Surgical Induced Astigmatism 1 Year After Implantation of New Short Arc Intrastromal Ring Segments
To evaluate the SIA of new intrastromal ring segments, INTACS SK, of 90° or 130° in patients diagnosed with astigmatic centered keratoconus.
A non-randomized experimental prospective controlled study with a non-probabilistic sample, including 20 patients with a diagnosis of centered keratoconus grade I, II, and III and astigmatism greater than the spherical defect. Two intracorneal rings were implanted according to Intacs nomogram version 3.1 in 7 mm tunnel. Magnitude and axis of topographical -total corneal power (TCP) and refractive astigmatism (RA) was obtaining pre- operative and 3 months postoperative. We measured the visual acuity and the surgical induced astigmatism (SIA) to determine if there were over or under astigmatic corrections.
Preoperative of INTACS 90°, UCVA and BSCVA were 0.78 and 0.20. The TCA and RA were 3.93 D @ 90° and 1.52 D @ 175°. One year postop, the UCVA and BSCVA were 0.49 and 0.18 , the TCA and RA were 2.67 @ 90 ° and 0.30 D @ 24°. Preoperative of INTACS 130°, UCVA and BSCVA were 1.22 and 0.29. The TCA and RA were 4.57 D @ 99° and 1.95 D @ 173°. One year post-op, the UCVA and BSCVA were 0.37 and 0.19, the TCA and RA were 3.12 @ 109 ° and 0.86 D @ 167°. The total corneal and refractive SIA were 1.26 @ 178° and 1.38 @ 80° for 90° rings and 1.97 @ 173° and 1.50 @ 87° for 130° rings.
We found a total corneal SIA under-correction in keratoconus treatment with rings of 90° or 130°, which clinically is required to avoid an overcorrection of coupling effect in the flat meridian and then to avoid hyperopic shift post operative. Finally this is important to improve the visual rehabilitation of the patient. The good result of refractive SIA showed correlation with the improvement in the visual acuity in both rings.