Polar Value Analysis of Corneal Astigmatism in Intrastromal Corneal Ring Segment Implantation

Abstract

Purpose. To evaluate surgically induced astigmatism (SIA) and the average corneal power change in symmetric intrastromal corneal ring segment (ICRS) implantation. Methods. The study included 34 eyes of 34 keratoconus patients who underwent symmetric Intacs SK ICRS implantation. The corneal pocket incision meridian was the preoperative steep meridian. Corneal power data were obtained before and 3 months after Intacs SK ICRS implantation using scanning-slit topography. Polar value analysis was used to evaluate the SIA. Hotelling's trace test was used to compare intraindividual changes. Results. Three months postoperatively, the combined mean polar value for SIA changed significantly (Hotelling's T 2 = 0.375; P = 0.006). The SIA was 1.54 D at 99° and the average corneal power decreased significantly by 3.8 D. Conclusion. Intacs SK ICRS placement decreased the average corneal power and corneal astigmatism compared to the preoperative corneal power and astigmatism when the corneal pocket incision was made at the preoperative steep meridian.

Polar value analysis of astigmatic change and rotational stability after implantation of V4c toric implantable collamer lens

“…Therefore, it is necessary to analyze the causes of residual astigmatism after implantation of the V4c TICL. Astigmatic power is expressed as magnitude in diopters and direction in degrees (10)(11)(12)(13)(14)(15)18,19). Therefore, vector analysis should be used to evaluate the effect of the V4c TICL on astigmatic correction.…”

“…Although there are many methods of vector analysis to evaluate astigmatism correction, Naeser's polar value method ( 11) is an excellent way to understand the exact changes in the composition of astigmatism in refractive surgery. A number of studies (12)(13)(14) have applied this method to assess surgically induced astigmatism (SIA) and treatment errors, as well as size and orientationrelated changes in astigmatism, following various refractive operations. To the best of our knowledge, no studies to date have used Naeser's method to evaluate the astigmatic results and postoperative rotation of the V4c TICL.…”

Polar Value Analysis of Low to Moderate Astigmatism with Wavefront-Guided Sub-Bowman Keratomileusis

“…By flattening the preoperative steeper meridian, the surgery could achieve to correct astigmatism. However, the astigmatic power is characterized by magnitude in diopters and direction in degrees [ 3 – 7 , 10 , 16 ]. Therefore, analysis of surgically induced astigmatism (SIA) should be performed with power vector, such as the polar values.…”

“…The polar value method described by Næser [ 4 ] is an excellent way of understanding the precise change in the astigmatic component of refractive surgery. To use this method, some previous studies [ 5 – 7 ] assessed surgically induced astigmatism, error of treatment, and change in the astigmatic component after various refractive surgery. However, to our knowledge, few studies have examined quantitative astigmatic outcomes in wavefront-guided sub-Bowman keratomileusis (WFG-SBK) [ 8 , 9 ].…”