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