Correction of irregular astigmatism with the excimer laser

Topography-Guided Trans-Epithelial No-Touch Photorefractive Keratectomy for High Irregular Astigmatism After Penetrating Keratoplasty: A Prospective 12-Months Follow-Up

Purpose

To describe the efficacy and safety of topography-guided trans-epithelial no-touch photorefractive keratectomy (PRK) for the correction of highly irregular astigmatism after penetrating keratoplasty (PK).

Patients and Methods

A prospective study was conducted on 12 eyes of 12 patients affected by highly irregular astigmatism after PK for keratoconus. Each patient underwent a single-step topography-guided trans-epithelial ablation (CIPTA^®2 software, iVis Technologies). Corneal topography data as well as uncorrected (UDVA) and corrected distance visual acuity (CDVA) and spherical equivalent (SEQ) were collected preoperatively (T0) and at 1 (T1), 3 (T2) and 12 (T3) months after surgery.

Results

Mean UDVA and CDVA significantly improved, respectively, from 1.22±0.17 and 0.18±0.03LogMAR at T0 to 0.63±0.17 (CI 95%, P<0.001) and 0.04±0.03LogMAR at T3 (CI 95%, P<0.001). Mean SEQ significantly decreased from −3.75±1.32 to –1.60±1.32D (CI 95%, P<0.02). Mean subjective refractive astigmatism (SRAST) and mean keratometry astigmatism (SimK) significantly decreased, respectively, from 7.83±0.98 and 8.10±1.48D to 2.83±0.98 and 5.29±1.48D (CI 95%, P<0.001). Corneal Morphological Irregularity index (CMI) significantly decreased from 62.76±7.26 µm to 23.24±7.26 µm (CI 95%, P<0.001). Apart from a single episode of graft rejection 5 days after ablation, successfully reverted with topical steroids, no other complications were noted. A mild corneal haze was observed in two eyes (16.7%) at 3 months post-PRK, and no regression was observed at 12 months.

Conclusion

Our study demonstrates the safety and long-term effectiveness of a trans-epithelial topography-guided ablation in the treatment of post-PK highly irregular astigmatism.

[Combined transepithelial PTK and topography-guided PRK for treatment of trauma-related corneal scarring]

BACKGROUND

Corneal scars can severely impair visual performance and treatment can be challenging. The study aimed to evaluate a promising minimally invasive option in the treatment of corneal scars using transepithelial topography-guided ablation.

METHODS

This retrospective interventional study involved four eyes of four patients who developed corneal scarring and irregular surfaces due to trauma and were treated with topography-guided photorefractive keratectomy (TG-PRK) between 2017 and 2020. The ablation profile was calculated in all four cases using CRS-Master (Zeiss, Jena, Germany). The main outcome measures were uncorrected and best-corrected distance visual acuity, manifest refraction and corneal regularity by topographic images. The mean age was 34.75 ± 15.39 years and the follow-up time was 6 months for all patients.

RESULTS

In three cases full subjective refraction was corrected in one session and one patient had a refractive error of +0.5 D. Only corneal surface smoothing without additional refractive correction was performed in this case. All four patients showed improvement in uncorrected (2-3 Snellen lines) and corrected (3 Snellen lines) distance visual acuity. No complications occurred during or after the treatment and there was no reduction of visual acuity in any case.

CONCLUSION

The use of TG-PRK in patients with corneal scarring improves visual acuity in selected cases. In myopic patients most of the refractive error can also be corrected in a single session.

Phototherapeutic keratectomy: Indications, methods and decision making

Phototherapeutic keratectomy (PTK) involves treating anterior corneal lesions by superficial corneal ablation using an excimer laser (193 nm). Some of the commonly treated conditions include recurrent corneal erosions (RCE), corneal dystrophies, spheroidal degeneration, keratoconus, and corneal scars. We discuss various techniques of PTK including large area PTK, focal PTK, and multifocal PTK and alternatives to PTK. Masking agents like hyaluronate, methylcellulose, and dextran are recommended to help achieve a better outcome when ablating irregular corneal surfaces. Antifibrotic agents like mitomycin C reduce the chances of recurrence of the disease, apart from minimizing the postoperative scarring. Some of the complications include induced hyperopia and irregular astigmatism, haze, recurrence, and corneal thinning. However, earlier postoperative recovery, possibility of a repeat procedure, and ability to control the depth of ablation make PTK a promising, minimally invasive alternative to keratoplasty in cases with anterior corneal pathologies.

[Innovations in refractive laser surgery 2014]

BACKGROUND

Within less than 30 years refractive laser surgery has been developed from an experimental technique to one of the most frequently applied procedures in ophthalmology worldwide.

RESULTS

Regarding the success rate of refractive results, myopia correction has reached a level (95% within ± 0.5 D) that is comparable to manifest refraction so that there is not much room for improvement. The most recently developed technique is femtosecond laser lenticule extraction which was introduced in 2007 in Germany. Early clinical results were very promising but the awaited bilateral comparative studies are still lacking. Although new laser types that will be able to provide improved profiles are on the horizon, the problem of reoperations has not yet been solved. Topography-guided ablation is notoriously plagued by undercorrection so that topography-guided treatment is planned as a two step-procedure. The reason for the undercorrection is the leveling effect of the epithelium.

PERSPECTIVES

The evolution of refractive surgery has slowed down during the last years, however, some important innovations are at the advent.

Clinical results of topography-based customized ablations for myopia and myopic astigmatism

PURPOSE

To evaluate clinical outcomes after primary treatments for myopia and myopic astigmatism with topography-based ablation profiles on the Allegretto Wave Eye-Q platform (Alcon Laboratories Inc).

METHODS

Records of patients who underwent topography-guided, Q-adjusted LASIK were retrieved and analyzed. Patients with mean refractive spherical equivalent up to -16.00 diopters (D) and cylindrical errors up to 6.00 D were included (2051 eyes). Refractive outcomes and visual acuities were analyzed preoperatively and 3 months postoperatively.

RESULTS

Manifest spherical refractive error decreased from -5.05 +/- 2.33 to +0.04 +/- 0.35 D. Manifest cylindrical refractive error decreased from 0.83 +/- 0.75 to 0.23 +/- 0.22 D. At 3 months postoperatively, 86.1% (1766 eyes) had a spherical equivalent refraction within +/- 0.50 D of targeted refraction. The number of eyes with uncorrected distance visual acuity of 20/16 and 20/20 was 851 (41.5%) and 1495 (72.9%), respectively. At 3 months, 0.10% (2 eyes) lost more than 2 lines of corrected distance visual acuity and a loss of 2 lines occurred in 0.24% (5 eyes). All patients who lost lines of visual acuity were found to have corneal erosions related to dryness and recovered vision on further follow-up.

CONCLUSIONS

The results of this retrospective study demonstrate refractive predictability, efficacy, and safety comparable to other treatment modalities such as wavefront-optimized and wavefront-guided treatments. Results are also similar to those reported with other topography-guided systems.

Phototherapeutic Keratectomy for Epithelial Irregular Astigmatism: An Emphasis on Map-Dot-Fingerprint Degeneration

PURPOSE

To study the changes in irregular astigmatism in patients with recurrent corneal erosion syndrome due to map-dot-fingerprint degeneration and to demonstrate that both symptomatic and asymptomatic map-dot-fingerprint degeneration/recurrent corneal erosion syndrome may be related to irregular astigmatism, which can effectively be corrected by phototherapeutic keratectomy (PTK) or standard spherical photorefractive keratectomy (PRK).

METHODS

Eleven eyes with irregular astigmatism related to map-dot-fingerprint degeneration/recurrent corneal erosion syndrome with and without changes at the slit-lamp microscope were treated with PTK or spherical PRK, which was performed with a VISX S2 or S4 excimer laser. All eyes underwent videokeratography performed pre- and postoperatively using either the Tomey TMS-2N Topographic Modeling System or EyeSys Technologies Corneal Analysis System 2000.

RESULTS

Mean pre- and postoperative best spectacle-corrected visual acuity (BSCVA) was -0.18 +/- 0.14 logMAR and 0.04 +/- 0.04 logMAR, respectively. This improvement in BSCVA was statistically significant. The mean gain in Snellen lines was 2.4 +/- 2.1. Preoperative corneal videokeratography showed irregular astigmatism with an elevation pattern that was corrected in all eyes despite the fact that no astigmatic photorefractive correction was performed.

CONCLUSIONS

Following PTK, eyes with irregular astigmatism related to map-dot-fingerprint degeneration showed significant improvement in BSCVA and correction of irregular astigmatism as revealed by videokeratography. This study shows that irregular astigmatism can be exclusively of epithelial origin and in some eyes abnormal corneal epithelium may create optical aberrations. This possibility should be taken into account when, for example, wavefront-guided stromal photoablation procedures are being planned.

Varieties of Contact Lens Fittings After Complicated Hyperopic and Myopic Laser In Situ Keratomileusis

PURPOSE

To determine whether contact lenses with a special back surface design can improve visual acuity after complicated laser in situ keratomileusis (LASIK).

METHODS

Fifteen eyes (six after myopic LASIK and nine after hyperopic LASIK) of eight patients were fitted with contact lenses with a special back surface design for optical rehabilitation. Four different types of lenses (aspheric, tricurve, keratoconus, and reverse) were used selectively, depending on the abnormal eccentricity (positive and exceeding 0.5-0.7 in all preoperatively hyperopic eyes, negative in all preoperatively myopic eyes) determined by videokeratoscope and on individual conditions. The patients were followed up retrospectively for an average period of 12.3 months. Lens tolerance and corrected visual acuity were evaluated and compared with the results obtained with spectacles.

RESULTS

Visual acuity improved in nine (60%) of 15 eyes (three eyes by more than three lines and six eyes by three lines or fewer), with an absence of halos and ghost images in four (26.7%) of 15 eyes accompanied by good contact lens tolerance and a satisfactory contact lens fit. There were no noticeable complications.

CONCLUSIONS

Contact lens fitting after LASIK is a safe and reliable procedure for improving visual acuity and reducing complications, such as ghost images or irregular corneal surface. Depending on the eccentricity and therefore on the preoperative refraction, contact lenses with a special back surface design can minimize problems in contact lens fitting and can improve tolerance and visual results.

Contact lenses and special back surface design after penetrating keratoplasty to improve contact lens fit and visual outcome

AIMS

To describe the fitting of patients with high or irregular astigmatism following penetrating keratoplasty with contact lenses and to answer the question whether or not contact lenses with special back surface design can improve visual acuity in complex cases after penetrating keratoplasty.

METHODS

28 eyes were included. They were fitted with contact lenses with a special back surface that was designed for optical rehabilitation after penetrating keratoplasty. Four different types of these lenses (tricurve, keratoconus, reverse, oblong) were used selectively depending on abnormal eccentricity determined by videokeratoscope. The patients were followed up for an average period of 15.5 months. Lens tolerance and corrected visual acuity were evaluated and compared with that corrected with spectacles.

RESULTS

The visual acuity was significantly improved in nearly all eyes with an average increase of 3.6 lines (maximal nine lines) accompanied by good contact lens tolerance and satisfactory contact lens fit. No noticeable complications were observed.

CONCLUSION

Contact lenses with special back surface design can improve visual results and lens tolerance, and minimise problems in contact lens fitting. This is in favour of contact lenses as an alternative to surgical procedures for correction of high or irregular astigmatism after penetrating keratoplasty. This procedure is recommended especially in cases of patients who decline further operative interventions.

Phototherapeutic keratectomy in children: 5-year results

PURPOSE

To evaluate the efficacy and safety of phototherapeutic keratectomy (PTK) for the treatment of superficial corneal opacities, surface irregularities, epithelial instability, and reepithelialization failure in pediatric patients and study the visual and refractive changes after combined PTK and photorefractive keratectomy (PRK).

SETTING

Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic.

METHODS

This retrospective clinical study comprised children who had PTK or PTK combined with PRK from September 1996 to January 2000. The goals of treatment were to improve visual acuity and reduce or eliminate subjective ocular discomfort (eg, pain, lacrimation, and photophobia). A Nidek EC-5000 excimer laser was used in PTK mode with a 3.0 to 6.0 mm optical zone and a 4.0 to 7.5 mm transition zone.

RESULTS

Forty-one pediatric patients (41 eyes) were included. Twenty-three eyes had PTK only, and 18 eyes had PTK combined with PRK to reduce preoperative myopia (11 eyes) or hyperopia (7 eyes). The mean patient age was 11.4 years (range 8 to 18 years) and the mean follow-up, 4.8 years (range 3 to 6 years). The best spectacle-corrected visual acuity (BSCVA) improved in all patients, and episodes of ocular pain or discomfort, lacrimation, and photophobia diminished. The mean preoperative BSCVA of 6/38 (range 6/10 to 1/60) improved to 6/12 (range 6/6 to 6/38) at the last postoperative examination. Eight eyes gained 5 or more Snellen lines of BSCVA; 11 gained 4 lines, 9 gained 3 lines, 7 gained 2 lines, 5 gained 1 line, and 1 eye was unchanged. No eye lost a line of BSCVA. The mean preoperative spherical equivalent (SE) decreased from -5.32 to -1.16 diopters (D) in the 11 myopic eyes and from +4.72 to +1.51 D in the 7 hyperopic eyes within 3 years of the combined procedure.

CONCLUSIONS

Phototerapeutic keratectomy is an effective and safe procedure for the treatment of various surface corneal disorders in children. It can improve best corrected visual acuity and eliminate ocular pain and irritation. Preoperative myopia and hyperopia were effectively reduced by a combination of PTK and PRK.

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.

Topography-guided Laser in situ Keratomileusis (TOPOLINK) to Correct Irregular Astigmatism After Previous Refractive Surgery

PURPOSE

To assess whether topography-driven laser in situ keratomileusis (LASIK) can correct induced corneal irregular astigmatism.

METHODS

A prospective non-comparative case series of 41 eyes (38 patients) with irregular astigmatism following corneal refractive surgery, included two groups: Group 1 (26 eyes) with a defined topographic pattern and Group 2 (15 eyes) with no pattern. Ablation was performed using the Technolas 217C excimer laser with a software ablation program (TOPOLINK) based on corneal topography. Uncorrected and best spectacle-corrected visual acuity, manifest and cycloplegic refraction, corneal topography, superficial corneal surface quality, and image distortion were measured.

RESULTS

At 6 months follow-up in Group 1 eyes (defined topographic pattern) mean preoperative BSCVA improved from 0.16 +/- 0.11 LogMAR (0.4 to 0) to 0.09 +/- 0.10 LogMAR (0.2 to 0) (P = .001) (safety index of 1.1). In Group 2 eyes (no pattern), mean preoperative BSCVA was 0.18 +/- 0.11 LogMAR (0.4 to 0), similar to the postoperative BSCVA of 0.17 +/- 0.10 LogMAR (0.3 to 0) (safety index of 0.98). Mean postoperative UCVA was > or = 0.3 LogMAR in 25 eyes (96.2%) in Group 1 (efficacy index of 0.8) and 7 eyes (46.6%) in Group 2 (efficacy index of 0.5). Both superficial corneal surface quality and image distortion significantly improved in Group 1; there were no significant changes in Group 2. We reoperated nine eyes (21.9%).

CONCLUSIONS

Topographic-assisted LASIK was helpful in selected cases where irregular astigmatism showed a pattern. It was ineffective in undefined irregular astigmatism. Partial correction of the irregularity and regression of the obtained effect was common.

Arcuate keratotomy for asymmetrical steep islands after laser in situ keratomileusis and automated lamellar keratoplasty

PURPOSE

To determine the safety and efficacy of arcuate keratotomy (AK) to reduce or eliminate steep asymmetrical islands after laser in situ keratomileusis (LASIK) and automated lamellar keratoplasty (ALK).

SETTING

Rancho Bernardo Laser and Vision Center, San Diego, California, USA.

METHODS

This retrospective and noncomparative interventional study comprised 8 eyes of 5 patients who received arcuate incisions to reduce topographically defined asymmetrical steep islands after LASIK (n = 7) and ALK for hyperopia (n = 1). The islands occurred unexpectedly after standard excimer laser treatment (VISX Star and S2) for myopic astigmatism that induced irregular astigmatism and unwanted optical effects. Cases occurred consecutively over 16 months, an incidence of less than 1%. Arcuate incisions extended 30 or 45 degrees in LASIK eyes based on the amount of residual refractive astigmatism and were placed at 7.0 mm on the steep axis. Radial incisions were limbal sparing to a 5.0 mm optical zone following the Casebeer nomogram. Outcome measures were uniformity of postenhancement topography, uncorrected visual acuity (UCVA), postenhancement refraction, and reduction in unwanted optical effects.

RESULTS

The preenhancement mean spherical equivalent (SE) in the LASIK eyes was -0.99 diopters (D) +/- 0.48 (SD); the astigmatism ranged from 0.50 to 1.75 D. After incisional keratotomy, the mean SE was -0.21 +/- 0.12 D and the net residual astigmatism was reduced to a range of 0 to 0.75 D. All 8 eyes had AK to reduce topographically defined steep islands that were causing visual blurring and unwanted optical effects including ghosting, halos, and polyplopia. After enhancement, there was a marked reduction in the asymmetrical steep islands by topography, fewer unwanted optical effects, less refractive astigmatism, and improved UCVA. Two patients retained small inferior steep areas that may indicate forme fruste keratoconus, although this condition was not detected preoperatively by topographical indices.

CONCLUSION

Uncorrected visual acuity improved and unwanted optical effects were reduced after AK on the peripheral axis of asymmetrical steep islands that occurred after uneventful LASIK and hyperopic ALK. This relatively simple incisional approach may be used until more advanced topography-linked ablations with rapid and precise eye tracking are perfected and widely available.

Subclinical inflammation after laser in situ keratomileusis in corneal grafts

PURPOSE

To evaluate postoperative inflammatory reaction in the eye after laser in situ keratomileusis (LASIK) in corneal grafts.

SETTING

Department of Ophthalmology, Helsinki University Central Hospital, Helsinki, Finland.

METHODS

Ten eyes of 9 patients with penetrating keratoplasty (PKP) and significant postoperative refractive errors and astigmatism had LASIK 22 months or more after the PKP. All patients were treated with the VISX Star excimer laser and the Bausch & Lomb Hansatome microkeratome. Preoperative and early postoperative inflammation was evaluated by quantifying the aqueous flare intensity with a laser flare photometer (Kowa FM-500). A full ophthalmic assessment was also performed before LASIK and up to 6 months postoperatively.

RESULTS

The inflammatory response was mild and limited to the first postoperative hour. The mean anterior chamber flare increased from 6.0 photons/millisecond (ph/ms) preoperatively to 14.0 ph/ms at 1 hour and then decreased to 6.7 ph/ms (hour 3), 6.8 ph/ms (day 1), and 8.2 ph/ms (day 7). The mean spherical equivalent (SE) refraction decreased from -3.81 diopters (D) (range -9.63 to -0.25 D) to -0.46 D (range -1.13 to +0.38 D), and the mean preoperative astigmatism decreased from 3.0 D (range 6.5 to 0.5 D) to 0.7 D (range 0.0 to 2.0 D). At the last examination, 9 eyes were within +/-1.0 D (6 within +/-0.5 D) and all were within +/-1.5 D of the intended SE refraction. Three eyes achieved full cylinder correction, and 7 were within +/-1.0 D of the intended correction. Eight eyes had a best corrected visual acuity of 20/40 or better (unchanged or gain of 1 to 4 lines [6], loss of 1 line [1], and loss of 3 lines [1]), and 8 had an uncorrected visual acuity of 20/50 or better.

CONCLUSIONS

Uneventful LASIK induced subtle, short-lasting anterior chamber flare when measured by the laser flare meter. In corneal grafts, LASIK appeared to be a safe and effective procedure for residual refractive errors.

Correction of irregular astigmatism with excimer laser assisted by sodium hyaluronate

PURPOSE

To demonstrate the usefulness of excimer laser surgery assisted by sodium hyaluronate for the correction of irregular astigmatism after previous corneal refractive surgery.

DESIGN

Prospective noncomparative case series.

PARTICIPANTS

Fifty eyes with surgically induced irregular astigmatism. All the patients had been subjected previously to one or more of the following: laser in situ keratomileusis (LASIK), incisional keratotomy, photorefractive keratotomy, phototherapeutic keratotomy, laser thermokeratoplasty, and corneal trauma. Irregular astigmatism developed thereafter.

METHODS

Stability of the corneal topography pattern before surgical decision was observed for at least 6 months with the C-SCAN corneal topography with Ray Tracing (Technomed GmbH, Germany) and the Eye-Sys 2000 Corneal Analysis System (Eye Sys Co., Houston, TX). The lowest pachymetry value was 310 microm in the thinnest portion of the cornea. Ablation was performed with the Technolas 217 C-LASIK excimer laser (Bausch and Lomb Chiron Technolas GmbH, Dornach, Germany), in phototherapeutic keratectomy mode, assisted by a mask of 0.25% sodium hyaluronate. We performed our ablation either on the surface or under a flap, whether elevated or newly cut.

MAIN OUTCOME MEASURES

Uncorrected and best-corrected visual acuity, manifest and cycloplegic refraction, superficial corneal surface quality, image distortion, and predicted corneal visual acuity.

RESULTS

At 3 months of follow-up, the irregular corneal surface was significantly improved in all cases (n = 50). The superficial corneal surface quality improved from 70.5% +/- 9.16% to 75.6% +/- 10.38 (P < 0.0001). Six eyes lost 1 line of best-corrected visual acuity, three eyes lost 2 lines, and five eyes lost 3 or more lines. The real corneal ablation depth obtained was equal to 63% of that programmed because of the influence of masking substance. Mean uncorrected visual acuity improved from 20/80 +/- 20/125 to 20/63 +/- 20/100 (P = 0.01). Predicted corneal visual acuity improved from a mean of 20/32 +/- 20/80 to 20/25 +/- 20/63 (P = 0.004). Image distortion improved from a mean of 13.95 +/- 3.64 to 12.16 +/- 3.92 (P < 0.0001). We obtained a hyperopic shift in 56% and myopic shift in 40% of eyes. After 6 months of follow-up the irregular corneal surface continued to improve in all cases (n = 32). The superficial corneal surface quality improved from 69.38% +/- 9.48% to 73.13% +/- 8.87 (P = 0.002). Two eyes lost 2 lines of best-corrected visual acuity, and 3 eyes lost 1 line. Ray tracing was significantly improved in all cases at the end of follow-up regarding superficial corneal surface quality (P = 0.002) and the image distortion (P = 0.05). Improvement of predicted corneal visual acuity was not significant (P = 0.11). The procedure proved to be safe, with a safety index of 1.1. Differences between the surface and stromal treatments and between pattern and nonpattern irregular astigmatism were not statistically significant.

CONCLUSION

It is possible to produce a more regular corneal surface and to improve best-corrected visual acuity in patients with irregular astigmatism using plano-scan excimer laser assisted by viscous masking solution of 0.25% sodium hyaluronate.

Customized ablation for asymmetrical corneal astigmatism

PURPOSE

To evaluate laser in situ keratomileusis (LASIK) cases in which a customized ablation assisted by corneal topography was performed.

SETTING

Instituto de la Visión, Buenos Aires, Argentina.

METHODS

The study group comprised 23 cases with asymmetrical corneas; 17 had myopia and 6, hyperopia. Visual acuity, spherical equivalent (SE), and cylinder vectorial change measurements, along with keratometry and corneal topography, were performed in all cases preoperatively and postoperatively.

RESULTS

In the myopic cases, the mean preoperative SE was -4.92 diopters (D) +/- 2.46 (SD); it was -0.38 +/- 0.66 D after a mean follow-up of 4.41 +/- 2.32 months. In the hyperopic cases, the preoperative SE was +3.54 +/- 1.57 D; it was +0.33 +/- 0.50 D after a mean follow-up of 3.42 +/- 3.23 months. Cylinder vectorial change, visual acuity, and the number of visual acuity lines gained or lost were also evaluated in both groups.

CONCLUSION

Although some features of our algorithm for corneal-topography-assisted customized ablations should be modified, the results of our treatment of cases with asymmetrical astigmatism were encouraging.

Early clinical experience using custom excimer laser ablations to treat irregular astigmatism

PURPOSE

To assess the viability of custom excimer laser ablations for treating irregular astigmatism.

SETTING

Single-center prospective study of a new custom-ablation technique.

METHODS

Twelve patients received 15 custom ablations for irregular astigmatism resulting from keratoconus, penetrating keratoplasty for keratoconus, prior decentered laser in situ keratomileusis, or incisional refractive surgery. Follow-up ranged from 6 weeks to 14 months. Initially, the laser beam was manually decentered; later, the Contoured Ablation Patterns (CAP) method (VISX, Inc.) was used to automatically decenter the ablation over the corneal elevation.

RESULTS

Results are presented in a case-by-case fashion. In the manual decentration group, the uncorrected visual acuity (UCVA) was 20/50 or better in 9 of 11 eyes (81.8%) and 20/40 or better in 7 eyes (63.6%). Surgery resolved or decreased visual symptoms when present. The best corrected visual acuity (BCVA) was maintained or improved in all eyes. Persistent </=grade 1 haze developed in the 2 patients (n = 3 eyes) treated for keratoconus. In the CAP group, the UCVA was between 20/40 and 20/80; the BCVA improved in 3 of 4 eyes (75.0%) and declined from 20/20 to 20/25 at 3 months in the remaining eye due to haze. The ablation produced some spherical flattening in both groups, resulting in induced hyperopia that was generally clinically insignificant.

CONCLUSION

Early results of this experimental custom-ablation technique are promising.

Management of irregular astigmatism

Using a liberal definition of corneal irregularity, modern videokeratoscopy may define approximately 40% of normal corneas with a toric refractive error as possessing primary irregular astigmatism. The causes of secondary forms of irregular astigmatism include corneal surgery, trauma, dystrophies, and infections. Internal refractive surface and media irregularity or noncorneal astigmatism (ocular residual astigmatism) contribute to irregular astigmatism of the entire refractive path of which crystaline lenticular astigmatism is usually the principal contributing component. Treatment options have increased in recent years, particularly, though not exclusively, through the advent of tailored corneal excimer laser ablations. However, discussion continues concerning the systematic approach necessary to enable treatment to achieve an optimal optical surface for the eye. Discussion also continues as to what constitutes the optimal corneal shape. Some refractive procedures may increase higher order aberrations in the attempt to neutralize refractive astigmatism. The way to further refinement of the commonly performed refractive techniques will ultimately lie in the integrated inclusion of a trio of technologies: topographic analysis of the corneal surface, wavefront analysis of ocular refractive aberrations, and vector planning to enable the appropriate balance in emphasis between these two diagnostic modalities. For the uncommon, irregularly roughened corneas, the ablatable polymer techniques show some promise.

Topographically-guided laser in situ keratomileusis to treat corneal irregularities

OBJECTIVE

To evaluate the predictability and safety of topographically guided laser in situ keratomileusis (LASIK) to treat corneal irregularities.

DESIGN

Prospective, noncomparative interventional case series.

PARTICIPANTS

Twenty-seven patients (29 eyes) with postsurgical corneal irregularities, divided into four subgroups (postkeratoplasty, 6 eyes; posttrauma, 6 eyes; postphotorefractive keratectomy (PRK)/LASIK with decentered or small ablations, 11 eyes; post-PRK/LASIK with central islands, 6 eyes).

INTERVENTION

LASIK was performed using the Automatic Corneal Shaper and the Keracor 117 C spot-scanning excimer laser (Bausch & Lomb Surgical Technolas, Munich, Germany). Individual ablation patterns were calculated on the basis of axial radii of curvature data obtained with the Corneal Analysis System (EyeSys Premier, Irvine, CA).

MAIN OUTCOME MEASURES

Change of corneal topography pattern, patient satisfaction, manifest spectacle refraction, and visual acuity at 12 months after surgery.

RESULTS

Corneal topography showed improved corneal regularity in 66% of eyes in the postkeratoplasty group, whereas 34% remained irregular. In the posttrauma group, 83% improved and 17% remained irregular. In the decentered/small optical zone group, 91 % improved and 9% remained irregular. In the central islands group, 50% improved and 50% remained irregular. Refractive cylinder decreased from 5.83 +/- 1.25 diopters (D) to 2.96 +/- 1.23 D in the postkeratoplasty group (P = 0.01), from 2.21 +/- 1.35 D to 0.50 +/- 0.84 D in the posttrauma group (P = 0.001), from 0.73 +/- 0.71 D to 0.36 +/- 1.05 D in the decentered/small optical zone group (NS), and from 1.42 +/- 1.13 D to 0.50 +/- 0.84 D in the central island group (P = 0.01). Uncorrected visual acuity improved from 20/200 +/- 0.07 to 20/50 +/- 0.17 in the postkeratoplasty group (P = 0.01), from 20/83 +/- 0.12 to 20/50 +/- 0.28 in the posttrauma group (P = 0.01), from 20/60 +/- 0.16 to 20/50 +/- 0.29 in the decentered/small optical zone group (NS), and from 20/71 +/- 0.12 to 20/60 +/- 0.24 in the central island group (NS).

CONCLUSIONS

The topographically-guided LASIK method used in this study resulted in a significant reduction of refractive cylinder, a significant increase of uncorrected visual acuity, and improved corneal regularity in a large percentage of patients with severe corneal irregularities such as decentered/small optical zones after LASIK or irregular astigmatism after keratoplasty or trauma. With small irregularities such as central islands, results were sufficiently poor to advise against the use of our technique in these patients.

Selective zonal ablations with excimer laser for correction of irregular astigmatism induced by refractive surgery

OBJECTIVE

To demonstrate the safety and efficacy of selective zonal ablations with excimer laser for the correction of irregular astigmatism induced by refractive surgery.

DESIGN

Thirty-one eyes of 26 patients. Retrospective and noncomparative case series.

METHODS

The authors reviewed the medical results of the two series of consecutive cases of irregular astigmatism induced by refractive surgery. One group showed a topography map with a defined pattern: decentered ablation, decentered steep central island, central irregularity, and peripheral irregularity. The other group showed an irregular astigmatism without defined pattern. Selective zonal ablation was performed with a broad-beam excimer laser. Laser ablations were adjusted according to the Munnerlyn formula. A phototherapeutic keratectomy (PTK) mode was used in all cases without using viscous masking solution.

MAIN OUTCOME MEASURES

Uncorrected visual acuity, best spectacle-corrected visual acuity (BCVA), and Holladay diagnostic summary (Eye Sys 2.000) were considered before and after surgery to obtain the qualitative and quantitative characteristics of the visual acuity and corneal topography. The corneal uniformity index (CUI) was used to evaluate the corneal surface changes induced by the selective zonal ablations in the correction of irregular astigmatism. It proved to be a useful tool in the understanding of astigmatic changes when it is not possible to apply the vector analysis.

RESULTS

In group 1, the irregular astigmatism was significantly improved in 96.4% of cases. The CUI was improved from 58+/-0.3% to 87+/-0.8%, P < 0.005 (Student's t-test). The improvement of the BCVA was from 20/40+/-20/100 to 20/25+/-20/100, P < 0.005 (Student's t-test). The results obtained in group 2 were not clinically significant in terms of improvement of CUI and BCVA.

CONCLUSIONS

Using the corneal topographic map as a guide, selective zonal ablations with excimer laser can be used to create a more regular corneal surface, when a defined pattern of topographic irregularities can be defined.

Laser in situ keratomileusis to correct refractive errors after keratoplasty

PURPOSE

To assess the safety and effectiveness of excimer laser in situ keratomileusis (LASIK) to correct refractive myopia, astigmatism, or both after keratoplasty.

SETTING

Eye Clinic Day Hospital, São Paulo, Brazil.

METHODS

Twenty-two eyes that had previously had corneal transplantation were studied. Laser in situ keratomileusis was performed using the Chiron automated microkeratome and the VISX Twenty-Twenty B excimer laser.

RESULTS

Mean follow-up after LASIK was 10.09 months +/- 3.87 (SD). The spherical equivalent refraction dropped from -4.55 +/- 3.66 D before LASIK to -0.67 +/- 1.24 D after surgery. At the last examination, 72.7% of patients had a refractive error within +/- 1.00 D of emmetropia and 54.5% had uncorrected visual acuity of 20/40 or better. Vector analysis of astigmatic correction showed an index of success of 54.0%. Best spectacle-corrected visual acuity was unchanged in 8 cases, improved in 9, and decreased in 5. Significant endothelial cell loss, keratoplasty wound dehiscence, and other serious complications did not develop in any eye.

CONCLUSION

The correction of refractive error with LASIK in postkeratoplasty patients proved to be safe, effective, and predictable. Further studies with longer follow-up are needed to determine the method's clinical value.

Laser in situ keratomileusis assisted by corneal topography

PURPOSE

To assess whether laser in situ keratomileusis (LASIK) assisted by corneal topography can successfully treat corneal irregularities or irregular astigmatism in patients with previous ocular surgery or ocular trauma.

SETTING

University Eye Hospital, Klinikum Mannheim, Mannheim, Germany.

METHODS

In a prospective clinical study, LASIK was performed in 23 eyes of 22 patients. Reasons for surgery were irregular astigmatism after penetrating keratoplasty or penetrating injury or corneal irregularity after previous excimer laser surgery. Excimer ablation was based on preoperative corneal topography data (Corneal Analysis System, EyeSys Technologies) using a proprietary algorithm (Topographic Assist LASIK, Chiron Vision). Follow-up was 6 months.

RESULTS

Mean preoperative uncorrected visual acuity (UCVA) was 20/80 and mean best spectacle-corrected visual acuity (BSCVA), 20/35. Uncorrected visual acuity improved in all but two cases. Postoperatively, mean UCVA increased to 20/50; mean BSCVA was unchanged. No eye lost two or more lines of BSCVA. Postoperative topography showed less corneal irregularity in 81.3% of eyes; full correction was achieved in 19.4%. Four eyes (19.4%) needed re-treatment for undercorrection and three eyes (14.3%) for regression.

CONCLUSION

Preliminary results indicate that the concept of topographic-assisted LASIK is feasible. However, most eyes were undercorrected and had regression. One reason might be that corneal topography underestimated corneal irregularity, causing significant undercorrection.

Experimental correction of irregular corneal astigmatism using topography-based flying-spot-mode excimer laser photoablation

PURPOSE

To present a novel experimental approach for treating irregular corneal astigmatism.

METHODS

After decomposition of topographic analysis data into orthogonal Zernike polynomials, a regular target surface was defined, and the ablation profile was calculated. In a polymethylmethacrylate with an irregular surface, computer-controlled ablation was performed using a 193-nm excimer laser in "flying-spot mode."

RESULTS

The difference between flattest and steepest hemimeridians in the 3-mm zone, surface regularity index, and surface asymmetry index were reduced from 8.7 to 1.1 diopters, 1.19 to 0.39, and 1.84 to 0.14, respectively.

CONCLUSION

Tying corneal topography into laser software offers a straightforward concept for correction of irregular corneal astigmatism in an experimental model.

Treatment of Irregular Astigmatism with a Broad Beam Excimer Laser

BACKGROUND

Four basic types of irregular astigmatism are described: central elevation, central flat area, eccentric elevation, and eccentric flat area.

METHODS

The importance of the Munnerlyn formula is shown for the treatment of irregular astigmatism. A new diagnostic entity is described, the steep/flat ratio, modeled on the inferior/superior ratio described previously in keratoconus. Calculation of the steep/flat ratio is described using the cross sectional view of videokeratography, leading to specific treatments for the four types of irregular astigmatism. Surgical technique using the VISX Star excimer laser for repeated laser in situ keratomileusis (LASIK) is described.

RESULTS

Case studies are given for each of the forms of irregular astigmatism showing improved topographic appearance and indicating treatment parameters. In each case, improvement of both uncorrected and spectacle-corrected visual acuity is demonstrated.

CONCLUSIONS

Irregular astigmatism is an important complication of refractive surgery. Four basic forms of irregular astigmatism can be treated with a broad beam excimer laser.

Combined PRK and PTK in myopic patients with recurrent corneal erosion

AIM

To study the results of combined photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) in myopic patients with recalcitrant recurrent corneal erosion.

METHODS

PRK was performed in 16 eyes with the Visx 20/20 excimer laser at a central 6.0 mm zone, following total epithelial scraping. Subsequently, confluent 3.0 mm zones of PTK were ablated at a depth of 6.0 microns, surrounding the zone of PRK. The follow up period ranged from 26 to 42 months.

RESULTS

Complete alleviation of symptoms was demonstrated and there was no recurrence of corneal erosion. Visual acuity (VA) improved slowly following treatment, with a final uncorrected VA ranging between 6/9 and 6/12. A final myopic spherical equivalent < or = -1.0 D was found in 14 out of 16 eyes.

CONCLUSIONS

A combination of PRK and PTK is effective in the alleviation of symptoms and prevention of recurrences of corneal erosion. It is suggested that recalcitrant recurrent corneal erosion is a diffuse disease, although it often manifests as a local problem, and therefore extensive excimer laser ablation is required to prevent recurrence and to alleviate symptoms completely.

Enlargement of the photorefractive keratectomy optical zone

PURPOSE

To evaluate the safety and efficacy of a photorefractive keratectomy (PRK) re-treatment procedure that enlarges the optical zone and treats undercorrection.

SETTING

Rotterdam Eye Hospital and Medisch Centrum Alkmaar, The Netherlands.

METHODS

This study evaluated 16 eyes that had PRK for myopia with the Summit excimer laser that resulted in a mean undercorrection of -2.82 diopters (D). Patients also reported impaired night vision including difficulty in driving, halos, and stray light and ghost images. These phenomena persisted after spectacle correction of residual refractive error, necessitating further treatment with a larger ablation zone. With a VISX 20/20 excimer laser, the optical zone was enlarged to 6.0 mm and undercorrection treated with a 6.0 mm ablation.

RESULTS

At 13.5 months after re-treatment, mean reduction in myopia was 1.70 D, resulting in a residual undercorrection of -1.08 D. In seven eyes, final refraction was within 1.00 D of emmetropia. Only two patients continued to report night-driving problems.

CONCLUSIONS

Re-treating undercorrections combined with enlarging the ablation zone resulted in a reduction in myopia from a mean of 2.82 to 1.08 D. Subjective reports of halos and stray light images were decreased in all cases.

Direct objective quantification of corneal haze after excimer laser photorefractive keratectomy for high myopia

PURPOSE

The purpose of the study is to measure regional distribution differences in corneal haze after excimer laser photorefractive keratectomy for high myopia.

METHODS

The authors developed computerized gradient edge detectors with which were analyzed digitized anterior slit-lamp photographs of 40 eyes, an average of 21.0 plus or minus 14.5 weeks after photorefractive keratectomy for high myopia (-6 to -22 diopters). A treated area an adjacent untreated area on the anterior corneal surface, each containing six regions, were quantified, and the difference was correlated with various parameters.

RESULTS

Mean differences between scarred and clear areas for haze grade 0.5, 1.0, 2.0, 3.0, and 4.0 were 16.9, 26.6, 42.6, 60.4, and 76.4 gray levels, respectively (rs = 0.96; P = 0.0001). A low but statistically significant correlation between the intended correction and postoperative corneal haze was found (r = 0.33; P = 0.037). The mean coefficient of variation of the amount of opacification within each treated area was 9.4%. This coefficient of variation increased with a longer follow-up time (r = 0.88; P = 0.0001). The difference in the intensity of haze between the center and more peripheral regions over the entrance pupil did not correlate with the attempted correction. However, a strong association between a relatively less severe central corneal haze with respect to more peripheral haze and longer follow-up time was found (r = -0.96; P = 0.0001).

CONCLUSION

The amount of corneal haze showed a weak positive association with the attempted correction in excimer laser photorefractive keratectomy for high myopia. Corneal haze appeared fairly uniformly distributed within the ablation zone, but a more heterogeneous distribution was found with a longer follow-up time. Furthermore, later postoperative examinations disclosed a clear trend toward diminishing central opacification relative to peripheral regions over the entrance pupil.

Excimer laser phototherapeutic keratectomy. Surgical strategies and clinical outcomes

PURPOSE

To assess the different strategies and analyze clinical outcomes of excimer laser phototherapeutic keratectomy (PTK) for a variety of superficial corneal disorders.

METHODS

Twenty-eight eyes of 26 patients with one of five general categories of corneal disorders were treated with a variety of PTK techniques. Patients were assessed for preoperative and postoperative corneal thickness, uncorrected and best spectacle-corrected visual acuity, refractive changes, corneal topography and astigmatism, and results of a subjective patient questionnaire. Follow-up ranged from 6 to 30 months.

RESULTS

The average number of laser pulses was 418, with a mean decrease in corneal thickness of 31 microns. Uncorrected visual acuity improved in 20 eyes and decreased in 5. Best spectacle-corrected visual acuity improved in 20 eyes and decreased in 5; two patients had two Snellen lines of best-corrected vision loss. Nineteen patients (21 eyes) noted symptomatic improvement. Corneal topography improved in 17 eyes and worsened in 1. The average refractive shift was +1.4 diopters; patients undergoing general PTK, PTK combined with mechanical superficial keratectomy, and superficial scar removal had greater degrees of hyperopic shift. Complications were rare. Two patients who did not appreciate adequate improvement in vision after PTK underwent subsequent penetrating keratoplasty.

CONCLUSIONS

A number of PTK techniques are available to treat particular corneal disorders. Planning of surgical strategy is guided by careful patient selection which will minimize optical side effects and optimize visual outcome and subjective symptomatology after the PTK procedure.

Excimer laser keratectomy for astigmatism occurring after penetrating keratoplasty

PURPOSE

To review the results of photorefractive keratectomy used to treat astigmatism occurring after penetrating keratoplasty.

METHODS

Seven patients who had undergone corneal transplantation previously and had significant postoperative astigmatism were included. All these patients were intolerant of spectacle and contact lens correction. Excimer laser keratectomy was performed to reduce the astigmatic error. Minimum follow-up of 12 months was necessary for study inclusion.

RESULTS

The average refractive cylinder decreased from 5.32 diopters (D) preoperatively to 2.79 D postoperatively. The refractive cylinder was reduced in six of the seven eyes attempted. The average preoperative keratometric cylinder decreased from 5.54 D (range, 1.50-10.00 D) to 4.00 D (range 1.00-7.50 D) postoperatively. The best spectacle-corrected visual acuity was unchanged (within 1 line) in three eyes, improved in two, and decreased in two. The complications included a loss of at least two lines in spectacle-corrected visual acuity in two eyes and scarring in one.

CONCLUSIONS

Excimer laser keratectomy can reduce the astigmatism after penetrating keratoplasty. The excellent results in some eyes offer promise for this technique in the future.

PRK in patients with a keratoconic topography picture. The concept of a physiological 'displaced apex syndrome'

AIMS/BACKGROUND

Keratoconus is generally held to be an absolute contraindication for photorefractive keratectomy (PRK). Corneas with inferior steepening on corneal topography are widely thought to have subclinical keratoconus. We were not convinced that this is always the case, as there seems to be a group of patients with a stable inferior steepening pattern on topography who show no other characteristics of clinical keratoconus. We thus decided to offer PRK to some of these patients under strictly defined criteria.

METHOD

Four myopic patients with a topography pattern of inferior steepening were submitted to PRK. They were selected on the basis of being aged over 35, with a stable refraction, no slit-lamp signs of keratoconus, and a corrected vision of not less than 6/7 (0.9) with a spherical spectacle correction. They gave fully informed consent that this was an experimental procedure.

RESULTS

The refractive results at 6 months after operation were within the range one would expect for PRK on corneas with a regular 'bow-tie' topography and similar level of myopia. No unusual problems were encountered.

CONCLUSION

We feel that the corneal topography pattern of inferior steepening is not always a contraindication for PRK. The concept of a physiological 'displaced apex syndrome' is discussed and illustrated by corneal topography in different positions of gaze.

Excimer laser photorefractive keratectomy

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.