Table 4.
The SA.ANA classification (Symmetric, Asymmetric, Axial, Non-Axial classification), keratometry, and aberrometry as the main parameters were considered in AI systems. The table has been re-created; courtesy of Dr. Barraquer and Dr. Alfonso.119–121
| Type | Segment | Implantation Axis Axial: same, minus cyl axis Non-axial: different axis |
Indication | Topography | Frequency | Looks like | |
|---|---|---|---|---|---|---|---|
| SA | Symmetric, Two equal ICRS |
Axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Minimal |
|
Central (symmetric) ectasia Regular astigmatism (Congenital or post PK) Mild myopia congenital or residual after Rx. |
|
~10% |
 Bowtie |
| AA1 | Asymmetric, One ICRS |
Axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward flat axis |
|
Asymmetric ectasia markedly displaced inferiorly Coma ± toward minus cyl axis (Roughly coincidence < 30° dif.) |
|
~68% |
 Croissant |
| AA2 | Asymmetric, Two unequal ICRS |
Axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward flat axis |
|
Same as AA1, but: Higher cylinder or sphere combinations Additive effect of ICRS thickness/width Coma be corrected by asymmetry Upper ICS must be smaller/thinner |
|
||
| SNA | Symmetric, Two equal ICRS |
Non-axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward steep axis • Black: Mid-ICS axis, displaced |
|
Intermediate ectasia (paracentral, relatively orthogonal) Sphere mild/moderate Cylinder moderate/high Coma ± toward plus cyl axis |
|
~6% |
 Snowman |
| ANA1 | Asymmetric, One wide ICRS: 120°–160° at coma axis or intermediate |
Non-axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward steep axis |
|
Intermediate ectasia (paracentral, non-orthogonal) Sphere mild Cylinder moderate/high Coma ± toward plus cyl axis (inferiorly) |
|
||
| ANA2 | Asymmetric, Two unequal ICRS: • Inferior wider (160°) at coma • Superior small (90°–120°) at flat axis |
Non-axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward steep axis |
|
Intermediate ectasia (paracentral, non-orthogonal) Sphere moderate/high Cylinder moderate/high Coma ± toward plus cyl axis (inferiorly) |
|
~11% |
 Duck |
| ANA3 | Asymmetric, Three ICRS, Two steps | Non-axial • Red: Steep ast. axis • Blue: Flat ast. axis • Coma: Significant, toward steep axis |
|
Intermediate ectasia (peripheral, ±incipient) Sphere mild Cylinder mild/moderate Coma ± toward plus cyl axis (±vertical @ 260°) |
|
ast., Astigmatic; cyl, Cylinder; ICRS, IntraCorneal Ring Segments.