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First Author: N.Franqueira PORTUGAL
Co Author(s): T. Monteiro M. Teles C. Almeida R. Leite F. Vaz
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To assess the effectiveness and safety of 2 types of 6.0 mm zone intrastromal corneal ring segments (ICRS) in patients with mild to severe keratoconus.
Department of ophthalmology, Braga Hospital; Braga; Portugal
Retrospective comparative study of 49 consecutive eyes of 45 patients implanted with Intacs SK ICRS (group 1) or Keraring SI6 ICRS (group 2), both with manual technique. Parameters studied after a 6 month follow-up: snellen uncorrected visual acuity (UCVA), snellen best corrected visual acuity (BCVA), refractive error (spherical and cylinder refraction in D), keratometry values in diopters (D) (K1 flat; K2-steep, Kmax-maximum), corneal higher order aberrations: vertical coma (ṁm), spherical aberration (ṁm) and trefoil with 6,00 mm pupil diameter; topography (Pentacam HR, Oculus®) symmetry parameters: ISV (index of surface variance), IVA (index of vertical asymmetry) and ABR (aberration coefficient) and the rate of postoperative complications.
Group 1 comprised 26 eyes and Group 23 eyes. There was a significant improvement in snellen UCVA for both groups (0,11 preop and 0,32 postop, p<0,05 for group1 and 0,12 preop and 0,33 postop, p<0,05 for group2). BCVA improved in group 1 from 0,516 to 0,574 (p=0,212) and in Group 2 from 0,407 to 0,550 (p<0,05). In group 1, we observed a significant reduction on refractive sphere from -2,454 to -0,056 (p<0,001), in group 2 the reduction was from -4,429 to -3,339 (p=0,071); cylinder refractive values were significantly improved in group 2 (from -3,607 to -1,661, p<0,001) than in group 1 (from -3,732 to -2,380, p<0,001). There was a statistically significant decrease in all topographic keratometric values (K1, K2 and Kmax, p<0,05) after surgery for both groups. In group 1 there was a non significant increase of vertical coma after follow-up (from -3,547 to -3,536, p=0,704), in group 2 there was a significant decrease of the vertical coma value ( from -3,958 to -2,651, p=0,003).
The implantation of corneal ring segments is a safe and effective method for the correction of visual impairment in keratoconic patients: Intacs SK ICRS seem more effective in central keratoconus with high spherical refractive error while Keraring SI6 ICRS provide better refractive results for assimetric cones with higher refractive cylinder and worse higher order aberrations (vertical coma).