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Topography in keratoconus
Abolfazl Kashfi MDIsfarhan medical university
Pattern recognition
Pattern recognition
inferior steepening asymmetric or broken bowtie
Pattern recognition
• Advantages easy and quick • Disadvantages subjective qualitative severely affected by scale
Keratometric data normal cornea
• Flatten from center to periphery 2-4D• Nasal is flatter than temporal• 41 to 47 D at center average 43.5 D• Each eye is mirror images of the fellow eye
Simulated keratometry (Sim K)
Central corneal power (D)
< 47.2 Normal 47.2 < Keratoconus suspect<48.7> 1 D difference between SimK(S) of fellow eyes >48.7 Keratoconus> 2 D difference between SimK(S) of fellow eyes
Inferior - Superior (I-S) index
• Rabinowitz- McDonnel I-S index (difference between average of five superir points and five inferior points in central 3mm of cornea each 30 degrees apart)
< 1.4 Normal 1.4< Keratoconus suspect < 1.9 > 1.9 keratoconus
maybe normal in central KC
Corneal Surface Asphericity index (CAI)
Q valueAbout – 0.26 normal
Less (more negative) than -0.26 keratoconus suspect
Corneal Surface Asymmetry index (SAI)
(Sum of difference between symmetric points )
Normal less than 0.5 D
Surface Regularity Index (SRI)
compares differences between neighbor points within central 4.5 mm
0 < normal < 1>1 keratoconus suspect
non specific
Differential Sector Index (DSI)Divides the cornea to 8 equal sectors (each sector 45 degrees)Reports the greatest difference in average power betweenany two sectors
0.21< Normal < 3.51
Opposite Sector Index (OSI)Divides the cornea to 8 equal sectors (each sector 45 degrees)Represents the greatest difference of average powerin opposite sectors
-0.55 < Normal < 2.09
Center Surrond Index (CSI)
The difference in the average area corrected corneal power between the central corneal zone 3 mm in diameter and a 3 mm annulus surrounding the central area
-0.28 < Normal < 0.80
Keratoconus Predictability Index (KPI)Maeda and Klyce has generated KPI using 8 keratometric indices and 11 quantitative criteria and a complex data analysis system called “neural network system”.
Keratoconus >23 %
Keratoconus index (KCI)the keratoconus-like pattern is determined and expressed as a percentage
0 < keratoconus suspect < 5%Keratoconus >5 %
Skewed Radial Axes (SRAX)
>20 degree abnormal
KISA% index (keratometry, I-S, skew percentage, astigmatism)
Normal < 60 %60% < keratoconus suspect < 100 %keratoconus >100%
Keratoconus Severity Index (KSI)
Normal < 15%15% < suspect < 30%Keratoconus > 30 %
Highest rate of steepening (HRS)Abnormal > 1.5 D per 1 mm
Thanks for your attention