A critical evaluation of longitudinal changes of astigmatism following implantation of toric implantable collamer lens (TICL): a comparison between treated and untreated cases over 4 years.

PURPOSE: To evaluate residual astigmatism following correction with toric implantable collamer lens (TICL) (group I) over a period of 4 years and compare with the change of astigmatism in spectacle wearers (group II).

METHODS: Groups I (86 cases implanted with TICL [EVO + Visian ICL, Staar Surgical, Nidau, Switzeland], preop refractive error [sphere and cylinder] - 22.25 DS to - 1.00 DS and - 5.50 DC to - 1.00 DC) and II (80 cases initial refractive error [sphere and cylinder] - 18.00 DS to 0.00 DS and - 7.00 DC to - 1.00 DC) were reviewed annually. Refractive and tomography data were subjected to vector analysis to determine surgically induced astigmatism (SIA), angle of error [Δθ° = angle of target-induced astigmatism (TIA) - angle of SIA], and ΔC [TIA-SIA powers] and total corneal astigmatism (TCA) in group I and induced change in astigmatism (ICA) in group II.

RESULTS: In group I, on all occasions, SIA correlated with TIA (p < 0.05); differences between SIA and TIA means were insignificant and changes in TCA were not correlated with ΔC. Mean (± sd, 95% CI) residual astigmatic powers (RA) in attending group I cases (1-4 years) were - 0.40 DC (0.58, - 0.52 to - 0.28), - 0.40 DC (0.59, - 0.52 to - 0.27), - 0.41 DC (0.58, - 0.54 to - 0.28), and - 0.61 DC (0.74, - 0.82 to - 0.40). In group II, the corresponding ICA powers were - 0.47 DC (0.53, - 0.61 to - 0.32), - 0.49 DC (0.48, - 0.69 to - 0.29), - 0.60 DC (0.40, - 0.76 to - 0.44), and - 0.86 DC (0.71, - 1.19 to - 0.52). Differences between RA and ICA were not significant. Of the group I cases presenting at 1-4 years postop, 23, 18, 16, and 28 had RA powers ≤  - 0.75 DC. Of these 12, 10, 6, and 16 were associated with Δθ° > 5° (ΔC - 0.50 to 0 DC) and 5, 1, 4, and 4 were related to ΔC (Δθ° < 5°).

CONCLUSION: The development of astigmatism after TICL implantation is on par with the natural change in astigmatism in untreated cases. In about 50% of TICL cases presenting with astigmatism ≤  - 0.75 DC, the residual astigmatism could be neutralized by realigning the TICL.