Aberration-sensing and Wavefront-guided Laser in situ Keratomileusis: Management of Decentered Ablation

Simultaneous Topography-guided Custom Ablation With Corneal Cross-linking for Keratoconus: 10-Year Prospective Outcomes

PURPOSE

To assess 10-year visual and tomographic outcomes of topography-guided custom ablation (T-CAT) with corneal cross-linking (CXL) in eyes with keratoconus.

METHODS

T-CAT with CXL was performed in 600 eyes (522 patients). Based on the T-CAT ablation plan, the theoretical maximum ablation depth was 50 µm after epithelium removal. After ablation, accelerated corneal cross-linking (CXL) was performed in the central 8-mm zone (9 mW/cm2 for 10 minutes in "epi-off" mode). The visual acuity and tomography were assessed.

RESULTS

There was significant improvement in uncorrected (P = .001) and corrected (P = .001) distance visual acuity after the procedure. Keratometry, root mean square lower order aberrations and higher order aberrations, defocus, coma 90°, and spherical aberration reduced significantly after surgery at 10 years of follow-up (P < .005). All Pentacam (Oculus Optikgerate GmbH) tomographic variables showed significant changes indicating regularization after T-CAT (P < .005). Flattening of greater than 5.00 diopters in maximum keratometry was noted in 6 eyes (1%). Two of 600 eyes progressed postoperatively and required repeat CXL.

CONCLUSIONS

T-CAT plus CXL is a safe and effective technique even in the long term for regularizing the anterior corneal surface with significant visual improvement and reduction in higher order corneal aberrations. [J Refract Surg. 2023;39(11):759-766.].

Outcomes of topography-guided PRK/CXL in keratoconus using the NIDEK CXIII system-"Bharat Protocol" (Pilot study)

Purpose

Outcome of topography-guided excimer laser ablation in conjunction with accelerated, high-fluence cross-linking in corneal ecstatic disease using the NIDEK CXIII equipped with CATz algorithm from the FinalFit software-"Bharat Protocol."

Methods

Retrospective case record review of 30 eyes of 17 patients of stage 1-3 keratoconus who underwent the procedure was performed. Data collected were for visual acuity, distortion-induced eye pain, and keratometry. Pachymetry, lower order and higher order aberrations, spherical aberrations, and topographic cylinder were documented from by Scheimpflug imaging (Pentacam 70700: Oculus, Wetzlar, Germany).

Results

At a minimum follow-up of 6 months (range 6.2-13 months), there was significant improvement in UCVA (P < 0.00001), BCVA (P = 0.0061), decrease in Kmax (P = 0.0349), Ksteep (P < 0.0411), Kflat (P = 0.0099), and pachymetry (P = 0.0001). Significant improvement was also seen in distortion-induced eye pain (27/30 to 2/30; P < 0.00001). A more than two-line improvement in UCVA and BCVA was seen in 23/30 and 17/30 cases, respectively. Ectasia was stabilized in all cases at the last follow-up, and no complications were seen.

Conclusions

The "Bharat" Protocol to arrest keratectasia progression and improve corneal regularity is a safe and efficacious alternative as a keratoconus management option. This is the first such study on Nidek Platform for the same.

Aberrometric, Keratometric, and Visual Outcomes After Trans-Epithelial Topography-Guided Phototherapeutic Keratectomy for the Treatment of Irregular Corneas

Purpose

To assess the safety, aberrometric and keratometric changes, and stability of trans-epithelial topography-guided phototherapeutic keratectomy (TE-TG-PTK) with mitomycin C (MMC) using the ALLEGRO Topolyzer platform for the treatment of irregular astigmatism.

Methods

This is a retrospective case series including 57 eyes that underwent TE-TG-PTK + MMC using the ALLEGRO Topolyzer platform for the treatment of irregular astigmatism. CDVA, manifest refraction (MR), keratometry readings, and aberrometry readings were analyzed at 1, 3, 6, and 12 months.

Results

Causes of corneal irregularity included non-infectious leucoma (n=23), infectious leucoma (n=7), adenoviral keratitis (n=20), corneal haze (n=2), post-penetrant keratoplasty (PKP) (n=1), and others (n=4). Overall, 76% of the eyes (n=40) gained lines of vision; patients gained 1, and 2 or more lines of vision in 76%, and 38% of cases, respectively. Only 1 patient (2%) lost 5 lines of vision. Mean preoperative CDVA (LogMAR) was 0.37 ±0.31 and improved to 0.14 ±0.18 (p<0.001) at final follow-up (12 months). CDVA remained unchanged in 10 eyes (21%). No significant changes were observed in mean keratometry (Kmean) and keratometric astigmatism readings. Regarding aberrometry, only changes in coma proved to be significant 6 months after surgery (P<0.01). No intraoperative/postoperative complications were reported.

Conclusion

At final follow-up, significant improvements were observed in CDVA and coma. TE-TG-PTK + MMC proved to be an effective and safe procedure for the treatment of corneal irregular astigmatism due to several causes.

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 wavefront aberrations and subjective quality of vision after small incision lenticule extraction

PURPOSE

To analyse in depth the associations between objectively measured corneal higher-order aberrations (HOAs) and subjectively perceived visual quality after small incision lenticule extraction (SMILE) as quantified with the standardized and clinically validated quality of vision (QOV) questionnaire.

METHODS

This cross-sectional study included patients after bilateral simultaneous SMILE for the treatment of myopia and/or myopic astigmatism with plano target refraction. Scheimpflug imaging (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany) was used to objectively quantify corneal HOAs. The standardized and validated QOV questionnaire was employed to gauge patients' subjectively perceived visual quality regarding frequency, severity and bothering effect of visual disturbances.

RESULTS

A total of 394 eyes of 197 patients with a mean age of 32.4 ± 7.7 years and a mean postoperative follow-up of 24.3 ± 14.1 months were included. SMILE induced a statistically significant (p < 0.001) increase in spherical aberration (0.074 ± 0.131 µm), coma (0.142 ± 0.179 µm), trefoil (0.018 ± 0.067 µm) as well as in total HOAs (0.191 ± 0.176 µm). Surgically induced and postoperative levels of HOA showed no correlation with the three QOV scores representative of overall visual symptom frequency, severity and bothering effect (all R² values ≤ 0.016). In addition, the associations between specific visual symptoms (e.g. starburst) and singular HOA terms (e.g. haloes) were very weak (all Rho values ≤ 0.164).

CONCLUSIONS

Small incision lenticule extraction induced significant amounts of corneal HOAs that, however, showed no clear relationships to patient-reported QOV or specific long-term visual symptoms.

Deep Intrastromal Arcuate Keratotomy With In Situ Keratomileusis (DIAKIK) for the Treatment of High Astigmatism After Keratoplasty: 2-Year Follow-up

PURPOSE

To describe 2-year results of deep intrastromal arcuate keratotomy with in situ keratomileusis (DIAKIK) for the treatment of high astigmatism after keratoplasty.

METHODS

This prospective study included 20 eyes from 20 patients presenting with high astigmatism after keratoplasty. All were treated by two-step femtosecond laser surgery, with two intrastromal arcuate keratotomies and a corneal flap, followed a few months later by excimer photoablation after reopening of the flap.

RESULTS

At 24 months, both uncorrected (UDVA) and corrected (CDVA) distance visual acuity had improved from 1.12 ± 0.42 logMAR (20/200 Snellen) before surgery to 0.58 ± 0.23 logMAR (20/80 Snellen) (P < .001) and from 0.31 ± 0.26 logMAR (20/40 Snellen) to 0.20 ± 0.20 logMAR (20/32 Snellen) (P = .04), respectively. The mean spherical equivalent improved from -5.01 ± 4.35 to -1.54 ± 2.42 diopters. The mean efficacy index was 0.63. The mean correction index was 0.93 ± 0.32. The mean flattening index was 1.09 ± 0.75 and the mean safety index was 1.39. No graft rejection or epithelial ingrowth was observed.

CONCLUSIONS

This two-step procedure was an effective treatment for high astigmatism after keratoplasty. The use of both femtosecond and excimer lasers helped to avoid some complications that would have jeopardized the grafts. Refractive and topographic stability was good 2 years after surgery. [J Refract Surg. 2019;35(4):239-246.].

Outcomes of a Management Strategy in Eyes with Corneal Irregularity and Cataract

Purpose. To evaluate the outcomes of a management strategy in patients with irregular corneas and cataract. Methods. Six eyes of four patients presented for cataract surgery with irregular corneas following corneal refractive surgery. Topoguided ablation regularised the cornea, followed by phacoemulsification and intraocular lens implantation. Zonal keratometric coefficient of variation (ZKCV) measured structural changes and visual quality metrics measured functional improvement. Results. The mean duration after corneal refractive surgery was 7.83 ± 2.40 years. The logmar uncorrected distance visual acuity (0.67 ± 0.25) and the corrected distance visual acuity (0.38 ± 0.20) improved to 0.34 ± 0.14 and 0.18 ± 0.10, respectively. The changes in the standard deviations of the zonal keratometry values and the ZKCV were statistically significant in the 2, 3, and 4 mm zones. The changes in the Strehl ratio (ANOVA p = 0.043) were also statistically significant. Conclusions. Corneal regularisation followed by phacoemulsification resulted in lower residual refractive error with improved visual quality metrics. This strategy is a viable option in patients with symptomatic cataracts and irregular corneas.

Cone location-dependent outcomes after combined topography-guided photorefractive keratectomy and collagen cross-linking

PURPOSE

To evaluate the effect of keratoconus cone location on the change in refractive outcomes, corneal aberrations, and biomechanics after combined topography-guided photorefractive keratectomy (PRK) and collagen cross-linking (CXL).

DESIGN

Prospective, comparative case series.

METHODS

Topography-guided PRK was performed followed by accelerated CXL using riboflavin A and enhanced-intensity (30 mW/cm(2)) ultraviolet light. Outcome parameters including uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (BDVA), corneal tomography and biomechanics (corneal hysteresis [CH] and corneal resistance factor [CRF]), and corneal wavefront aberrations were assessed before and a year after the procedure. Eyes were subdivided into 2 groups preoperatively for statistical analysis: Group 1, cone located within the central 2-mm zone; and Group 2, cone located outside the central 2-mm zone.

RESULTS

UDVA, BDVA, sphere, cylinder, and simulated keratometry improved after treatment in both groups (P < .05). However, BDVA improved more in Group 1 than in Group 2 (P = .04) and the other variables were not affected by cone location. A few corneal wavefront Zernike aberrations changed after treatment (P < .05) but none were affected by cone location (P > .05). CH and CRF increased after treatment in both groups (P > .05). Interestingly, the increases in CH and CRF were greater in Group 2 than in Group 1 (P > .05).

CONCLUSIONS

Cone location appeared to impact only visual acuity and biomechanics after the combined procedure. The greater increase in CH and CRF in Group 2 may indicate differences in the ablation profile and variability in CXL outcomes and requires further study.

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.

Visual outcomes of topography-guided excimer laser surgery for treatment of patients with irregular astigmatism

The aim of this study was to evaluate the efficacy, safety, and predictability of topography-guided treatments to enhance refractive status following other corneal surgical procedures. In a prospective case series study, 28 consecutive eyes of 26 patients with irregular astigmatism after radial keratotomy, corneal transplant, small hyperopic and myopic excimer laser optical zones, and corneal scars were operated. Laser-assisted in situ keratomileusis (LASIK) (n = 8) and photorefractive keratectomy (PRK) (n = 20) were performed using the ALLEGRETTO WAVE excimer laser and topography-guided customized ablation treatment software. Preoperative and postoperative uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest and cycloplegic refraction, and corneal topography with asphericity were analyzed in 12 months follow-up. Uncorrected visual acuity (UCVA) changed from 0.2 ± 0.2 or (20/100 ± 20/100) to 0.51 ± 0.31 or (20/40 ± 20/60) in the LASIK group (P = 0.01) and from 0.34 ± 0.16 or (20/60 ± 20/120) to 0.5 ± 0.23 or (20/40 ± 20/80) in the PRK group (P = 0.01). Refractive cylinder decreased from -3.2 ± 0.84 diopters (D) to -2.06 ± 0.42 D in the LASIK group (P = 0.07) and from -2.25 ± 0.39 D to -1.5 ± 0.23 D in the PRK group (P = 0.008). Best corrected visual acuity did not change significantly in either group. Topography-guided treatment is effective in correcting the irregular astigmatism after refractive surgery. Topography-guided PRK can significantly reduce irregular astigmatism and increase the UCVA and BCVA.

Effect of air-flow on the evaluation of refractive surgery ablation patterns

An Allegretto Eye-Q laser platform (Wavelight GmbH, Erlangen, Germany) was used to study the effect of air-flow speed on the ablation of artificial polymer corneas used for testing refractive surgery patterns. Flat samples of two materials (PMMA and Filofocon A) were ablated at four different air flow conditions. The shape and profile of the ablated surfaces were measured with a precise non-contact optical surface profilometer. Significant asymmetries in the measured profiles were found when the ablation was performed with the clinical air aspiration system, and also without air flow. Increasing air-flow produced deeper ablations, improved symmetry, and increased the repeatability of the ablation pattern. Shielding of the laser pulse by the plume of smoke during the ablation of plastic samples reduced the central ablation depth by more than 40% with no-air flow, 30% with clinical air aspiration, and 5% with 1.15 m/s air flow. A simple model based on non-inertial dragging of the particles by air flow predicts no central shielding with 2.3 m/s air flow, and accurately predicts (within 2 μm) the decrease of central ablation depth by shielding. The shielding effects for PMMA and Filofocon A were similar despite the differences in the ablation properties of the materials and the different full-shielding transmission coefficient, which is related to the number of particles ejected and their associated optical behavior. Air flow is a key factor in the evaluation of ablation patterns in refractive surgery using plastic models, as significant shielding effects are found with typical air-flow levels used under clinical conditions. Shielding effects can be avoided by tuning the air flow to the laser repetition rate.

Changes in wave-front aberrations after rigid gas permeable contact lens fitting in post-laser in situ keratomileusis patients with visual complaints

OBJECTIVE

To evaluate the effect of rigid gas permeable (RGP) contact lenses in reducing wave-front aberrations in post-laser in situ keratomileusis (LASIK) myopic patients.

DESIGN

Cross-sectional study.

PARTICIPANTS

Thirty patients with visual complaints after conventional LASIK procedure for correcting myopia.

METHODS

The 30 patients were fitted with RGP contact lenses. Wave-front measurements were taken before and after RGP contact lens wearing.

RESULTS

Compared with bare eye examinations, root mean-square values of higher-order aberrations (HOAs) significantly decreased with RGP contact lens use. Among these, spherical aberration decreased from 0.507 (SD 0.304) microm to 0.164 (SD 0.121) microm (t = 7.186, p < 0.001); coma decreased from 0.470 (SD 0.312) microm to 0.165 (SD 0.090) microm (t = 5.566, p < 0.001); secondary coma decreased from 0.079 (SD 0.050) microm to 0.044 (SD 0.027) m (t = 4.118, p < 0.001); and total HOAs decreased from 0.782 (SD 0.449) microm to 0.307 (SD 0.140) microm (t = 6.710, p < 0.001).

CONCLUSIONS

Fitting RGP contact lenses effectively decreased HOAs induced by conventional myopic LASIK surgery. Possible reasons may be the elimination of irregularity and dissymmetry on the corneal anterior surface, relief of the aspherical extent of the central corneal surface, and enlargement of the effective optical zone.

Reverse geometry rigid gas permeable contact lens wear reduces high-order aberrations and the associated symptoms in post-LASIK patients

PURPOSE

This study evaluated the efficacy of custom-made reverse geometry rigid gas permeable (RGP) contact lenses in the control of symptoms related to increased wavefront aberrations after LASIK correction of myopia.

MATERIALS AND METHODS

Twenty-eight myopes treated with LASIK were assessed for post-LASIK symptoms (declined night vision, glare, halos and/or monocular diplopia) and corneal topography. A set of RGP contact lenses was selected as trial lenses based on the matching between the lens and the patient's corneal topography. If the fluorescein pattern between the trial lens and the corneal surface showed a central alignment, a mid-peripheral bearing and peripheral clearance and if the patient felt comfortable with the lens wear, a duplicated lens was ordered for the patient. Otherwise, a lens satisfied with corneal topography of the patient and clinical judgment was used. Visual acuity (VA) and wavefront aberrations were measured after the lens wear.

RESULTS

The custom-made lenses well matched the host cornea with no dislodgment in all subjects. The post-LASIK eyes showed an increase of 1 Snellen line in VA (from 0.90 +/- 0.33 to 1.11 +/- 0.24) and a significant improvement in all symptoms after the lens wear. The total higher-order aberration is significantly reduced after the lens wear with at least 70% reduction in either spherical aberration, coma, third or fourth aberration but only 33% reduction in the fifth aberration.

CONCLUSIONS

Reverse geometry RGP lenses with the design based on individual topographic data can improve visual performance of post-LASIK eyes by reducing higher order aberrations.

Wavefront aberrations in eyes with decentered ablations

PURPOSE

To compare the refractive and functional outcomes and wavefront profiles in eyes with decentered ablations and eyes with well-centered ablations.

SETTING

Medical Research Foundation, Chennai, Tamil Nadu, India.

METHODS

This retrospective analysis comprised eyes with topographically diagnosed decentered ablations after laser in situ keratomileusis (LASIK). Refraction, contrast sensitivity, and ocular wavefront aberrations were measured preoperatively and 1 month postoperatively. The induced aberrations in these eyes were compared with those in eyes with well-centered ablations.

RESULTS

Forty-six eyes (38 patients) had decentered ablations and 60 eyes (32 patients), well-centered ablations. The mean decentration in the study group was 0.86 mm +/- 0.29 (SD) (range 0.35 to 1.61 mm). There was no significant correlation between decentration and attempted refractive correction. There was, however, a statistically significant (P<.05) linear correlation between the distance of decentration and the magnitude of induced tilt (r = -0.31), coma (r = -0.41), and secondary astigmatism (r = 0.36). The induced changes in tilt, oblique astigmatism, vertical coma, and spherical aberration were statistically significantly higher in eyes with decentered ablations than in eyes with well-centered ablations. A statistically significantly higher percentage of eyes (87%) with well-centered ablations than eyes with decentered ablations (70%) had a postoperative uncorrected visual acuity (UCVA) of 20/20 or better. There was no significant difference in contrast sensitivity between groups.

CONCLUSION

Eyes with decentered ablations had a significantly higher magnitude of induced aberrations and lower UCVA than eyes with well-centered ablations.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

Impact of ablation efficiency reduction on post-surgery corneal asphericity: simulation of the laser refractive surgery with a flying spot laser beam

We developed a rigorous simulation model to evaluate ablation algorithms and surgery outcomes in laser refractive surgery. The model (CASIM: Corneal Ablation SIMulator) simulates an entire surgical process, which includes calculating an ablation profile from measured wavefront errors, generating a shot pattern for a flying spot laser beam, simulation of the shot-by-shot ablation process based on a measured or modeled beam profile, and healing of the cornea after surgery. Using simulated post-surgery corneal shapes for various ablation parameters and beam fluences, we calculated angular dependence of ablation efficiency and the amount of increase in corneal asphericity. Without considering the effect of corneal healing, our result shows the following; 1) ablation efficiency reduction in the periphery depends on the peak fluence of the laser beam, 2) corneal asphericity increases even in the surgery using an ablation profile based on the exact Munnerlyn formula, contrary to previous reports, and 3) post-surgery corneal asphericity increases by a smaller amount in high fluence small Gaussian beam surgery than in low fluence truncated Gaussian beam. Our model can provide improved ablation profiles that compensate for the change of corneal asphericity and induction of spherical aberration in a flying spot laser system, resulting in better surgery outcomes in laser refractive surgeries.

Topography-guided Ablation for Treatment of Patients With Irregular Astigmatism

PURPOSE

To evaluate the customized aspheric treatment zone (CATz) topography-guided ablation for the correction of irregular astigmatism induced by initial corneal refractive surgery or corneal injury.

METHODS

CATz ablation was performed on 32 eyes of 28 patients. Each procedure was performed by photorefractive keratectomy (PRK) or LASIK using a NIDEK EC-5000 excimer laser. The eyes had decentered ablations, small optical zones, decreased best spectacle-corrected visual acuity (BSCVA), and asymmetrical astigmatism. Subjective symptoms, uncorrected visual acuity (UCVA), BSCVA, refraction, corneal topography, and higher order aberrations were measured. Mean follow-up was 161.9 +/- 129.9 days (range: 90 to 492 days).

RESULTS

Data obtained at final postoperative follow-up show that UCVA and BSCVA increased by > or = 2 lines after CATz ablation in 17 and 11 eyes and decreased in 4 and 2 eyes, respectively. Higher order aberrations were decreased in 16 eyes and increased in 1 eye. Topographical maps were improved with decreased surface regularity index (20 eyes) and surface asymmetry index (22 eyes). Seven eyes required further enhancement for residual refractive errors. Thirteen patients (15 eyes) claimed they were satisfied with the outcome, 6 patients (7 eyes) stated that the outcome was lower than expected, and 4 patients (4 eyes) stated they were dissatisfied.

CONCLUSIONS

CATz topographic ablation effectively improves the quality of vision and symptoms in the majority of patients with irregular corneal astigmatism from previous excimer laser refractive surgery. However, residual or induced refractive errors may need to be corrected with a second operation after CATz.

Customized ablation algorithm for the treatment of steep central islands after refractive laser surgery

Steep central island (SCI) formation after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) represents a major drawback in the visual rehabilitation of patients after refractive laser surgery. Because of the small size of SCIs, current ablation algorithms are unable to properly calculate an ablation pattern for customized retreatment. We present the use of a new ablation algorithm for the treatment of SCIs that occurred after PRK or LASIK surgery. This algorithm uses a smaller zone of approximation and takes into account the spherical shift induced by removal of the SCI. In all 3 eyes treated, best spectacle-corrected visual acuity increased to 20/16 and remained stable at the 1- and 3-month follow-up, with disappearance of the SCI in corneal topography. This new treatment algorithm may be of benefit to patients experiencing visual side effects due to SCI formation after PRK or LASIK surgery.

Avoidance, recognition, and management of LASIK complications

PURPOSE

To provide important concepts of the latest developments in laser in situ keratomileusis (LASIK) complication avoidance, recognition, and management.

DESIGN

A perspective.

METHODS

A comprehensive literature search and review of a total of 816 publications that discussed LASIK complications from 1992 to 2005 was conducted.

RESULTS

The risk of visually threatening complications is inherent in any ophthalmologic surgical procedure. Not only does LASIK require the use of several complex medical devices, but there can be significant human variation in response to this surgical intervention. As a result, many potential complications can occur after LASIK. The risk of many complications can be mitigated by appropriate patient selection and preoperative, surgical, and postoperative care. Unforeseen complications will occur, despite meticulous planning, and must be managed. Important current developments in the avoidance, recognition, and management of LASIK complications are reviewed.

CONCLUSIONS

Complications as a result of LASIK can threaten vision and may cause debilitating symptoms in an otherwise healthy eye. Advancing our understanding of the prevention and management of the complications of LASIK is an endeavor that must be continued as long as refractive surgery is performed.

Topography-guided Treatment of Irregular Astigmatism With the WaveLight Excimer Laser

PURPOSE

To evaluate the feasibility, safety, and predictability of correcting high irregular astigmatism in symptomatic eyes with the use of topography-guided photoablation.

METHODS

In a prospective, non-comparative case series, 16 consecutive symptomatic eyes of 11 patients with small hyperopic and myopic excimer laser optical zones, decentered and irregular ablation after corneal graft, and corneal scars were operated. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest and cycloplegic refraction, and corneal topography, with asphericity and regularity, were analyzed. LASIK (n = 10) and photorefractive keratectomy (n = 6) were performed using the ALLEGRETTO WAVE excimer laser and T-CAT software (Topography-guided Customized Ablation Treatment; WaveLight Laser Technologie AG, Erlangen, Germany).

RESULTS

In the LASIK group, UCVA improved from 0.81 +/- 0.68 IogMAR (20/130) (range: 0.2 to 2.0) to 0.29 +/- 0.21 logMAR (20/39) (range: 0.1 to 0.7) at 6 months. In the PRK group, mean UCVA improved from 0.89 +/- 0.87 IogMAR (20/157) (range: 0.1 to 2.0) to 0.42 +/- 0.35 logMAR (20/53) (range: 0.1 to 1.0) at 6 months. Best spectacle-corrected visual acuity did not change significantly in either group. One PRK patient lost one line of BSCVA. Refractive cylinder for the LASIK group improved from -2.53 +/- 1.71 diopters (D) (range: -0.75 to -5.75 D) to -1.28 +/- 0.99 D (range: 0 to -2.50 D) at 6 months. Refractive cylinder in the PRK group improved from -2.21 +/- 2.11 D (range: -0.25 to -5.50 D) to -1.10 +/- 0.42 D (range: -0.50 to -1.50 D). Index of surface irregularity showed a decrease from 60 +/- 12 (range: 46 to 89) to 50 +/- 9 (range: 32 to 63) at 6 months in the LASIK group whereas no significant change was noted in the PRK group. Subjective symptoms, such as glare, halos, ghost images, starbursts, and monocular diplopia, were not present postoperatively.

CONCLUSIONS

Topography-guided LASIK and PRK resulted in a significant reduction of refractive cylinder and increase of UCVA, without a significant loss of BSCVA.

Ablationsprofile in der kornealen refraktiven Laserchirurgie

The predictability and quality of results in corneal refractive laser surgery are determined by a number of factors. Here, the calculation and choice of the ablation profile represent central elements. Our growing knowledge about the physical and optical properties of the eye in recent years has led to the development of different strategies in the generation of ablation profiles. This review describes the currently used ablation profiles with their advantages and disadvantages and provides an outlook on future methods for the calculation of ablation profiles.

Higher-Order Aberrations in Eyes with Irregular Corneas after Laser Refractive Surgery

PURPOSE

To investigate the distribution of the eye's higher-order aberrations in postoperative laser refractive surgery patients with visual complaints and highly irregular corneal shapes.

DESIGN

Retrospective case-control study.

PARTICIPANTS

Thirty-three symptomatic postoperative LASIK and/or photorefractive keratectomy eyes with subjective visual complaints not corrected by spectacles more than 6 months after surgery are compared with 46 normal preoperative and 46 asymptomatic successful postoperative conventional LASIK eyes.

METHODS

Postoperative wave aberrations were measured for each patient using a Shack-Hartmann wavefront sensor (Zywave, Bausch & Lomb, Rochester, NY) over a 6-mm pupil. These measurements were averaged across patients with similar corneal topographic diagnoses (central islands, decentered ablations, a new group termed baby bowties, and irregularly irregular corneas).

MAIN OUTCOME MEASURES

Higher-order aberrations and corneal topography.

RESULTS

The average (+/-1 standard deviation) higher-order root-mean-square (rms) wavefront error values (third, fourth, and fifth orders) for the symptomatic patients was 1.31+/-0.58 microm. This was an average of 3.46 times greater than the average magnitude of normal preoperative eyes (mean rms, 0.38+/-0.14 microm), and an average of 2.3 times greater than the average magnitude of asymptomatic successful postoperative conventional LASIK eyes (mean rms, 0.58+/-0.21 microm) over a 6-mm pupil. Higher-order rms wavefront error increased with pupil size, roughly doubling for every millimeter of increasing pupil diameter. On average, eyes with central islands (n = 6) had the most vertical coma (Z3(-1); mean, -1.35+/-0.43 microm). Eyes with central islands and decentered ablations (n = 2) also had elevated amounts of spherical aberration (Z4(0); means of 0.83+/-0.11 microm and 0.69+/-0.29 microm, respectively) compared with successful postoperative LASIK eyes (mean of 0.42+/-0.20 microm). Eyes with a topographic central baby bowtie demonstrated the most secondary astigmatism (Z4(2) and Z4(-2); mean rms, 0.56+/-0.17 microm; n = 3), despite the lowest average higher-order rms (mean, 0.84+/-0.05 microm) among symptomatic topographic subgroups. Eyes with irregularly irregular corneas had a mean higher-order rms of 1.10+/-0.39 mum.

CONCLUSIONS

Symptomatic postoperative laser refractive surgery patients with irregular corneas have higher-order aberrations that are 2.3 to 3.5 times greater than asymptomatic postoperative LASIK and normal preoperative eyes, respectively. The higher-order aberrations seem to correlate with corneal topography.

Strategic Planning in Topography-guided Ablation of Irregular Astigmatism After Laser Refractive Surgery

PURPOSE

To identify an optimal customized ablation strategy in the treatment of eyes with secondary irregular astigmatism.

METHODS

Corneal anterior surface elevation maps of 50 eyes with secondary irregular astigmatism after decentered laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) and 50 virgin eyes were used for customized ablation simulations. Two ablation simulations with targeted postoperative surfaces perpendicular to either the visual or corneal morphological axis were made for each eye. All ablations were programmed for correction of corneal irregularities, including corneal astigmatism. The manifest refractive error was not corrected. Optical diameter was 6.5 mm and total diameter was 7.5 mm. Maximum ablation depths and maximum transition zone gradients were registered and analyzed.

RESULTS

In eyes with secondary irregular astigmatism, mean maximum ablation depth was 48.21 +/- 25.96 microm and 26.31+/- 14.08 microm, whereas mean maximum transition zone gradient was 29.07 +/- 25.15 microm and 9.88 +/- 6.41 microm in ablation simulations based on the visual and corneal morphological axes, respectively. The difference between the ablation strategies was highly statistically significant for both parameters (P < .001). In virgin eyes, only a minor difference was noted between the visual and corneal morphological axis ablation simulations (P = .15 for maximum ablation depths and P=.19 for maximum transition zone gradient).

CONCLUSIONS

In secondary irregular astigmatism, ablation based on the corneal morphological axis appears to minimize corneal tissue consumption and allows a smoother transition zone.

Wavefront's role in corneal refractive surgery

In the 5 years since the first wavefront-based LASIK treatment on normal eyes, the ophthalmology profession has had to confront a new language based on astronomy, optics and mathematics. Over this time wavefront technology has been used for diagnosis and treatment, and its application has made the profession define what is meant by good vision, and determine whether, with psychophysical and psychometric tests, it is possible understand how an individual perceives the world. The clinical application of wavefront technology has forced ophthalmologists and vision scientists with an engineering bias to talk to those with a biological bias, and to appreciate that if you try and change the corneal shape, its biological, anatomical and optical properties exist within a complex external eye environment. This perspective article demonstrates that wave-front analysis is a useful diagnostic tool, and that wavefront-based corneal refractive surgery is an improvement over conventional techniques. Its use by an ophthalmologist is a clinical decision specific to an individual patient.

Clinical Photoablation With a 500-Hz Scanning Spot Excimer Laser

PURPOSE

The aim of this study was to use a 500-Hz scanning spot laser (Concept500, WaveLight Laser Technologie AG, Erlangen, Germany) to investigate potential side effects that might be associated with the use of a high repetition rate laser platform.

METHODS

Seven eyes were treated using a 500-Hz scanning spot laser for laser in situ keratomileusis (LASIK). The local frequency of the ablation was kept below 40 Hz to avoid local heating of corneal tissue. With the exception of the high repetition rate (500 Hz), all other laser parameters such as fluence, algorithm, ablation profile, and spot diameter were identical to a standard WaveLight Allegretto laser system. Patients were examined at 1 month and 1 year after initial treatment. Preoperative and postoperative examination included manifest sphere and cylinder, uncorrected and best spectacle-corrected visual acuity (BSCVA).

RESULTS

All eyes were treated for myopia or myopic astigmatism. Five eyes received spherocylindrical and two eyes spherical ablation only. No adverse events correlated with the use of a high repetition rate laser system were observed during surgery or at any point during follow-up. All eyes maintained or had improved BSCVA at 12 months after treatment when compared to preoperative values.

CONCLUSION

The use of an excimer laser with a maximal repetition rate of 500 Hz and a local repetition rate of less than 40 Hz was free of any specific side effect that might be associated with the use of such a high repetition rate.

Custom-contoured ablation pattern method for the treatment of decentered laser ablations

PURPOSE

To evaluate the custom-contoured ablation pattern (C-CAP) method as a tool for providing customized laser ablations for decentered ablations based on corneal topography data.

SETTING

Department of Ophthalmology, Stanford University, Stanford, California, USA.

METHODS

In a prospective noncomparative interventional case series, 8 eyes from 7 post-laser in situ keratomileusis (LASIK) patients and 1 post-photorefractive keratectomy (PRK) patient with symptomatic laser decentration were treated with the C-CAP method. The Zeiss Humphrey topography system was used to identify and analyze decentered ablations. The computer software allowed the surgeon to preoperatively model the effect of various ablation schemes on the preoperative topography until a scheme that alleviated the decentration was identified. The planned ablation parameters, which included size, depth, and location of the ablation, were programmed into the Visx S4 excimer laser before treatment.

RESULTS

The mean follow-up after C-CAP ablation was 4.2 months (range 1.8 to 6.3 months). At the last postoperative examination, no eye lost a line of best spectacle-corrected visual acuity (BSCVA). The uncorrected visual acuity (UCVA) improved by 3 lines in 1 eye (12.5%), by 2 lines in 1 eye (12.5%), and by 1 line in 3 eyes (37.5%); it remained unchanged in 2 eyes (25.0%) and decreased by 1 line in 1 eye (12.5%). The BSCVA improved by 3 lines in 1 eye (12.5%), by 2 lines in 2 eyes (25.0%), and by 1 line in 3 eyes (37.5%); it remained unchanged in 2 eyes (25.0%). In all eyes, including those without improvement in UCVA or BSCVA, a significant improvement in centration and subjective complaints was achieved. The pre-C-CAP and post-C-CAP root-mean-square (RMS) wavefront data were available in 5 of 8 eyes. The total and higher-order RMS aberrations decreased by 41.7% (P =.0027) and 45.5% (P =.039), respectively, after C-CAP treatment.

CONCLUSIONS

Early U.S. results show the topography-driven C-CAP method is an effective tool to address untreatable postsurgical decentration. This method is presented as a technique to enhance the overall quality of vision, reduce patient-perceived visual aberrations, regularize the corneal surface, and maximize BSCVA.

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.

Update on customized excimer ablations: recent developments reported in 2002

Customized corneal ablation is an exciting frontier in refractive surgery that incorporates wavefront technology to detect and correct higher order aberrations in addition to spherocylindrical refractive errors. The goal is to achieve super normal vision in terms of acuity and contrast. As the concept of wavefront customized ablations is still new, there are a number of aspects of its clinical application that need analysis and understanding. Numerous reports have appeared in the literature during the past year that address the developments, concerns, and limitations of wavefront technology and custom ablation. We have attempted to summarize and discuss the significant reports in this current review. Our focus is on the optical and physiologic limits of wavefront customized correction, including the effect of accommodation, aging, and flap creation on the aberration profile. In addition, we also present the laser technology requirements, and clinical outcomes of customized excimer ablations that are reported to date.

Correlation Between Corneal and Total Wavefront Aberrations in Myopic Eyes

PURPOSE

Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality depends on all optical elements of the eye, including the human lens. We investigated correlations between corneal and total wavefront aberrations and the relevance of corneal aberrations for representing the optical quality of the total eye.

METHODS

Thirty-three eyes of 22 myopic patients were measured using a corneal topography system and a Tscherning-type wavefront analyzer. Pupils were dilated to at least 6 mm in diameter. All measurements were centered with respect to the line of sight. Corneal and total wavefront aberrations were calculated up to the 6th Zernike order in the same reference plane.

RESULTS

Statistically significant correlations (P<.05) between corneal and total wavefront aberrations were found for astigmatism (C3,C5) and all 3rd Zernike order coefficients such as coma (C7,C8). No statistically significant correlations were found for 4th, 5th, or 6th order Zernike coefficients. On average, all Zernike coefficients for corneal aberrations were larger than the Zernike coefficients for total wavefront aberrations.

CONCLUSIONS

Due to the lack of correlation between corneal and total wavefront aberrations in most of the higher order aberrations, measurement of corneal aberrations are of limited use for representation of the optical quality of the human eye, especially after corneal laser surgery. Corneal aberrations and optical elements within the eye are optically balanced. As a consequence, ideal customized ablations must take both corneal and total wavefront aberrations into consideration.

Anterior Lamellar Keratoplasty With a Microkeratome: A Method for Managing Complications After Refractive Surgery

PURPOSE

To demonstrate a technique of anterior lamellar keratoplasty with standardized and automated preparation of surface-parallel cuts in both donor and recipient appropriate for addressing several problems after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).

METHODS

We report a noncomparative series of ten eyes with complications after LASIK and PRK. Lamellar cuts were performed in donor and recipient eyes by means of an automated microkeratome. Lamellar grafts were fixed by only four single sutures. In two eyes, a re-lift LASIK was performed after 6 months.

RESULTS

Surgery was uneventful and visual acuity was improved in all eyes. Residual irregular astigmatism and refractive error were corrected in two eyes by means of excimer laser computer-assisted ablation and resulted in a further improvement of uncorrected and best spectacle-corrected visual acuity.

CONCLUSIONS

Anterior lamellar keratoplasty with a microkeratome can be used for the management of certain complications of PRK and LASIK.