Keratoconus patterns and intrastromal segments

Purpose Intrastromal corneal segments (ICS) are a popular alternative for the treatment of keratoconus. However, its variability makes difficult a simple approach to ICS implantation. The SA.ANA classification of ICS implant modalities was developed to enable comparability between case series, with implications on the best ICS combinations for the different keratoconus patterns. Methods A multicenter database was established including ICS implanted during the 2004 to 2011 period. Based on 1097 cases, a simple classification of ICS implantation modalities was devised using 2 basic criteria: symmetry and axiality, whose combination results in 4 major types. The observed series was fitted into this framework. Results 2 equal ICS facing each other define symmetrical (S) implantation. Asymmetrical (A) means only 1 or 2 different ICS. Axial (A) implants are those placed with their center at the flatter astigmatism axis, while non-axial (NA) refers to those at an axis differing ≥30º from that of astigmatism. This results in 4 main types (SA, AA, SNA, ANA), while the asymmetric types can include 1 or 2 ICS (AA1, AA2, ANA1, ANA2). The most frequent modality was asymmetrical-axial (AA) totaling almost 70% of the implants. Symmetric-axial (SA) represent about 10%. The non-axial groups account for the remaining minority (20%). Conclusion The SAANA classification employs simple criteria for a comprehensive description of the ICS implantation types. Identifying these types is a prerequisite for a meaningful comparison of the clinical results. This classification is also useful as a guideline to select the best ICS combinations for a particular keratoconus case. While axial implantation constitutes 80% of the cases, the non-axial types may address special problems as non-coincident astigmatism & coma. Commercial interest