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SOCT User Manual Version 10.0 rev. A
maps. If the system detects a result a calculated KPI value greater than 0.23 or K2 greater than
38.5, it is indicative of keratoconus, which later is distinguished by the method of elimination.
See Figure 291 Keratoconus screening classification.
Keratoconus prediction index (KPI) is calculated by a combination of 8 topographic indices and
relies on a linear discriminant function. The indices DSI, OSI, CSI, SAI, K1, K2, IAI and AA are
described below.
Caution: KPI bases on a publication by Naoyuki Maeda and can only be treated as
supplementary information and cannot be treated as disease confirmation. Use for
reference only.
Source: Automated Keratoconus Screening with Corneal Topography Analysis by Naoyuki Maeda, Stephen D. Klyce, Michael K. Smolek,
and Hilary W. Thompson in 1994.
KPI is a result of linear function, calculated according to the following formula:
KPI = 0,30 + 0,01(–41,23 – 0,15DSI + 1,18OSI + 1,49CSI + 4,13SAI – 0,56K1 + 1,08K2 – 3,74IAI +
0,10AA)
KPI value is calculated on the basis of Quantitative Indices, which are the components of the
formula.
20.4.4.2 Definition of Quantitative Indices
DSI (Differential Sector Index) – the greatest difference in average power between any two
(out of eight) sectors
OSI (Opposite Sector Index) – the greatest difference of the average power in opposite
sectors
To calculate Differential Sector Index and Opposite Sector Index, the analyzed area is divided
into eight equal sectors. One of the sectors covers the area with the greatest power. Each
sector has a specific average power calculated by the system (see picture below).
Before the calculation of Differential Sector Index and Opposite Sector Index, the sectors are
rotated at an angle, until the average power of one of the sectors reaches the highest value
(D
max)
.
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