Efficacy of laser in situ keratomileusis in correcting anterior and non-anterior corneal astigmatism: comparative study

Clinical outcomes after topography-guided FS-LASIK for myopia with nonastigmatic eyes

BACKGROUND

To analyze the clinical outcomes after topography-guided femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) with Phorcides Analytic Engine (PAE) algorithm or Custom-Q FS-LASIK for myopia with nonastigmatic eyes.

METHODS

In this retrospective study, a total of 90 eyes with myopia without manifest astigmatism (82 patients) were included. All surgeries were performed by topography-guided FS-LASIK planned with a PAE algorithm (42 eyes) or Custom-Q system (48 eyes). Refractive, visual outcomes and corneal aberrations were compared between the two groups.

RESULTS

At 6 months postoperatively, the postoperative uncorrected distance visual acuity (UDVA) was 20/20 or better in 42 eyes (100%) in the PAE compared with 44 eyes (92%) in Custom-Q (P = .120). The postoperative UDVA of 20/16 or better was measured in 92% of eyes in the PAE group and 81% of eyes in the Custom Q group (P = .320). Postoperative corrected distance visual acuity, manifest refractive spherical equivalent and refractive astigmatism were similar between the two groups (P > .05). The postoperative optical path difference (OPD) and Strehl ratio (SR) were significantly better in the PAE group compared with the Custom Q group.

CONCLUSIONS

Topography-guided FS-LASIK with PAE algorithm or Custom Q demonstrated similar refractive efficacy and predictability. PAE for the patients with zero manifest astigmatism demonstrated better results in correcting corneal aberrations.

Ocular residual astigmatism (ORA) does not seem to correlate with baseline refractive error among refractive surgery candidates

PURPOSE

Ocular residual astigmatism (ORA) is defined as the difference between refractive astigmatism and anterior corneal astigmatism. A high ORA may be correlated with poorer results in patients undergoing corneal-based laser surgery. Is a high baseline refractive error related to a higher degree of ORA?

METHODS

This was a retrospective analytical study including 181 right eyes of an equal number of refractive surgery candidates. Manifest subjective refraction was measured, along with a Pentacam AXL Wave corneal tomography. Via a vector analysis with this methodology, subjective cylinder was translated into the corneal plane and a vectorial subtraction was performed in order to measure ORA. Spearman's rank order test, one-way ANOVA and Chi-square were used to determine whether different levels of baseline refractive error correlate with different levels of ORA.

RESULTS

Mean age was 28.33 ± 4.71 years with a female preponderance (65.7%). Mean ORA was 0.74 ± 0.39 D, with 33.1% of eyes having an ORA ≥ 0.90 D. There was not a correlation between ORA and level of myopia (rho = - 0.022; p = 0.764), nor between ORA and spherical equivalent (rho = 0.009; p = 0.903). Refractive astigmatism did not demonstrate to be correlated with ORA level either (rho = 0.078; p = 0.329). One-way ANOVA tests failed to demonstrate an association between different classifications of refractive error and level of ORA.

CONCLUSIONS

In the studied population, ORA is not correlated with baseline refractive error. Every patient presenting for possible corneal-based laser refractive surgery should be evaluated for a possible high level of ORA, irrespective of their baseline ametropia level.

Changes in aberrations and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in eyes with high astigmatism: a retrospective case control study

BACKGROUND

To compare the 6-month changes in aberration and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for high astigmatism.

METHODS

In this retrospective case control study, 47 eyes with high astigmatism (≥ 2.5 D, HA group) and 47 eyes with low astigmatism (≤ 1.0 D, LA group) underwent FS-LASIK. Preoperative and follow-up examinations included visual outcomes, higher order aberrations (HOAs) and biomechanics. Biomechanical parameters include a deformation amplitude ratio of 2 mm (DA ratio 2 mm), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), and ambrosio relational thickness through the horizontal meridian (ARTh).

RESULTS

Six months postoperatively, there was no significant difference in the efficacy and safety index (both P > 0.05) between the two groups, but the cylinder was higher in the HA group. The HOAs increased significantly after surgery in both groups (all P < 0.05). Six months postoperatively, the changes in spherical aberration and HOAs were larger in the HA group (both P < 0.005), but there was no significant difference between the changes in coma (P > 0.05). Significant decreases in SP-A1 and ARTh and significant increases in the IIR and DA ratio of 2 mm (all P < 0.05) were observed after surgery in both groups. The changes in the DA ratio 2 mm, IIR, SP-A1, and ARTh were not significantly different between the groups.

CONCLUSION

FS-LASIK had relative comparable efficacy and safety in correcting high and low myopic astigmatism, with higher astigmatic under-correction in eyes with high astigmatism. High astigmatism in eyes after FS-LASIK could introduce larger corneal aberrations, but the impact on corneal stiffness was the same as that in eyes with low astigmatism.

Comparison of refractive and visual acuity results after Contoura® Vision topography-guided LASIK planned with the Phorcides Analytic Engine to results after wavefront-optimized LASIK in eyes with oblique astigmatism

PURPOSE

To compare visual acuity and refractive results between topography-guided laser in situ keratomileusis (LASIK) planned with the Phorcides Analytic Engine (PAE) to results after wavefront-optimized (WFO) LASIK in subjects with preoperative oblique astigmatism in their manifest refraction.

METHODS

This was a retrospective chart review of clinical results from eyes treated with topography-guided LASIK planned with PAE compared to eyes treated with WFO LASIK using the same Wavelight® excimer laser system. All included subjects had preoperative oblique astigmatism. Residual refractive error and visual acuity (uncorrected and corrected) were the measures of interest, at the visit closest to 90 days postoperative.

RESULTS

A matched data set from 100 WFO and 97 PAE eyes was extracted from clinical records. At the postoperative visit the PAE group showed lower residual refractive cylinder (p = 0.04), uncorrected distance visual acuity (UDVA) (-0.06 PAE vs. -0.02 WFO, p < 0.01) and distance corrected visual acuity (CDVA) (p < 0.01). The percentage of eyes with a mean refraction spherical equivalent (MRSE) magnitude within 0.25 D and 0.50 D of plano was statistically significantly higher in the PAE group (p = 0.04 and 0.01, respectively). A statistically significantly higher percentage of eyes in the PAE group had UDVA better than or equal to -0.10 logMAR (20/16 Snellen, 36% vs 22%, p = 0.04). More eyes gained CDVA after surgery in the PAE group (53% vs 32%, p < 0.01). There were five enhancements in the WFO group versus none in the PAE group, a statistically significant difference (p = 0.03).

CONCLUSIONS

Visual acuity and refractive outcomes after LASIK using PAE in eyes with oblique astigmatism in their preoperative refraction were statistically significantly better than those obtained when WFO treatment was used. The number of refractive outliers and the number of retreatments were also significantly lower with PAE treatment.

Evaluation of Ocular Residual Astigmatism in Eyes with Myopia and Myopic Astigmatism and Its Interaction with Other Forms of Astigmatism

Purpose

To evaluate the prevalence, magnitude, and direction of ocular residual astigmatism (ORA) in eyes with myopia and myopic astigmatism, and its interaction with refractive, anterior corneal, posterior corneal, and true net power astigmatism.

Patients and Methods

Refractive surgery candidates with myopia and myopic astigmatism were studied. Refractive astigmatism (RA) was measured using the Nidek^® AR-310A autorefractometer. Anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA), and true net power astigmatism (TNP) were measured using the Wavelight^® Oculyzer II. Astigmatism was converted from polar to vector notation. ORA was calculated by vector subtraction of ACA from RA vertexed to corneal plane. Compensation factor (CF) was calculated as the ratio of ORA that compensates ACA for both J₀ and J₄₅.

Results

154 eyes of 88 patients (mean age 31.7±7.1 years) were included. With-the-rule (WTR) astigmatism was the most common for both RA (55.6%) and ACA (74%), while against-the-rule (ATR) was the most common for PCA (87.7%) and ORA (74.0%). The axes of RA and ACA were within 10° of each other in 46.8% of the eyes, and within 30° of each other in 76.0%. The mean difference in value between the axis of RA and ACA was 25.6°. 71.4% of eyes in the study had an ORA ≥ 0.5D, 44.1% had ORA ≥ 0.75D and 26% had ORA ≥ 1D. There was a statistically significant difference between ACA and each of RA and TNP. Using TNP to calculate ORA instead of ACA reduced its magnitude. RA is positively correlated to ACA and more strongly to TNP. The most common pattern of compensation between ORA and ACA was under-compensation for J₀ (49%) and same-axis-augmentation for J45 (35%).

Conclusion

ORA, PCA, and the interaction between ORA and ACA can affect results during refractive planning.

Influence of Ocular Residual Astigmatism on the Correction of Myopic Astigmatism by Toric Implantable Collamer Lens: A Comparative Study With Femtosecond Laser Small Incision Lenticule Extraction

Purpose

To evaluate the influence of the origin of astigmatism on the correction of myopic astigmatism by toric implantable collamer lens (TICL) and compare it with femtosecond laser small incision lenticule extraction (SMILE).

Methods

Ocular residual astigmatism (ORA) was determined by vector analysis using manifest refraction and Scheimpflug camera imaging of the anterior cornea. One-to-one matching between the TICL and SMILE groups was performed by preoperative manifest refractive astigmatism (RA) and ORA, tolerating a maximum difference of 0.50 diopter (D) for RA and 0.25 D for ORA. Patients of each group were further divided into groups according to ORA (high &gt; 1.0 D; low ≤ 1.0 D). The baseline and 12-month postoperative data were analyzed. Data are expressed as mean ± standard deviation (SD). A value of p less than 0.05 was considered statistically significant.

Results

For the TICL group, no significant differences in the postoperative RA, safety index, efficacy index, index of success (IOS), correction index (CI), and angle of error (AOE) were found between high (n = 36) and low ORA (n = 36) groups (Mann–Whitney U test, p &gt; 0.05). For the SMILE group, the postoperative RA (high: −0.67 ± 0.43 D, low: −0.39 ± 0.29 D, Mann–Whitney U test, p = 0.003) and IOS (high: 0.50 ± 0.43, low: 0.25 ± 0.23, Mann–Whitney U test, p = 0.003) were greater in the high ORA group. When comparing TICL and SMILE groups, the mean postoperative RA (TICL: −0.48 ± 0.29 D, SMILE: −0.67 ± 0.43 D, Mann–Whitney U test, p = 0.03) and IOS (TICL: 0.32 ± 0.23, SMILE: 0.50 ± 0.43, Mann–Whitney U test, p = 0.03) were significantly higher in the SMILE group when the ORA was &gt;1.0 D.

Conclusion

Both TICL and SMILE are effective in correcting myopic astigmatism. ORA has a lesser effect on TICL than on SMILE.

The Distribution Pattern of Ocular Residual Astigmatism in Chinese Myopic Patients

Purpose

We aimed to investigate the distribution of ocular residual astigmatism (ORA) and its associations with age, gender, manifest refraction, and other ocular indicators in Chinese patients with myopia.

Design

This is a multi-center retrospective cross-sectional study.

Method

The study included 7,893 patients with myopia (7,893 eyes) aged 18–40 years from five ophthalmic centers. Anterior segment biometrics of the eyes were collected from the Pentacam. ORA and its summated vector mean were calculated using Alpins vector analysis. Compensation factor (CF) was used to evaluate the relation between ORA and corneal astigmatism. ORA in different age, gender, and refraction groups was compared. The Spearman correlation was adopted to reveal multiple ocular indicators associated with ORA, which were integrated into a multiple linear regression model to predict ORA.

Results

Distribution of ORA was slightly positively skewed (Skewness= 2.111, Kurtosis = 19.660, KS P < 0.0001). Mean ORA was 0.74 ± 0.39 D (95% normal range: 0.14–1.54 D). Among all the subjects, 22.4% of the eyes had an ORA magnitude of 1.0 D or more. Undercompensation or full-compensation of anterior corneal astigmatism (ACA) by ORA prevailed in both J₀ (76.99%) and J₄₅ (58.48%). Women had higher ORA power than men (0.77 ± 0.36 D vs. 0.73 ± 0.41 D, P < 0.0001). Participants with less negative spherical equivalent (SE) or higher manifest astigmatism (MA) also had higher ORA (all P < 0.0001). ORA was significantly correlated with ACA (r = 0.405) and posterior corneal astigmatism (PCA, r = 0.356). The multivariate logistic regression analysis showed strong predictability of ORA magnitude >1.0 D using anterior segment parameters (area under the receiver operating characteristic curve: 0.739).

Conclusion

ORA is present in Chinese adults with myopia and is affected by multiple ocular factors. Our findings may provide valuable information about ORA distribution in candidates for refractive surgery, helping optimize the outcome of astigmatism correction.

Topography-Guided FS-LASIK With PAE Algorithm and Sirius Tomography Data for Correction of Myopia and Myopic Astigmatism

PURPOSE

To compare the clinical outcomes after topography-guided and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) planned with the Phorcides Analytic Engine (PAE) algorithm system and Sirius tomography data for correction of myopia and myopic astigmatism when the ocular residual astigmatism (ORA) was great or not.

METHODS

In this retrospective study, a total of 163 eyes with myopia and myopic astigmatism (99 patients) were included. Eyes with myopic astigmatism and high ORA of 0.75 diopters (D) or greater were assigned to the high ORA group and the others to the low ORA group. All surgeries were performed by topography-guided FS-LASIK planned with a PAE algorithm system. PAE took anterior and posterior corneal negative cylinder of the 5-mm zone from the Sirius combined topography and tomography. Refractive and visual outcomes, vector analysis, and corneal aberrations were compared between the two groups.

RESULTS

At 6 months postoperatively, the uncorrected distance visual acuity of 20/16 or better was measured in 59% of eyes in the high ORA group and 66% of eyes in the low ORA group (P = .307). Postoperative corrected distance visual acuity, manifest refractive spherical equivalent, refractive astigmatism, target induced astigmatism, surgically induced astigmatism, and difference vector were similar between the two groups (P > .05). The postoperative corneal astigmatism was significantly higher in the high ORA group (P = .008), and the high ORA group over-corrected astigmatism with the rule and showed a higher correction index (P = .003) compared with the low ORA group.

CONCLUSIONS

Topography-guided FS-LASIK with PAE algorithm and Sirius combined topography and tomography data for correction of myopia and myopic astigmatism achieved the predicted surgical outcomes and there was a tendency to have a similar clinical outcome for PAE when the ORA was great or not. However, the PAE with high ORA overcorrected astigmatism with-the-rule and showed a higher correction index compared with the low ORA group. [J Refract Surg. 2022;38(4):235-242.].

Tilted disc syndrome (TDS): New hypotheses for posterior segment complications and their implications in other retinal diseases

Tilted disc syndrome (TDS) is considered a congenital anomaly due to a delayed closure of the embryonic fissure. It is characterized by an oblique orientation of the axis of the optic disc, associated with other posterior pole anomalies such as inferior crescent, situs inversus and inferior staphyloma. The aim of this review was to summarize the data supporting the current hypotheses for the pathogenesis of TDS, and its anatomical and functional clinical consequences. Recent imaging techniques, such as magnetic resonance imaging, wide-field fundus imaging, and 2- and 3-D optical coherence tomography have provided a new perspective on TDS and its complications. Different abnormalities have previously been reported, both in the anterior and posterior segments. The focus was on vision-threatening chorioretinal changes or complications, including choroidal neovascularization and serous retinal detachments and their therapeutic options. Based on clinical observations, assumptions were proposed to understand the occurrence of complications such as chorioretinal degenerative changes, choroidal neovascularization and polypoidal choroidal vasculopathy, macular serous retinal detachment, myopic foveoschisis and chorioretinal folds. These hypotheses could be referred to as the curvature "breaking point" hypothesis, the uneven growth "tractional" hypothesis, the "container-content" imbalance hypothesis, and the "choroidal funnel" hypothesis. Because these complications could also occur in other contexts, understanding the pathogenesis of TDS complications could help to understand their pathophysiology.

Comparison of clinical outcomes between vector planning and manifest refraction planning in SMILE for myopic astigmatism

PURPOSE

To compare clinical outcomes of small-incision lenticule extraction (SMILE) between manifest refraction (MR) and vector planning for myopic astigmatism with high ocular residual astigmatism (ORA).

SETTING

Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea.

DESIGN

Prospective, randomized, comparative case series.

METHODS

Patients with myopic astigmatism and ORA of 0.75 diopters (D) or greater were randomized into the MR or vector planning group and underwent SMILE without applying any nomogram for cylinder correction. Visual acuity, MR, corneal topography, and corneal aberration were measured preoperatively and postoperatively. Outcomes at 6 months postoperatively were compared between the groups.

RESULTS

The study comprised 114 patients (114 eyes): 58 eyes in MR planning and 56 eyes in vector planning. The mean uncorrected and corrected distance visual acuity, safety and efficacy indices were comparable between the 2 groups. Postoperative refractive cylinder reached statistically significant differences between the groups (-0.22 ± 0.18 D and -0.14 ± 0.16 D in the MR and vector planning groups, respectively, P = .02). Postoperative corneal toricity and ORA reached statistically significant lower in the vector planning group.

CONCLUSIONS

In myopic astigmatism with high ORA, MR and vector planning in SMILE were effective with comparable visual outcomes; vector planning showed statistically significant lower postoperative refractive and corneal astigmatism and ORA. Use of vector planning may improve refractive outcomes in SMILE cases with high ORA. However, the results may have been different had a nomogram adjustment been applied, as is often used for cylinder corrections with SMILE.

The contribution of ocular residual astigmatism to anterior corneal astigmatism in refractive astigmatism eyes

To determine the distribution of ocular residual astigmatism (ORA) in astigmatic eyes and the influence on the anterior corneal (ACA) and refractive astigmatism (RA). A total of 165 children met the inclusion criteria. Right eyes' data were analyzed. Using Thibos vector analysis to calculate ORA. Spearman correlation analysis was used to obtain the correlation between the magnitude of ORA, ACA and RA. The median magnitude of ORA in astigmatic eyes was 0.57 D, with interquartile range was 0.42 D. And they were main against-the-rule (57.6-75.8%) and oblique astigmatism (13.9-34.5%) ORA. The ORA in 140 eyes (84.8%) acted as an offset to ACA, meanwhile, 25 eyes (15.2%) superimposed it. About 98% (97.9-98.4%) against-the-rule and 75% (73.9-82.5%) oblique ORA counteracted ACA, nevertheless, all with-the-rule ORA had a superimposed effect on ACA. For with-the-rule ACA, about 86% (85.4-85.9%) ORA worked to offset it. There was statistically correlations between ORA and ACA (r = 0.17, P = 0.03), ORA and RA (r = - 0.27, P = 0.001). The magnitude of ocular residual astigmatism was relatively small in children's astigmatic eyes. Both against-the-rule and oblique ORA can counteract with-the-rule ACA.

Excimer laser programming of refractive astigmatism vs. anterior corneal astigmatism in the case of ocular residual astigmatism (ORA)

PURPOSE

To determine whether manifest refractive astigmatism (RA) or anterior corneal astigmatism (CA) is the best value for excimer laser programming in cases of ocular residual astigmatism (ORA).

PATIENTS AND METHODS

Patients who had undergone LASIK surgery with a disagreement between manifest refractive and corneal cylinder (ocular residual astigmatism ORA)>0.75 D were included retrospectively in this study. We calculated target induced astigmatism vector (TIA), surgically induced astigmatism vector (SIA), difference vector between the astigmatism correction programmed in the excimer laser and refractive astigmatism (DVRA), difference vector between the astigmatism correction programmed in the excimer laser and corneal astigmatism (DVCA) and difference vector between TIA and SIA (DV), by the Alpins method. Vectorial differences between DV and DVRA, and between DV and DVCA, were then calculated to determine whether RA or CA was closest to the ideal cylinder for laser programming.

RESULTS

Of a total of 104 eyes undergoing LASIK, 22 eyes of 12 patients (21.1%) had an ORA>0.75 D and were included. Mean ORA was 0.9±0.2 D and mean postoperative subjective cylinder was 0.45 D. The DV-DVRA difference vector was 0.57±0.2 D, and the DV-DVCA difference vector was 0.86±0.4 D (P=0.02). RA was closer than CA to the ideal astigmatism correction.

CONCLUSION

In cases of discrepancy between manifest astigmatism and corneal astigmatism, correction of manifest refractive astigmatism seems to give a better refractive result.

A multicenter study of the distribution pattern of posterior corneal astigmatism in Chinese myopic patients having corneal refractive surgery

Including posterior corneal astigmatism (PCA) into consideration may increase the accuracy of astigmatism correction after corneal refractive surgery. In the present study we aim to investigate the distribution pattern of PCA in a large number of myopic patients from multiple ophthalmic centers. There were 7829 eyes retrospectively included in the study. Pentacam data of the eyes were retrieved from the machine and only results with image quality labelled with ‘OK’ were included. Distribution of PCA was slightly positively skewed (Skewness = 0.419, Kurtosis = 0.435, KS P < 0.0001). Mean PCA was 0.34 ± 0.14 D (range: 0.00 D-0.99 D). PCA was ≥ 0.25 D in 74.91% of the eyes and was ≥ 0.50 D in 11.61% of the eyes. In 97.55% of the eyes the steep meridian of PCA was vertical (SMV). PCA magnitude was significantly higher in eyes with SMV PCA (P < 0.0001) or high manifest astigmatism (MA, P < 0.0001). There was a significant correlation between anterior corneal astigmatism (ACA) magnitude and PCA magnitude in all of the eyes (r = 0.704, P < 0.0001). There was also a trend of decreasing frequency and magnitude of SMV PCA with aging (both P < 0.0001). In conclusion, PCA is present in myopic patients having corneal refractive surgery and PCA magnitude is increased with higher MA or ACA. Consideration of the impact of PCA on laser astigmatism correction may be necessary.

Astigmatism Correction Using SMILE

Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high efficacy and safety profile and also carries potential advantages over laser in situ keratomileusis such as a better corneal biomechanical stability, reduction in dry eyes rate, and the avoidance of flap complications. However, there have been concerns regarding the precision of astigmatism correction that undercorrection has been reported to be apparent. Various factors that affect astigmatism correction have been identified in the literature. The purpose of this review is to discuss the factors that affect astigmatism correction in SMILE and several techniques to improve the refractive outcomes.

Primary Topography-Guided LASIK: Treating Manifest Refractive Astigmatism Versus Topography-Measured Anterior Corneal Astigmatism

PURPOSE

To investigate whether topography-guided laser in situ keratomileusis (LASIK) with anterior corneal astigmatism measured on the WaveLight Contoura (Alcon Laboratories, Inc., Fort Worth, TX) leads to better refractive outcomes compared to treating on the clinically measured manifest refractive astigmatism axis in eyes with primary myopic astigmatism.

METHODS

Retrospective analysis of 1,274 consecutive LASIK eyes treated on the topography-measured anterior corneal astigmatism axis compared to eyes treated on the conventional clinical manifest refractive astigmatism axis.

RESULTS

In eyes with a small axis discrepancy between anterior corneal astigmatism and refractive astigmatism of 5° to 20°, there was no significant difference in efficacy index, refractive astigmatism accuracy, and most Alpins vector analysis parameters. Both treatment modalities achieved 20/20 uncorrected distance visual acuity (UDVA) in 90% of eyes, with 95% having postoperative cylinder of 0.50 diopters (D) or less. In eyes with a large axis discrepancy between 21° and 45° treated on the anterior corneal astigmatism axis, outcomes were both statistically and clinically inferior. Fewer eyes achieved UDVA of 20/20 (88.9% vs 73.6%; P = .01) and fewer had a defocus equivalent of 0.25 (65.6% vs 52.7%), 0.50 (86.9% vs 80.0%), and 0.75 (97.5% vs 90.9%) D or less (P < .05 for all). Significantly more eyes achieved an angle of error greater than 15° (25.4% vs 8.1%; P = .004), had postoperative residual astigmatism of 0.75 D or less (18.2% vs 7.4%; P = .03), and needed an excimer laser re-treatment (11% vs 1.6%; P = .007).

CONCLUSIONS

Topography-guided myopic astigmatism LASIK treated on the topography-measured anterior corneal astigmatism axis resulted in inferior refractive and visual outcomes compared to treating on the clinical manifest refractive astigmatism axis. [J Refract Surg. 2019;35(1):15-23.].

Transepithelial Photorefractive Keratectomy in Moderate to High Astigmatism With a Non-wavefront-Guided Aberration-Neutral Ablation Profile

PURPOSE

To evaluate the outcomes of transepithelial photorefractive keratectomy (PRK) in moderate to high astigmatism with a non-wavefront-guided aberration-neutral ablation profile using SmartPulse allocation.

METHODS

In this retrospective study, myopic patients with a preoperative cylinder of 2.00 diopters (D) or greater were analyzed at 3 months of follow-up. Transepithelial PRK treatments were performed in each patient with the Amaris 1050RS laser (SCHWIND eye-tech-solutions, Kleinostheim, Germany) creating aspheric ablation profiles by applying a SmartPulse allocation. Standard examinations and wavefront analyses were included for low and high ocular residual astigmatism subgroups.

RESULTS

Fifty-eight eyes (44 patients) were included in the cohort. The eyes were divided into separate ocular residual astigmatism subgroups: 17 eyes presented with less than 0.50 D (low ocular residual astigmatism) and 24 eyes with greater than 0.75 D (high ocular residual astigmatism). The mean refractive cylinder in the entire cohort was 2.84 ± 0.86 D preoperatively and 0.40 ± 0.39 D postoperatively, with 81% of the eyes within 0.75 D of the target astigmatism. At 3 months of follow-up, significant improvement (P < .05) was seen in terms of sphere, cylinder, spherical equivalent, and uncorrected (UDVA) and corrected (CDVA) distance visual acuity. CDVA improved in 40% of eyes and 3% of eyes lost one line of CDVA. No clinically relevant changes were seen in higher order aberrations. The refractive changes showed an excellent match with the keratometric changes. The difference between the low and high ocular residual astigmatism subgroups was not significant except for the change of Snellen lines of CDVA (P < .05).

CONCLUSIONS

Transepithelial PRK using a non-wavefront-guided aberration-neutral ablation profile performed by applying SmartPulse allocation yielded excellent visual outcomes. The preoperative astigmatism was reduced to subclinical values. Both subgroups were effective in terms of UDVA, CDVA, spherical and astigmatic correction, and preserving higher order aberrations. However, the low ocular residual astigmatism subgroup was slightly more prone to gain lines of CDVA. [J Refract Surg. 2018;34(7):466-474.].

Agreement Between Internal Astigmatism and Posterior Corneal Astigmatism in Pseudophakic Eyes

PURPOSE

To directly measure internal astigmatism and evaluate its agreement with posterior corneal astigmatism in pseudophakic eyes.

METHODS

This prospective study enrolled 32 eyes of 32 patients (18 women, 56.3%) who underwent phacoemulsification with implantation of a non-toric monofocal intraocular lens (IOL). Two months postoperatively, posterior corneal astigmatism was measured using a Pentacam Scheimpflug analyzer (Oculus Optikgeräte GmbH, Wetzlar, Germany). Manifest refractive astigmatism was measured after fitting a spherical hard contact lens. This refractive astigmatism that was vertexed to the corneal plane was considered internal astigmatism. The magnitudes of internal and posterior corneal astigmatism were compared. The relationship and agreement between these two astigmatisms were investigated using the Spearman correlation coefficient and Bland-Altman plots, respectively.

RESULTS

The mean patient age was 56.3 ± 9.6 years. IOL decentration or tilt and posterior segment abnormalities were not encountered in any cases postoperatively. The mean refractive astigmatism measured before fitting the hard contact lens was -0.81 ± 0.56 diopters (D). Internal astigmatism (-0.17 ± 0.21 D) was significantly different from posterior corneal astigmatism (-0.30 ± 0.15 D; P = .046). Regression analysis demonstrated a weak association between internal astigmatism and posterior corneal astigmatism (r² = 0.22, P = .013). Bland-Altman plots produced 95% limits of agreement for these two astigmatisms from -0.49 to 0.75 D.

CONCLUSIONS

A significant but weak correlation was found between the magnitudes of internal astigmatism and posterior corneal astigmatism in the pseudophakic eyes. This result indicates that Pentacam measurement of the posterior cornea did not compare well with a "gold standard" of refraction-derived values. [J Refract Surg. 2018;34(6):379-386.].

Astigmatic treatment with photorefractive keratectomy: Investigations of non-keratometric ocular astigmatism

PURPOSE

To evaluate the effect of non-keratometric ocular astigmatisms on visual and refractive outcomes after photorefractive keratectomy (PRK) for correction of myopic astigmatisms.

METHODS

Seventy one eyes of 36 subjects were enrolled in this study. Patients underwent PRK for treatment of myopia. Subjects were evaluated for refractive error, keratometry, and visual acuity before and six months after surgery. Pre- and post-op non-keratometric astigmatisms were calculated by vectorial analysis of the difference between the corneal plane refractive astigmatism and keratometric astigmatism. Astigmatic analysis explored the contribution of non-keratometric astigmatisms.

RESULTS

The pre-op spherical equivalent (SE) was -6.27 ± 1.48 with 1.16 ± 1.02 diopters of corneal plane refractive astigmatism and 1.44 ± 0.47 diopters keratometric astigmatism. Post-op values were -0.60 ± 0.85, 0.56 ± 0.47, and 1.06 ± 0.57, respectively, 6 months after surgery. Pre- and post-op non-keratometric astigmatisms were 0.76 ± 0.41 and 0.76 ± 0.46, respectively, (P = 0.976) with significant correlation (r = 0.37, P = 0.002). Pre-op non-keratometric astigmatisms correlated to the pre-op SE (r = -0.25, P = 0.04). Pre-op non-keratometric astigmatisms had significant correlation with keratometric difference vector of astigmatic correction (r = 0.369, P = 0.002). Post-op non-keratometric astigmatisms correlated to keratometric induced astigmatism (r = 0.334, P = 0.006), keratometric index of success (r = 0.571, P < 0.001), and post-op keratometric astigmatism (r = 0.736, P < 0.001).

CONCLUSIONS

Higher or lower non-keratometric ocular astigmatisms did not have any effect on refractive and visual outcome after PRK. PRK effectively corrected total refractive astigmatism through correction of keratometric astigmatism and additional adjustment to compensate for non-keratometric ocular astigmatisms.

Pseudolentogenic astigmatic effect of multifocal intraocular lenses: non-corneal ocular residual astigmatism (N-CORA) as a new parameter in astigmatic change analysis

PURPOSE

This study was initiated to introduce the term non-corneal ocular residual astigmatism (N-CORA) as a new parameter in astigmatic change analysis after implantation of two different types of non-toric, multifocal intraocular lenses (MIOL).

METHODS

Seventy-two eyes from 72 consecutive patients after MIOL surgery were studied in terms of a retrospective, cross-sectional data analysis. Two types of spherical MIOL were used. Surgical technique in all patients was a 2.4-mm incision phacoemulsification, performed by one surgeon. To investigate the magnitude and axis of astigmatic changes, the true corneal astigmatism and Alpins vector method were applied.

RESULTS

There were no statistically significant between-group differences related to the preoperative refraction or ocular residual astigmatism (ORA). After surgery, the mean refractive surgically induced astigmatism (RSIA) and the topographic SIA (TSIA) did not differ significantly between the lenses. The magnitude and orientation of ORA and N-CORA changed after surgery.

CONCLUSIONS

There are no statistically significant differences in postoperative ORA in magnitude or axis when implanting different types of MIOL. The similarity of N-CORA between both MIOL types shows that both diffractive and refractive asymmetric MIOLs with plate haptics have the same pseudolentogenic astigmatic effect which could be presented in terms of the newly introduced parameter N-CORA.

Ocular residual astigmatism (ORA) in pre-cataract eyes prior to and after refractive lens exchange

The purpose of this study was to analyze ocular residual astigmatism (ORA) before and after implantation of two different optical types of non-toric multifocal intraocular lenses (MIOL) in pre-cataract patients. This retrospective cohort study analyzed 72 eyes from 72 consecutive patients after MIOL surgery . To investigate magnitude and axis of astigmatic changes, the concepts of true corneal astigmatism and Alpins vector method were applied. There were no statistically significant between-group differences prior to surgery. The mean refractive surgically induced astigmatism (RSIA) (P = 0.063) and the topographic SIA (TSIA) (P = 0.828) did not differ significantly between the lenses, and the summated vector mean for ORA was reduced in terms of magnitude by approximately 0.30 Diopter. ORA in pseudophakic eyes mainly results from the posterior corneal surface and less from IOL tilting, postoperative posterior capsule shrinkage, or secondary cataract.

Internal Astigmatism in Myopes and Non-myopes: Compensation or Constant?

PURPOSE

To examine internal astigmatism (IA) in myopes and non-myopes using a new method to assess compensation of corneal astigmatism (CA) by IA, to look for predictors of high IA in young adult myopes, and to determine if as CA changes IA changes to reduce refractive astigmatism (RA) in an active compensatory process in myopes.

METHODS

Right eye keratometry and cycloplegic autorefraction were measured annually over 14 years in 367 myopes and once in 204 non-myopes age- (mean 21.91 ± 1.47 years), gender-, and ethnicity-matched to myopes at year 12. CA and RA at the corneal plane were expressed as J0, J45. IA = RA - CA. Inverse power transformation provided cylinder power and axis of IA for the compensation factor (IA/CA). Analyses included (1) paired and unpaired t-tests (refractive data), (2) chi-square tests (distributions of compensation factor), (3) logistic regression analysis (predictors of high IA), and (4) linear mixed models (time effect on RA, CA, and IA).

RESULTS

The magnitude of IAJ0 varied by refractive error (myopes -0.25 ± 0.24 vs. non-myopes -0.32 ± 0.21, p < 0.001). Compensation of CA by IA was poorer in myopes than non-myopes (χ p < 0.001). When matched by CA, compensation remained poorer in myopes than non-myopes (χ all p ≤ 0.04). Within each refractive group, compensation was better when CA was low than high (χ p < 0.001). When CA was low in myopes, high IA (≥1.00D) was less likely (p = 0.01). Longitudinal follow-up of myopes found no evidence for an active compensatory role for IA as CA increased over time. There were differences in IAJ0 by ethnicity over time (p < 0.0001).

CONCLUSIONS

In myopic and non-myopic eyes with low amounts of CA, IA may reduce CA's contribution to RA, but IA is not a constant. However, there is no evidence for an active compensatory role for IA reducing CA in myopes.

Correlation of major components of ocular astigmatism in myopic patients

PURPOSE

To investigate the correlation of major components of ocular astigmatism in myopic patients in an academic hospital.

METHODS

This cross-sectional study was conducted on 376 eyes of 188 patients who were referred to Farabi Eye Hospital for refractive surgery. Preoperative examinations including refraction and corneal topography were performed for all candidates to measure refractive and corneal astigmatism. Ocular residual astigmatism was calculated using vector analysis. Pearson's correlation and ANOVA analysis were used to evaluate the strength of the association between different types of astigmatism. Both eyes were defined as cluster and the Generalized Estimating Equations (GEE) analysis were performed.

RESULTS

Mean age of 119 women (63.3%) and 69 men (36.7%) was 27.8 ± 5.7 years. Mean refractive error based on spherical equivalent was -3.59 ± 1.95D (range, -0.54 to -10.22D). Mean refractive and corneal astigmatism was 1.97 ± 1.3D and 1.85 ± 1.01D, respectively. Mean amount of ORA was 0.65 ± 0.36D.There was a significant correlation between ORA and refractive astigmatism(r=0.23, p<0.001), corneal and refractive astigmatism (r=0.91, p<0.001) and a weak correlation between ORA and corneal astigmatism (r=0.13, p=0.014). There was a significant correlation between J0 and J45 values of ORA and corneal astigmatism (p<0.001).

CONCLUSION

There is a significant correlation between ORA and refractive astigmatism, refractive and corneal astigmatism and a weak correlation between ORA and corneal astigmatism in refractive surgery candidates. Identifying the type of astigmatism and preoperative measurement of ocular residual astigmatism is highly recommended prior to any refractive surgery, especially in cases with significant astigmatism.

LASIK for spherical refractive myopia: effect of topographic astigmatism (ocular residual astigmatism, ORA) on refractive outcome

Purpose

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.

Results

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.

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.

Influence of the difference between corneal and refractive astigmatism on LASIK outcomes using solid-state technology

PURPOSE

To evaluate the influence of the difference between preoperative corneal and refractive astigmatism [ocular residual astigmatism (ORA)] on outcomes obtained after laser in situ keratomileusis (LASIK) surgery for correction of myopic astigmatism using the solid-state laser technology.

METHODS

One hundred one consecutive eyes with myopia or myopic astigmatism of 55 patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd, currently CV Laser) were included. Visual and refractive changes at 6 months postoperatively and changes in ORA and anterior corneal astigmatism and posterior corneal astigmatism (PCA) were analyzed.

RESULTS

Postoperatively, uncorrected distance visual acuity improved significantly (P < 0.01). Likewise, refractive cylinder magnitude and spherical equivalent were reduced significantly (P < 0.01). In contrast, no significant changes were observed in ORA magnitude (P = 0.81) and anterior corneal astigmatism (P = 0.12). The mean overall efficacy and safety indices were 0.96 and 1.01, respectively. These indices were not correlated with preoperative ORA (r = -0.15, P = 0.15). Furthermore, a significant correlation was found between ORA (r = 0.81, P < 0.01) and PCA postoperatively, but not preoperatively (r = 0.12, P = 0.25). Likewise, a significant correlation of ORA with manifest refraction was only found postoperatively (r = -0.38, P < 0.01).

CONCLUSIONS

The magnitude of ORA does not seem to be a predictive factor of efficacy and safety of myopic LASIK using a solid-state laser platform. The higher relevance of PCA after surgery in some cases may explain the presence of unexpected astigmatic residual refractive errors.

Ocular residual astigmatism's effect on high myopic astigmatism LASIK surgery

PURPOSE

To analyze the effect of ocular residual astigmatism (ORA) on the effectiveness of LASIK for treating high myopic astigmatism.

METHODS

This is an observational, cross-sectional study. We studied 116 consecutive myopic eyes with -3 diopters (D) or more of astigmatism that underwent LASIK surgery. The magnitude of uncorrected residual refractive astigmatism 3 months postoperatively was measured.

RESULTS

The mean preoperative cylinder was -4.0±0.83 D (range, -7.5 to -3 D) and the mean preoperative ORA was 0.82±0.5 D. The mean residual refractive cylinder 3 months postoperatively was -0.78±0.83 D (range, -3 to 0 D). No correlation was found between ORA and the refractive cylinder 3 months postoperatively (P=0.6).

CONCLUSION

In eyes with high myopic astigmatism undergoing LASIK, ORA was not correlated with the residual postoperative cylinder.

Influence of intraocular astigmatism on the correction of myopic astigmatism by laser-assisted subepithelial keratectomy

PURPOSE

To assess the influence of the origin of astigmatism on the correction of myopic astigmatism by laser-assisted subepithelial keratectomy (LASEK).

SETTING

Ophthalmology Department, Eye and ENT Hospital, Shanghai, China.

DESIGN

Prospective study.

METHODS

Patients having LASEK to correct myopia or myopic astigmatism were divided into 2 groups according to their ocular residual astigmatism (ORA). Patients were examined preoperatively and 1 and 3 months postoperatively. The efficacy of LASEK was compared between those with and those without a significant amount of intraocular astigmatism.

RESULTS

The study comprised 54 eyes of 54 patients. The mean index of success (ratio of magnitude of remaining uncorrected astigmatism to that of initial preoperative astigmatism) in the high ORA group (n=21) and low ORA group (n=33) was 0.85 and 0.48, respectively, 1 month after surgery (t=2.17, P=.04) and 0.88 and 0.32, respectively, 3 months after surgery (t=2.18, P=.04). The Zernike coefficient of horizontal coma, Z(3,+1), increased more after surgery in the high ORA group than in the low ORA group (1 month versus preoperative, t=2.32, P=.024; 3 months versus preoperative, t=2.07, P=.048).

CONCLUSIONS

Nine percent and 2% of the eyes had minimal corneal haze at 1 month and 3 months, respectively. Laser-assisted subepithelial keratectomy was less effective in correcting myopic astigmatism when astigmatism was mainly located at the internal optics. Horizontal coma increased more after LASEK in patients with higher ORA.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Ocular residual astigmatism: effects of demographic and ocular parameters in myopic laser in situ keratomileusis

PURPOSE

To analyze the influence of demographic and ocular factors on ocular residual astigmatism (ORA) in myopic laser in situ keratomileusis (LASIK).

SETTING

University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

DESIGN

Retrospective cross-sectional data analysis.

METHODS

Eyes of consecutive myopic patients scheduled for LASIK were studied to evaluate the influence on preexisting ORA of age, sex, ocular dominance, subjective cylinder and topographic astigmatism, subjective sphere, and mesopic pupil size. The ORA was determined using Alpins vector analysis. Two subgroups, defined by the ratio of ORA to preoperative refractive cylinder (R), were formed: ORA:R ≥ 1.0 and ORA:R <1.0).

RESULTS

The study comprised 2991 eyes (2991 patients). The mean ORA was 0.75 diopter (D) ± 0.39 (SD) (range 0.00 to 2.00 D); 1372 (46%) eyes had ORA of 1.00 D or more. Ordinary least square estimations and odds ratios showed that subjective sphere, male sex, and dominant eye were negative predictors of the degree of preoperative ORA, while increasing age and larger mesopic pupils did not indicate ORA orientation. With-the-rule astigmatism meridian was more likely in eyes with low ORA, while oblique and against-the-rule meridians were related to high ORA.

CONCLUSIONS

The preoperative assessment of refractive surgery candidates should consider the interaction between topographic, refractive, and ORA because corneal refractive surgery is more successful in eyes in which the cylinder mainly originates from the anterior cornea. The current data can help identify patients at high risk for having a significant difference between subjective cylinder and topographic astigmatism.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Ocular residual astigmatism and topographic disparity vector indexes in normal healthy eyes

PURPOSE

To define a range of normality for the vectorial parameters Ocular Residual Astigmatism (ORA) and topography disparity (TD) and to evaluate their relationship with visual, refractive, anterior and posterior corneal curvature, pachymetric and corneal volume data in normal healthy eyes.

METHODS

This study comprised a total of 101 consecutive normal healthy eyes of 101 patients ranging in age from 15 to 64 years old. In all cases, a complete corneal analysis was performed using a Scheimpflug photography-based topography system (Pentacam system Oculus Optikgeräte GmbH). Anterior corneal topographic data were imported from the Pentacam system to the iASSORT software (ASSORT Pty. Ltd.), which allowed the calculation of the ocular residual astigmatism (ORA) and topography disparity (TD). Linear regression analysis was used for obtaining a linear expression relating ORA and posterior corneal astigmatism (PCA).

RESULTS

Mean magnitude of ORA was 0.79 D (SD: 0.43), with a normality range from 0 to 1.63D. 90 eyes (89.1%) showed against-the-rule ORA. A weak although statistically significant correlation was found between the magnitudes of posterior corneal astigmatism and ORA (r=0.34, p<0.01). Regression analysis showed the presence of a linear relationship between these two variables, although with a very limited predictability (R(2): 0.08). Mean magnitude of TD was 0.89D (SD: 0.50), with a normality range from 0 to 1.87D.

CONCLUSION

The magnitude of the vector parameters ORA and TD is lower than 1.9D in the healthy human eye.

Laser-assisted in situ keratomileusis in high mixed astigmatism with optimized, fast-repetition and cyclotorsion control excimer laser

PURPOSE

To evaluate the visual refractive and aberrometric outcomes of laser-assisted in situ keratomileusis (LASIK) surgery for the correction of high mixed astigmatism using a new-generation excimer laser and optimized aspherical profiles.

DESIGN

Retrospective interventional case series.

METHODS

Fifty-two eyes of 36 patients (21-53 years) with primary mixed astigmatism over 3.0 diopters (D) were included. All cases underwent LASIK surgery using the sixth-generation excimer laser Amaris with cyclotorsion control and a femtosecond platform for flap creation. Visual, refractive, corneal topographic, and aberrometric outcomes were evaluated during a 3-month follow-up. Refractive astigmatic changes were analyzed by Alpins method.

RESULTS

A significant reduction of refractive sphere and cylinder was observed 3 months postoperatively (P = .001), with an associated improvement of uncorrected distance visual acuity (P = .001). Best-corrected distance visual acuity (CDVA) remained unchanged in 31 eyes (59.6%), while 3 eyes (5.76%) lost 2 lines of CDVA. Fourteen eyes (26.9%) had spherical equivalent (SE) within ±0.5 D of emmetropia and 34 (65.3%) had SE within ±1.0 D of emmetropia. No significant difference was observed when comparing surgically induced and target astigmatism. A significant induction of higher-order aberration attributable to increase of spherical aberration was found (P = .003). Seven eyes (13.4%) required retreatment.

CONCLUSIONS

LASIK for primary high mixed astigmatism using optimized aspherical profiles and a fast-repetition-rate excimer laser with cyclotorsion control is a safe, effective, and predictable procedure. Induction of higher-order aberrations is still present in the correction of the refraction error of the magnitude included in this study.

Evaluation of the efficacy of the Allegretto Wave and the Wavefront-optimized ablation profile in non-anterior astigmatisms

PURPOSE

To assess the efficacy of the Allegretto Wave and the wavefront-optimized ablation profile (WFO) in non-anterior astigmatism correction, in both LASIK and photorefractive keratectomy (PRK) treatments.

METHODS

Seventy-four refractive surgery candidates were recruited prospectively in a non-randomized trial. Only one eye from each candidate was randomly enrolled in the study. Of them, 40 eyes underwent LASIK treatment (LG group), while 34 eyes underwent PRK treatment (PG group). Preoperatively, the ocular residual astigmatism (ORA) was calculated for each eye, according to which each astigmatism fault was characterized as primarily anterior or non-anterior. Twenty LG eyes and 16 PG eyes presented primarily anterior astigmatism (LG-A and PG-A subgroups, respectively), while 20 LG eyes and 18 PG eyes demonstrated primarily non-anterior astigmatism (LG-NA and PG-NA subgroups, respectively). Postoperatively, vector analysis of astigmatism correction was conducted. The following indexes were calculated: (i) correction index (CI), (ii) difference vector (DV) and (iii) index of success (IOS).

RESULTS

Preoperatively, mean differences between manifest and topographic astigmatisms for the LG and the PG subgroups were significant (p:0.006 and p<0.001, respectively), while postoperatively, aforementioned differences were non-significant (p:0.18 and p:0.09, respectively). Regarding vector analysis in the LG group, mean CI, IOS and DV were 1.39±1.26, 0.37±1.06 and 0.30±0.51, respectively. Differences in CI, IOS and DV between LG-A and LG-NA subgroups were non-significant. Regarding vector analysis in the PG group, mean CI, IOS and DV were 1.22±0.33, 0.47±0.46 and 0.27±0.25, respectively. Differences in CI, IOS and DV between PG-A and PG-NA subgroups were non-significant.

CONCLUSIONS

Our results suggest that the Allegretto Wave and WFO profile seem to be equally effective in both anterior and non-anterior astigmatism correction, regardless of treatment type.

Influence of internal optical astigmatism on the correction of myopic astigmatism by LASIK

PURPOSE

To investigate the influence of the origin of astigmatism on the correction of myopic astigmatism by LASIK.

METHODS

A retrospective study was conducted of the records of 192 patients (192 eyes) undergoing LASIK for correction of myopia and myopic astigmatism from January to September 2010. Ocular residual astigmatism (ORA) and lenticular astigmatism (LA) were determined by vector analysis using objective refraction and Pentacam (Oculus Optikgeräte GmbH) imaging of both corneal surfaces. Patients were divided into two groups according to ORA (high ORA group: ORA/preoperative refractive astigmatism >1; normal ORA group: ORA/preoperative refractive astigmatism ≤ 1) and LA (high LA group: LA/preoperative refractive astigmatism >1; normal LA group: LA/preoperative refractive astigmatism ≤ 1). Procedural efficacy was compared between those eyes with and without a significant amount of internal optical astigmatism using index of success.

RESULTS

Mean preoperative vectors for the astigmatism of the anterior cornea, posterior cornea, and lens were -1.33 × 3.0°, -0.33 × 95.3°, and -0.27 × 103.3°, respectively. Mean indices of success in the high and low ORA groups were 1.75 and 0.59, respectively (t=7.81, P<.001). Mean indices of success in the high and low LA groups were 2.07 and 0.70, respectively (t=12.36, P<.001). The higher indices of success in the high ORA and high LA groups suggest a lower efficacy of LASIK in treating astigmatism primarily located intraocularly.

CONCLUSIONS

Myopic LASIK is less effective in correcting astigmatism when astigmatism is mainly located at the internal optics. Topography and refractive value should be incorporated in the treatment of patients when a significant amount of internal optical astigmatism is detected preoperatively.