Researchers examined the structural and functional results of implanting asymmetric thickness intrastromal corneal ring segments (AC-ICRS), in eyes with keratoconus and asymmetric or irregular astigmatism in type 2 and type 3 cones in a study published in Clinical Ophthalmology. The data shows that the AC-ICRS implant helped improve clinical and topographic parameters, while also decreasing aberrations with the greatest effect in type 2 phenotype cones.
The retrospective study took into account 21 eyes of 19 patients with a mean age of 35.3, who had been diagnosed with keratoconus and who had undergone AC-ICRS implantation. Patients were all classified as either type 2 or type 3 phenotype cones per the Fernandez-Vega/Alfonso morphologic keratoconus classification. Demographic and clinical data were taken as well as Pentacam measurements, including topographic astigmatism, topographic flat meridian (K1), topographic steep meridian (K2), and maximum keratometry (Kmax). A total root mean square (RMS), higher-order aberrations, and comatic Zernike coefficients (Z31; Z3-Z1) were also taken at 0º and 90º meridians. Participants were followed up between 6 and 12 months after the procedure to compare the data.
The results show that the implants had the greatest effects in K2 (P <.001) and astigmatism (P <.001). An improvement was also noted in uncorrected distance visual acuity (P =.017) and corrected distance visual acuity (P =.05). Aberrometry analysis showed a reduction of total RMS (P =.085) and higher order aberrations (P =.227) as well as a reduction in the 90º component of comatic aberration (P <.001).
Researchers noted that the topographic and aberrometric parameters were higher in type 2 cones compared with type 3 cones. Limitations of the research include its retrospective non-randomized design, the limited number of cases and the manual implantation technique.
Vega-Estrada A, Chorro E, Sewelam A, Alio JL. Clinical outcomes of a new asymmetric intracorneal ring segment for the treatment of keratoconus. Cornea. 2019;38(10):1228-1232. doi:10.1097/ICO.0000000000002062