Topography in keratoconus Abolfazl Kashfi MD Isfarhan medical university

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 value About – 0.26 normal Less (more negative) than 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 between any 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 power in opposite sectors < 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 < 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