Effects of decentration of photorefractive keratectomy on the induction of higher order wavefront aberrations

A comparative study of pupil offset measurement using Pentacam and Keratron Scout in myopic young adults

CLINICAL RELEVANCE

Assessing the consistency of pupil offset measurements between the Pentacam and Keratron Scout is essential for the refractive surgery design of young myopic patients.

BACKGROUND

Accurate preoperative measurement of pupil offset is critical to achieving a better quality of vision after refractive surgery. The Pentacam and Keratron Scout are commonly used in hospitals, and evaluating their consistency is essential for accurate measurement of pupil offset.

METHODS

Six hundred eyes (600 subjects) were included in this study. Pupil offset and its X, Y-component were measured by Pentacam and Keratron Scout, respectively. Agreement and repeatability between the two devices were identified by intraclass correlation coefficient and Bland-Altman plots with 95% limits of agreement. Paired t-tests and Pearson analysis were used to compare the differences and correlations between the two devices.

RESULTS

The mean age of all subjects was 23 ± 5 years. The mean pupil offset magnitude obtained from Pentacam and Keratron Scout was 0.16 ± 0.08 mm and 0.15 ± 0.07 mm. The 95% limits of agreement (-0.11-0.13, -0.09-0.11, and -0.11-0.12) and intraclass correlation coefficient (0.82, 0.84, and 0.81) demonstrated good agreement and repeatability of the two devices in measuring pupil offset and its X, Y-component. A significant correlation between the two devices was found (r = 0.71, 0.73, and 0.70). The direction of pupil offset measured by the devices was both predominately towards the superonasal quadrant.

CONCLUSION

Pentacam and Keratron Scout showed good agreement in measuring pupil offset and its X, Y-component, which can be used interchangeably in clinical practice.

Effect of preoperative pupil offset on corneal higher-order aberrations after femtosecond laser-assisted in situ keratomileusis

BACKGROUND

This study aimed to investigate the relationship between multiple higher-order aberrations (HOAs) subgroups and pupil offset, as well as to analyze the factors affecting postoperative corneal HOAs in patients with different degrees of refractive errors.

METHODS

We enrolled 160 patients (316 eyes) aged ≥ 18 years who had undergone femtosecond laser-assisted in situ keratomileusis (FS-LASIK) treatment. Based on the relationship between the preoperative pupil offset and the postoperative ΔHOAs, all patients were divided into two groups: group I (pupil offset ≤ 0.20 mm) and group II (pupil offset > 0.20 mm). All of the eyes had low to high myopia with or without astigmatism (manifest refraction spherical equivalent (MRSE) < -10.00 D). Uncorrected distance visual acuity, corrected distance visual acuity, MRSE, pupil offset, central corneal thickness, corneal HOAs, vertical coma (Z₃^-1), horizontal coma (Z₃¹), spherical aberration (Z₄⁰), trefoil 0° (Z₃³), and trefoil 30° (Z₃^-3) over a 6 mm diameter central corneal zone diameter were evaluated preoperatively and at 1 and 3 months postoperatively.

RESULTS

Our result revealed significant differences in postoperative corneal total root mean square (RMS) HOAs, RMS vertical coma, RMS horizontal coma, RMS spherical aberration, and RMS trefoil 30° between group I and group II. ΔMRSE was found to be an effective factor for ΔRMS HOAs (R² = 0.383), ΔRMS horizontal coma (R² = 0.205), and ΔRMS spherical aberration (R² = 0.397). In group II, multiple linear regression analysis revealed a significant correlation between preoperative pupillary offset and Δtotal RMS HOAs (R² = 0.461), ΔRMS horizontal coma (R² = 0.040), and ΔRMS trefoil 30°(R² = 0.089). The ΔRMS vertical coma effect factor is the Y-component, and the factor influencing ΔRMS spherical aberration was ΔMRSE (R² = 0.256).

CONCLUSION

A small pupil offset was associated with a lower induction of postoperative corneal HOAs. Efforts to optimize centration are critical for improving surgical outcomes in patients with FS-LASIK.

Long-Term Observation of Higher-Order Aberrations and Microdistortions in Bowman’s Layer After Small Incision Lenticule Extraction for the Correcting Myopia With Spherical Equivalent Higher Than −9.0 Diopters

Purpose

To evaluate the outcomes in corneal higher-order aberrations (HOAs) and microdistortions in the Bowman’s layer after femtosecond laser small incision lenticule extraction (SMILE) for correcting extremely high myopia.

Methods

This prospective study included patients with myopia with spherical equivalent ≥ -9.0 Diopters (D). SMILE was performed in forty eyes of 40 patients. Pentacam was used to evaluate HOAs before and at 1 day, 3 months, 6 months, and 2 years after surgery. Fourier-domain optical coherence tomography was used to evaluate microdistortions at 2 years postoperatively. Thirty-two eyes of 32 patients receiving femtosecond laser-assisted in situ keratomileusis (FS-LASIK) were enrolled as the control group. HOAs were measured before, at 1 day and at least 1 year postoperatively.

Results

After SMILE, the long-term safety and effectiveness index was 1.25 and 0.85, respectively. Microdistortions were observed in 73.5% of the eyes at 2 years, with an average number of 1.20 ± 1.22 microdistortions and an average width of 287.37 ± 259.00 μm. We detected more microdistortions in the horizontal meridian than in the vertical meridian (p = 0.035). The average number and width of microdistortions were both higher in the central region (≤4 mm) than in the peripheral region (4–8 mm) (both p < 0.001). With the exception of horizontal trefoil in the SMILE group and vertical trefoil in the FS-LASIK group, significant changes over time were observed in all other HOAs (all p < 0.05). Meanwhile, we detected significant increases in the total corneal HOA, spherical aberration (SA), and coma at all time-points after both surgeries (all p < 0.01). Compared with FS-LASIK, SMILE induced less SA (p < 0.001) and more horizontal coma (p = 0.036). In the SMILE group, the HOA, SA, and trefoil were more in the small optical zone (≤6.0 mm) than in the large optical zone (>6.0 mm) (all p < 0.05). The increase in SA and most trefoil correlated with the mean number of central microdistortions number (all p < 0.05).

Conclusion

For myopia over −9.0D, the microdistortions in the Bowman’s layer were still detectable in most eyes long-term after SMILE. Both SMILE and FS-LASIK induced more HOAs, mainly HOA, SA, and coma. The small optical zone and microdistortions may affect postoperative aberrations.

Prospective, Randomized, Contralateral Eye Comparison of Functional Optical Zone, and Visual Quality After SMILE and FS-LASIK for High Myopia

Purpose

To compare the functional optical zone (FOZ) and visual quality after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in correcting high myopia.

Methods

Ninety-two eyes of 46 high myopic patients with the same programmed optical zone (POZ) received SMILE in one eye and FS-LASIK in the contralateral eye. FOZ was calculated using a refractive power method. The decentration, visual outcomes, wavefront aberrations, contrast sensitivity, and quality of vision (QoV) questionnaire were analyzed at 6 months postoperatively.

Results

The postoperative visual and refractive outcomes were comparable between SMILE and FS-LASIK. The FOZ for SMILE (5.62 ± 0.31 mm) was larger than for FS-LASIK (5.35 ± 0.28 mm; P < 0.001). Moreover, the total decentration for SMILE (0.29 ± 0.14 mm) was greater than in FS-LASIK (0.22 ± 0.11 mm; P < 0.001). The induced change in spherical aberration was less for SMILE than for FS-LASIK (P < 0.001). There was better contrast sensitivity under the mesopic condition with glare for SMILE than for FS-LASIK (P = 0.024). However, no significant difference was found in QoV scores between the two groups.

Conclusions

SMILE created a larger FOZ and greater decentration than FS-LASIK when the same POZ was designed in high myopia. Objective and subjective visual symptoms were comparable between SMILE and FS-LASIK.

Translational Relevance

The differences in FOZ and decentration between SMILE and FS-LASIK have little effect on vision outcomes. Surgeons should consider the FOZ and decentration in surgical options in high myopia.

Clinical Outcomes of Aberration-Free All Surface Laser Ablation (ASLA) vs. Aberration-Free ASLA Assisted by Smart Pulse Technology in High Myopia: A One-Year Follow-Up Study

Purpose

To compare the clinical outcomes of aberration-free all surface laser ablation (ASLA) with and without the use of smart pulse technology (SPT) in high myopia.

Methods

This study retrospectively analyzed 138 eyes (138 patients, only the right eye was selected) treated for high myopia (spherical equivalent ≥−6.00 diopters) using aberration-free ASLA (non-SPT group; 85 eyes) and aberration-free ASLA assisted by SPT (SPT group; 53 eyes). Examinations such as visual acuity, refraction, and haze were performed before the 12-month follow-up. Corneal epithelial healing time was assessed in the first postoperative day. Visual acuity and refraction examination were performed at 7 days and 1, 3, 6, and 12 months postoperatively. Corneal haze was evaluated in 1, 3, 6, and 12 months. Safety, efficacy, and corneal wavefront aberrations were assessed 12 months after the treatment.

Results

At 12 months postoperatively, 60% versus 40% of eyes achieved 20/16 Snellen lines or better, and 92% versus 82% of eyes achieved 20/20 Snellen lines or better visual acuity in the SPT and the non-SPT groups, respectively. The average postoperative epithelial healing time was 3.75 ± 1.00 days in the SPT group and 3.73 ± 1.30 days in the non-SPT group (P ≥ 0.05). The safety and the efficacy index of the SPT group were better than those of the non-SPT group in the follow-ups. The attempted spherical equivalent before the surgery and the achieved spherical equivalent at 12 months were comparable between the two groups. Regarding the aberrations, the results of Coma 90° in the SPT group were better than those in the non-SPT group (P ≤ 0.05), but the increase of RMS HOAs (root mean square higher order aberrations), Coma 0°, and spherical aberration postoperatively had no statistical difference between the two groups (P ≥ 0.05). Conclusions: Both aberration-free ASLA with and without SPT showed favorable safety, effectiveness, and predictability within 12 months for high myopia. And, ASLA using SPT might have potential advantages in the long-term visual quality.

Clinical outcomes of corneal refractive surgery comparing centration on the corneal vertex with the pupil center: a meta-analysis

PURPOSE

To compare the visual and refractive outcomes between centration on the corneal vertex and the pupil center in corneal refractive surgery.

METHODS

A comprehensive literature search was conducted using PubMed, MEDLINE, EMBASE, and the Cochrane Library to identify relevant studies. The primary outcomes were the postoperative spherical equivalent (SE), effectiveness [uncorrected distance visual acuity (UDVA) ≥ 20/20, eyes within ± 0.50 diopter (D) of target refraction], and safety [loss ≥ 2 lines of corrected distance visual acuity (CDVA)]. Higher-order aberrations were considered secondary outcomes.

RESULTS

Seven studies describing a total of 1964 eyes were included in this meta-analysis. A statistical significance in postoperative SE was found between the two centration methods for the correction of myopia that favor the CV-centered method (p < 0.001). No significant differences were observed in the proportion of eyes with UDVA ≥ 20/20 or loss ≥ 2 lines of CDVA postoperatively. However, the proportion of eyes within ± 0.50 D was slightly higher (p = 0.02) and the coma aberration was much lower in the corneal vertex-centered method (p < 0.001).

CONCLUSION

Preferable visual and refractive outcomes could be achieved with either centering on the corneal vertex or pupil center in corneal refractive surgery; however, the corneal vertex-centered method has shown partial benefits in some clinical indices. In order to obtain higher quality of clinical evidences, more randomized controlled trials (RCTs) are required in further investigations.

Wavefront properties of the anterior and posterior corneal surface after transepithelial photorefractive keratectomy in myopia

The present study aimed to evaluate the changes of corneal higher-order aberrations (HOAs) after transepithelial photorefractive keratectomy (TransPRK) in patients with myopia. A total of 80 eyes of 80 patients with myopia with or without astigmatism were evaluated. Prior to and 1 year after the surgery, uncorrected and corrected distance visual acuity in logMAR were assessed. Wavefront aberrations on the anterior surface of the cornea, as well as the posterior and total cornea, were measured via Pentacam. The HOA of the anterior surface and total values of spherical and coma aberrations increased significantly (P<0.001). However, HOAs of the anterior surface, and posterior and total values of the trefoil were not significantly changed (P=0.442, 0.805 and 0.936, respectively). A significant correlation of the pre-operative mean spherical equivalent refraction (MSER), astigmatism and central corneal ablation depth (CCAD) with the changes in coma aberration (r=0.268, P=0.016; r=0.260, P=0.020; r=0.323, P=0.004, respectively) and HOA (r=0.554, P<0.001; r=0.312, P=0.005; r=0.583, P<0.001, respectively) of the anterior surface of the cornea was determined. Furthermore, a significant correlation of the pre-operative MSER and CCAD with the changes in spherical aberration of the anterior corneal surface (r=0.462, P<0.001; r=0.510, P<0.001, respectively) was obtained. In conclusion, TransPRK offers an effective option for improving visual function in patients with myopia. The anterior corneal HOA, as well as spherical and coma aberrations, were significantly increased post-operatively. The HOA of the posterior cornea was not significantly changed. The change in the trefoil aberration was significantly correlated with pre-operative astigmatism, but the pre- and post-operative values were not significantly different.

Visual Outcomes after Small Incision Lenticule Extraction and Femtosecond Laser-Assisted LASIK for High Myopia

PURPOSE

The aim of this study was to compare visual outcomes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for high myopia.

METHODS

In this prospective, comparative study, a total of 52 eyes of 34 consecutive highly myopic patients with spherical equivalent within the range of -8.00 to -10.00 diopters were recruited. Twenty-three eyes of 16 patients were in the FS-LASIK group and 29 eyes of 18 patients were in the SMILE group. Visual outcomes and wavefront aberrations were analyzed preoperatively and 6 months postoperatively.

RESULTS

At the postoperative 6-month visit, 96.6% in the SMILE group and 91.3% in the FS-LASIK group achieved unchanged or better corrected distance visual acuity (CDVA). As for uncorrected distance visual acuity (UDVA), 96.6% in the SMILE group and 95.7% in the FS-LASIK group achieved UDVA of 20/20 or better. As for wavefront aberrations, high-order aberrations (HOAs) and spherical aberrations increased significantly after surgery in both groups relative to corresponding preoperative values (p < 0.001), and vertical coma increased after SMILE (p < 0.001). No statistically significant differences in changes of HOAs (p =0.90), spherical aberrations (p = 0.07), horizontal coma (p = 0.56), coma (p =0.08), horizontal trefoil (p =0.19), vertical trefoil (p = 0.90), and trefoil (p = 0.45) were detected between the 2 groups, except for vertical coma (p < 0.01).

CONCLUSIONS

SMILE is as effective as FS-LASIK in correcting high myopia, but attention should be paid to the induction of vertical coma in highly myopic patients following a SMILE procedure.

Decentration following femtosecond laser small incision lenticule extraction (SMILE) in eyes with high astigmatism and its impact on visual quality

Background

To measure the decentration following SMILE in eyes with high myopic astigmatism and investigate its impact on visual quality.

Methods

The prospective study was conducted to analyze patients who underwent SMILE for correction of myopia and myopic astigmatism ≥2.5D (high astigmatism group, HA) at the ophthalmology department, Eye and ENT hospital, Shanghai, China.. Patients with myopic astigmatism < 1.5D served as controls (low astigmatism group, LA). Decentration was measured using a Scheimpflug camera with a difference map of the tangential curvature at 12 months postoperatively. Also the associations between decentration from the coaxial sighted corneal light reflex (CSCLR) and the visual outcomes, correction efficacy of astigmatism, wavefront aberrations and objective scatter index (OSI) were analyzed.

Results

No significant differences were observed in the decentered distance between HA and LA in either eyes (OD: HA: 0.18 ± 0.10 mm, LA: 0.20 ± 0.14 mm, P = 0.659; OS: HA: 0.22 ± 0.11 mm, LA: 0.20 ± 0.11 mm, P = 0.637). The analysis across the three levels of decentration (< 0.1 mm, 0.1–0.2 mm, and > 0.2 mm) showed no significant association between decentration and visual outcomes of predictability, efficiency, safety, MTF cutoff, OSI, SR and OVs in both groups. Also no significant association was observed between decentration and postoperative astigmatism in either group. A significant relationship between the magnitude of decentration and induced coma and spherical aberration was observed in HA.

Conclusions

The amount of decentration between HA and LA groups showed no differences. Decentration > 0.20 mm from CSCLR resulted in greater induction of coma and SA after SMILE in eyes with HA.

Relationship Between Decentration and Induced Corneal Higher-Order Aberrations Following Small-Incision Lenticule Extraction Procedure

Purpose

To investigate the amount of lenticule decentration following small-incision lenticule extraction (SMILE) by using the Keratron Scout tangential topography difference map, and the relationship between the magnitudes of total decentration and induced corneal higher-order aberrations (HOAs).

Methods

This retrospective observational case series study analyzed decentration values obtained from the Keratron Scout tangential topography difference map of 360 eyes (360 patients) that underwent SMILE. Root mean square total HOAs, third order coma aberration, fourth order spherical aberration, as well as individual coefficients for vertical and horizontal coma were measured preoperatively and 3-months postoperatively. Simple linear regression analysis and piecewise regression models were used to determine the relationship between the magnitudes of total decentration and induced corneal HOAs.

Results

The mean total decentration distance from the corneal vertex was 0.36 ± 0.22 mm (range, 0.02-1.27 mm). There were significant differences in total HOAs, coma, vertical and horizontal comas, and spherical aberration between preoperative and 3-month postoperative assessments. Significant relationships between the magnitudes of total decentration and induced corneal HOAs were noted. Subgroup analysis according to the degree of total decentration (group I, total decentered displacement ≤0.335 mm; and group II, total decentered displacement >0.335 mm) revealed that induced changes in total HOAs, coma, vertical coma, and spherical aberration were significantly larger in group II than in group I.

Conclusions

A minimal degree of decentration was closely related to a smaller induction of corneal HOAs. Efforts to optimize centration are critical for achieving better surgical outcomes in SMILE.

Influence of Refractive Status on the Higher-Order Aberration Pattern After Small Incision Lenticule Extraction Surgery

PURPOSE

To study the effect of myopia on the pattern change in higher-order aberrations after small incision lenticule extraction.

METHODS

Sixty eyes of 60 patients were included: low myopia (≤-3.00 D), moderate myopia (-3.00 D to -6.00 D), and high myopia (≥-6.00 D). Total higher-order aberrations (tHOA), vertical coma ((Equation is included in full-text article.)), horizontal coma ((Equation is included in full-text article.)), and spherical aberration ((Equation is included in full-text article.)) were measured preoperatively and at postoperative 3 months.

RESULTS

At the end of 3 months, tHOA changed significantly compared with the preoperative values (P < 0.05), except for (Equation is included in full-text article.)and (Equation is included in full-text article.)in the low myopia group. The change in (Equation is included in full-text article.), (Equation is included in full-text article.), and (Equation is included in full-text article.)in the moderate group (-0.299, -0.175, and 0.108 μm) was 2.020, 4.861, and 4.696 times higher than the low group (-0.148, -0.036, 0.023 μm) (P = 0.002, 0.001, 0.001), respectively. The value in the high group (-0.331, -0.192, 0.154 μm) was 1.107, 1.097 (P = 0.478, 0.665), and 1.426 times (P = 0.047) higher than the moderate group. The degree of myopia was positively correlated with Δ(Equation is included in full-text article.)(r = 0.447; P < 0.001) and Δ(Equation is included in full-text article.)(r = 0.496; P < 0.001), and negatively correlated with ΔtHOA (r = -0.363, P = 0.004) and Δ(Equation is included in full-text article.)(r = -0.599; P < 0.001).

CONCLUSIONS

The study showed a different pattern of change in ocular aberrations after small incision lenticule extraction in patients with varying degrees of myopia. In patients with low myopia, there was no increase in (Equation is included in full-text article.)or (Equation is included in full-text article.). In high myopia, however, (Equation is included in full-text article.)increased with the degree of myopia, whereas the rising rate of coma was slowing.

Impact of Treatment Decentration on Higher-Order Aberrations after SMILE

Purpose. To evaluate decentration following femtosecond laser small incision lenticule extraction (SMILE) and sub-Bowman keratomileusis (SBK) and its impact on higher-order aberrations (HOAs). Methods. Prospective, nonrandom, and comparison study. There were 96 eyes of 52 patients who received SMILE and 96 eyes of 49 patients who received SBK in this study. Decentration was calculated 6 months after surgery with Pentacam. HOAs and visual acuity after the surgery were examined for patients in both groups before and 6 months after surgery. Results. The mean decentration displacement in SMILE group was significantly less than SBK group (P = 0.020). 89 eyes were decentered within 0.50 mm after SMILE and SBK. The association between vertical decentration and the induced spherical aberration was insignificant in SMILE group (P = 0.035). There was an association between decentration and safety index, efficacy index, vertical coma, spherical aberration, and HOAs in root mean square (RMS, μm) after SBK (all P < 0.05). No difference was found in uncorrected and corrected distance visual acuity, safety index, efficacy index, and wavefront aberrations between the two subgroups at any delimited value after SMILE (all P > 0.05). Decentration exceeding 0.37 mm affected vertical coma and RMSh of SBK eyes (P = 0.002, 0.005). Conclusion. SMILE surgery achieved more accurate centration than SBK surgery. Vertical decentration is associated with the induced spherical aberration in SMILE.

Effect of Iris registration on visual outcome in wavefront-guided LASEK for myopic astigmatism

PURPOSE

This study aimed to investigate the effect of iris registration (IR) on visual outcomes in wavefront-guided LASEK for myopic astigmatism.

METHODS

The retrospective chart review was performed for wavefront-guided LASEK using VISX Star S4 in patients with myopic astigmatism (cylinder ≥ 1.00 diopter[D]). Eyes were divided into IR group (LASEK with IR at the time of surgery) and Non-IR group (LASEK without IR system + failed-IR engagement during LASEK). Visual acuity (VA), astigmatism, higher-order aberration (HOA), and contrast sensitivity were assessed preoperatively and 3 months postoperatively. The IR and Non-IR groups were subcategorized depending on the spherical equivalent (lower myopia ≤-5.00 D vs. higher myopia >-5.00 D) for the comparison of HOA changes.

RESULTS

Postoperative uncorrected VAs showed no differences between IR (n = 30) and Non-IR (n = 46). In astigmatic vector analyses, no differences were noted in the mean magnitude of error and the mean angle of error between two groups. There were no differences in postoperative total HOA, spherical aberration (SA), coma, and trefoil between the groups, either. The total HOA and SA increased in both groups, while coma increased only in Non-IR. In higher myopia, ΔRMS of coma was smaller in IR. Preoperative and postoperative total HOA were linearly correlated in Non-IR, but not for IR. Contrast sensitivity of 12 cycles per degree improved in both groups.

CONCLUSION

IR had similar outcomes to conventional trackers in wavefront-guided LASEK, with less tendency of inducing coma, especially in higher myopia.

LASIK ablation centration: an objective digitized assessment and comparison between two generations of an excimer laser

PURPOSE

To objectively define the effective centration of myopic femtosecond laser-assisted LASIK ablation pattern, evaluate the difference between achieved versus planned excimer laser ablation centration, and compare these results from two different generations of an excimer laser system.

METHODS

The study retrospectively evaluated 280 eyes subjected to myopic LASIK. Digital image analysis was performed on Scheimpflug sagittal curvature maps (difference of preoperative to postoperative). Centration was assessed via proprietary software digital analysis of the coordinate displacement between the achieved ablation geometric center and the planned ablation center, which was the corneal vertex. Results from two different excimer laser generations (Eye-Q 400 [140 eyes] and EX500 [140 eyes]; Alcon/WaveLight, Fort Worth, TX) were compared.

RESULTS

Radial displacement was on average 360 ± 220 µm (range: 0 to 1,030 µm) in the Eye-Q 400 laser group and 120 ± 110 µm (range: 0 to 580 µm) in the EX500 laser group (P < .01). The percentage of eyes with displacement of greater than 300 µm was 52% in the Eye-Q 400 laser group and 4% in the EX500 laser group.

CONCLUSIONS

Displacement of ablation pattern may depend on the laser platform used. The improvement in the efficiency of centration indicates that newer generation excimer lasers with faster eye tracking and active centration control appear to achieve a significantly more accurate centration of myopic ablation patterns. The authors propose this novel, objective technique for laser refractive surgeon evaluation may point out significant outcome measures not currently used in standard metrics of refractive laser efficiency.

Effect of pupil size on residual wavefront aberration with transition zone after customized laser refractive surgery

The analysis of the change in residual wavefront aberrations after laser refractive surgery is important for the development of visual correction technology. Based on the ablation profile for wavefront-guided refractive surgery including optical zone and transition zone, the effect of pupil size on residual wavefront aberrations was studied. The research revealed that the optical zone to pupil ratio had a significant influence on the residual wavefront aberrations. The residual spherical aberration and coma were obviously larger than other individual Zernike higher-order terms when pupil diameter was larger than the optical zone size, and they increased rapidly as the pupil size increased. In addition, when the ablation zone diameter was kept constant, the residual higher-order aberrations increased rapidly as the blend coefficient increased for a 6 mm or 7 mm pupil. Furthermore, the residual higher-order aberrations with treatment decentration were distinctly larger than those without decentration. In the achievement of the best postoperative visual performance, the design of ablation profile played a crucial role in decrease of the residual wavefront aberrations after refractive surgery, especially optical zone size and the ablation pattern of transition zone.

Visual simulation through an aspheric aberration-correcting intraocular lens in subjects with different corneal profiles using adaptive optics

BACKGROUND

The aim of this study was to analyse the visual quality of the AcrySof IQ SN60WF(®) intraocular lens (IOL) when combined with different corneal profiles.

METHODS

Ten eyes of 10 participants with no prior history of refractive or cataract surgery were evaluated. An adaptive optics visual simulator was used to simulate the wavefront aberration pattern of an aspheric aberration-correcting IOL (AcrySof IQ SN60WF(®)). Normal corneas (group A), low and high myopic corneal ablations (groups B and C, respectively) and low and high hyperopic corneal ablations (groups D and E, respectively) were also simulated. Monocular distance visual acuities at 100, 50 and 10 per cent of contrast were measured.

RESULTS

At 100, 50 and 10 per cent contrast, no differences were found between groups A and B (p > 0.06 for all contrasts). Group A obtained better values than groups C, D and E for all contrasts (p = 0.031, p = 0.038, p = 0.032 at 100, 50 and 10 per cent of contrast, respectively). At the same time, group B obtained better values than groups C, D and E (p = 0.041, p = 0.042, p = 0.036 at 100, 50 and 10 per cent of contrast, respectively). Within the five groups, the worst results were always obtained for group E (p = 0.017, p = 0.021 and p = 0.025 at 100, 50 and 10 per cent of contrast, respectively).

CONCLUSIONS

The results suggest that the aspheric aberration-correcting IOL studied provides comparable results, when it is combined with normal corneas and with corneas with simulated low myopic ablations. When negative amounts of residual spherical aberration after cataract surgery are expected to be achieved, IOLs with more positive spherical aberration should be considered.