Causes of spherical aberration induced by laser refractive surgery

Influence of different parameters on the corneal asphericity (Q value) assessed with progress in biomedical optics and imaging - A review

The corneal eye diseases such as Keratoconus cause weakening of the cornea, with this disease the cornea can change in shape. This condition affects between 1 in 3,000 to 1 in 10,000 people. The main reason for the development of such conditions is unknown and can have significant impacts. Over the last decade, with advancements in computerized corneal topography assessments, researchers have increasingly expressed interest in corneal topography for research as well as clinical activities. Up till now, several aspheric numerical models have been developed as well as proposed to define the complex shape of the cornea. A commonly used term for characterizing the asphericity in an eye is the Q value, a common indicator of the aspherical degree of the cornea. It is one of the critical parameters in the mathematical description model of the cornea as it represents the cornea's shape and the eye's characteristics. Due to the utmost importance of this Q value of the cornea, a couple of studies have attempted to explore this parameter and its distribution, merely in terms of its influence on the human eye's optical properties. The corneal Q value is an important factor that needs to be determined to treat for any refractive errors as corneal degeneration are disease that can lead to potential problems with the structure of the cornea. This study aims to highlight the need to understand Q value of the cornea as this can essentially assist with personalising corneal refractive surgeries and implantation of intraocular lenses. Therefore, the relevance of corneal Q value must be studied in association with different patients, especially ones who have been diagnosed with cataracts, brain tumours, or even COVID-19. To address this issue, this paper first carries out a literature review on the optics of the cornea, the relevance of corneal Q value in ophthalmic practice and studies corneal degenerations and its causes. Thereafter, a detailed review of several noteworthy relevant research studies examining the Q value of the cornea is performed. To do so, an elaborate database is created, which presents a list of different research works examined in this study and provides key evidence derived from these studies. This includes listing details on the age, gender, ethnicity of the eyes assessed, the control variables, the technology used in the study, and even more. The database also delivers important findings and conclusions noted in each study assessed. Next, this paper analyses and discusses the magnitude of corneal Q value in various scenarios and the influence of different parameters on corneal Q value. To design visual optical products as well as to enhance the understanding of the optical properties of an eye, future studies could consider the database and work presented in this study as useful references. In addition, the work can be used to make informed decisions in clinical practice for designing visual optical products as well as to enhance the understanding of the optical properties of an Eye.

Evaluation of Higher-Order Aberrations After the Smooth Incision Lenticular Keratomileusis (SILKTM) Procedure Using the ELITATM Femtosecond Platform for Correction of Myopic and Astigmatic Refractive Errors

Purpose

To evaluate the changes of higher-order wavefront aberrations following the Smooth Incision Lenticular Keratomileusis (SILKTM) procedure for correction of myopic refractive errors with and without astigmatism, using the ELITATM Femtosecond Platform.

Methods

This prospective study included 24 eyes that underwent SILK procedure using one ELITA femtosecond laser system for the correction of myopic refractive errors with and without astigmatism. Preoperative and postoperative 1-day, 1-week, 1-month, 3-month, and 9-month eye exams were measured with a commercial wavefront aberrometer (iDESIGN ® Refractive Studio, Johnson & Johnson Surgical Vision, Inc). Wavefront aberrations up to the 6th order Zernike coefficients, including coma Z(3, -1) and Z(3, 1), spherical aberration Z(4, 1), and the wavefront error of all higher-order aberrations (HOAs RMS), were evaluated across a 6 mm pupil.

Results

The mean manifest refractive spherical equivalent changed from the preoperative refractions -3.82 ± 1.26 D (range -6.00 to -2.25 D) to the postoperative refractions -0.20 ± 0.15 D (range -0.50 to 0.00 D) at the 9-month follow-up. Compared to baseline preoperative HOAs, the mean postoperative HOAs were significantly increased at the 1-day follow-up. On average, at the 9-month postoperative assessment the vertical coma Z(3, -1) was -0.054 ±0.186 µm, horizontal coma Z(3, 1) was 0.016 ± 0.124 µm, spherical aberration Z(4, 0) was 0.046 ± 0.163 µm, and HOAs RMS was 0.363 ± 0.115 µm across a 6 mm pupil. There is no significant difference in the mean HOAs starting at 1-week follow-up for the horizontal coma (P = 0.346) and spherical aberration (P = 0.095).

Conclusions

The visual outcomes demonstrated that the SILK procedure for refractive lenticule extraction using ELITA femtosecond laser system is effective and predictable for the correction of myopic refractive errors with and without astigmatism. The ELITA femtosecond laser system induced minimal HOAs in surgical eyes following the SILK procedures. These results demonstrate fast corneal recovery starting at 1-week follow-up, and spherical aberration was not induced.

Risk Factors for Corneal Monochromatic Aberrations and Implications for Multifocal and Extended Depth-of-Focus Intraocular Lens Implantation

PURPOSE

To discuss factors influencing corneal aberrations that might influence the optical quality after intraocular lens (IOL) implantation.

METHODS

PubMed and Scopus were the main resources used to search the medical literature. An extensive search was performed to identify relevant articles concerning factors influencing the level of corneal aberrations as of August 27, 2023. The following keywords were used in various combinations: corneal, aberrations, defocus, astigmatism, spherical aberration, coma, trefoil, quadrafoil, intraocular lens, and IOL.

RESULTS

Conclusive evidence is lacking regarding the correlation between age and changes in corneal aberrations. Patients with astigmatism have greater corneal higher-order aberrations than those with minimal astigmatism, particularly concerning trefoil and coma. Increased levels of corneal higher-order aberrations are noted following contact lens wear, in patients with dry eye disease, and with pterygium. Increased higher-order aberrations have been reported following corneal refractive surgery and for 3 months following trabeculectomy; regarding intraocular lens surgery, the results remain controversial.

CONCLUSIONS

Several factors influence the level of corneal higher-order aberrations. Multifocal and extended depth-of-focus IOLs can share similarities in their optical properties, and the main difference arises in their design and performance with respect to spherical aberration. Preoperative evaluation is critical for proper IOL choice, particularly in corneas with risk of high levels of aberrations. [J Refract Surg. 2024;40(6):e420-e434.].

Limitations of and Solutions to Using 6 mm Corneal Spherical Aberration and Q Value after Laser Refractive Surgery

This study aimed to evaluate the spherical aberration (SA) in different corneal areas before and after femtosecond laser-assisted in situ keratomileusis (fLASIK) and transepithelial photorefractive keratectomy (tPRK), with the goal of identifying the limitations of and potential improvements in using SA within a 6 mm area. The study included 62 patients who underwent fLASIK and tPRK. Complete eye examinations including keratometry, corneal epithelial thickness, central corneal thickness, and topography were performed preoperatively and postoperatively. Anterior, posterior, and total corneal aberrations were measured preoperatively and three months postoperatively, with pupil diameters ranging from 2 to 8 mm. In the fLASIK group, compared to the preoperative SA, the anterior and total SA increased postoperatively in the 6 and 7 mm areas. In the tPRK group, meanwhile, the anterior and total SA of the 5 mm or larger areas increased postoperatively. An area of 6 mm or larger showed an increase in correlation with the changes in Q value and refractive correction. As the corneal SA and asphericity in the 6 mm zone cannot specifically demonstrate the status of areas smaller than 6 mm or changes in the optical zone after laser refractive surgery, comparison with normal values in various areas of the cornea is necessary.

Effects of Neural Adaptation to Habitual Spherical Aberration on Depth of Focus

We investigated how long-term visual experience with habitual spherical aberration (SA) influences subjective depth of focus (DoF). Nine healthy cycloplegic eyes with habitual SAs of different signs and magnitudes were enrolled. An adaptive optics (AO) visual simulator was used to measure through-focus high-contrast visual acuity after correcting all monochromatic aberrations and imposing +0.5 μm and -0.5 μm SAs for a 6-mm pupil. The positive (n=6) and negative (n=3) SA groups ranged from 0.17 to 0.8 μm and from -1.2 to -0.12 μm for a 6-mm pupil, respectively. For the positive habitual SA group, the median DoF with positive AO-induced SA (2.18D) was larger than that with negative AO-induced SA (1.91D); for the negative habitual SA group, a smaller DoF was measured with positive AO-induced SA (1.81D) than that with negative AO-induced SA (2.09D). The difference in the DoF of individual participants between the induced positive and negative SA groups showed a quadratic relationship with the habitual SA. Subjective DoF tended to be larger when the induced SA in terms of the sign and magnitude was closer to the participant's habitual SA, suggesting the importance of considering the habitual SA when applying the extended DoF method using optical or surgical procedures.

A Nationwide Multicenter Study on 1-Year Outcomes of Posterior Chamber Phakic Intraocular Lens Implantation for Low Myopia

Purpose

To assess the nationwide multicenter outcomes of posterior chamber phakic intraocular lens implantation with a central hole (EVO-ICL, STAAR Surgical) for patients with low myopia.

Methods

This multicenter study comprised 172 eyes of 111 consecutive patients undergoing hole ICL implantation to correct low myopia and myopic astigmatism [manifest spherical equivalent (MSE);-3 diopters (D) or less] at seven nationwide major surgical facilities. We retrospectively determined safety, efficacy, predictability, stability, and adverse events at 1 week, 1, 3, 6, and 12 months postoperatively, and at the final visit.

Results

The mean follow-up period was 1.4 ± 1.0 years. Uncorrected and corrected visual acuities at 1 year postoperatively were -0.17 ± 0.12 and -0.24 ± 0.07 logarithm of the minimal angle of resolution (logMAR), respectively. At 1 year postoperatively, 91% and 100% of eyes were within 0.5 and 1.0 D of the target correction, respectively. No significant manifest refraction changes of -0.07 ± 0.26 D occurred from 1 week to 1 year. No vision-threatening complications occurred at any time in this series.

Conclusions

According to our experience, the EVO-ICL performed well without significant complications throughout the 1-year observation period, even for the correction of low myopia. It is suggested that current ICL implantation is one of the viable surgical options for correcting low myopia.

Blue-LIRIC in the rabbit cornea: efficacy, tissue effects, and repetition rate scaling

Laser-induced refractive index change (LIRIC) is being developed as a non-invasive way to alter optical properties of transparent, ophthalmic materials including corneas ex vivo and in vivo. This study examined the optical and biological effects of blue-LIRIC (wavelengths 400-405 nm) of ex-vivo rabbit corneas. Following LIRIC treatment at low and high repetition rates (8.3 MHz and 80 MHz, respectively), we interferometrically measured optical phase change, obtained transmission electron microscopy (TEM) micrographs, and stained histological sections with collagen hybridizing peptides (CHP) to assess the structural and organizational changes caused by LIRIC at different repetition rates. Finally, we performed power and scan speed scaling experiments at three different repetition rates (1 MHz, 8.3 MHz, and 80 MHz) to study their impact on LIRIC efficacy. Histologic co-localization of CHP and LIRIC-generated green autofluorescence signals suggested that collagen denaturation had occurred in the laser-irradiated region. TEM imaging showed different ultrastructural modifications for low and high repetition rate writing, with discrete homogenization of collagen fibrils at 80 MHz, as opposed to contiguous homogenization at 8.3 MHz. Overall, this study confirmed that LIRIC efficacy can be dramatically increased, while still avoiding tissue ablation, by lowering the repetition rate from 80 MHz to 8.3 MHz. Modeling suggests that this is due to a higher, single-pulse, energy density deposition at given laser powers during 8.3 MHz LIRIC.

Comparison of Corneal Wavefront-optimized and Wavefront-guided Alcohol-assisted Photorefractive Keratectomy Using Schwind Amaris 750S Laser for Myopia

Purpose

To compare the visual outcomes and corneal aberrations between wavefront-optimized (WFO) and corneal wavefront-guided (WFG) photorefractive keratectomy (PRK) in low to moderate myopia.

Methods

Twenty-seven eyes treated with WFO and 29 eyes treated with WFG PRK using a Schwind Amaris 750S Excimer laser were included after 6 months of postoperative follow-up. Uncorrected distance visual acuity, corrected distance visual acuity, refractive errors, corneal higher-order aberrations (HOA) and corneal thickness obtained using a Scheimpflug system, and central ablation depth and volume were evaluated during the preoperative period and again at the postoperative 6-month visits.

Results

Postoperatively, uncorrected distance visual acuity, corrected distance visual acuity, manifest spherical equivalent, and refractive astigmatism were improved in both groups, and there was no statistically significant difference between the two groups. There was no significant difference in safety, efficacy, or predictability of the refractive outcome. Postoperative total corneal HOA root mean square (RMS), coma RMS, and spherical aberration were significantly increased in both groups. Among these, only spherical aberration showed a significant difference between the two groups, with greater increase in the WFO group at 6 months postoperatively. The changes in corneal HOA RMS and spherical aberration were smaller in the WFG group, and this benefit was marked in eyes with high HOA RMS (≥0.4 µm) and spherical aberration (≥0.2 µm). Even though ablation volume in the WFG group was much larger than that of the WFO group, there was no significant difference in postoperative central and peripheral corneal thickness between the two groups.

Conclusions

Both WFO and WFG PRK using a Schwind Amaris 750S laser for low to moderate myopia were safe and effective at improving visual and refractive outcomes. However, WFG PRK induced fewer spherical aberrations than WFO PRK and may be more advantageous for eyes with high HOA root mean square or spherical aberration.

Comparison of outcomes of laser refractive surgery (LRS) alone and LRS with laser asymmetric keratectomy in patients with myopia: A retrospective study

To compare and analyze the postoperative 1-year outcomes of laser refractive surgery (LRS) alone vs LRS with laser asymmetric keratectomy (LAK), in patients with myopia, for preventing and resolving LRS complications.This retrospective study compared the preoperative and 1-year postoperative outcomes between the control and comparison groups using a sum of deviations in corneal thickness in 4 directions >80 μm. The control group included 41 patients with myopia (41 eyes) who underwent LRS. The comparison group included 33 patients (33 eyes) who received LAK-linked LRS. Age, spherical equivalent (SE), sphere, cylinder, uncorrected distance visual acuity (UDVA), pupil size, kappa angle, central corneal thickness, corneal irregularity in the 3.0 mm zone on Orbscan maps (SUM), distance between the maximum posterior elevation (best-fit-sphere) and the visual axis (DISTANCE), postoperative blurring scores, frequency of postoperative myopic regression, and efficiency index were compared.Preoperative age (P = .198), SE (P = .686), sphere (P = .562), cylinder (P = .883), UDVA (P = .139), pupil size (P = .162), kappa angle (P = .807), central corneal thickness (P = .738), corneal irregularity (P = .826), SUM (P = .774), and DISTANCE (P = .716) were similar between the 2 groups. The 1-year postoperative SE (P = .024), sphere (P = .022), corneal irregularity (P = .033), SUM (P = .000), DISTANCE (P = .04), blurring scores (P = .000), and frequency of postoperative myopic regression (P = .004) were significantly decreased in the comparison group compared to the control group. UDVA (P = .014) and the efficiency index (P = .035) were higher in the comparison group.LAK with LRS improved corneal symmetry by reducing the SUM and DISTANCE. UDVA and efficiency index were also improved and blurring and myopic regression were reduced postoperatively.

Three-Year Outcomes of Implantable Collamer Lens Followed by Excimer Laser Enhancement ("Bioptics") in the Treatment of High Myopic Astigmatism

Purpose

Describe three-year outcomes of spherical implantable Collamer lens (ICL) followed by excimer laser enhancement (bioptics) in eyes with high myopic astigmatism.

Patients and Methods

Retrospective case series of thirty-four cases that underwent bioptics enhancement at the Johns Hopkins Wilmer Eye Institute. All eyes had a preoperative sphere of −6.00 D or more with a cylinder of at least 2.00 D. Uncorrected and corrected distance visual acuity (UDVA and CDVA), manifest spherical equivalent refraction (MSE), ICL vault measurements and central corneal thickness (CCT) were collected. Endothelial cell counts (ECC), root mean square (RMS) of higher order aberrations (HOAs), adverse events and subsequent surgeries were also assessed.

Results

All patients had a minimum follow-up of 3 years. Preoperative UDVA was 2.29 ± 0.46 logMAR and improved to 0.03 ± 0.23 logMAR at 3 years (p<0.05). MSE was −12.30 ± 4.05 preoperatively and changed to −0.21 ± 0.46 at 3 years (p<0.05). The efficacy and safety indices were 1.28 ± 0.32 and 1.47 ± 0.27 at 3 years post-enhancement. HOA did not significantly change throughout the follow-up (p<0.05). Endothelial cell loss at 12 months was calculated at 5.7%. Two eyes required ICL exchange due to vault-related issues.

Conclusion

Bioptics offered excellent long-term safe, predictable, and efficient outcomes for high myopic astigmatism and can be considered an option if toric ICL is not available. Results confirm that wavefront-guided photoablation remains an excellent option to manage residual refractive error after phakic IOL.

Corneal Topography for Intraocular Lens Selection in Refractive Cataract Surgery

The purpose of this review is to evaluate the usefulness of corneal topography to select premium intraocular lenses (IOLs), including aspherical IOLs, toric IOLs, and multifocal IOLs, in refractive cataract surgery. Corneal topography can detect corneal regular astigmatism, corneal irregular astigmatism (higher-order aberrations [HOAs]) including spherical aberration, and corneal shape abnormalities after corneal refractive surgery. Surgeons can explain to the patients with significant corneal HOAs about its effect on postoperative visual function before surgery. Multifocal IOLs should not be selected for such eyes. For eyes with abnormal corneal shape, appropriate IOL power calculation formulae can be applied. In the case of toric IOLs, regular astigmatism and corneal HOAs should be checked. Before implanting an aspheric IOL, it is ideal to confirm spherical aberration of the cornea is not below the normal range. Because corneal HOAs, abnormal corneal shape after corneal refractive surgery, corneal regular astigmatism, and corneal spherical aberration increase postoperative refractive errors and poor vision quality with premium IOLs, corneal topography before cataract surgery is helpful in screening patients who are not appropriate candidates for premium IOLs.

Correlation Analysis of Refractive and Visual Quality after Wavefront-Optimized Laser In Situ Keratomileusis for 50% and 100% Angle Kappa Compensation

Purpose

To analyze the distribution of the offset between the pupil center and the coaxially sighted corneal light reflex (P-Dist), the effects of 50% and 100% angle kappa adjustments on refractive and visual quality in patients with moderate myopia were investigated.

Methods

A randomly selected 254 patients (254 eyes) with moderate myopia who underwent femtosecond laser-combined LASIK were examined. During the operation, the P-Dist of the patients was recorded by the x- and y-axis eyeball-tracking adjustment program of the WaveLight Eagle Vision EX500 excimer laser system. Preoperatively and 3 months postoperatively, the WaveLight® ALLEGRO Topolyzer was used to measure the pupil size and center position, and the wavefront sensor was used to measure the wavefront aberrations. The visual function tester (OPTEC 6500) measured contrast sensitivity.

Results

The average P-Dist was 0.220 ± 0.102 mm. When the P-Dist >0.220 mm, the postoperative residual cylinder was 0.29 ± 0.34 D in the group with the 50% adjustment and 0.40 ± 0.32 D in the 100% group, which was significantly higher than the 50% group (P=0.036). The coma was 0.21 ± 0.17 μm in the 50% adjusted group and 0.34 ± 0.25 μm in the 100% group, which was significantly higher than that in the 50% group (P=0.021). At the 1.5 c/d spatial frequency, contrast sensitivity in the adjusted 100% group was significantly lower than that in the 50% group under visual glare conditions (P=0.039).

Conclusion

The postoperative visual acuity and spherical equivalent were not affected in the two groups. However, when P-Dist >0.220 mm, the residual astigmatism and coma were lower in the 50% group. Individualized operations for those with moderate myopia and large-angle kappa in which 100% adjustment is chosen may not result in a better visual quality effect than 50%.

Comparison between Surgical Outcomes of LASIK with and without Laser Asymmetric Keratectomy to Avoid Conventional Laser Refractive Surgery Adverse Effects

This study compared one-year postoperative outcomes of laser refractive surgery combined with laser asymmetric keratectomy (LAK) and laser in situ keratomileusis (LASIK)for myopia correction in middle-aged patients (aged 40–49 years) with a total corneal thickness deviation (summed across four directions) ≥ 80 microns. The control group (n = 26; 52 eyes) underwent LASIK; the comparison group (n = 26; 52 eyes) underwent combined laser refractive surgery and LAK. Age, spherical equivalence, uncorrected visual acuity (near and far), corneal irregularity on the Orbscan map, sum of corneal thickness deviations in four directions, corneal thickness distribution, distance between the maximum posterior elevation (best-fit sphere; BFS) and visual axis, and postoperative blurring scores were analysed retrospectively between the groups. Both groups had similar preoperative findings. Postoperatively, the sum of corneal thickness deviations in four directions (p = 0.000), distance between maximum posterior elevation (BFS) and visual axis (p = 0.003),blurring score (p = 0.001), and corneal irregularity in the 3.0 and 5.0 mm zones on the Orbscan map (p = 0.033 and p < 0.0001, respectively) were significantly lower in the comparison group (p = 0.000). LAK reduced total corneal thickness deviation, improved corneal symmetry, and reduced blurring scores significantly, one-year postoperatively. LAK could resolve shortcomings of LASIK, producing better surgical outcomes.

Influence of corneal spherical aberration on prediction error of the Haigis-L formula

The purpose of this study is to investigate the relationships between corneal asphericity and Haigis-L formula prediction errors in routine cataract surgery after refractive surgery for myopic correction. This retrospective study included 102 patients (102 eyes) with a history of previous PRK or LASIK and cataract surgery. Axial length, anterior chamber depth, and central corneal power were measured using the optical biometer. On the anterior corneal surface, Q-value, spherical aberration, and ecentricity at 6.0 and 8.0 mm were measured using a rotating Scheimpflug camera. The postoperative refractive outcome at 6 months, mean error, and mean absolute error were determined. Correlation tests were performed to determine the associations between pre-cataract surgery data and the prediction error. The Q-values for 6.0 and 8.0 mm corneal diameter were 1.57 ± 0.70 (range: 0.03~3.44), and 0.82 ± 0.5 (range: -0.10~-2.66). The spherical aberration for 6.0 and 8.0 mm diameter was 1.16 ± 0.39 µm (range: 0.24~2.08 µm), and 3.69 ± 0.87 µm (range: 0.91~5.91 µm). eccentricity for 6.0 and 8.0 mm diameter was -1.22 ± 0.31 (range: -1.85 to -0.17), and -0.82 ± 0.39 (range: -1.63 to 0.32). The spherical aberration for 8.0 mm cornea diameter showed the highest correlations with the predicion error (r = 0.750; p < 0.001). When the modified Haigis-L formula considering spherical aberration for 8.0 mm produced smaller values in standard deviation of mean error (0.45D versus 0.68D), mean absolute error (0.35D versus 0.55D), and median absolute error (0.31D versus 0.51D) than the Haigis formula. Corneal asphericity influences the predictive accuracy of the Haigis-L formula. The accuracy was enhanced by taking into consideration the corneal spherical aberration for the 8.0 mm zone at pre-cataract surgery state.

Factors predicting successful customized excimer laser treatment in irregular corneas

PURPOSE

To identify factors associated with a successful wavefront-guided customized treatment (WG-CT) with an excimer laser in highly aberrated corneas.

SETTING

VISSUM Alicante Spain.

DESIGN

Retrospective consecutive noncomparative case series.

METHODS

Treatment was performed with the WG-CT Amaris excimer laser using the ORK-CAM software for the calculation of the ablation profile. Eyes of patients with significantly aberrated corneas, including postrefractive and keratoplasty procedures or high irregular astigmatism with significant higher-order aberrations (HOAs) that had WG-CT were included. Refractive outcomes, HOAs, and visual outcomes were recorded. Statistical analysis was performed to identify factors associated with technical (based on HOAs) or refractive outcome success.

RESULTS

The study included 55 treatments of 51 eyes (35 patients). The postoperative uncorrected distance visual acuity was 0.2 logarithm of the minimum angle of resolution or better in 72% of the eyes, and the postoperative residual manifest refraction spherical equivalent was ±0.50 diopter in 56% of the eyes, whereas 11% of the eyes lost 1 line or more in corrected distance visual acuity. Successful reduction in the total root mean square (RMS) of HOAs occurred in 36 eyes (65%), and these eyes had a significantly higher preoperative RMS of HOAs (1.45 ± 0.93 μ vs 0.91 ± 0.34 μ, P = .003) and preoperative coma-like aberrations (1.09 ± 0.83 μ vs 0.55 ± 0.28 μ, P = .001). In multivariate analysis, posthyperopic treatment eyes were less likely to achieve refractive outcome success (odds ratio = 0.09, P = .02).

CONCLUSIONS

WG-CT in highly aberrated corneas had a limited refractive predictability. Eyes with preoperative coma-like aberrations are more likely to benefit from a reduction in HOAs. Posthyperopic treatment is associated with a higher rate of refractive surprises.

Comparison of Higher-Order Aberrations after LASEK between Two Different Laser Platforms for Low-to-Moderate Myopia

PURPOSE

To compare the differences in higher-order aberrations (HOAs) after laser subepithelial keratomileusis (LASEK) between two different laser platforms.

METHODS

One hundred and seven eyes of 107 patients were included in this study. Fifty-six eyes underwent LASEK with the Triple-A profile (an ablation profile of the MEL 90 excimer laser) and 51 eyes underwent LASEK with the aspheric (Aberration Smart Ablation [ASA]) profile. Uncorrected distance visual acuity, corrected distance visual acuity (CDVA), corneal topography, and ocular aberrations were measured before and 6 months postoperatively.

RESULTS

In the ASA group, the values of horizontal trefoil, vertical coma, horizontal coma, spherical aberrations, and total HOAs increased significantly after surgery (all P < 0.05). There were no significant differences in the vertical trefoil between the preoperative and 6-month postoperative periods. In the Triple-A group, there were no differences in vertical trefoil and horizontal trefoil values between the preoperative and 6-month postoperative periods. Compared with the preoperative values, vertical coma, horizontal coma, spherical aberrations, and total HOAs were significantly increased at 6 months after surgery (all P < 0.05). Compared to the Triple-A group, higher horizontal trefoil and horizontal coma were introduced in the ASA group at 6 months postoperatively.

CONCLUSION

The Triple-A ablation profile of the MEL 90 excimer laser at a 500-Hz pulse rate was an efficient method to correct myopia, especially for mild-to-moderate myopia, compared with the aspheric ablation model, fewer horizontal trefoil and horizontal coma were induced at 6 months after LASEK.

ABBREVIATIONS

HOAs, Higher-Order Aberrations; LASEK, laser subepithelial keratomileusis; ASA, Aberration Smart Ablation; UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity.

Relating wavefront error to visual acuity in pre- and post-LASIK eyes: a comparison of methods

Contrast threshold and visual Strehl ratio methods are used to predict visual acuity from wavefront error for a sample population of pre- and post-LASIK patients. Relative error (in logMAR) between predicted and measured visual acuity values are computed for each method and compared using paired t-tests. Differences in aberration data between pre- and post-LASIK eyes are then evaluated. The visual acuity prediction using visual Strehl proved to be more accurate for pre-LASIK patients than contrast threshold. However, both methods are comparable for post-LASIK patients.

Varifocal Versus Monofocal LASIK in Presbyopic Hyperopic Eyes

PURPOSE

To compare varifocal (SupraCor; Technolas Perfect Vision GmbH, Munich, Germany) to monofocal (Zyoptix TissueSaving; Bausch & Lomb, Rochester, NY) LASIK in patients with hyperopic presbyopia.

METHODS

In this prospective, non-randomized, comparative case series, consecutive patients with hyperopia, presbyopia, and emmetropia as target refraction were bilaterally treated with varifocal (8 patients) or monofocal (7 patients) LASIK. The study was designed for 35 patients, but was terminated early after interim analysis. Outcomes (preoperative and 1 day, 1 week, 1 month, and 3 months postoperative) were: monocular and binocular uncorrected near visual acuity (UNVA), distance-corrected near visual acuity (DCNVA), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), low-contrast UDVA and CDVA, efficacy, and safety.

RESULTS

Preoperative data were similar in both groups. Monocular and binocular UNVA were not significantly different between both groups at any follow-up visit. At 3 months, mean monocular UNVA was 0.40 logMAR in both groups. Monocular DCNVA and binocular CDVA were not significantly different between groups. Monocular mean CDVA was 0.00 ± 0.06 logMAR after varifocal LASIK and -0.06 ± 0.04 logMAR after monofocal LASIK. The efficacy index was 0.9 after vari-focal LASIK and 0.88 after monofocal LASIK (not significant). The safety index was 1.08 after varifocal LASIK and 1.125 after monofocal LASIK (not significant).

CONCLUSIONS

With emmetropia as target refraction, varifocal ablations yielded no additional benefit compared to monofocal ablations in hyperopic presbyopic LASIK. The authors speculate that epithelial remodeling masks the impact of a varifocal ablation pattern and that a myopic postoperative refraction (modified monovision) may be necessary to further improve near and intermediate vision. These results demonstrate the value of a control group in studies evaluating presbyopia corrections. [J Refract Surg. 2019;35(7):459-466.].

Excimer Laser Correction of Myopia Using Aspheric Technology. Literature Review

The article presents a literature review of scientific sources on the use of aspheric technology for the correction of refractive errors at the present stage of development of excimer laser surgery. The article highlights the pressing challenge of developing algorithms that improve quality indicators, maintaining subtle visual functions (low-contrast visual acuity, visual acuity in various illuminating conditions) after excimer laser correction of ametropy. The literature data on the etiology of visual acuity reduction after refractive operations are given. Special consideration is given to the description of asphericity indicators by the researchers, the importance of influence of the indicators on the qualitative characteristics of vision. The mechanism of influence of the modified aberration balance of the cornea after refractive interventions on the indicators of spatial-contrasting characteristics of vision in refractive patients is clarified; the importance of evaluating these indicators before and after refractive surgeries is emphasized. The types of aspherical ablation algorithms used in modern, both foreign and domestic, excimer laser systems, and their differences are described. Advantages and disadvantages of the aspherical algorithms used have been analyzed, historical evolution of the software that was developed and introduced into the new excimer laser systems for aspherical operations has been traced. Fundamental difference between aspheric ablation optimized with respect to wavefront with average asphericity index, introduced by the manufacturer of the facility, and the algorithm, where aspheric ablation is performed with personalized Q-factor, which can be controlled by the surgeon himself, is presented in detail. The problem of developing optimized technology of aspheric ablation algorithm in correcting myopia due to the existence of restrictions on the use of aspheric techniques on domestic “Microscan-VIZUM” excimer laser unit is emphasized.

Refractive outcomes following cataract surgery in patients who have had myopic laser vision correction

Objective

Prediction errors are increased among patients presenting for cataract surgery post laser vision correction (LVC) as biometric relationships are altered. We investigated the prediction errors of five formulae among these patients.

Methods and analysis

The intended refractive error was calculated as a sphero-cylinder and as a spherical equivalent for analysis. For determining the difference between the intended and postoperative refractive error, data were transformed into components of Long's formalism, before changing into sphero-cylinder notation. These differences in refractive errors were compared between the five formulae and to that of a control group using a Kruskal-Wallis test. An F-test was used to compare the variances of the difference distributions.

Results

22 eyes post LVC and 19 control eyes were included for analysis. Comparing both groups, there were significant differences in the postoperative refractive error (p=0.038). The differences between the intended and postoperative refractive error were greater in post LVC eyes than control eyes (p=0.012), irrespective of the calculation method for the intended refractive error (p<0.01). The mean difference between the intended and postoperative refractive error was relatively small, but its variance was significantly greater among post LVC eyes than control eyes (p<0.01). Among post LVC eyes, there were no significant differences between the mean intended target refraction and between the intended and postoperative refractive error using five biometry formulae (p=0.76).

Conclusion

Biometry calculations were less precise for patients who had LVC than patients without LVC. No particular biometry formula appears to be superior among patients post LVC.

Vector Analysis of 1-Year Astigmatic Outcomes From a Randomized Fellow Eye Comparison of Photorefractive Keratectomy Using 2 Excimer Laser Platforms

OBJECTIVE

To compare the astigmatic outcomes of photorefractive keratectomy (PRK) with a wavefront-guided (WFG) and a wavefront-optimized (WFO) excimer laser performed on two different platforms.

METHODS

Setting: institutional.

DESIGN

Prospective, randomized, fellow eye comparison clinical trial.

PARTICIPANTS

A total of 142 eyes of 71 patients with myopia of 12 diopters (D) or less and astigmatism of 3D or less were enrolled at the Byers Eye Institute at Stanford between April 2009 and March 2011.

INTERVENTION

One eye of each patient underwent WFG-PRK with the VISX CustomVue Star S4 IR (Abbott Medical Optics, Abbott Park, IL) and the contralateral eye underwent WFO-PRK with the Wavelight Allegretto Eye-Q 400-Hz laser platform (Alcon, Inc., Hüenberg, Switzerland). Alpins vector analysis of astigmatism was performed using manifest refraction measured preoperatively and 12 months postoperatively and vertexed to the corneal plane. Eyes were stratified for subgroup analysis based on preoperative manifest astigmatism.

RESULTS

WFG-PRK and WFO-PRK were similar regarding surgically induced astigmatism, difference vector, magnitude of error, correction index, flattening index, and index of success. The angle of error was 60% less in the WFG group compared with the WFO group (4.9±1.1° vs. 11.8±2.4°, P=0.01).

CONCLUSIONS

WFG-PRK with the VISX CustomVue Star S4 IR and WFO-PRK with the Alcon WaveLight Allegretto Eye-Q 400-Hz excimer laser platform produce similar astigmatic results in myopic patients; however, the WFG mode may produce slightly more predictable astigmatic corrections.

The art of nomograms

Background

To retrospectively analyse strategies for adjusting refractive surgery plans with reference to the preoperative manifest refraction.

Methods

We constructed seven nomograms based on the refractive outcomes (sphere, cylinder, axis [SCA]) of 150 consecutive eyes treated with laser in situ keratomileusis for myopic astigmatism. We limited the initial data to the SCA of the manifest refraction. All nomograms were based on the strategy: if for x diopters (D) of attempted metric, y D is achieved; we can reverse this sentence and state for achieving y D of change in the metric, x D will be planned. The effects of the use of plus or minus astigmatism notation, spherical equivalent, sphere, principal meridians notation, cardinal and oblique astigmatism, and astigmatic axis were incorporated.

Results

All nomograms detected subtle differences in the spherical component (p < 0.0001). Nomograms 5 and 7 (using power vectors) and 6 (considering axis shifts) detected significant astigmatic differences (nomogram 5, p < 0.001; nomogram 6, p < 0.05; nomogram 7, p < 0.005 for cardinal astigmatism, p = 0.1 for oblique astigmatism). We observed mild clinically relevant differences (~ 0.5 D) in sphere or astigmatism among the nomograms; differences of ~ 0.25 D in the proposals for sphere or cylinder were not uncommon. All nomograms suggested minor improvements versus actual observed outcomes, with no clinically relevant differences among them.

Conclusions

All nomograms anticipated minor improvements versus actual observed outcomes without clinically relevant differences among them. The minimal uncertainties in determining the manifest refraction (~ 0.6 D) are the major limitation to improving the accuracy of refractive surgery nomograms.

Ocular higher-order aberrations changes after implantable collamer lens implantation for high myopic astigmatism

Purpose

To investigate the changes in higher-order aberrations (HOAs) induced by the implantation of implantable collamer lenses (ICLs) and Toric ICL (TICL) in eyes with high myopia and high myopic astigmatism.

Methods

We investigated 33 eyes of 18 consecutive patients (in a prospective, interventional case series study), with spherical equivalent errors of -6.00 to -21.09 diopters (D) and cylindrical errors of -0.5 to -4.75 D, who underwent ICL and TICL implantation. Before and after 5 days, 2 and 6 months of surgery, the uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), defocus and adverse events of the surgery were assessed. Ocular HOAs were also evaluated by Hartmann-Shack aberrometry (Technolas PV, Rochester, New York, USA) before and after 6 months of surgery.

Results

At 6.0 months after surgery, the UCVA and BCVA in 40% and 66.7% of eyes were 20/20, respectively. Mean defocus refraction and astigmatism was reduced to -0.66 and 0.65 D from -12.79 and 2.18 at baseline, respectively. For a 6 mm pupil, HOAs were not significantly changed, merely from 0.417 ± 0.162 μ before surgery to 0.393 ± 0.119 μ after surgery (P = 0.45). Spherical aberration (Z400) increased significantly (P = 00.0). Surgical induced astigmatism was lower than 0.25 D, and there were no changes in trefoils and coma aberration. No vision-threatening complications occurred during the observation period.

Conclusion

This study shows that the ICL and TICL performed well in correcting high myopic astigmatism without significant changes in HOAs during a 6-month observation period, although the spherical aberration (Z400) increased significantly.

Posterior chamber phakic intraocular lens implantation: comparative, multicentre study in 351 eyes with low-to-moderate or high myopia

AIM

To compare the clinical outcomes of posterior chamber phakic intraocular lens implantation with a central hole (Hole Implantable Collamer Lens (ICL), STAAR Surgical) for low-to-moderate myopia and for high myopia.

METHODS

This multicentre retrospective case series comprised 351 eyes of 351 consecutive patients undergoing ICL implantation. Eyes were divided into groups based on preoperative degree of myopia: group 1; 57 eyes, manifest spherical equivalent less than -6 dioptres (D), and group 2; 294 eyes, -6 D or more. Safety, efficacy, predictability, stability and adverse events were compared preoperatively; and at 1 day, 1 week and 1, 3, 6 and 12 months postoperatively, RESULTS: Uncorrected and corrected visual acuities were -0.17±0.14 and -0.21±0.10 logMAR in group 1, and -0.16±0.09 and -0.21±0.08 logMAR in group 2, 1 year postoperatively. In groups 1 and 2, 98% and 99% of eyes were within 1.0 D of the targeted correction. Manifest refraction changes of -0.12±0.34 D (group 1) and -0.18±0.43 D (group 2) occurred from 1 day to 1 year. ICL exchanges were necessary in two eyes (0.7%) in group 2. No vision-threatening complications occurred at any time.

CONCLUSIONS

The ICL performed well for the correction of both low-to-moderate myopia and high myopia throughout the 1-year observation period. The clinical outcomes of ICL implantation for low-to-moderate myopia are essentially equivalent to those for high myopia.

Transepithelial Photorefractive Keratectomy for Hyperopia: A 12-Month Bicentral Study

PURPOSE

To investigate the safety, efficacy, and stability of transepithelial photorefractive keratectomy (PRK) for hyperopia.

METHODS

This interventional case series study at two sites included 55 eyes (31 patients) with hyperopia (0.50 to 6.00 diopters [D]), with or without astigmatism (0.00 to -3.00 D), that underwent one-step transepithelial PRK with a Amaris 500-Hz excimer laser (SCHWIND eye-tech-solutions, Kleinostheim, Germany). A 12-month follow-up was conducted. Preoperative and successive postoperative visual acuity, manifest refraction, haze, and other complication data were analyzed.

RESULTS

The preoperative mean spherical equivalent of 2.56 ± 1.90 D improved to emmetropia (-0.08 ± 0.14 D) by 6 months, with subsequent slight mean regression of 0.024 D (range: -0.75 to 0.50) until month 12. Of the treated eyes, 75% and 76.2% were within the target refraction of ±0.50 D at 6 and 12 months postoperatively, respectively. The final mean cylindric refraction was comparable to the preoperative value (-0.94 ± 0.12 to -0.71 ± 0.12 D, P = .17); however, it was induced in 23% of eyes. The preoperative mean uncorrected distance visual acuity logMAR of 0.54 ± 0.05 significantly improved to 0.15 ± 0.03 by month 12 (P < .0001), and 64.2% of the treated eyes gained an uncorrected distance visual acuity of 20/25 or better. Ten eyes (23.8%) lost one line of preoperative corrected distance visual acuity (CDVA). No eye lost two or more lines of preoperative CDVA. Four eyes with a 3+ degree of haze were observed by the final visit. No other notable complications occurred. The low hyperopic eyes exhibited better overall results compared to the moderate hyperopic group.

CONCLUSIONS

One-step transepithelial PRK with the Amaris 500-Hz excimer laser provided reasonable outcomes for the correction of hyperopia with or without mild to moderate astigmatism.

Effect of postoperative keratometry on quality of vision in the postoperative period after myopic wavefront-guided laser in situ keratomileusis

PURPOSE

To determine whether postoperative keratometry is a predictor of patient-reported satisfaction and night-vision phenomena after wavefront-guided myopic laser in situ keratomileusis (LASIK).

SETTING

Optical Express, Glasgow, United Kingdom.

DESIGN

Retrospective case series.

METHODS

Myopic eyes treated with wavefront-guided LASIK were analyzed in this study. All patients completed pre-operative and 1-month postoperative questionnaires, in which the satisfaction with visual outcomes and pre-operative and postoperative night-vision symptoms (glare, halos, starburst, ghosting/double-vision) were rated. Multivariate regression analysis was performed to determine factors associated with questionnaire outcomes.

RESULTS

This study evaluated 8672 myopic eyes of 4602 patients. The mean pre-operative manifest spherical equivalent was -3.72 diopters (D) ± 2.00 (SD) (range -0.50 to -11.00 D) and the mean pre-operative keratometry (K) value was 43.64 ± 1.43 D (38.38 to 49.00). At 1 month after surgery, 93.7% and 99.1% of eyes were within 0.50 D and 1.00 D of emmetropia, and 94.6% and 98.3% of eyes achieved monocular and binocular uncorrected-distance visual acuity(UDVA) of 20/20 or better, respectively. There were 48.7% of eyes that had the flat corneal meridian (minimum K) of 40.0 D or less. Although postoperative keratometry was a significant predictor of patient-reported satisfaction and the change in halo reports in the regression analysis, its relative contribution was very low and accounted for less than 0.50% of the variance explained by either model. Postoperative keratometry was not a significant predictor of a change in reports of glare, starburst, and ghosting or double vision.

CONCLUSION

In this large cohort of patients, postoperative keratometry played a minimal and clinically insignificant role in predicting post-LASIK halo visual phenomena and patient-reported satisfaction.

FINANCIAL DISCLOSURE

Dr. Schallhorn is a consultant to Abbott Medical Optics and Zeiss and a Global Medical Director for Optical Express. None of the other authors have a financial or proprietary interest in the products and materials presented in this paper.

Retrospective Analysis Comparing the Preoperative and Postoperative "Q" Values for 2 Different Lasers in Refractive Surgery

PURPOSE

To compare the presurgical and postsurgical corneal asphericity, or "Q value," between VISX Wavefront-guided treatment and Allegretto Wave Wavefront-optimized treatment in photorefractive keratectomy for the correction of myopia.

METHODS

This is a retrospective database analysis performed at the Joint Warfighter Refractive Surgery Center, Lackland Air Force Base, TX. All data were accessed through the Institutional Review Board-approved Joint Warfighter Refractive Surgery Center database. Fifty-one patient records (102 eyes) were reviewed to determine the change in the Q value after photorefractive keratectomy for the correction of myopia.

RESULTS

The average change in the Q value per diopter of treatment sphere over the entire study population was 0.12 (±0.04) for Allegretto and 0.14 (±0.04) for VISX (P = 0.004). There was no statistical difference among the preoperative and postoperative best-corrected visual acuities (BCVAs), low-contrast BCVA (BCVA 5%), or quality of vision complaints between both platforms.

CONCLUSIONS

Low to moderate myopic correction with the Allegretto laser was associated with a smaller change in the Q value per diopter of treatment and therefore more closely maintained the original prolate shape of the cornea when compared with VISX. No difference in the postoperative visual outcome between both groups was detected.

Effect of Myopic Defocus on Visual Acuity after Phakic Intraocular Lens Implantation and Wavefront-guided Laser in Situ Keratomileusis

This study aimed to investigate the effect of myopic defocus on visual acuity after phakic intraocular lens (IOL) implantation and wavefront-guided laser in situ keratomileusis (wfg-LASIK). Our prospective study comprised thirty eyes undergoing posterior chamber phakic IOL implantation and 30 eyes undergoing wfg-LASIK. We randomly measured visual acuity under myopic defocus after cycloplegic and non-cycloplegic correction. We also calculated the modulation transfer function by optical simulation and estimated visual acuity from Campbell &Green's retinal threshold curve. Visual acuity in the phakic IOL group was significantly better than that in the wfg-LASIK group at myopic defocus levels of 0, -1, and -2 D (p < 0.001, p < 0.001, and p = 0.02, Mann-Whitney U-test), but not at a defocus of -3 D (p = 0.30). Similar results were also obtained in a cycloplegic condition. Decimal visual acuity values at a myopic defocus of 0, -1, -2, and -3 D by optical simulation were estimated to be 1.95, 1.21, 0.97, and 0.75 in the phakic IOL group, and 1.39, 1.11, 0.94, and 0.71 in the wfg-LASIK group, respectively. From clinical and optical viewpoints, phakic IOL implantation was superior to wfg-LASIK in terms of the postoperative visual performance, even in the presence of low to moderate myopic regression.

Comparison of visual outcomes after variable spot scanning ablation versus wavefront-optimized myopic LASIK

PURPOSE

To compare the refractive and visual outcomes of variable spot scanning ablation versus the wavefront-optimized ablation for myopia and myopic astigmatism.

METHODS

Fifty patients with myopia who underwent LASIK (100 eyes) were divided into two equal groups. Myopic correction performed using the variable spot scanning (VSS) ablation with the VISX STAR S4/IR platform (Abbott Medical Optics, Inc., Santa Ana, CA) (VSS group) and wavefront-optimized (WFO) ablation profile with the WaveLight Allegretto Wave Eye-Q platform (Alcon Laboratories, Inc., Fort Worth, TX) (WFO group). Manifest refraction, uncorrected distance visual acuity, and corrected distance visual acuity were obtained preoperatively and 1 day and 1 and 3 months postoperatively. Wavefront measurement and contrast sensitivity testing were done preoperatively and 3 months postoperatively.

RESULTS

Postoperative mean refractive spherical equivalent was -0.14 ± 0.2 diopters for the VSS group and -0.15 ± 0.28 diopters for the WFO group. Forty-eight eyes of the VSS group and 47 eyes of the WFO group were within ±0.5 diopters. Postoperative mean corrected distance visual acuity was 1.05 ± 0.13 for the VSS group and 1.06 ± 0.12 for the WFO group. The postoperative uncorrected distance visual acuity was 1.01 ± 0.16 for the VSS group and 1.01 ± 0.11 for the WFO group. The safety index was 1.12 for the VSS group and 1.06 for the WFO group, whereas the efficacy index was 1.07 for the VSS group and 1.01 for the WFO group. The mean induced positive spherical aberration was 0.041 ± 0.046 µm for the VSS group and 0.195 ± 0.171 µm for the WFO group (P < .001). Mesopic contrast sensitivity testing showed no statistically significant differences between groups at all tested spatial frequencies.

CONCLUSIONS

Both VSS and WFO treatments showed similar refractive and visual outcomes. Both induced significant positive spherical aberration, significantly more with WFO.

Aquaporin 0 plays a pivotal role in refractive index gradient development in mammalian eye lens to prevent spherical aberration

Aquaporin 0 (AQP0) is a transmembrane channel that constitutes ∼45% of the total membrane protein of the fiber cells in mammalian lens. It is critical for lens transparency and homeostasis as mutations and knockout cause autosomal dominant lens cataract. AQP0 functions as a water channel and as a cell-to-cell adhesion (CTCA) molecule in the lens. Our recent in vitro studies showed that the CTCA function of AQP0 could be crucial to establish lens refractive index gradient (RING). However, there is a lack of in vivo data to corroborate the role of AQP0 as a fiber CTCA molecule which is critical for creating lens RING. The present investigation is undertaken to gather in vivo evidence for the involvement of AQP0 in developing lens RING. Lenses of wild type (WT) mouse, AQP0 knockout (heterozygous, AQP0(+/-)) and AQP0 knockout lens transgenically expressing AQP1 (heterozygous AQP0(+/)(-)/AQP1(+/)(-)) mouse models were used for the study. Data on AQP0 protein profile of intact and N- and/or C-terminal cleaved AQP0 in the lens by MALDI-TOF mass spectrometry and SDS-PAGE revealed that outer cortex fiber cells have only intact AQP0 of ∼28kDa, inner cortical and outer nuclear fiber cells have both intact and cleaved forms, and inner nuclear fiber cells have only cleaved forms (∼26-24kDa). Knocking out of 50% of AQP0 protein caused light scattering, spherical aberration (SA) and cataract. Restoring the lost fiber cell membrane water permeability (Pf) by transgene AQP1 did not reinstate complete lens transparency and the mouse lenses showed light scattering and SA. Transmission and scanning electron micrographs of lenses of both mouse models showed increased extracellular space between fiber cells. Water content determination study showed increase in water in the lenses of these mouse models. In summary, lens transparency, CTCA and compact packing of fiber cells were affected due to the loss of 50% AQP0 leading to larger extracellular space, more water content and SA, possibly due to alteration in RING. To our knowledge, this is the first report identifying the role of AQP0 in RING development to ward off lens SA during focusing.

Stability of axis and patient satisfaction after toric implantable collamer lens implantation for myopic astigmatism

Objectives: To assess the stability of axis and patient satisfaction after toric visian implantable collamer lens (TICL) implantation for moderate to high myopic astigmatism.

Methods: Total 33 eyes of 21 consecutive patients who underwent implantation of TICL for the correction of moderate to high myopic astigmatism were recorded and a minimum follow-up of six months was performed. The deviation of axis of TICL was detected from one week to six months postoperatively. The evaluation of the visual functions was done by the same clinician at six months after surgery.

Results: The mean refractive cylinder decreased from -2.48±0.91 diopters (D) preoperatively to -0.54±0.25D and -0.50±0.19D at one week and six months after surgery respectively. Mean changes in astigmatism from one week to six months after surgery was 0.03±0.17D. The mean deviation of axis of TICL from one week to six months postoperatively was 2.48±1.25°(range,1°~ 6°) and no TICL required secondary repositioning. 14.3% patients felt difficult about the middle distant visual function (Reading Computer Screen). Evaluations of other visual functions were positive or very positive.

Conclusions: Six months after implantation of the TICL, it showed slightly axis rotation and high satisfaction about the visual functions.

Impact of pupil transmission apodization on presbyopic through-focus visual performance with spherical aberration

PURPOSE

To investigate the impact on through-focus retinal image quality and visual performance of apodizing the pupil's transmission function in combination with extended depth of focus presbyopic corrections, such as spherical aberration (SA).

METHODS

Through-focus retinal image quality was determined theoretically for various magnitudes of pupil transmission apodization and Zernike primary SA (-0.5 to +0.5 μm) for a 4-mm pupil. The impact of pupil transmission apodization was also assessed psychophysically with a vision simulator equipped with a liquid crystal spatial light modulator for controlling pupil transmission. Through-focus visual acuity (VA) was measured with and without apodization in three cyclopleged subjects from distance to near with monochromatic light (550 nm) under two multifocal aberration conditions. Phase plates induced +0.2 and -0.2 μm of SA over a 4-mm artificial pupil. A baseline condition of zero SA was also included for comparison.

RESULTS

The theoretical investigation showed that pupil transmission apodization significantly improved distance image quality in the presence of positive and negative SA. Retinal image quality at all target vergences for negative SA conditions was improved by apodization. Pupil transmission apodization improved through-focus VA by 0.1 to 0.2 logMAR at intermediate and near object distances for the zero and negative SA conditions. In the positive SA condition, apodization degraded VA by approximately 0.1 logMAR at intermediate object distances.

CONCLUSIONS

Pupil transmission apodization had a significant impact on though-focus visual performance. Pupil transmission apodization affects through-focus retinal image quality by diminishing the relative contribution to the retinal image from the peripheral region of the wavefront aberration. Through-focus visual performance in presbyopic eyes with negative SA was improved due to pupil transmission apodization.

Intraocular lens power calculation by ray-tracing after myopic excimer laser surgery

PURPOSE

To investigate the refractive outcomes of intraocular lens (IOL) power calculation by ray-tracing after myopic excimer laser surgery.

DESIGN

Prospective, interventional case series.

METHODS

setting: Multicenter study. participants: Twenty-one eyes of 21 patients undergoing phacoemulsification and IOL implantation after myopic laser in situ keratomileusis or photorefractive keratectomy were enrolled. intervention: IOL power calculation was performed using internal software of a Scheimpflug camera combined with a Placido disc corneal topographer (Sirius; CSO). Exact ray-tracing was carried out after the axial length (measured either by immersion ultrasound biometry or partial coherence interferometry), target refraction, and pupil size had been entered. main outcome measures: Median absolute error, mean absolute error, and mean arithmetic error in refraction prediction, that is, the difference between the expected refraction (as calculated by the software) and the actual refraction 1 month after surgery.

RESULTS

The mean postoperative refraction was -0.43 ± 1.08 diopters (D), with a range between -1.28 and 0.85 D. The mean arithmetic error was -0.13 ± 0.49 D. The median and mean absolute errors were +0.25 D and 0.36 D, respectively. Also, 71.4% of the eyes were within ± 0.50 D of the predicted refraction, 85.7% were within ± 1.00 D, and 100% within ± 1.50 D.

CONCLUSIONS

Ray-tracing can calculate IOL power accurately in eyes with prior myopic laser in situ keratomileusis and photorefractive keratectomy, with no need for preoperative data.

Analytical optimization of the ablation efficiency at normal and non-normal incidence for generic super Gaussian beam profiles

We suggest a general method to determine the optimum laser parameters for maximizing the ablation efficiency for different materials (in particular human cornea) at different incidence angles. The model is comprehensive and incorporates laser beam characteristics and ablative spot properties. The model further provides a method to convert energy fluctuations during ablation to equivalent ablation deviations in the cornea. The proposed model can be used for calibration, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.

Effect of corneal aberrations on intraocular lens power calculations

PURPOSE

To use ray tracing to determine the influence of corneal aberrations on the prediction of the optimum intraocular lens (IOL) power for implantation in normal eyes and eyes with previous laser in situ keratomileusis (LASIK).

SETTING

Hospital Universitario Virgen de la Arrixaca, Murcia, Spain.

DESIGN

Case series.

METHODS

The optimum IOL power was calculated by ray tracing using a patient-customized eye model in cataract surgery cases. The calculation can be performed with or without inclusion of the patient's corneal aberrations. Standard predictions were also generated using current state-of-the-art IOL power calculation techniques. The results for all predictions were compared with the optimum IOL power after cataract surgery.

RESULTS

For patients without previous LASIK (n = 18), the standard approaches and the ray-tracing procedure gave a similar mean absolute residual error and variance. The incorporation of corneal aberrations did not improve the accuracy of the ray-tracing prediction in these cases. For post-LASIK patients (n = 10), the ray-tracing prediction incorporating corneal aberrations generated the most accurate results. The difference between the prediction with and without considering corneal aberrations correlated with the amount of corneal spherical aberration (r(2) = 0.82), resulting in a difference of up to 3.00 diopters in IOL power in some cases.

CONCLUSIONS

Ray tracing using patient-customized eye models was a robust procedure for IOL power calculation. The incorporation of corneal aberrations is crucial in post-LASIK eyes, primarily because of the elevated corneal spherical aberration.

FINANCIAL DISCLOSURE

Mrs. Canovas and Dr. Artal hold a provisional patent application on the ray-tracing procedure. Mrs. Canovas is an employee of Abbott Medical Optics Groningen B.V. No other author has a financial or proprietary interest in any material or method mentioned.

Visual performance of Acrysof ReSTOR compared with a monofocal intraocular lens following implantation in cataract surgery

The aim of this study was to compare the visual performance of Acrysof ReSTOR and Acrysof Natural intraocular lenses (IOLs) following cataract surgery. A randomized prospective study was performed in which 64 eyes (51 patients) were divided randomly into two groups. Monofocal IOLs (Acrysof Natural) were implanted into 34 eyes (27 patients) and multifocal IOLs (Acrysof ReSTOR) were implanted into 30 eyes (24 patients) using phacoemulsification surgery. The corrected distance visual acuity, near visual acuity, pseudoaccommodation, contrast sensitivity (CS) and wavefront analysis were measured at 1 week, 1 month and 3 months after surgery. The distance vision of the monofocal and ReSTOR patients improved equally with glasses (P<0.05). A greater improvement in near vision without glasses was observed in the ReSTOR-implanted patients (P<0.01). The CS values of the multifocal IOL group were significantly lower than those of the monofocal IOL group for all spatial frequencies tested (P<0.05). The spherical aberration was significantly higher in the multifocal IOL group compared with the monofocal IOL group (P<0.05). We observed no differences in coma between the two groups. The difference in the amplitude of pseudoaccommodation between the two groups was statistically significant (-3.14±0.91 D in the ReSTOR group vs. -1.03±0.33 D in the Natural group, P<0.01). The improvement in near vision was significantly more evident in the ReSTOR patients. Compared with the monofocal IOL lens, the multifocal lens is able to increase the amplitude of pseudoaccommodation. However, increased spherical aberration may contribute to lower CS values in the multifocal IOL group.

A contralateral, randomized comparison of optimized prolate ablation and conventional LASIK for myopia with the NIDEK excimer laser platform

PURPOSE

To compare the refractive, visual acuity, topographic, and spherical aberration outcomes of LASIK using the Quest excimer laser platform with the optimized prolate ablation (OPA) profile (NIDEK Co Ltd) in one eye and conventional ablation profile in the fellow eye of the same patient.

METHODS

Thirty-seven myopic patients underwent LASIK bilaterally, with one eye randomized to receive OPA ablation (-3.88±1.42 diopters [D], range: -1.53 to -7.50 D) and the fellow eye to receive conventional ablation (-3.89±1.37 D, range: -1.75 to -7.00 D). Independent and paired t tests were used for testing differences between groups at last postoperative follow-up (6 or 12 months).

RESULTS

Postoperatively, 97% (32/33) of OPA eyes and 94% (31/33) of conventional eyes saw 20/20 or better without correction (P>.05). No eyes lost 2 or more lines of distance corrected visual acuity. Manifest refraction spherical equivalent was -0.16 D in the OPA group and -0.05 D in the conventional group (P>.05). Ocular spherical aberration was -0.003 μm in the OPA group and +0.102 μm in the conventional group (P<.05). Corneal asphericity was statistically lower after OPA (0.07±0.26) compared to conventional ablation (0.30±0.26) (P<.001). The mean programmed optical zone and achieved postoperative horizontal diameter of the effective optical zone were statistically significantly larger in the OPA group (P<.05).

CONCLUSIONS

Postoperative visual acuity and refractive outcomes were similar between groups. Laser in situ keratomileusis using the OPA profile for the correction of myopia induced significantly less corneal and ocular spherical aberration, resulted in normal postoperative asphericity in 94% of eyes, and larger horizontal diameter of the effective optical zone compared to the conventional profile.