI variation. Intrainstrument calibration for LI variation reduced mean differences from -38.3% to 1.7% (60% LI) and from 33.9% to -0.6% (80% LI). The mean difference between similar microscopes decreased from 18.4% to 1.2%, after calibration of the second microscope. CONCLUSIONS. Large interinstrument differences necessitate calibration of corneal backscatter measurements. With AMCO Clear suspension and PMMA slabs, standardization was achieved in a wide backscatter range corresponding to normal and opaque corneas. These methods can easily be applied in ophthalmic practice. © 2011 The Association for Research in Vision and Ophthalmology, Inc.
Original languageEnglish
Pages (from-to)2136-2146
Number of pages11
JournalInvestigative Ophthalmology and Visual Science
Issue number5
Publication statusPublished - 2011


Dive into the research topics of 'Wide-Range Calibration of Corneal Backscatter Analysis by In Vivo Confocal Microscopy'. Together they form a unique fingerprint.

Cite this