Corneal asphericity after hyperopic laser in situ keratomileusis

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.

Investigating the topographic effect of epithelium in myopic eyes with subtle topographic preoperative abnormalities

PURPOSE

To explore the topographic effect of the epithelium in keratoconus suspected (KCS) and in normal Placido classified corneas.

SETTING

Rothschild Foundation, Paris, France.

DESIGN

Prospective interventional case series.

METHODS

Anterior corneal specular Placido topography using OPD-Scan II was performed in 97 eyes of 67 patients undergoing photorefractive keratectomy for myopia, before and after epithelium removal. The differences in axial keratometry, asphericity, and astigmatism were computed.

RESULTS

After epithelial peeling, some Placido-normal classified corneas became KCS. Therefore, we have subdivided this group into 2 groups: one of normal classified corneas which stayed normal after epithelium removal (Group NN) and another of corneas that became KCS classified (Group NK). The mean difference in axial mean keratometry in the third central millimeter rings was +0.50 ± 0.24 diopters (D), 0.69 ± 0.31 D, and 0.49 ± 0.35 D and the mean difference in the magnitude of epithelial-induced astigmatism in the first central millimeter ring was 0.37 D × 89 degrees (positive cylinder), 0.54 D 86 degrees, and 0.52 D 86 degrees, respectively, in Group NN, NK, and KK (KCS corneas that stayed KCS). These differences were significant ( P < .0001). Preoperative keratometry was the only predictive factor differentiating Group NN from NK ( P < .001).

CONCLUSIONS

The epithelial layer tended to reduce the magnitude of the Bowman layer's astigmatism, prolateness, and keratometry, more importantly in Group NK. In the KK group, we found a similar trend as in normal eyes (Group NN). The epithelium would be able to mask Bowman layer's irregularities until a certain degree of severity.

Comparison of Visual Outcomes and Higher-order Aberrations Between FS-LASIK and SMI-LIKE for Moderate to High Hyperopia: A 2-Year Result

PURPOSE

The aim of the study was to evaluate and compare the long-term visual outcomes and higher-order aberrations (HOAs) between femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small-incision lenticule intrastromal keratoplasty (SMI-LIKE) in the correction of moderate to high hyperopia.

METHODS

In this study, 16 subjects (20 eyes) underwent FS-LASIK and 7 subjects (10 eyes) underwent SMI-LIKE. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, mean keratometry (Km), anterior asphericity (Q), and HOAs preoperatively and 2 years postoperatively were obtained in both procedures.

RESULTS

The efficacy indices of the FS-LASIK group and the SMI-LIKE group were 0.85 ± 0.14 and 0.87 ± 0.17, respectively. The safety indices of the FS-LASIK and SMI-LIKE groups were 0.99 ± 0.15 and 1.08 ± 0.24, respectively. No significant difference in safety index or efficacy index was found between the FS-LASIK and SMI-LIKE groups (all P > 0.05). The correlation coefficient of the attempted versus achieved spherical equivalent postoperatively was 0.69 ( P < 0.01) and 0.89 ( P < 0.01) in the FS-LASIK group and SMI-LIKE groups, respectively. The front Km, negative Q value, negative spherical aberrations (SAs), coma, and total HOAs significantly increased postoperatively in the 2 groups ( P < 0.05). The FS-LASIK group had greater changes in Q value and SA postoperatively than the SMI-LIKE group ( P < 0.01).

CONCLUSIONS

SMI-LIKE had similar safety and efficacy to FS-LASIK in the correction of moderate to high hyperopia. However, SMI-LIKE may equip better visual quality postoperatively for its lower Q value and SA changes than FS-LASIK.

Computational simulation of the optical performance of an EDOF intraocular lens in post-LASIK eyes

PURPOSE

To evaluate computationally the optical performance of AcrySof IQ Vivity extended depth-of-focus (EDOF) intraocular lenses (IOLs) in post-laser in situ keratomileusis (LASIK) eyes.

SETTING

Visual Optics and Biophotonics Laboratory, Madrid, Spain.

DESIGN

Experimental study.

METHODS

Computer pseudophakic eye models were implemented using reported post-LASIK corneal aberrations (refractive corrections from -7.5 to +4.5 diopters [D]) and virtually implanted with monofocal (AcrySof IQ) or EDOF (AcrySof IQ Vivity) IOLs. Retinal image quality was quantified through visual Strehl (VS). The depth of focus (DOF) was calculated from the through-focus VS curves. Halos were estimated from the light spread in the image of a pinhole. Those quantitative parameters were obtained for 5.0 and 3.0 mm pupil diameters.

RESULTS

Simulated virgin eyes showed VS of 0.89/0.99 with monofocal IOLs and 0.74/0.52 with EDOF IOLs for 5.0/3.0 mm pupils at best focus. VS decreased with induced spherical aberration (SA) by 25% and with induced SA + coma by 61% on average (3.0 mm pupils). The DOF was 2.50 D in virgin eyes with EDOF IOLs, 1.66 ± 0.30 and 2.54 ± 0.31 D ( P < .05) on average in post-LASIK eyes for 3.0 mm pupils, monofocal and EDOF IOLs, respectively. Halos were more sensitive to SA induction for 5.0 mm pupils, and induction of positive SA (myopic LASIK) resulted in reduced halos with the EDOF when compared with the monofocal IOLs, by 1.62 (SA) and 1.86 arc min (SA + coma), on average.

CONCLUSIONS

Computer post-LASIK pseudophakic eye models showed that the DOF was less dependent on the presence of SA and coma with EDOF IOLs and that halos were reduced with EDOF IOLs compared with the monofocal IOL for a range of SA.

Visual performance and impact of residual refractive errors with trifocal intraocular lenses of different aspheric design

BACKGROUND

To assess the visual quality and the tolerance to low refractive errors of two trifocal intraocular lenses (IOL) with different amounts of spherical aberration (SA).

METHODS

The study included patients having bilateral implantation of the AcrySof® IQ PanOptixTM (aberration-correcting) or the RayOneTM (aberration-free) Trifocal IOL. Three months after the surgery patients underwent: monocular/binocular and uncorrected/corrected distance visual acuity (VA) and binocular defocus curves. Binocular contrast sensitivity (CSF) and subjective halo perception were assessed with the best distance correction (CDVA), with a positive defocus of + 0.50D and with a negative defocus of -0.50D. Patient's satisfaction was evaluated with the Catquest9-SF questionnaire.

RESULTS

This study included 54 eyes (28 with PanOptix and 26 with RayOne) of 27 patients. Both groups achieved corrected/uncorrected and monocular/binocular distance VA values better than 0.0 logMAR (1.0 decimal) with no statistically significant differences between them (p > 0.05 for all cases). Defocus curves showed a VA of 0.1 logMAR or better between -2.5 and + 1.0D with no differences between groups (p > 0.05 at all distances). Overall CSF values remained stable under the induced residual refractions for both groups. The halo effect remained stable for the PanOptix group but increased with myopization in the RayOne group (p = 0.02). The questionnaire showed high rates of patient's satisfaction with no differences between groups.

CONCLUSION

Both lenses showed overall good visual outcomes and offered high rates of patient's satisfaction. Moreover, in normal patients with trifocal IOLs, the combination of residual refractive errors and certain amounts of SA may increase some visual disturbances.

Trifocal IOL Implantation in Eyes With Previous Laser Corneal Refractive Surgery: The Impact of Corneal Spherical Aberration on Postoperative Visual Outcomes

PURPOSE

To analyze corneal aberrations and factors affecting visual outcomes after implantation of a trifocal intraocular lens (IOL) in eyes previously treated with laser corneal refractive surgery.

METHODS

This retrospective case series included 222 consecutive eyes implanted with the trifocal FineVision Micro-F IOL (PhysIOL) after laser corneal refractive surgery. The series was divided into two groups according to safety outcomes after lensectomy: eyes with loss of one or more lines of corrected distance visual acuity (CDVA) [n = 59, 26.5%]) (failed eyes group) and eyes with no loss or gain in CDVA lines (n = 163, 73.4%]) (successful eyes group). Distribution of tomographic corneal aberrations (spherical aberration [Z⁴₀], comatic and root mean square of higher order aberrations [RMS-HOA]), laser corneal refractive surgery error, kappa angle, and CDVA after laser corneal refractive surgery were compared among both groups.

RESULTS

Mean CDVA after lensectomy was 0.15 ± 0.07 logMAR (range: 0.05 to 0.30 logMAR) versus 0.03 ± 0.04 logMAR (range: 0.00 to 0.15 logMAR) in the failed and successful eyes groups, respectively (P < .001). Comparison of both groups showed that failed eyes had a statistically significantly higher grade of hyperopic laser corneal refractive surgery than successful eyes measured as mean sphere (+0.71 ± 3.10 diopters [D] [range: -7.75 to +6.00 D] vs -0.46 ± 3.70 D [range: -10.75 to +6.00 D], P < .01), spherical equivalent (+0.27 ± 3.10 D [range: -8.00 to +5.50 D] vs -0.97 ± 3.60 D [range: -12.50 to +4.90 D], P < .05), and percentage of hyperopic laser corneal refractive surgery (64% vs 43.5%, P < .05). Corneal aberration analysis showed that mean Z⁴₀ values were significantly more negative in the failed eyes group than in the successful eyes group (+0.07 ± 0.40 mm [range: -0.82 to +0.65 mm] vs +0.18 ± 0.37 mm [range: -0.79 to +0.87 mm], P < .05). Laser corneal refractive surgery cylinder was distributed homogeneously between both groups, as well as coma and RMS-HOA, kappa angle, and CDVA after laser corneal refractive surgery that were not statistically significant.

CONCLUSIONS

Surgeons should consider tomographic corneal spherical aberration after implantation of a trifocal IOL in eyes after keratorefractive surgery, particularly in eyes previously treated with hyperopic laser corneal refractive surgery, to prevent loss of lines of visual acuity after lensectomy. [J Refract Surg. 2022:38(4):222-228.].

Corneal asphericity and related factors in the geriatric population: A population-based study

PURPOSE

To determine the distribution of the corneal asphericity coefficient (Q value) and related factors in an Iranian geriatric population.

METHODS

This population-based study was conducted in 2019 in Tehran, using stratified multistage random cluster sampling. The study population was ≥60 years of age. Participants underwent corneal imaging using a Pentacam HR. Mean keratometry, corneal astigmatism, central corneal thickness, anterior chamber depth and the overall anterior and posterior Q values (for 8 mm chord diameter) were recorded. Axial length measurements were performed using the IOL Master 500.

RESULTS

2457 eyes of 2457 individuals were analysed. The mean age was 67.3 ± 5.82 years and 1479 (60.2%) were female. The mean Q value for the anterior corneal surface was -0.35 ± 0.17 (95% CI: -0.35 to -0.34). The anterior Q value showed a statistically significant inverse relationship with axial length and mean keratometry, and a significant direct association with anterior chamber depth and corneal astigmatism. The mean posterior Q value was -0.41 ± 0.15 (95% CI: -0.42 to -0.40). The posterior Q value had a significant direct relationship with age, anterior chamber depth, mean keratometry and corneal astigmatism.

CONCLUSION

The corneal Q values in this geriatric Iranian population were more negative than the values reported in most previous studies. Corneal asphericity was greater affected by ocular biometry and corneal curvature than demographic factors and refractive status.

Recent advances in measurement of monochromatic aberrations of human eyes

The field of aberrations of the human eye is moving rapidly, being driven by the desire to monitor and optimise vision following refractive surgery. It is important for ophthalmologists and optometrists to have an understanding of the magnitude of various aberrations and how these are likely to be affected by refractive surgery and other corrections. In this paper, I consider methods used to measure aberrations, the magnitude of aberrations in general populations and how these are affected by various factors (for example, age, refractive error, accommodation and refractive surgery) and how aberrations and their correction affect spatial visual performance.

Corneal power changes with Scheimpflug rotating camera after hyperopic LASIK

To evaluate surgically induced refractive change (SIRC) by manifest refraction and corneal power changes using an automated keratometer and Scheimpflug rotating camera, and to find the best keratometric measurements reflecting SIRC after hyperopic laser-assisted in situ keratomileusis (LASIK).This retrospective study included 18 eyes of 18 patients undergoing hyperopic LASIK using the Schwind Amaris 750S excimer laser. All measurements were performed preoperatively and 12 months postoperatively. Cycloplegic manifest refractions were performed and keratometric measurements were obtained via an RK-5 automated keratometer and a Pentacam rotating Scheimpflug camera. Sim K, true net power (TNP), and total corneal refractive power (TCRP) at 2.0 to 5.0 mm were analyzed using a Scheimpflug camera.The mean manifest refractive changes in the spherical equivalent (SE) at the corneal plane were 2.32 ± 1.65 D at 12 months postoperatively. The refractive power changes by the automated keratometer and Sim K were significantly less than SIRC (P = .043 and P = .048, respectively). Both TNP and the TCRP in the 5.0 mm zone produced lesser mean differences with SIRC (0.05 D and 0.06 D) and showed closer agreements with SIRC on Bland-Altman plots and higher correlation coefficients with SIRC.Corneal power measured on the anterior corneal surface underestimated SIRC. TCRP at the 5.0 mm zone provided by a Pentacam Scheimpflug camera reflected the SIRC accurately and precisely, and would be applicable for prediction of intraocular power before cataract surgery and follow-up measurement of corneal refractive power.

Changes of Functional Optical Zone After LASIK for Hyperopia and Hyperopic Astigmatism

PURPOSE

To evaluate which factors may influence the size of the postoperative functional optical zone after hyperopic LASIK.

METHODS

Thirty-three eyes with a mean spherical equivalent of +3.55 ± 1.28 diopters (D) underwent LASIK with a Technolas 217 C-LASIK laser (Bausch & Lomb Surgical, Munich, Germany). After 1 week and 1, 4, and 12 months, the authors examined refraction, corneal refractive power by means of computerized videokeratography (Technomed C-Scan; Baesweiler, Germany), and uncorrected/corrected distance visual acuity (UDVA/CDVA). According to the degree of hyperopia, they were divided into low hyperopia (spherical equivalent ≤ 3.00 D) and high hyperopia (spherical equivalent > 3.00 D) groups.

RESULTS

One year postoperatively, 82% of all eyes had a UDVA of 0.5 or better; in 88%, the spherical equivalent did not deviate more than 1.00 D from the attempted value. Three eyes were slightly undercorrected. After an initial overcorrection (-0.27 D) with subsequent regression, the refraction remained stable at +0.17 D from the fourth postoperative month (low hyperopia group: +0.14 D; high hyperopia group: +0.19 D after 1 year). After 1 year, the functional optical zone diminished by 32%; the reduction was more pronounced in eyes with higher hyperopia: -1.85 ± 1.09 mm (range: +0.5 to -3.4 mm) in the low hyperopia group (P < .0001) and -2.25 ± 1.24 mm (range: +1 to -3.9 mm) in the high hyperopia group (P < .0001). Preoperative spherical equivalent and preoperative corneal refractive power affected the postoperative size of the functional optical zone additively.

CONCLUSIONS

An expected small functional optical zone in high hyperopia may not be regarded as a compelling exclusion criterion, but can induce possible side effects such as glare and halos. [J Refract Surg. 2018;34(7):476-481.].

Age-Related Variations in Corneal Asphericity and Long-Term Changes

PURPOSE

Corneal front-surface asphericity is directly related with the optical quality of the eye and with contact lenses fitting. The purpose of this study was to evaluate the corneal asphericity as a function of age, sex, and refractive error measured with autokeratometry and corneal topography and its long-term changes (5- to 10-year period).

METHODS

The asphericity and corneal curvature were obtained with the autorefractometer/autokeratometer NIDEK ARK-700A and with the videokeratoscope MODI 2.0 and compared. Corneal asphericity was retrospectively analyzed with NIDEK ARK-700A. The longitudinal study of asphericity was conducted with the same device between 2 appointments within an interval of 5 to 10 years.

RESULTS

NIDEK ARK-700A showed agreement of asphericity values with those of MODI 2.0 (P=0.172) for a 7-mm diameter chord. The mean Q value of 1,484 right eyes (58.6% female), with a mean age of 40.2±18.4 years, was -0.24±0.12. No differences were found for Q value between sexes (P=0.424), age groups (P=0.268), and refractive error groups (P=0.107). The longitudinal analysis of corneal asphericity in 190 eyes (62.1% female) over a mean period of 5.9±1.4 years showed no significant differences in the Q value (0.00±0.08, P=0.813) over time. However, 14% showed asphericity changes of ±0.10 or higher while 86% of the subjects showed a change below ±0.10.

CONCLUSIONS

The mean Q value observed in this study agrees with the average values of a white population and contributes to slightly reduce the positive spherical aberration of the eye. For the large majority of this population, the asphericity did not show significant changes within a period of 5 to 10 years, but significant changes can be observed in some patients.

Comparison of ocular higher-order aberrations after SMILE and Wavefront-guided Femtosecond LASIK for myopia

Background

To compare changes in higher-order aberrations (HOAs) following small incision lenticule extraction (SMILE) and wavefront-guided femtosecond laser-assisted in situ keratomileusis (WFG FS-LASIK), and to investigate correlations between preoperative spherical equivalence (SE) and components of HOAs affecting visual quality.

Methods

Sixty-five myopic eyes from 38 patients were enrolled in the study retrospectively, either having undergone SMILE or WFG FS-LASIK. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive error, and individual Zernike coefficients of 3rd- to 6th-order HOAs were measured before and 3 months after the surgeries and were compared using the Mann-Whitney test or Student’s t-test. Additional generalized estimating equation analyses (GEE) were used to control for within-subject biases in individual Zernike coefficients between the right and left eyes of the same patients.

Results

There was no significant difference in UDVA or CDVA after WFG FS-LASIK (Mean ± SD: −0.02 ± 0.07 and −0.04 ± 0.22 respectively, in logMAR) and after SMILE (−0.01 ± 0.06 and −0.04 ± 0.04 respectively). However, greater vertical coma aberration was found after SMILE (p = 0.036). Preoperative SE was correlated to induced horizontal coma (r = −0.608, p = 0.001) in WFG FS-LASIK, and correlated to induced vertical coma (r = −0.459, p = 0.003) in SMILE.

Conclusions

Both SMILE and WFG FS-LASIK can achieve planned visual outcomes in correcting myopia and myopic astigmatism. However, higher vertical coma was shown in SMILE than WFG FS-LASIK which might be a potentially impact factor for patients’ vision under certain lighting conditions and needs further investigation.

Hyperopic Q-optimized algorithms: a theoretical study on factors influencing optical quality

In this work, we analyze the way in which pupil size, optical zone, and initial hyperopic level influence optical quality for hyperopic Q-optimized corneal refractive surgery. Different Q-optimized algorithms and the Munnerlyn formula were tested to analyze the optical quality of the final retinal image for initial hyperopic errors from 1D to 5D. Three optical zones (5.5, 6, and 6.5 mm) and two pupil diameters (5 and 7 mm) were considered. To evaluate optical quality, we computed the modulation transfer function (MTF) and the area under MTF (MTFa). Q-optimized values at around Q = -0.18 were found to provide the best optical quality for most of the conditions tested. This optimum final asphericity for hyperopic ablation was not depending on the degree of hyperopia corrected, the optical zone or the pupil size being this information important for clinical practice.

Role of percent peripheral tissue ablated on refractive outcomes following hyperopic LASIK

Objectives

To determine the effect of hyperopic laser in situ keratomileusis (H-LASIK) on corneal integrity, by investigating relationships between proportionate corneal tissue ablated and refractive outcomes at 3 months.

Methods

18 eyes of 18 subjects treated with H-LASIK by Technolas 217c Excimer Laser were included in the study. Orbscan II Topography System was used to determine corneal volume and pachymetry 3mm temporally (3T). The volume of corneal tissue ablated was determined from the laser nomogram. Univariate associations between age, treatment, corneal volume, overall proportion of tissue removed, proportion of tissue removed at 3T, residual bed thickness at 3T and refractive outcomes 3 months post-LASIK were examined and independent factors associated with refractive outcomes determined using linear regression models.

Results

At 3 months post-LASIK, the mean difference to expected refractive outcome was -0.20 ± 0.64 (Range -2.00 to +1.00). In univariate analysis, difference to expected refractive outcome was associated with proportion of tissue removed at 3T (P<0.01, r = -0.605) and total number of pulses (P< 0.05, r = -0.574). In multivariable analysis, difference to expected refractive outcome was associated with the proportion of tissue removed at 3T only.

Conclusion

Subjects undergoing H-LASIK, may present as either over or under-corrected at 3 months. The proportion of tissue removed at 3T was the single significant determinant of this outcome, suggesting unexpected biomechanical alterations resulting in corneal steepening. Future hyperopic LASIK procedures could consider proportionate volume of corneal tissue removed at 3T in addition to laser nomograms to achieve improved refractive outcomes.

Factors Predicting the Need for Retreatment After Laser Refractive Surgery

PURPOSE

To identify the potential risk factors that increase the likelihood of requiring retreatment after refractive surgery.

METHODS

This retrospective study included patients who underwent laser in situ keratomileusis or photorefractive keratectomy between January 2005 and December 2012 at the Care-Vision Laser Centers, Tel-Aviv, Israel. Patients were divided into 2 groups according to whether they underwent additional refractive surgery (retreatment) during the study period.

RESULTS

Overall, 41,504 eyes (n = 21,313) were included in the final analysis of this study. Throughout the study period, there was a significant reduction in the 2-year annual retreatment rates with a decline from 4.52% for primary surgeries done in 2005 to 0.18% for surgeries performed in 2012 (quadratic R = 0.96, P < 0.001). The retreatment group had significantly higher preoperative age, maximum keratometric power, sphere, cylinder, and better best-corrected visual acuity. They were more likely to have preoperative hyperopia, photorefractive keratectomy as opposed to laser in situ keratomileusis, intraoperative higher humidity conditions and lower temperature, and higher ablation depths. Significant differences in retreatment rates were found between the 5 high-volume surgeons (>1500 procedures performed) ranging from 0.48 to 3.14% (P < 0.0001). Multiple logistic regression analysis demonstrated that age, astigmatism, hyperopia, temperature, and surgeon's experience all significantly affected the need for retreatment.

CONCLUSIONS

The following factors significantly increase the need for refractive retreatment: older preoperative age, higher degrees of astigmatism, hyperopia, colder operating room temperature, and less surgeon experience. Some of these factors may be incorporated into nomograms to reduce future retreatment rates.

Laser in Situ Keratomileusis for High Hyperopia with Corneal Vertex Centration and Asymmetric Offset

Purpose

To investigate refractive outcomes and induction of corneal higher order aberrations (HOA) in eyes that underwent laser-assisted in situ keratomileusis (LASIK) for high hyperopia correction using an aberration neutral profile with corneal vertex centration and asymmetric offset.

Methods

A total of 24 consecutive patients (38 eyes) who underwent LASIK by one surgeon using AMARIS 750S excimer laser and a Carriazo-Pendular microkeratome for flap creation were retrospectively analyzed. Eyes targeted for plano and with correction in the maximum hyperopic meridian strictly higher than +4D were included in the retrospective analysis. Patients were reviewed at 1, 3, and 6 months postoperatively. Postoperative monocular corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA), manifest refraction, and corneal wavefront aberrations were compared with respective preoperative metrics.

Results

Mean preoperative spherical equivalent and refractive astigmatism was +4.07 ± 0.90 D and 1.37 ± 1.26 D, respectively, reducing to +0.28 ± 0.58D (p<0.0001) and 0.49 ± 0.47 D (p = 0.0001) at the last postoperative visit. Six months postoperatively, 78% of eyes achieved a UDVA of 20/25 or better. No eye lost more than 2 Snellen lines of CDVA at any follow-up. There was a statistically significant induction of vertical trefoil (+0.104 ± 0.299 µm, p<0.05), vertical coma (-0.181 ± 0.463 µm, p<0.01), horizontal coma (+0.198 ± 0.663 µm, p<0.05), spherical aberration (-0.324 ± 0.281 µm, p<0.0001), secondary vertical trefoil (+0.018 ± 0.044 µm, p<0.01), and secondary horizontal coma (+0.026 ± 0.083 µm, p<0.05)

Conclusions

Laser-assisted in situ keratomileusis for high hyperopia using corneal vertex centration with asymmetric offset results in significant improvement in refraction and visual acuity although affected by significant induction of some higher order aberrations.

Cryopreservation of extracted corneal lenticules after small incision lenticule extraction for potential use in human subjects

Purpose:

To describe the technique of cryopreservation of corneal lenticules extracted after small incision refractive lenticule extraction (ReLEx SMILE) and initial results of femtosecond laser intrastromal lenticular implantation for hyperopia.

Methods:

Lenticules were collected from patients undergoing ReLEx SMILE for the correction of myopia and subjected to a tissue processing technique and cryopreservation. These lenticules were subsequently used to treat 8 hyperopic eyes and 1 aphakic eye. A femtosecond laser was used to create a pocket into each patient's cornea, followed by implantation of a cryopreserved lenticule. The patients were monitored through follow-up examinations for a mean 155.4 days (38–310 days).

Results:

The mean interval from storage of lenticules to removal from liquid nitrogen was 96 days (range, 19–178 days). Mean spherical equivalent of hyperopic eyes treated was +4.50 ± 1.1 diopter (D). Mean keratometry and pachymetry changed from preoperative 43.9 D and 531.6 μm to 47.4 D and 605.2 μm, respectively, postoperatively. Mean residual spherical equivalent for hyperopic eyes was +0.6 D and +4.1 D for the aphakic eye. None of the eyes showed evidence of rejection or loss of best-corrected visual acuity at the end of the follow-up period.

Conclusions:

The cryopreservation technique seems to be a safe method of long-term storage of refractive lenticules extracted after ReLEx SMILE for use in allogeneic human subjects. It may potentially be a safe and effective alternative to excimer laser ablation for hyperopia because of the low risks of regression, haze, flap-related complications, postoperative dry eye, and higher-order aberrations.

Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: CTRI/2014/01/004331.

Pilot study of hyperopic LASIK using the solid-state laser technology

BACKGROUND

To evaluate and report the visual, refractive, and aberrometric outcomes of LASIK for the correction of low to moderate hyperopia in a pilot group using a commercially available solid-state laser

METHODS

Prospective pilot study including 11 consecutive eyes with low to moderate hyperopia of six patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd., currently CV Laser). Visual, refractive, and aberrometric changes were evaluated. Potential complications were evaluated as well. Mean follow-up time was 6.6 months (range, 3 to 11 months).

RESULTS

A significant improvement in LogMAR uncorrected distance visual acuity (UDVA) was observed postoperatively (p = 0.01). No significant change was detected in LogMAR corrected distance visual acuity (CDVA) (p = 0.21). Postoperative LogMAR UDVA was 0.1 (about 20/25) or better in ten eyes (90.9 %). Mean overall efficacy and safety indices were 1.03 and 1.12. Postoperatively, no losses of lines of CDVA were observed. Postoperative spherical equivalent was within ± 1.00 D in ten eyes (90.9 %). With regard to aberrations, no statistically significant changes were found in higher order and primary coma RMS postoperatively (p ≥ 0.21), and only minimal but statistically significant negativization of primary spherical aberration (p = 0.02) was observed. No severe complications were observed.

CONCLUSION

LASIK surgery using the solid-state laser technology seems to be a useful procedure for the correction of low to moderate hyperopia, with minimal induction of higher order aberrations.

Wavefront analysis and Zernike polynomial decomposition for evaluation of corneal optical quality

Wavefront-guided excimer laser refractive surgery and new customized intraocular lens and contact lens designs are major clinical applications of corneal wavefront analysis. Other therapeutic applications include corneal disorders, conventional excimer laser refractive surgery, incisional techniques and cataract surgery, corneal transplantation, intrastromal corneal ring segment implantation, and crosslinking therapy. Basic data regarding corneal wavefront aberrations, such as distribution in the population and changes with aging, are essential for understanding the nature of each aberration and correcting it. Corneal aberrometry also improved our comprehension of the optical effects of the aforementioned topics while helping us assess the success of the procedures. Zernike polynomials are representations of the higher- and lower-order aberrations of the cornea, allowing a mathematical approach to their determination. Polynomials are used to model individual components of the wavefront in familiar terms. This article reviews the current knowledge of the wavefront aberrations of the human cornea and analyzes studies in the fields of anterior segment surgery and/or therapy, diseases, and optical quality in the context of this knowledge.

Corneal asphericity and spherical aberration after refractive surgery

PURPOSE

To evaluate changes in corneal asphericity (Q) and spherical aberrations after refractive surgery using Scheimpflug imaging.

SETTING

University of California, San Diego, Shiley Eye Center, La Jolla, California, USA.

DESIGN

Cohort study.

METHODS

After wavefront-guided laser in situ keratomileusis, patients within ± 0.50 diopter of plano and with an uncorrected distance visual acuity of at least 20/20 were evaluated. The Q values and corneal spherical aberration Zernike values were obtained using Scheimpflug imaging preoperatively and 1 to 3 months postoperatively.

RESULTS

The study enrolled 177 myopic eyes and 32 hyperopic eyes. The mean Q value was -0.28 ± 0.11 (SD) and -0.22 ± 0.15, respectively, preoperatively and +0.35 ± 0.44 and -0.64 ± 0.31, respectively, postoperatively. The asphericity change was highly correlated with preoperative spherical equivalent (r(2) = 0.81; P ≤ .001). The mean corneal spherical aberration was +0.21 ± 0.08 μm in myopic eyes and +0.36 ± 0.11 μm in hyperopic eyes preoperatively and +0.36 ± 0.17 μm and 0.00 ± 0.29 μm, respectively, postoperatively. The corneal spherical aberration changes were correlated with the amount of preoperative refractive error (r(2) = 0.34; P < .001). There was a tendency for Q values and spherical aberrations to become more positive after myopic ablation and more negative after hyperopic ablation.

CONCLUSIONS

Myopic and hyperopic corrections induced changes in the Q value and spherical aberrations in opposite directions (ie, positive and negative, respectively). The changes depended on the magnitude of the refractive correction.

FINANCIAL DISCLOSURE

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

Analysis of optimized profiles for 'aberration-free' refractive surgery

PURPOSE

To provide a model of an aberration-free profile and to clinically evaluate the impact of treatments based upon these theoretical profiles in the post-operative cornea.

METHODS

Aberration-free profiles were deduced from the Zernike expansion of the difference between two corneal cartesian-ovals. Compensation for the focus-shift effects of removing corneal tissue were incorporated by preserving the location of the optical focus of the anterior corneal surface. Simulation of the surgical performance of the profile was performed by means of simulated ray-tracing through a cornea described by its anterior surface and pachymetry. Clinical evaluation was retrospectively analysed in terms of visual outcomes, corneal wavefront aberration and asphericity changes at 3-month follow-up compared to the baseline on 100 eyes treated for compound myopic astigmatism.

RESULTS

The proposed 'aberration-free' profiles theoretically preserve aberrations, becoming more oblate asphericity after myopic treatments, and more prolate after hyperopic ones. In the clinical evaluation, 94% of eyes were within +/-0.50 D of emmetropia. BSCVA improved significantly (p < 0.001). Induced corneal aberrations at 6-mm were below clinically relevant levels: 0.123 +/- 0.129 microm for HO-RMS (p < 0.001), 0.065 +/- 0.128 microm for spherical aberration (p < 0.001) and 0.058 +/- 0.128 microm for coma (p < 0.01), whereas the rate of induced aberrations per achieved D of correction were -0.042, -0.031, and -0.030 microm D(-1) for HO-RMS, SphAb, and coma (all p < 0.001). Induction of positive asphericity correlated to achieved correction (p < 0.001) at a rate 3x theoretical prediction.

CONCLUSIONS

'Aberration-free' patterns for refractive surgery as defined here together with consideration of other sources of aberrations such as blending zones, eye-tracking, and corneal biomechanics yielded results comparable to those of customisation approaches. Having close-to-ideal profiles should improve clinical outcomes decreasing the need for nomograms, and diminishing induced aberrations after surgery.

Laser in situ keratomileusis for mixed astigmatism using a modified formula for bitoric ablation

PURPOSE

To evaluate the results of treatment of mixed astigmatism with laser in situ keratomileusis (LASIK) by means of a modified Chayet formula for bitoric ablation and personalized nomogram calculations.

METHODS

A retrospective study was conducted in 19 consecutive eyes of 13 patients who underwent LASIK treatment of mixed astigmatism with a mean sphere of +1.63-/+1.23 D and a mean cylinder of -3.55-/+1.17 D. The authors used the Schwind ESIRIS Laser platform. The ablation was shifted from the pupil center to the vertex normal of the cornea.

RESULTS

Three months postoperatively, the mean sphere was 0.08-/+0.24 D and the mean astigmatism -0.45-/+0.31 D. At 3 months, an uncorrected visual acuity (UCVA) of 20/50 or better could be found in 100% of the eyes, and of 20/25 or better in 59%. All eyes were within -/+0.5 D spherical equivalent (SE) at 3, 6, and 12 months. No eye lost more than one line of best spectacle-corrected visual acuity (BSCVA). Postoperatively, the corneal wavefront showed a reduction of spherical aberrations and coma, which were analyzed at 4 and 6 mm pupil diameter. The postoperative higher-order aberrations decreased at 4 mm and increased at 6 mm pupil sizes after surgery.

CONCLUSIONS

Modified bitoric treatment with the Schwind ESIRIS laser showed an excellent postoperative UCVA and BSCVA with applying external nomogram adjustments. The method demonstrated good predictability, safety, and effectiveness in the treatment of mixed astigmatism.

Corneal aberrations and objective visual quality after hyperopic laser in situ keratomileusis using the Esiris excimer laser

PURPOSE

To evaluate the changes in visual performance and ocular optical quality after hyperopic laser in situ keratomileusis (LASIK) using the Esiris excimer laser (Schwind eye-tech-solutions).

SETTING

Vissum-Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

Excimer laser surgery was performed with the Esiris laser in 51 eyes of 29 patients with hyperopia or hyperopic astigmatism. The follow-up was 6 months. Changes in visual acuity, refraction, and corneal and ocular wavefront aberrations (6.0 mm pupil) were recorded and analyzed.

RESULTS

The mean preoperative sphere was +4.45 diopters (D)+/-1.08 (SD) (range +2.50 to +7.25 D) and the mean preoperative cylinder, -0.55+/-0.36 D (range 0.00 to 1.00 D). Ten eyes (19.61%) had a LASIK enhancement during the follow-up for the correction of the residual refractive error and were excluded from the refractive analysis. Of the 41 remaining eyes, 95.12% had the same or improved distance best spectacle-corrected visual acuity (BSCVA) 6 months after surgery; 90.25% had no change or a gain of lines of near BSCVA. Moreover, 80.50% of eyes were within +/-0.50 D of emmetropia. Regarding corneal aberrations, statistically significant changes were observed in higher-order aberrations (HOAs), coma-like aberrations, and the primary spherical aberration coefficient Z(4,0), which changed from positive to negative values (all P<.01). Regarding total ocular aberrations, statistically significant changes were observed in total and higher-order root-mean-square values (P<.01).

CONCLUSIONS

Hyperopic LASIK using the Esiris excimer laser for the correction of 2nd-order aberrations was safe and effective. Ocular and corneal HOAs increased significantly postoperatively.

Topographic changes after hyperopic LASIK with the SCHWIND ESIRIS laser platform

PURPOSE

To analyze and compare refractive power changes with topographic changes after hyperopic LASIK using the ESIRIS laser platform.

METHODS

Sixty-six consecutive eyes of 37 patients were evaluated retrospectively. Outcomes were evaluated at 3 months. In all cases, standard examinations including pre- and postoperative topographic and corneal wavefront analysis with a Keratron topographer were performed. Preoperative mean spherical equivalent was +/- 2.74 diopters (D) with a mean cylinder of 0.67 D. The ESIRIS excimer laser system was used to perform ablations. Topographic changes of Maloney index, simulated keratometry (sim-K), and K-reading at 5 and 7 mm were evaluated.

RESULTS

Ninety-two percent of eyes were within +/- 0.50 D manifest refraction at 3 months postoperatively. Changes in refraction, Maloney indices, and sim-K indices after surgery were strongly correlated with the intended correction. Induction of negative corneal spherical aberrations and increased prolate asphericity was correlated with the achieved defocus correction. No other Zernike mode was significantly correlated. Topographically, an overcorrection within the central 3 mm and a gradual peripheral undercorrection also was observed.

CONCLUSIONS

Analyzing the topographic maps, the corneal power change of the Maloney indices correlated with the intended correction. After hyperopic LASIK, an overcorrection was observed in the 3-mm central zone, and progressive undercorrections were observed in the 5- and 7-mm zones.

Four corneal presbyopia corrections: Simulations of optical consequences on retinal image quality

PURPOSE

To investigate the possibility of multifocal or aspherical treatment of the cornea with optical ray tracing.

SETTING

Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland.

METHODS

The optical consequences of 4 corneal shapes-global optimum (GO) for curvature and asphericity, central steep island (CSI), decentered steep island (DSI), and centered steep annulus (CSA)-for presbyopia correction were analyzed using a modified Liou-Brennan eye model and ray tracing with a commercial optic design software (Zemax, Zemax Development Corp.). The ocular optical configuration for far vision was a point light source at a distance of 5 m, 1 degree up, and a pupil diameter of 5.0 mm and for near vision, 0.4 m distance, 1 degree up, and a pupil diameter of 2.5 mm. The curvature radius (R) of the cornea and its asphericity (Q) were used as operands to optimize (simultaneously for near and far vision) the quality of the retinal image described by means of the minimum spot diameter or the root-mean-square (RMS) wavefront error.

RESULTS

Starting from an emmetropic eye optimized for R and Q, the RMS wavefront error in the retina was 0.07 microm (far) and 1.42 microm (near). The GO resulted in a wavefront error of 1.42 microm (far) and 0.52 microm (near); improvement of near vision using reading glasses is possible. The CSI yielded 0.91 microm (far) and 0.13 microm (near); spectacles did not improve far or near vision. The DSI and CSA had significantly worse results for near and far vision.

CONCLUSIONS

Of the options studied, GO and CSI seemed the most promising alternatives for corneal presbyopia correction. Although reading glasses can improve near vision in GO, reading glasses did not improve near vision in CSI-treated eyes. The CSI treatment is critically dependent on centration and a reverse treatment is difficult to achieve.

Surgical Correction of Hyperopia

Surgical attempts to correct hyperopia have yielded varying results over the last 130 years. These techniques include the reshaping of the cornea through incisions, burns, or lamellar cuts with removal of peripheral tissue; the addition of central inlays; laser ablations; and the replacement of the crystalline lens. By examining the success of each surgical technique, the refractive surgeon may be able to make an informed decision on its indications and limitations, based on the specific patient's characteristics. Reporting the outcomes and complications of hyperopic surgery will help refine our approach to the management of an increasingly hyperopic and presbyopic population.

Correlations Between Central and Peripheral Changes in Anterior Corneal Topography After Myopic LASIK and Their Implications in Postsurgical Contact Lens Fitting

PURPOSE

To investigate the changes in central and peripheral anterior corneal curvatures after myopic laser in situ keratomileusis (LASIK) and to correlate them with the manifest refractive change to discuss how such results could affect post-LASIK corneal topography profiles and midterm stability and their implications in postsurgical contact lens fitting.

METHODS

Topographic and refractive data from 18 eyes of 11 patients that had undergone myopic LASIK were collected for 6 months after surgery. Short-term and midterm topographic responses were investigated and correlated with spherical equivalent manifest refractive changes.

RESULTS

There was a strong correlation between eccentricity changes and manifest refractive change 15 days after surgery (r = 0.753, P < 0.001), with no significant changes thereafter for the following 6 months (r = 0.148, P = 0.114). A strong linear relationship was found between baseline manifest refraction and changes in corneal curvature at the center (r = 0.810, P < 0.001), 4-mm chord (r = 0.895, P < 0.001), and 6-mm chord (r = 0.696, P < 0.001). Statistically significant changes were also found after the first 15 days (P < 0.005) and showed a regression effect that affects the three zones. In this case, a weaker relationship was found between curvature regression and the final refractive change for the central location (r = 0.412, P = 0.004), 4-mm chord area (r = 0.430, P = 0.003), and 6-mm chord area (r = 0.283, P = 0.023). CONCLUSIONS.: After myopic LASIK, the anterior corneal dioptric power is expected to change, on average, approximately 77% of the attempted spherical equivalent correction at the center; 60% at the 4-mm chord region, where the stronger correlation between topographic and refractive change is found; and 30% at the 6-mm chord area. The paracentral area 4 mm from the center seems to be more likely to predict baseline corneal curvature from manifest refractive change. Some degree of regression in the midterm period is expected to occur after myopic LASIK, which shows a significant correlation with the manifest refractive change. Again, this effect is more evident and more accurately predicted at the 4-mm chord area. The results of the current study are of interest for those fitting contact lenses after myopic LASIK.

A New Formula for Intraocular Lens Power Calculation After Refractive Corneal Surgery

PURPOSE

When calculating the power of an intraocular lens (IOL) with conventional methods in eyes that have previously undergone refractive surgery, in most cases the power is inaccurate. To minimize these errors, a new IOL power calculation formula was developed.

METHODS

A theoretical formula empirically adjusted two variables: 1) the corneal power and 2) the anterior chamber depth (ACD). From the average curvature of the entrance pupil area, weighted according to the Stiles-Crawford effect, the corneal power is calculated by using a relative keratometric index that is a function of the actual corneal curvature, type of keratorefractive surgery, and induced refractive change. Anterior chamber depth is a function of the preoperative ACD, lens thickness, axial length, and the ACD constant. We used our formula in 20 eyes that previously underwent refractive surgery (photorefractive keratectomy [n = 6], laser subepithelial keratomileusis [n = 3], laser in situ keratomileusis [n = 6], and radial keratotomy [n = 5]) and compared our results to other formulas.

RESULTS

Mean postoperative spherical equivalent refraction was +0.26 diopters (D) (standard deviation [SD] 0.73, range: -1.25 to +/- 1.58 D) using our formula, +2.76 D (SD 1.03, range: +0.94 to +4.47 D) using the SRK II, +1.44 D (SD 0.97, range: +0.05 to +4.01 D) with Binkhorst, 1.83 D (SD 1.00, range: -0.26 to +4.21 D) with Holladay I, and -2.04 D (SD 2.19, range: -7.29 to +1.62 D) with Rosa's method. With our formula, 60% of absolute refractive prediction errors were within 0.50 D, 80% within 1.00 D, and 93% within 1.50 D.

CONCLUSIONS

In this first series of patients, we obtained encouraging results. With a greater number of cases, all statistical adjustments related to the different types of surgery should be improved.

Optical Factors in Increased Best Spectacle-corrected Visual Acuity After LASIK

PURPOSE

To study the factors that correlate with improved best spectacle-corrected visual acuity (BSCVA) after LASIK.

METHODS

This was a nonrandomized, prospective clinical trial of 850 eyes from 480 patients undergoing LASIK for myopia, hyperopia, and mixed astigmatism. The mean preoperative spherical equivalent refraction was -3.75+/-4.82 diopters (D) (range: -13.88 to 6.00 D). From this population, 72 eyes (including 22 amblyopic eyes) from 43 patients were found to have improved BSCVA 6 months after LASIK. All patients underwent LASIK with the NAVEX platform. These eyes were analyzed to evaluate factors that correlated with improved BSCVA. Pre- and postoperative BSCVA, refraction, pupil diameter, corneal topography, asphericity (Q value), total aberrations, and higher order wavefront aberrations were analyzed. All wavefront aberrations were measured using the NIDEK Optical Path Difference Scan aberrometer (OPD-Scan) preoperatively and at 6 months postoperatively.

RESULTS

Postoperatively, the mean sphere was -0.44 1.30 D (range: -4.50 to +2.50 D). The mean increase in BSCVA was 0.15+/-0.09 logMAR. A statistically significant negative correlation was observed between the increase in BSCVA and the preoperative BSCVA (P<.01). Mixed astigmatic and highly myopic eyes are more likely to gain BSCVA after LASIK than moderately myopic (P<.05) and hyperopic eyes (P<.001). In patients with myopia, the amount of BSCVA improvement correlated with the magnitude of the correction (P<.05). The induction of spherical aberration negatively correlated with the increase in BSCVA (P<.05). There were no significant differences between normal eyes and amblyopic eyes with respect to postoperative improvement in BSCVA (P>.05).

CONCLUSIONS

Decreased preoperative BSCVA, lower total spherical aberration induction, and preoperative mixed astigmatism and high myopia correlate with an increase in BSCVA after LASIK.

Corneal irregular astigmatism after hyperopic laser in situ keratomileusis

PURPOSE

To evaluate the changes in irregular astigmatism after hyperopic laser in situ keratomileusis (LASIK).

METHODS

In a prospective case series, 15 eyes of 12 patients who had hyperopic LASIK were evaluated. Corneal topography was obtained before and after hyperopic LASIK. Corneal irregular astigmatism (asymmetry and higher-order irregularity) was calculated using Fourier harmonic analysis of the topography data.

RESULTS

Hyperopic LASIK significantly increased the asymmetry component at 3 (P = 0.0085) and 6 months (P = 0.0307) postoperatively. The mean higher-order irregularity was not significantly changed at any postoperative time-point (P = 0.222). The achieved change in the spherical equivalent was significantly correlated with the post/preoperative ratio of asymmetry (R = 0.695, P = 0.0030).

CONCLUSION

Hyperopic LASIK significantly increases the asymmetry component of the cornea, which is correlated with the achieved change in the spherical equivalent.

Off-axis refraction and aberrations following conventional laser in situ keratomileusis

PURPOSE

To investigate off-axis refraction and aberrations following conventional laser in situ keratomileusis (LASIK) for myopia and hypermetropia.

SETTING

School of Optometry, Queensland University of Technology, Australia.

METHODS

Using an autorefractor, off-axis refractions were analyzed along the horizontal visual field between 35 degrees nasally and 35 degrees temporally in 1 eye each of 15 emmetropic subjects (-0.50 to +0.50 diopters [D]), 6 myopic subjects (-2.25 to -6.50 D), 6 hyperopic subjects (+1.50 to +3.00 D), 6 myopic LASIK patients (presurgical refraction -2.75 to -9.00 D), and 6 hyperopic LASIK patients (presurgical refraction +0.75 to +2.00 D). Wavefront sensing measured off-axis higher-order aberrations in 2 myopic LASIK patients.

RESULTS

In myopic LASIK, the mean spherical components of refraction M became highly myopic away from the center of the visual field; in emmetropic and untreated myopic eyes, there were relatively small myopic shifts and hyperopic shifts, respectively. Off-axis 90-degree to 180-degree astigmatisms J180 in myopic LASIK subjects were greater than in untreated subjects. In hyperopic LASIK, there were mainly hyperopic shifts in M, opposite the direction in emmetropic and untreated hyperopic subjects. Off-axis J180 was less than in emmetropic and untreated hyperopic subjects. Some hyperopic LASIK patients had greater off-axis 45-degree to 135-degree astigmatisms J45 than patients in the other groups. In 2 myopic LASIK patients, Zernike root-mean-square 4th-order aberrations were higher than in the near-emmetropia group because of higher levels of positive spherical aberration.

CONCLUSIONS

Off-axis aberrations can be dramatically affected by conventional myopic and hyperopic LASIK. In myopic LASIK, the increased off-axis refractive errors may have adverse effects on peripheral visual tasks that are dependent on off-axis refractive errors. The relatively low off-axis refractive errors in hyperopic LASIK patients may improve peripheral visual tasks.

Corneal Higher Order Wavefront Aberrations After Hyperopic Laser in situ Keratomileusis

PURPOSE

To evaluate the changes in corneal higher order wavefront aberrations after hyperopic laser in situ keratomileusis (LASIK).

METHODS

In a prospective case series, 15 eyes of 12 patients who had hyperopic LASIK were evaluated. Corneal topography was obtained before and after hyperopic LASIK with a Nidek EC 5000 laser using 5.5/8.0 ablation zones. Using anterior corneal height data, the changes in corneal higher order wavefront aberrations were calculated.

RESULTS

The surgery significantly increased both corneal coma-like aberration (preoperative/6 months postoperative, 0.054/0.147 [172% increase] for 3-mm pupil and 0.381/1.076 [182% increase] for 6-mm pupil) and corneal spherical-like aberration (preoperative/6 months postoperative, 0.039/0.067 [72% increase] for 3-mm pupil and 0.297/0.959 [223% increase] for 6-mm pupil). The surgery significantly decreased Zernike coefficient 12 and the polarity of corneal spherical aberration changed from preoperative positive value to negative postoperatively. For a 3-mm pupil, the achieved changes in spherical equivalent refraction significantly correlated with the induced changes in the corneal coma-like aberration (R = 0.629, P = .010), but not with those in corneal spherical-like aberration (R = 0.408, P=.133) or Zernike coefficient 12 (R = -0.301, P = .282). For a 6-mm pupil, the achieved changes in spherical equivalent refraction significantly correlated with the induced changes in the corneal spherical-like aberration (R = 0.862, P < .0001) and Zemike coefficient 12 (R = -0.872, P < .001) but not with those in corneal coma-like aberration (R = 0.449, P = .094).

CONCLUSIONS

Hyperopic LASIK significantly increases corneal coma-like and spherical-like aberrations and changes corneal spherical aberration from a positive to negative value.

Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis

PURPOSE

To evaluate the size, shape, and uniformity of the videokeratographic functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) in 2 cohorts of patients with equivalent amounts of preoperative myopic or hyperopic astigmatism.

SETTING

Pepose Vision Institute, St. Louis, Missouri, USA.

METHODS

Eyes with myopic or hyperopic astigmatism (n=27 in each group) that had LASIK with the Visx Star S3 laser were retrospectively selected to match for level of preoperative refractive error. Slit-scanning videokeratography was performed preoperatively and 6 months postoperatively and analyzed using custom software. The FOZ was calculated by analyzing refractive power maps using a region-growing algorithm. Difference maps were generated from slit images and compared for interval change in corneal elevation, tangential curvature, and refractive power. The difference maps were also averaged (mean difference maps) for each target population. A Zernike decomposition of corneal first-surface elevation was performed to compare postoperative values with baseline parameters.

RESULTS

The mean postoperative refractive sphere at 6 months was -0.17 diopter (D) +/- 0.66 (SD) and +0.25 +/- 0.85 D in the myopia group and hyperopia group, respectively, and the mean postoperative astigmatism, -0.49 +/- 0.32 D and -0.65 +/- 0.52 D, respectively (P=.11). Based on the refractive power maps, the mean preoperative and postoperative myopic FOZ was 33.09 +/- 7.30 mm(2) and 30.94 +/- 5.43 mm(2), respectively, and the mean hyperopic FOZ, 33.19 +/- 7.96 mm(2) and 37.99 +/- 6.88 mm(2), respectively. After LASIK, there was an increase in magnitude of negative anterior corneal surface spherical-like Zernike values in the myopia group (P<.0001) and an increase in magnitude of positive spherical-like Zernike values in the hyperopia group. Postoperatively, significant induction of corneal surface horizontal coma was noted in hyperopic eyes (P<.0001). Hyperopic eyes, on average, had larger topographic FOZs after LASIK, but with less uniformity of curvature and power change than myopic eyes.

CONCLUSIONS

Hyperopic LASIK, which involves more transition points along the ablation diameter, produced a less uniform topographic FOZ than typical myopic treatments. Less predictable biomechanical changes from the circumferential release of tension on collagen bundles after midperipheral hyperopic ablation and greater variation in beam centration and the angle of incidence may contribute to the greater variability in corneal curvature and power in hyperopic LASIK than in myopic LASIK.

Autorefraction as an outcome measure of laser in situ keratomileusis

PURPOSE

To determine the limits of agreement between subjective refraction and autorefraction before and after laser in situ keratomileusis (LASIK) to assess whether autorefraction is a valid refractive outcome measure of refractive surgery.

SETTING

Ultralase, Leeds, United Kingdom.

METHOD

The prospective study involved consecutive preoperative normal patients and post-LASIK patients who had autorefraction using the Nidek ARK 700A autorefractor and careful subjective refraction (masked to autorefraction). Inclusion criteria were age greater than 18 years and healthy eyes with a visual acuity better than 0.1 logMAR (6/7.5) with or without previous LASIK. Refractions were compared by spherical equivalent (SE) using Bland-Altman limits of agreement and astigmatic vector difference using the median and the 95th percentile. The effect of time after treatment and treatment strength were explored.

RESULTS

Data were collected from 208 preoperative patients and 237 post-LASIK patients. Preoperatively, the agreement between subjective refraction and autorefraction for the SE was -0.10 diopter (D) +/- 0.35 (SD) and the median difference for the astigmatic vector was 0.28 D with a 95th percentile of 0.72 D. Post-LASIK, the SE agreement was similar, -0.09 +/- 0.39 D, but the astigmatic vector agreement decreased slightly with a median of 0.31 D and a 95th percentile of 1.02 D. This decrease reflected poorer agreement in patients whose pre-LASIK refractive error was greater than +4.00 D. Removing this group brought the median astigmatic difference post-LASIK to 0.27 D with a 95th percentile of 0.87 D, similar to that in the preoperative normals. The percentage within +/-0.50 D and +/-1.00 D of the attempted correction was 56.1% and 78.5%, respectively, with subjective refraction and 51.2% and 78.1%, respectively, with autorefraction.

CONCLUSIONS

Autorefraction showed excellent agreement with subjective refraction and was unaffected by refractive surgery except after LASIK for high hyperopia. Most outcomes were correctly classified in the standard categories (+/-0.50 D, +/-1.00 D), illustrating that autorefraction is a valid outcome measure of refractive surgery.

Wavefront Aberrations Following Laser in situ Keratomileusis and Refractive Lens Exchange for Hypermetropia

PURPOSE

To compare the magnitude of aberrations in eyes after elective hypermetropic laser in situ keratomileusis (LASIK) and refractive lens exchange (clear lens replacement).

METHODS

Forty-nine patients (92 eyes) had hypermetropic LASIK and 28 (48 eyes) had refractive lens exchange; 23 hypermetropic subjects (41 eyes) were the control group. LASIK was performed with the Nidek EC-5000 excimer laser; ablation zones 5.5 to 6.0-mm in diameter with transition zones 7.5 to 8-mm in diameter. For refractive lens exchange, all but four IOLs were made of foldable acrylic. Aberrations and corneal topography were measured with the Nidek OPD-Scan model ARK-10000 more than 12 months after surgery. The higher-order root-mean-square (HORMS) wave aberrations for combined third to sixth Zernike aberration orders and the Zernike spherical aberration coefficient C(0)(4) at both 4.2-mm and 6.0-mm pupil sizes were calculated.

RESULTS

For the LASIK group, surgical refractive change correlated significantly with total, corneal, and internal HORMS and spherical aberrations (except with internal spherical aberration for a 4.2-mm diameter pupil). For the refractive lens exchange group, there were no significant correlations of surgical refractive change with any of these factors. Similarly, there were no significant correlations of refraction with any of these factors for the control group. For a 3-diopter change in refraction with 6-mm pupils, LASIK doubled the total HORMS aberrations. LASIK changed the sign of spherical aberration from positive to negative by increasing the negative asphericity of the anterior cornea. Taking age differences between groups into account, refractive lens exchange increased the total HORMS aberrations by 40% compared with that of the control group, but this was not statistically significant. However, refractive lens exchange significantly increased total spherical aberration.

CONCLUSION

Refractive lens exchange was a better refractive procedure than LASIK for minimizing total higher order optical aberrations that accompany hypermetropic refractive surgery.

Videokeratography in Conductive Keratoplasty

PURPOSE

We used EyeSys videokeratography to evaluate corneal shape changes induced by conductive keratoplasty, a procedure that utilizes radio frequency energy to alter corneal shape to correct hyperopia.

METHODS

Follow-up data were available for 19 eyes (out of 24 eyes of 13 patients). Preoperative spherical hyperopia ranged from +0.75 to +3.25 D with astigmatism <0.75 D. Manifest refractive spherical equivalent refraction (MRSE), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), topographical parameter predicted corneal acuity (PCA), corneal uniformity index (CU Index), regular astigmatism, total astigmatism, average simulated keratometry (Avg Sim K), effective refractive power, and asphericity were measured preoperatively and at 6 and 12 months postoperatively.

RESULTS

Twelve months postoperatively, mean PCA, CU Index, and BSCVA were maintained at preoperative levels. Mean UCVA (LogMAR) improved from 0.53+/-0.21 to 0.10+/-0.19 (P<.05) with a mean MRSE change from +1.62+/-0.76 D to -0.06+/-0.84 D (P<.05) from preoperative to 12 months postoperative. Mean asphericity increased +0.044+/-0.24 D (P>.05), mean Avg Sim K increased 1.88+/-0.72 D (P<.05), mean effective refractive power increased 1.71+/-0.79 D (P<.05), mean cylinder (cycloplegic refraction) increased 0.19+/-0.36 D (P<.05), mean regular astigmatism increased 0.25+/-0.49 D (P>.05), and mean irregular astigmatism decreased 0.01+/-0.13 D (P>.05) from preoperative to 12 months after conductive keratoplasty.

CONCLUSIONS

Avg Sim K and effective refractive power changes support the refractive results; 12-month postoperative maintenance of BSCVA, PCA, and CU Index suggest the procedure is safe. Conductive keratoplasty induced a slight regular astigmatism in some eyes, which decreased with time. The increase in mean corneal asphericity indicated possible induction of central and peripheral cornea changes.

Total and Corneal Optical Aberrations Induced by Laser in situ Keratomileusis for Hyperopia

PURPOSE

To evaluate changes induced by standard laser in situ keratomileusis (LASIK) for hyperopia on total and corneal optical quality.

METHODS

Total and corneal aberrations were measured before and after standard hyperopic LASIK in 13 eyes (preoperative spherical equivalent refractive error +3.17 +/- 1.10 D). The Chiron Technolas 217C laser with PlanoScan was used. Total aberrations (measured using laser ray tracing) and corneal aberrations (estimated from a videokeratoscope) were described using Zernike terms. Root-mean-square wavefront error for both total and corneal aberrations, and through-focus Strehl ratio for the point spread function of the whole eye were used to assess optical changes induced by surgery.

RESULTS

Third and higher order aberrations increased significantly after hyperopic LASIK (by a factor of 2.20 for total and 1.78 for corneal aberrations, for a 6.5-mm pupil). Spherical aberration changed to negative values (corneal average decreased by -0.85 +/- 0.48 microm and total average by -0.70 +/- 0.30 microm). Best Strehl ratio for the whole eye decreased by a factor of 1.84. Hyperopic LASIK induced larger changes than myopic LASIK, compared to an equivalent group of myopic eyes from a previous study. Induced corneal spherical aberration was six times larger after hyperopic LASIK, for a similar range of correction, and of opposite sign. As with myopic LASIK, changes in internal spherical aberration are of opposite sign to those induced on the corneal anterior surface.

CONCLUSIONS

Hyperopic LASIK induced significant amounts of aberrations. The largest increase occurred in spherical aberration, which showed a shift (toward negative values) of opposite sign; increase was greater than for myopic LASIK.

Corneal asphericity after refractive surgery when the Munnerlyn formula is applied

We deduce a mathematical equation for corneal asphericity after refractive surgery when the Munnerlyn formula is used. For this, an analytical least-squares procedure is used. The equation explains the discrepancies found by different authors when the Munnerlyn formula or its paraxial approximation is used. Equations for corneal asphericity deduced here may be of clinical relevance, for example, in studying quantitatively the role of different factors (decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures) during corneal ablation.