Placido-based indices of corneal irregularity
Purpose: To construct a set of metrics computed from the raw keratoscopic data collected by any Placido corneal topographer. These indices that measure the irregularity of the anterior corneal surface are computed directly from the image of the mires reflected on the cornea, which is the most pr...
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| Format: | info:eu-repo/semantics/article |
| Language: | English |
| Published: |
2018
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| Online Access: | http://hdl.handle.net/10835/5615 http://dx.doi.org/10.1097/OPX.0b013e3182279ff8 |
| Summary: | Purpose:
To construct a set of metrics computed from the raw keratoscopic data collected by any
Placido corneal topographer. These indices that measure the irregularity of the anterior
corneal surface are computed directly from the image of the mires reflected on the
cornea, which is the most primary data possible. Besides the high sensitivity and
specificity, this approach allows bypassing the surface or curvature reconstruction step
that is currently performed by the software of any commercial Placido topographer.
Methods:
Several basic indices are proposed in order to detect irregularities on the anterior
surface of the cornea, via analyzing some geometric and mathematical properties of
the mires. These individual primary indices are built in a natural and intuitive way
directly from the displacement of the digitized images of the rings reflected on the
cornea. Additionally, compound indices are proposed (such as the generalized linear
model or the classification trees) by combining some of the so-called primary indices to
improve their efficiency. The computed metrics were developed and tested for the CSO
topography system (CSO, Firenze,Italy), but the methodology proposed here extends
easily to any other commercial Placido disks topographer.
Results:
The primary indices allow to discriminate, with excellent accuracy, between normal
eyes and eyes with keratoconic corneas. Sensitivity and specificity of the primary
indices is analyzed by using the ROC (receiver operating characteristic) curve
methodology. Some combined indices are presented, and raise the efficiency to
optimal.
Conclusions:
All the primary indices proposed exhibit very good performance at discriminating
between normal and irregular corneas. The combined indices accuracy is optimal, so
avoiding their use in clinical practice as corneal markers of disease. All these indices
are fast to compute and can be easily implemented in any corneal topography system.
Keywords:
Corneal irregularities
keratoconus
irregularity index
diagnosis
corneal
topography
Placido disks |
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