RESEARCH ARTICLE
LASIK for Spherical Refractive Myopia: Effect of Topographic Astigmatism (Ocular Residual Astigmatism, ORA) on Refractive Outcome Andreas Frings*, Gisbert Richard, Johannes Steinberg, Christos Skevas, Vasyl Druchkiv, Toam Katz‡, Stephan J. Linke‡ Department of Ophthalmology, University Medical Centre Hamburg-Eppendorf (UKE), Hamburg, Germany ‡ Shared senior authorship. * [email protected]
Abstract Purpose
OPEN ACCESS Citation: Frings A, Richard G, Steinberg J, Skevas C, Druchkiv V, Katz T, et al. (2015) LASIK for Spherical Refractive Myopia: Effect of Topographic Astigmatism (Ocular Residual Astigmatism, ORA) on Refractive Outcome. PLoS ONE 10(4): e0124313. doi:10.1371/journal.pone.0124313 Academic Editor: Rajiv R. Mohan, University of Missouri-Columbia, UNITED STATES Received: October 9, 2014
In eyes with a preoperative plano refractive cylinder, it would appear that there is no rationale for astigmatic treatment. The aim of this retrospective, cross-sectional data analysis was to determine the amount of topographic astigmatism in refractive plano eyes that results in reduced efficacy after myopic laser in situ keratomileusis (LASIK).
Methods This study included 267 eyes from 267 consecutive myopic patients with a refractive plano cylinder. Receiver operating characteristic analysis was used to find the cut-off values of preoperative ocular residual astigmatism (= topographic astigmatism) that can best discriminate between groups of efficacy and safety indices in preoperative plano refractive cylinder eyes.
Accepted: March 11, 2015 Published: April 15, 2015
Results
Copyright: © 2015 Frings et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Preoperative ocular residual astigmatism (ORA) (or topographic astigmatism) of 0.9 diopters (D) resulted in an efficacy index of at least 0.8 statistically significantly more frequently than eyes with a preoperative ORA of >0.9 D. Eyes with a high ORA preoperatively also had a high ORA postoperatively. Regression analysis showed that each diopter of preoperative ORA reduced efficacy by 0.07.
Data Availability Statement: All relevant data are within the paper. Funding: The authors received no specific funding for this work. Competing Interests: The authors have declared that no competing interests exist.
Conclusion A preoperative corneal astigmatism of 0.9 D could (partially) be taken into account in the LASIK design, even if the subjective refractive astigmatism is neutral.
PLOS ONE | DOI:10.1371/journal.pone.0124313 April 15, 2015
1/9
Effect of Topographic Astigmatism on Refractive Outcome
Introduction The results of previous studies[1,2–4] have suggested that treating astigmatism with laser in situ keratomileusis (LASIK) based on manifest subjective refraction results in a more successful outcome if the preoperative refractive astigmatism arises primarily from the anterior corneal surface. However, in eyes with a preoperative plano refractive cylinder there is no rationale for astigmatic treatment and, therefore, any postoperative refractive cylinder is either induced by the ablation, the flap preparation or both. Recently, we assessed the influence of specific parameters on pre-existing ocular residual astigmatism (ORA) in patients scheduled for LASIK to treat myopic astigmatism.[5] To determine the amount of ORA before LASIK, we performed a standard double-angle vector analysis in which the magnitude and orientation of ORA were determined by the vector difference between the preoperative refractive astigmatism (R) (corneal plane) and the topographic (simulated keratometry [K]) astigmatism.[1,2–4] Following Kugler et al.[1], the R value was obtained from the manifest refraction, and the simulated K value was calculated from corneal topography based on the difference between the steepest meridian and the flattest meridian oriented at 90 degrees to each other. The ratio of ORA to preoperative refractive cylinder (R) was calculated for each patient. However, in eyes without preoperative refractive cylinder this value cannot be applied. The aim of the present study was to determine the amount of topographic astigmatism (= the amount of ORA) in refractive plano eyes that results in reduced efficacy after myopic LASIK. The current study was based on the Hamburg Refractive Database and was undertaken to investigate the effect of applying the new definition of high and low ORA for eyes with preexisting plano refractive cylinder using ROC (receiver operating characteristic) analysis.
Methods Patients and Methods This retrospective study included 267 eyes from 267 consecutive myopic patients treated between December 2010 and March 2013, and was based on the Hamburg Refractive Database (data retrieved from Care Vision Refractive Centres in Germany). In all eyes a refractive plano cylinder was present preoperatively. Patients with a significant pre-existing complication of the ocular surface or tear film, and eyes with intra- and postoperative flap complications were excluded from analysis. The latter included eyes with postoperatively dislocated flap, epithelial ingrowth, diffuse lamellar keratitis and central toxic keratopathy. Written informed consent for retrospective data analysis was obtained from refractive surgery candidates during their recruiting process. The study and consent procedure were approved by the local ethics committee of the University of Hamburg, Germany (no. 2882), and adhered to the tenets of the Declaration of Helsinki. Manifest spherical and cylindrical refractions, as well as visual acuity with and without correction were assessed preoperatively and 1 day, and 1, 3–4, and 6 months postoperatively, and recorded electronically. All outcome results reported here are based on the data from the 1-month follow-up (Table 1). The spherical and cylindrical refractions were acquired by subjective refraction, and topographic cylinder was obtained using Pentacam Scheimpflug topography (Oculus, Wetzlar, Germany). All refractions were acquired by subjective refraction by expert optometrists in different refractive centres using the same refractometers, visus tables and documentation protocol. Each patient was examined pre- and postoperatively by the same optometrist. Room conditions were standardized according to a protocol written by the medical director of Care Vision Germany (T.K.).The Alpins vector method, which has been described elsewhere [2–4], was applied to describe the effects of LASIK on refractive cylinder. Target induced astigmatic vector (TIA) is the astigmatic change
PLOS ONE | DOI:10.1371/journal.pone.0124313 April 15, 2015
2/9
Effect of Topographic Astigmatism on Refractive Outcome
Table 1. Descriptives. Preoperative ORA(1)
Low (0.8; 0.9 vs. >0.9 and 1.0 vs. >1.0. For SI, these groups were 0.9 vs. >0.9; 1.0 vs >1.0; 1.1 vs >1.1 and 1.2 vs 1.2. EI was defined as the mean of ratio of postoperative UDVA to preoperative CDVA; SI was defined as the mean of ratio of postoperative CDVA to preoperative CDVA. The area under the curve (AUC), sensitivity and specificity for the given cut-off values are shown in Table 2. The hypothesis that the AUC is significantly different from 0.5 was tested and the P values were reported. A P value 0.9 (probable) was possible, although with a lower sensitivity and specificity. Therefore, an ORA cut-off of 0.9 was chosen for the comparison of the high and low preoperative ORA or topographic cylinder groups (Table 1). For an SI of 0.9 or more, the preoperative ORA (topographic cylinder) should be maximally 0.8. Sex, eye dominance and side were equally distributed among the groups (Table 1).
Crosstabulation The crosstabulation (Table 3) shows that smaller values of preoperative ORA (= topographic astigmatism) resulted in a statistically significantly better EI (Chi-Square = 10.41, P = 0.001). Table 3 also shows that in 62% of the observed cases higher ORA values (0.9) were correlated with a low EI (true positive).
Refractive results I: Sphere, ORA and Visual acuity No statistically significant difference was found in the preoperative sphere (Table 1). On average, ORA was 0.51±0.21 D (range 0.1–0.8 D) in the low ORA group and 1.11±0.22 D (range 0.9–2.00 D) in the high ORA group; this difference was statistically significant (P
LASIK for Spherical Refractive Myopia: Effect of Topographic Astigmatism (Ocular Residual Astigmatism, ORA) on Refractive Outcome Andreas Frings*, Gisbert Richard, Johannes Steinberg, Christos Skevas, Vasyl Druchkiv, Toam Katz‡, Stephan J. Linke‡ Department of Ophthalmology, University Medical Centre Hamburg-Eppendorf (UKE), Hamburg, Germany ‡ Shared senior authorship. * [email protected]
Abstract Purpose
OPEN ACCESS Citation: Frings A, Richard G, Steinberg J, Skevas C, Druchkiv V, Katz T, et al. (2015) LASIK for Spherical Refractive Myopia: Effect of Topographic Astigmatism (Ocular Residual Astigmatism, ORA) on Refractive Outcome. PLoS ONE 10(4): e0124313. doi:10.1371/journal.pone.0124313 Academic Editor: Rajiv R. Mohan, University of Missouri-Columbia, UNITED STATES Received: October 9, 2014
In eyes with a preoperative plano refractive cylinder, it would appear that there is no rationale for astigmatic treatment. The aim of this retrospective, cross-sectional data analysis was to determine the amount of topographic astigmatism in refractive plano eyes that results in reduced efficacy after myopic laser in situ keratomileusis (LASIK).
Methods This study included 267 eyes from 267 consecutive myopic patients with a refractive plano cylinder. Receiver operating characteristic analysis was used to find the cut-off values of preoperative ocular residual astigmatism (= topographic astigmatism) that can best discriminate between groups of efficacy and safety indices in preoperative plano refractive cylinder eyes.
Accepted: March 11, 2015 Published: April 15, 2015
Results
Copyright: © 2015 Frings et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Preoperative ocular residual astigmatism (ORA) (or topographic astigmatism) of 0.9 diopters (D) resulted in an efficacy index of at least 0.8 statistically significantly more frequently than eyes with a preoperative ORA of >0.9 D. Eyes with a high ORA preoperatively also had a high ORA postoperatively. Regression analysis showed that each diopter of preoperative ORA reduced efficacy by 0.07.
Data Availability Statement: All relevant data are within the paper. Funding: The authors received no specific funding for this work. Competing Interests: The authors have declared that no competing interests exist.
Conclusion A preoperative corneal astigmatism of 0.9 D could (partially) be taken into account in the LASIK design, even if the subjective refractive astigmatism is neutral.
PLOS ONE | DOI:10.1371/journal.pone.0124313 April 15, 2015
1/9
Effect of Topographic Astigmatism on Refractive Outcome
Introduction The results of previous studies[1,2–4] have suggested that treating astigmatism with laser in situ keratomileusis (LASIK) based on manifest subjective refraction results in a more successful outcome if the preoperative refractive astigmatism arises primarily from the anterior corneal surface. However, in eyes with a preoperative plano refractive cylinder there is no rationale for astigmatic treatment and, therefore, any postoperative refractive cylinder is either induced by the ablation, the flap preparation or both. Recently, we assessed the influence of specific parameters on pre-existing ocular residual astigmatism (ORA) in patients scheduled for LASIK to treat myopic astigmatism.[5] To determine the amount of ORA before LASIK, we performed a standard double-angle vector analysis in which the magnitude and orientation of ORA were determined by the vector difference between the preoperative refractive astigmatism (R) (corneal plane) and the topographic (simulated keratometry [K]) astigmatism.[1,2–4] Following Kugler et al.[1], the R value was obtained from the manifest refraction, and the simulated K value was calculated from corneal topography based on the difference between the steepest meridian and the flattest meridian oriented at 90 degrees to each other. The ratio of ORA to preoperative refractive cylinder (R) was calculated for each patient. However, in eyes without preoperative refractive cylinder this value cannot be applied. The aim of the present study was to determine the amount of topographic astigmatism (= the amount of ORA) in refractive plano eyes that results in reduced efficacy after myopic LASIK. The current study was based on the Hamburg Refractive Database and was undertaken to investigate the effect of applying the new definition of high and low ORA for eyes with preexisting plano refractive cylinder using ROC (receiver operating characteristic) analysis.
Methods Patients and Methods This retrospective study included 267 eyes from 267 consecutive myopic patients treated between December 2010 and March 2013, and was based on the Hamburg Refractive Database (data retrieved from Care Vision Refractive Centres in Germany). In all eyes a refractive plano cylinder was present preoperatively. Patients with a significant pre-existing complication of the ocular surface or tear film, and eyes with intra- and postoperative flap complications were excluded from analysis. The latter included eyes with postoperatively dislocated flap, epithelial ingrowth, diffuse lamellar keratitis and central toxic keratopathy. Written informed consent for retrospective data analysis was obtained from refractive surgery candidates during their recruiting process. The study and consent procedure were approved by the local ethics committee of the University of Hamburg, Germany (no. 2882), and adhered to the tenets of the Declaration of Helsinki. Manifest spherical and cylindrical refractions, as well as visual acuity with and without correction were assessed preoperatively and 1 day, and 1, 3–4, and 6 months postoperatively, and recorded electronically. All outcome results reported here are based on the data from the 1-month follow-up (Table 1). The spherical and cylindrical refractions were acquired by subjective refraction, and topographic cylinder was obtained using Pentacam Scheimpflug topography (Oculus, Wetzlar, Germany). All refractions were acquired by subjective refraction by expert optometrists in different refractive centres using the same refractometers, visus tables and documentation protocol. Each patient was examined pre- and postoperatively by the same optometrist. Room conditions were standardized according to a protocol written by the medical director of Care Vision Germany (T.K.).The Alpins vector method, which has been described elsewhere [2–4], was applied to describe the effects of LASIK on refractive cylinder. Target induced astigmatic vector (TIA) is the astigmatic change
PLOS ONE | DOI:10.1371/journal.pone.0124313 April 15, 2015
2/9
Effect of Topographic Astigmatism on Refractive Outcome
Table 1. Descriptives. Preoperative ORA(1)
Low (0.8; 0.9 vs. >0.9 and 1.0 vs. >1.0. For SI, these groups were 0.9 vs. >0.9; 1.0 vs >1.0; 1.1 vs >1.1 and 1.2 vs 1.2. EI was defined as the mean of ratio of postoperative UDVA to preoperative CDVA; SI was defined as the mean of ratio of postoperative CDVA to preoperative CDVA. The area under the curve (AUC), sensitivity and specificity for the given cut-off values are shown in Table 2. The hypothesis that the AUC is significantly different from 0.5 was tested and the P values were reported. A P value 0.9 (probable) was possible, although with a lower sensitivity and specificity. Therefore, an ORA cut-off of 0.9 was chosen for the comparison of the high and low preoperative ORA or topographic cylinder groups (Table 1). For an SI of 0.9 or more, the preoperative ORA (topographic cylinder) should be maximally 0.8. Sex, eye dominance and side were equally distributed among the groups (Table 1).
Crosstabulation The crosstabulation (Table 3) shows that smaller values of preoperative ORA (= topographic astigmatism) resulted in a statistically significantly better EI (Chi-Square = 10.41, P = 0.001). Table 3 also shows that in 62% of the observed cases higher ORA values (0.9) were correlated with a low EI (true positive).
Refractive results I: Sphere, ORA and Visual acuity No statistically significant difference was found in the preoperative sphere (Table 1). On average, ORA was 0.51±0.21 D (range 0.1–0.8 D) in the low ORA group and 1.11±0.22 D (range 0.9–2.00 D) in the high ORA group; this difference was statistically significant (P
