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

Smart Contact Lenses for Healthcare Monitoring and Therapy

The eye contains a wealth of physiological information and offers a suitable environment for noninvasive monitoring of diseases via smart contact lens sensors. Although extensive research efforts recently have been undertaken to develop smart contact lens sensors, they are still in an early stage of being utilized as an intelligent wearable sensing platform for monitoring various biophysical/chemical conditions. In this review, we provide a general introduction to smart contact lenses that have been developed for disease monitoring and therapy. First, different disease biomarkers available from the ocular environment are summarized, including both physical and chemical biomarkers, followed by the commonly used materials, manufacturing processes, and characteristics of contact lenses. Smart contact lenses for eye-drug delivery with advancing technologies to achieve more efficient treatments are then introduced as well as the latest developments for disease diagnosis. Finally, sensor communication technologies and smart contact lenses for antimicrobial and other emerging bioapplications are also discussed as well as the challenges and prospects of the future development of smart contact lenses.

Optical Coherence Tomography-Guided Transepithelial Phototherapeutic Keratectomy for Central Corneal Opacity in the Pediatric Population

Purpose

To report the outcomes of optical coherence tomography- (OCT-) guided transepithelial phototherapeutic keratectomy (PTK) for central corneal opacity in the pediatric population.

Methods

The charts of 10 eyes of 8 children aged 9 to 17 with central corneal opacity from various pathologies who underwent a standardized OCT-guided transepithelial PTK technique at a single private practice institution were retrospectively reviewed. The corneal topographic findings, OCT measurements, and visual results with refractive outcomes were analyzed 6 months after the PTK treatment.

Results

All 10 eyes tolerated the procedure well without any significant intraoperative or postoperative complications. Uncorrected and best spectacle-corrected visual acuity (BSCVA) significantly improved postoperatively (p < 0.0001 and p=0.0045, respectively). The absolute value of spherical equivalent on cycloplegic refraction significantly improved postoperatively as well (p=0.0014), but there were no significant changes in topographic measurements. Seven out of the 10 eyes had complete resolution of the central corneal opacity on OCT imaging. None of the subjects lost any lines of BSCVA and developed recurrence of the corneal opacity from the primary disease condition or required keratoplasty during the follow-up period.

Conclusions

OCT-guided transepithelial PTK can provide excellent visual outcomes in pediatric patients with central corneal opacities.

Predicting transepithelial phototherapeutic keratectomy outcomes using Fourier domain optical coherence tomography

PURPOSE

The aim of this study was to use Fourier domain optical coherence tomography to predict transepithelial phototherapeutic keratectomy outcomes.

METHODS

This is a prospective case series. Subjects with anterior stromal corneal opacities underwent an excimer laser phototherapeutic keratectomy (PTK) combined with a photorefractive keratectomy using the VISX S4 excimer laser (AMO, Inc, Santa Ana, CA). Preoperative and postoperative Fourier domain optical coherence tomography images were used to develop a simulation algorithm to predict treatment outcomes. Main outcome measures included preoperative and postoperative uncorrected distance visual acuities and corrected distance visual acuity.

RESULTS

Nine eyes of 8 patients were treated. The nominal ablation depth was 75 to 177 μm centrally and 62 to 185 μm peripherally. Measured PTK ablation depths were 20% higher centrally and 26% higher peripherally, compared with those for laser settings. Postoperatively, the mean uncorrected distance visual acuity was 20/41 (range, 20/25-20/80) compared with 20/103 (range, 20/60-20/400) preoperatively. The mean corrected distance visual acuity was 20/29 (range, 20/15-20/60) compared with 20/45 (range, 20/30-20/80) preoperatively. The MRSE was +1.38 ± 2.37 diopters (D) compared with -2.59 ± 2.83 D (mean ± SD). The mean astigmatism magnitude was 1.14 ± 0.83 D compared with 1.40 ± 1.18 D preoperatively. Postoperative MRSE correlated strongly with ablation settings, central and peripheral epithelial thickness (r = 0.99, P < 0.00001). Central islands remained difficult to predict and limited visual outcomes in some cases.

CONCLUSIONS

Optical coherence tomography measurements of opacity depth and 3-dimensional ablation simulation provide valuable guidance in PTK planning. Post-PTK refraction may be predicted with a regression formula that uses epithelial thickness measurements obtained by optical coherence tomography. The laser ablation rates described in this study apply only to the VISX laser.

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.

Topography-guided treatment of decentered laser ablation using LaserSight's excimer laser

PURPOSE

To assess the efficacy of topography-guided laser ablation for correction of previously decentered laser ablation using LaserSight's excimer laser.

METHODS

Re-treatment was performed to correct decentered ablation using LaserSight's excimer laser for 18 patients who previously underwent LASIK surgery for myopia correction in both eyes. For each patient, only the decentered eye was re-treated while the other asymptomatic eye forms a control group for this study. Measurements were conducted on ablation center, best spectacle-corrected visual acuity (BSCVA), contrast sensitivity and corneal aberrations pre- and post-operatively.

RESULTS

For the retreated 18 eyes, the mean decentration was significantly reduced from 1.32+/-0.28mm to 0.61+/-0.23mm post-operatively (t=16.24, p<0.001), and with a significant improvement in mean BSCVA from 0.08+/-0.09 logMAR to 0.01+/-0.11 logMAR (t=4.58, p<0.001). The post-operative contrast sensitivity at the spatial frequencies (SF) of 1.00 and 0.70 was significantly improved (p<0.05 for both SFs). Corneal higher-order aberrations (HOAs), including the coma-like aberrations and spherical aberration, were decreased. In comparing the measurements for the retreated group to those for the control group, no significant differencewas found either in decentration or in BSCVA, but the contrast sensitivity at 0.70 was lower and the level of corneal aberrations was higher.

CONCLUSIONS

Topography-guided ablation with LaserSight excimer laser is effective to correct decentered ablation. However, the re-treated eye is still inferior to the eye with originally centered ablation in corneal optical quality or visual performance.

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.

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.

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.

Central Island Treatment Using Technolas 217 Based on Orbscan II Assessment

PURPOSE

To present a case of central island after myopic laser in situ keratomileusis and the treatment technique using Technolas 217 laser based on topography findings.

METHODS

Serial corneal topographies with Orbscan were taken and an ablation profile was generated with subsequent treatment using the phototherapeutic keratectomy mode and surface ablation technique.

RESULTS

Marked reduction was noted in the height of central island and the best spectacle-corrected visual acuity improved from 20/40 to 20/25.

CONCLUSIONS

Ablation profile based on corneal topography can provide a possible treatment option for patients with central island.

Treatment of irregular astigmatism with a 213 nm solid-state, diode-pumped neodymium:YAG ablative laser

PURPOSE

To present the outcome of photorefractive keratectomy (PRK) using a new neodymium:YAG (Nd:YAG) laser in patients with irregular astigmatism.

SETTING

Claremont Eye Clinic, Claremont, and the University of Western Australia, Perth, Australia.

METHODS

In 3 patients with irregular astigmatism, PRK was performed with a solid-state, 213 nm wavelength, 300 Hz scanning-spot, diode-pumped Nd:YAG ablative laser (CustomVis Pulzar laser system). The 3 patients had had previous PRK with penetrating keratoplasty, astigmatic keratotomy, or limbal relaxing incisions. At 3 and 6 months, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), manifest refraction, contrast sensitivity, and corneal topography were measured.

RESULTS

The first patient had a 1-line improvement in BSCVA and a 4-line improvement in UCVA, a 3.00 diopter (D) decrease in keratometric cylinder, and improvement in contrast sensitivity. The second patient had a 7.00 D decrease in myopia in 1 meridian and a 4.25 D decrease in the refractive cylinder in the other meridian. The third patient had a 2-line improvement in BSCVA, a 5-line improvement in UCVA, a 2.00 D decrease in the refractive cylinder, and improvement in contrast sensitivity.

CONCLUSION

The laser's combination of a small spot, a fast pulse rate, and ultrafast tracking/scanning resulted in good results in 3 patients with difficult irregular astigmatism.

Survey of complications and recommendations for management in dissatisfied patients seeking a consultation after refractive surgery

PURPOSE

To review complications associated with and management options for dissatisfied patients seeking a consultation after refractive surgery performed elsewhere.

SETTING

Refractive Eye Surgery Center, The Wilmer Institute, Lutherville, Maryland, USA.

METHODS

In this retrospective review, charts of consecutive dissatisfied patients who sought a refractive consultation between June 1999 and January 2003 after refractive surgery performed elsewhere were reviewed and the following parameters were analyzed: visual acuity (uncorrected and best spectacle corrected), prior manifest refraction, complications, and recommendations. The subjective complaints, complications, and visual acuity were reviewed, and the associated historical or visual risk factors as well as treatment options were analyzed.

RESULTS

One hundred sixty-one eyes in 101 patients with ocular complaints were identified. One hundred thirty-four eyes (83.2%) had had laser in situ keratomileusis; 22 eyes, photorefractive keratectomy; 4 eyes, radial keratotomy; and 1 eye, laser thermokeratoplasty. The most common subjective complaints were blurred distance vision (59.0%), glare and night-vision disturbances (43.5%), and dry eyes (21.1%). The most common complications were overcorrection (30.4%), irregular astigmatism (29.8%), dry eyes (29.8%), glare (26.1%), difficulty with night driving (16.7%), and corneal haze (16.7%). The most common cause identified in eyes with best spectacle-corrected visual acuity worse than 20/40 was irregular astigmatism (10 of 18 eyes [55.5%]). The most common recommendation for management was medical treatment or observation (68.3%). Medical therapies recommended included lubrication, punctal plugs, topical and systemic pharmaceutical agents to modulate ocular surface, spectacles, and contact lenses. Keratoplasty (lamellar or penetrating) was recommended in 4 patients (4 eyes [2.5%]). The diagnoses included corneal ectasia in 3 eyes and severe flap complication with irregular astigmatism in 1 eye. Nine patients (5.6% eyes) required nonkeratoplasty surgery. In other patients, waiting for advances in technology, including wavefront-guided customized retreatment, was recommended.

CONCLUSIONS

A spectrum of complications associated with refractive surgery may result in patient dissatisfaction. Proper patient selection, prevention strategies, and prompt diagnosis and medical or surgical intervention may be beneficial in managing complications and improving patient satisfaction.

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.

Videokeratography in Conductive Keratoplasty

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Contact lens fitting to correct irregular astigmatism after corneal refractive surgery

PURPOSE

To study a technique of contact lens fitting and its visual results in patients with irregular astigmatism induced by corneal refractive surgery.

SETTING

Department of Cornea and Refractive Surgery, Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

This prospective noncomparative study comprised 29 eyes with irregular astigmatism after corneal refractive surgery. Different types of contact lenses were used to correct the astigmatism: hard, gas permeable, hybrid, and toric hydrophilic. Preoperative and postoperative data were analyzed for proper fitting including the preoperative keratometeric reading and corneal ablation zone.

RESULTS

Proper contact lens fitting was achieved in 23 eyes (79.3%). In 6 eyes (20.7%), fitting was not possible despite an improvement in best corrected visual acuity (BCVA). Of the eyes with proper fitting, 14 (60.9%) had rigid gas-permeable lenses (9.80 mm), 6 (26.1%) had hydrophilic lenses (14.00 mm), and 3 (13.0%) had hybrid lenses (14.3 mm). Comparing the BCVA with that with spectacles, 23 eyes (79.3%) gained 2 lines or more of BCVA, 4 (13.8%) gained 1 line, and 2 (6.9%) maintained the same acuity as with spectacles. No eye lost lines of BCVA.

CONCLUSIONS

Results indicate that contact lens fitting is a good-and sometimes the only-alternative for patients with induced irregular astigmatism. Rigid gas-permeable contact lenses provided the best visual performance and patient tolerance.

Astigmatism and LASIK

Although laser in situ keratomileusis (LASIK) enjoys a high success rate, postoperative residual or induced astigmatism may limit uncorrected visual acuity and cause starbursts and glare at night. Irregular astigmatism can also cause loss of best-corrected visual acuity, monocular diplopia, and ghosting of images. Astigmatism may be measured by keratometry and refraction, while corneal topographic techniques help to define irregular astigmatism, in particular. Further information may be obtained regarding induced higher-order aberrations with aberrometry. Because astigmatism has both direction and magnitude, its analysis is more complex than that of the spherical component of the treatment. There are multiple approaches to the analysis of surgically induced astigmatism, including vector analysis, conversion to a Cartesian coordinate system, matrix formalism, and linear optics. Both excimer laser and incisional techniques may be used to correct astigmatism after LASIK, but the treatment of irregular astigmatism requires selective zonal ablation techniques or customized corneal ablations, using topographic or wavefront derived data.

Spot size and quality of scanning laser correction of higher-order wavefront aberrations

PURPOSE

To investigate the effect of laser spot size on the outcome of aberration correction with scanning laser corneal ablation.

SETTING

Cleveland Clinic Foundation, Cleveland, Ohio, USA.

METHODS

Corrections of wavefront aberrations of Zernike modes from the second to eighth order were simulated. Gaussian and top-hat beams of 0.6 to 2.0 mm full-width-half-maximum diameters were modeled. The fractional correction and secondary aberration (distortion) were evaluated.

RESULTS

Using a distortion/correction ratio of less than 0.5 as a cutoff for adequate performance, a 2.0 mm or smaller beam was adequate for spherocylindrical correction (Zernike second order), a 1.0 mm or smaller beam was adequate for correction of up to fourth-order Zernike modes, and a 0.6 mm or smaller beam was adequate for correction of up to sixth-order Zernike modes.

CONCLUSIONS

Since ocular aberrations above the Zernike fourth order are relatively insignificant in normal eyes, current scanning lasers with a beam diameter of 1.0 mm or less are theoretically capable of eliminating most higher-order aberrations.

Soft Contact Lenses for Irregular Astigmatism After Laser in situ Keratomileusis

PURPOSE

To investigate soft contact lenses for managing irregular astigmatism after laser in situ keratomileusis (LASIK). The prevailing notion has been that soft contacts conform to corneal surface irregularities and have a limited role for managing LASIK-induced irregular astigmatism.

METHODS

A 41-year-old man with bilateral central steep islands following LASIK had best spectacle-corrected visual acuity of 20/40(+1) in the right eye and 20/70+2 in the left eye, despite 20/20 acuity in each eye with rigid contact lenses. Three soft lenses made of etafilcon A (58% H2O) in different center thicknesses were placed sequentially on each eye. All lenses were -2.00 D sphere, in the flatter of the two available base curves. With each lens, corneal topography, spherical over-refraction, and the resulting visual acuity were recorded.

RESULTS

In all instances, corneal topography showed reduced surface irregularity although at least some irregularity still transmitted through the lenses. Each spherical over-refraction gave better visual acuity than the corresponding best spectacle-corrected visual acuity. The right eye achieved 20/20 with the thickest lens and spherical over-refraction. The left eye achieved 20/25 with the lens of intermediate thickness and spherical overrefraction. The patient reported functional vision and good comfort with these lenses.

CONCLUSIONS

Disposable soft contact lenses can modestly mask irregular astigmatism caused by excimer laser ablation.

Spot Size and Quality of Scanning Laser Correction of Higher Order Wavefront Aberrations

PURPOSE

To investigate the effect of laser spot size on the outcome of aberration correction with scanning laser corneal ablation.

METHODS

Numerical simulation of ablation outcome.

RESULTS

Correction of wavefront aberrations of Zernike modes from second to eighth order were simulated. Gaussian and top-hat beams of 0.6 to 2.0-mm full-width-half-maximum diameters were modeled. The fractional correction and secondary aberration (distortion) were evaluated. Using a distortion/correction ratio of less than 0.5 as a cutoff for adequate performance, we found that a 2 mm or smaller beam is adequate for spherocylindrical correction (Zernike second order), a 1 mm or smaller beam is adequate for correction of up to fourth order Zernike modes, and a 0.6 mm or smaller beam is adequate for correction of up to sixth order Zernike modes.

CONCLUSIONS

Since ocular aberrations above Zernike fourth order are relatively insignificant, current scanning lasers with a beam diameter of 1 mm or less are theoretically capable of eliminating most of the higher order aberrations of the eye.

Topography-driven excimer laser for the retreatment of decentralized myopic photorefractive keratectomy

OBJECTIVE

This study evaluated the efficacy, predictability, stability, and safety of a software program (Corneal Interactive Programmed Topographic Ablation, CIPTA, LIGI, Taranto, Italy), which, by transferring programmed ablation from the corneal topograph to a flying-spot excimer laser, provides customized laser ablation for correction of postmyopic photorefractive keratectomy (PRK) decentrations.

DESIGN

Noncomparative consecutive case series.

PARTICIPANTS

Thirty-two eyes of 32 subjects with a mean age of 35 years (range, 19-49; standard deviation [SD], 7.9) had CIPTA-guided PRK at the Clinica Oculistica of Bari University (Italy). All the subjects had irregular astigmatism after postmyopic PRK because of clinically significant, decentered treatments of more than 1 mm. OPERATION: Individual topographies were acquired by a corneal topograph (Orbscan II, Orbtek, Inc., Salt Lake City, UT). These, together with refractive data, were processed to obtain a customized altimetric ablation profile that was transferred to a flying-spot laser (Laserscan 2000, Lasersight, Orlando, FL).

MAIN OUTCOME MEASURES

The topographic study of centration and data on uncorrected (UCVA) and best-corrected (BCVA) visual acuity, predictability, and stability of refraction, and any complications, were analyzed.

RESULTS

Mean follow-up was 10.3 months (range, 4-18 months; SD, 5.8). At the last postoperative examination, 29 eyes (90.6%) had a UCVA superior to 20/40. Nineteen eyes (59.4%) had a UCVA of 20/20. Twenty-two eyes (68.75%) were within 0.50 diopters (D) of attempted correction in the spherical equivalent and 28 eyes (87.5%) were within 1 D. The index of success of astigmatic correction was 0.15. No eye lost Snellen lines of BCVA, whereas 18 eyes (56.25%) gained Snellen lines. Postoperative topographies revealed well-centered treatments.

CONCLUSIONS

The combination of topographic data with computer controlled flying-spot excimer laser ablation is a suitable solution for correcting irregular astigmatism after postmyopic PRK decentrations.

Astigmatism management: ablation patterns

Treatment of astigmatism is possible with the excimer laser. Results with this technology are more predictable and accurate than with incisional techniques. Ablation profiles differ for the various types of astigmatism, and the best approach is the one in which the least amount of tissue is removed from the cornea. Surgical success requires appropriate preoperative counseling, careful preoperative measurements, and meticulous intraoperative technique. Reported outcomes are excellent and future developments will lead to even better results.

Excimer laser phototherapeutic keratectomy

Excimer laser phototherapeutic keratectomy (PTK) is an important tool in the management of superficial corneal pathology. It works well in the treatment of anterior corneal dystrophies and degenerations, but we are learning that it may have a role in the treatment of certain patients with deeper corneal pathology. Indications also are being expanded to treat much less common conditions and also to treat children. Irregular astigmatism, which is not treated very well with current PTK techniques, may be addressed better with newer approaches, such as selective zonal ablation and the use of BioMask. As current PTK techniques are improved and newer methods are developed, this procedure will continue to be an excellent option for certain patients with superficial corneal problems.

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.

Laser in situ keratomileusis for undercorrection and overcorrection after radial keratotomy

PURPOSE

To evaluate laser in situ keratomileusis (LASIK) in the management of overcorrection and undercorrection after radial keratotomy (RK).

SETTING

Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

This prospective study comprised 20 eyes of 13 patients. The eyes were divided into 2 groups: 11 eyes that were overcorrected after RK and 9 eyes that were undercorrected after RK. Both groups were treated with LASIK after a mean interval of 22 months +/- 8.4 (SD) (range 12 to 45 months). The follow-up was 6 months.

RESULTS

Six months after LASIK, there was a significant decrease in the spherical equivalent in both groups. Ninety-one percent of eyes in the overcorrected group and 89% in the undercorrected group were within +/-1.0 diopter of the intended correction. There was a significant improvement in the uncorrected visual acuity in both groups. In the overcorrected group, 91% showed no change or improvement in their best corrected visual acuity; in the undercorrected group, 89% showed no change or improvement.

CONCLUSIONS

Laser in situ keratomileusis was relatively safe in treating both overcorrection and undercorrection after RK. With proper intraoperative precautions, LASIK can effectively treat the residual refractive defects after RK.