Showing papers in "Journal of Refractive Surgery in 2002"

Standards for reporting the optical aberrations of eyes.

Abstract: In response to a perceived need in the vision community, an OSA taskforce was formed at the 1999 topical meeting on vision science and its applications (VSIA-99) and charged with developing consensus recommendations on definitions, conventions, and standards for reporting of optical aberrations of human eyes. Progress reports were presented at the 1999 OSA annual meeting and at VSIA-2000 by the chairs of three taskforce subcommittees on (1) reference axes, (2) describing functions, and (3) model eyes.

A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.

Abstract: PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients. [J Refract Surg 2002;18: 683-691] T

Are all aberrations equal

Abstract: PURPOSE: To determine for a fixed RMS error (25 μm, over a 6-mm pupil) how each mode of the normalized Zernike polynomial (second through the fourth radial order) affects high and low contrast logMAR visual acuity. METHODS: Three healthy volunteers served as subjects. CTView was used to generate optically aberrated logMAR charts. Accommodation was paralyzed and pupils dilated. The foveal achromatic axis of the eye was aligned to a 3-mm pupil and the eye was optimally refracted. Aberrated acuity charts were read until five letters were missed. Data were normalized for each subject to the acuity obtained by reading unaberrated charts and plotted as letters lost as a function of Zernike mode. RESULTS: Defocus (Z 0 2 ) decreased letter acuity more than astigmatism (Z 2 2 , Z - 2 2 ). Coma (Z 1 3 , Z - 1 3 ) decreased acuity more than trefoil (Z 3 3 , Z - 3 3 ). Spherical aberration (Z 0 4 ) and secondary astigmatism (Z 2 4 , Z - 2 4 ) decreased acuity much more than quadrafoil (Z 4 4 , Z - 4 4 ). CONCLUSIONS: 1. For an equal amount of RMS error not all coefficients of the Zernike polynomial induce equivalent losses in high and low contrast logMAR acuity. 2. Wavefront error concentrated near the center of the pyramid adversely affects visual acuity more than modes near the edge of the pyramid. 3. Large changes in chart appearance are not reflected in equally large decreases in visual performance (ie, subjects could correctly identify highly aberrated letters). 4. Interactions between modes complicate weighting each Zernike mode for visual impact.

Prospective randomized trial of an anterior surface modified prolate intraocular lens.

Abstract: PURPOSE: We compare the contrast sensitivity obtained with an anterior surface modified prolate intraocular lens with the contrast sensitivity obtained with a standard spherical intraocular lens. METHODS: Patients presenting for cataract surgery in one eye were randomized to receive either the Tecnis Z9000 intraocular lens (Pharmacia) or the AMO AR40e Opti-Edge intraocular lens (AMO). Sine wave grating contrast sensitivity testing under mesopic and photopic conditions served as the principal outcome measure. RESULTS: The Tecnis Z9000 intraocular lens provided statistically significantly better contrast sensitivity at 1.5 and 3 cycles per degreee under mesopic conditions and at 6, 12 and 18 cycles per degree under photopic conditions. CONCLUSION: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.

Biomechanics of the cornea and wavefront-guided laser refractive surgery.

Abstract: PURPOSE: Wavefront-guided laser refractive surgery induces postoperative optical aberrations that are not explained by the ablation profile. METHODS: A conceptual model is presented for a potential mechanism of surgically-induced corneal shape change that is dependent on structural modification, rather than ablation profile. RESULTS: Examples are provided from clinical and basic studies that are consistent with the proposed model. CONCLUSION: Corneal biomechanical response to ablative surgery may significantly affect outcomes, and should be taken into account when planning customized procedures.

Validation of the estimation of corneal aberrations from videokeratography in keratoconus

Abstract: PURPOSE: To validate the estimation of corneal aberrations from videokeratography against a laser ray tracing technique that measured total eye aberrations, in eyes without keratoconus (ie, cornea-dominated wave aberrations) METHODS: We measured total and corneal wave aberrations of three eyes diagnosed with keratoconus by slit-lamp microscopy and corneal topography: two eyes from one patient with early keratoconus and one eye with more advanced keratoconus Total aberrations were measured with laser ray tracing Corneal aberrations were obtained from corneal elevation data measured with a corneal videokeratoscope using custom software that performs virtual ray tracing on the measured front corneal surface RESULTS: The keratoconus eyes showed a dramatic increase in aberrations (both corneal and total) particularly coma-like terms, which were 374 times higher on average than normal Anterior corneal surface aberrations and total aberrations were similar in keratoconus This similarity was greater for the early keratoconus patient, suggesting a possible implication of the posterior corneal surface in advanced keratoconus CONCLUSIONS: The similarity found between corneal and total aberration patterns in keratoconus provided a cross-validation of both types of measurements (corneal topography and aberrometry) Both techniques were useful in diagnosing and quantifying optical degradation imposed by keratoconus [J Refract Surg 2002;18:267-270]

Intracorneal ring segments for iatrogenic keratectasia after laser in situ keratomileusis or photorefractive keratectomy.

Abstract: PURPOSE: Intrastromal corneal ring segments (Intacs) were inserted in four eyes with iatrogenic keratectasia, 12 to 44 months after laser in situ keratomileusis (LASIK) in two patients and photorefractive keratectomy (PRK) in two patients, in order to avoid penetrating keratoplasty and to improve quality of vision. METHODS: A modified asymmetrical Intacs micro-thin prescription inserts implantation technique was used in three eyes where a 1.0-mm temporal incision and a superior-inferior dissection were performed. A thicker segment was implanted in the lower stromal channel and a thinner one was placed in the superior channel. In the fourth eye, because of the severity of the corneal bulging after PRK, two 5.0-mm optical zone symmetrical Ferrara Ring segments were implanted. RESULTS: Ten months after surgery, all eyes experienced a significant improvement of uncorrected and best spectacle-corrected visual acuity. The topographical indices showed an overall surface regularization with increased corneal uniformity and potential corneal visual acuity. No intraoperative or postoperative complications occurred. CONCLUSIONS: Asymmetrical or symmetrical corneal ring segment implantation in eyes with keratectasia after LASIK or PRK resulted in safe, fairly predictable corneal regularization, with significant improvement of aided and unaided vision. In the short term, these techniques seem to be helpful in reducing the progression of corneal ectasia after excimer laser surgery, delaying or avoiding the need of penetrating keratoplasty.

Incidence of lens opacities and clinically significant cataracts with the implantable contact lens: comparison of two lens designs.

Abstract: PURPOSE: To compare the incidence of anterior subcapsular lens opacities, clinically significant cataracts, secondary lens-related surgical reinterventions, and vaulting characteristics of the now discontinued V3 and currently used V4 Staar Surgical Implantable Contact Lens (ICL) phakic intraocular lens designs. METHODS: In this non-randomized prospective clinical trial, 87 eyes were implanted with the V3 and 523 eyes with the V4 ICL as part of the U.S. FDA clinical trial for myopia. LOCS III assessment of lens opacities, clinically significant cataract, ICL vaulting (clearance between ICL and crystalline lens), and secondary ICL-related surgeries were the main outcome measures. Mean follow-up in the V3 series was 30.7 ± 10.0 months (range 10.8 to 49.3 mo) and in the V4 series, 17.3 ± 6.9 months (range 0.25 to 38.5 mo). RESULTS: Incidence of anterior subcapsular opacities was significantly higher with the V3 vs. V4 ICL (12.6% vs. 2.9%, P<.001). The difference was largely due to the higher rate of late-appearing opacities ( 1 year after surgery; 9.2% vs. 0.6%, P<.001). The V3 group had a greater proportion of eyes with poor vault (23.6% vs. 4.3%, P<.001) and the presence of poor vault was highly associated with the development of late anterior subcapsular opacities (P<.001). Clinically significant cataract was more frequent in the V3 vs. V4 ICL (9.2% vs. 0.8%, P<.001), as was cataract extraction (6.9% vs. 0.2%, P<.001), and need for ICL replacement (5.7% vs. 1.1%, P<.001). Differences in opacity rate between the V3 and V4 designs were not due to differences in postoperative follow-up. CONCLUSION: Implantation of the currently used V4 Staar Surgical model ICL resulted in significantly less anterior subcapsular opacities, clinically significant cataracts, and secondary ICLrelated surgery. [J Refract Surg 2002;18:673-682]

Higher order aberrations in normal, dilated, intraocular lens, and laser in situ keratomileusis corneas.

Abstract: PURPOSE: To compare repeated measures of Zernike polynomial higher-order aberrations in 29 normal, 13 dilated normal, 11 intraocular lens (IOL), 11 laser in situ keratomileusis (LASIK), and one refractive keratectomy (RK)/IOL subject. METHODS: At least three Shack-Hartmann images were obtained from each subject, and higher order (uncorrectable by spectacles) Zernike representation was determined. For each subject, confidence intervals for each Zernike coefficient were determined as a function of pupil size. Significant (P<.05) coefficients were averaged within groups, and group means were compared to normal subjects. RESULTS: No differences were seen between the normal and dilated groups at P=.05. The patients with prior LASIK and IOL surgery showed statistically significant elevation of 4th order spherical aberration and total wavefront variance for pupil sizes greater than 5 mm, compared to normals. CONCLUSION: Both IOL and LASIK surgery elevate spherical aberration and wavefront variance, with increasing magnitude of effect with increasing pupil size, although pupillary dilation alone did not produce statistically different changes, as compared to normal subjects. These findings demonstrate that IOL implantation can produce more net aberrations than LASIK, and demonstrate a new opportunity to optimize surgical results.

Effect of laser in situ keratomileusis for hyperopia on tear film and ocular surface.

Abstract: PURPOSE: To examine the effects of laser in situ keratomileusis (LASIK) for hyperopia on the tear film and ocular surface. METHODS: A retrospective 12-month analysis of 88 eyes (88 participants) who had LASIK for hyperopia was performed. Participants were evaluated before and after (2 weeks, 1, 3, 6, and 12 months) surgery for dry eye symptoms (McMonnies Dry Eye Survey primary symptoms), tear film stability (fluorescein break-up time), tear volume (phenol red thread test), ocular surface staining (fluorescein), and conjunctival goblet cell density. RESULTS: Chronic dry eye was experienced by 32% of participants; symptoms were significantly associated with female gender, preoperative dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining after surgery, lower tear volume before and after surgery, and lower goblet cell densities after surgery. Regression rate 12 months after surgery was 32% and significantly associated with female gender, chronic dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining before and after surgery, and lower tear volume before and after surgery. CONCLUSIONS: Dry eye, particularly in females, is problematic after LASIK for hyperopia and is associated with refractive regression. Current methods for managing the tear film and ocular surface may not control LASIK-induced dry eye, particularly in some females during the first 6 months after surgery.

Implantation of a new accommodative posterior chamber intraocular lens.

Abstract: PURPOSE A new, potentially accommodative posterior chamber lens (PCIOL) was designed based on principles elaborated by Hanna using finite element computer simulation methods. We report 3-month postoperative results in patients. METHODS In a prospective study, 12 eyes of 12 patients (age 45 to 87 yr) underwent phacoemulsification for cataracts and PCIOL implantation. The PCIOL, 1 CU, has haptics designed for anterior optic movement following ciliary muscle contraction. Patients were examined postoperatively after 1 and 2 days, 1, 2 and 6 weeks, and 3 months, and results were compared with a control group of 12 eyes that received standard PMMA or acrylic PCIOLs. RESULTS Surgery was uncomplicated and all PCIOLs were well-tolerated and stable with good centration in the capsular bag. The results were (mean +/- SD [range] and median; 1 CU versus control PCIOL): near visual acuity (Birkhauser reading chart at 35 cm) with best distance correction 0.34 +/- 0.17 (0.2 to 0.6), 0.3 (J10-J1, median J7) versus 0.15 +/- 0.07 (0.1 to 0.3), 0.15 (J16-J7, median J13), P=.001; subjective near point 59 +/- 10 cm (40 to 100 cm), 53.5 cm versus 93 +/- 20 cm (64 to 128 cm), 86 cm, P=.004; retinoscopic accommodative range 1.2 +/- 0.4 D (0.63 to 1.5 D), 1.2 D versus 0.2 +/- 0.19 D (-0.25 to 0.5 D), 0.25 D, P < .001; decrease of anterior chamber depth after 2% pilocarpine 0.63 +/- 0.16 mm (0.40 to 0.91 mm), 0.63 mm versus 0.15 +/- 0.05 mm (0.08 to 0.20 mm), 0.17 mm, P < .001. CONCLUSIONS The new PCIOL appears to be safe at short to medium term. Our results indicate pseudophakic accommodation secondary to focus shift with this PCIOL. Additional larger and long-term studies are necessary for exact evaluation of safety and accommodative power of this new PCIOL.

A new method of calculating intraocular lens power after photorefractive keratectomy.

Abstract: PURPOSE To find a method of calculating intraocular lens (IOL) power that may be independent of preoperative data, in eyes that have developed a cataract after refractive surgery. METHODS Prior to and 1 month after PRK, the SRK/T formula was used to calculate IOL power in 88 eyes of 65 patients with a preoperative spherical equivalent refraction between -16.25 to +0.25 D (mean -5.39 +/- 3.19 D). IOL power was calculated by utilizing the spherical equivalent refraction as target both before and after PRK. Utilizing the postoperative corneal radius measurement (R2), an underestimation of the IOL power was found. For this reason, the mean postoperative corneal radius (R3) that gave the same IOL power found before surgery was calculated for each patient. The R3/R2 ratios were plotted against the axial eye length and a linear regression formula was used to calculate R2 correcting factors that gave the new corneal radius (R4). Patients were divided into classes according to axial eye length, and the mean R3/R2 ratios for each class were calculated and used to recalculate the new mean radius (R5). IOL power for emmetropia was calculated in all patients by utilization of R3, R4, R5, the historical method, and the "true corneal power" method. RESULTS Within +/-0.50 D from the IOL power calculated with R3, R4 gave 35 (39.3%) IOLs, while R5 gave 40 (45.5%) IOLs; the clinical history method gave 24 (27.3%) IOLs and "true corneal power" gave 23 (26.1%) IOLs, with a statistically significant difference P<.001). CONCLUSIONS Our theoretical method, based on correlation between axial eye length and corneal radius correcting factors, may represent an effective method of calculating IOL power after PRK, especially if the history of the patient is unknown.

Artisan phakic iris claw intraocular lens for high primary and secondary hyperopia.

Abstract: PURPOSE To evaluate the efficacy, predictability, and safety of the Artisan iris claw phakic intraocular lens for the correction of high primary and secondary hyperopia. METHODS Fifty-seven eyes were divided into two groups: 29 eyes had primary hyperopia (mean refraction 6.06 +/- 1.26 D, and 28 eyes had secondary hyperopia, (mean refraction 5.88 +/- 1.88 D) induced or residual following a previous corneal refractive procedure. Consecutive implantation of the Artisan iris claw phakic intraocular lens was performed. Main outcome measures recorded were BSCVA, UCVA, refraction, and astigmatic change, intraocular inflammation, and endothelial cell loss. RESULTS Primary hyperopic group: Preoperatively, mean UCVA was 0.4 +/- 0.7 and mean BSCVA was 0.2 +/- 0.6. After implantation, mean UCVA was 0.3 +/- 0.6 and BSCVA was 0.1 +/- 0.6. Mean cycloplegic residual spherical refractive error after surgery was 0.10 +/- 0.57 D (range -1 to +2 D). Mean surgically induced astigmatism was 1.48 +/- 0.89 D. Safety index was 1.11. Efficacy index was 0.83. Secondary hyperopic group: Preoperatively, mean UCVA was 0.5 +/- 0.7 and mean BSCVA was 0.2 +/- 0.6. Postoperatively, mean UCVA was 0.4 +/- 0.7 and mean BSCVA was 0.2 +/- 0.6. Mean cycloplegic residual spherical refractive error was 0.55 +/- 1.49 D. Mean surgically induced astigmatism was 1.85 +/- 1.19 D. Safety index was 1.05. Efficacy index was 0.7. Postoperative iridocyclitis was observed in one eye (3.4%) in the primary group and in three eyes (10.7%) in the secondary group. Overall corneal endothelial cell loss at 1 year of follow-up was 9.4%. CONCLUSION The Artisan iris claw phakic intraocular lens was reasonably safe and predictable for correcting high hyperopia.

Management of corneal ectasia after laser in situ keratomileusis with INTACS.

Abstract: Purpose To evaluate the safety and efficacy of intrastromal corneal ring segments (ICRS, INTACS, Keravision) for the correction of corneal ectasia after laser in situ keratomileusis (LASIK). Methods In this prospective, noncomparative case series, INTACS were implanted in three eyes (two patients) that were ectatic after LASIK. Mean follow-up was 8.7 months (range, 8 to 10 mo). Results No intraoperative complications occurred. After INTACS implantation, uncorrected visual acuity ranged from 20/20 to 20/25 at 6 months and remained stable until 9 months. Mean postoperative spherical equivalent refraction was 0.50 D at 1 month and no significant changes appeared up to 9 months after INTACS implantation. After INTACS implantation, no eye lost any lines of Snellen spectacle-corrected visual acuity and two eyes gained from one to two lines. There was an increase in topographical regularity in all three eyes. Conclusion Implantation of INTACS in eyes with corneal ectasia after LASIK resulted in good refractive outcome, absence of complications, and improvement in visual acuity.

Predictability of corneal flap thickness in laser in situ keratomileusis using three different microkeratomes.

Abstract: PURPOSE: To compare the accuracy and consistency of corneal flap thickness in the right and left eye created by three different widely used microkeratomes during consecutive laser in situ keratomileusis (LASIK). METHODS: Corneal thickness of 132 eyes of 66 patients was measured preoperatively and intraoperatively. Corneal flap thickness was calculated by subtracting the corneal stromal thickness from the total corneal thickness. Three different microkeratomes were used for creating the corneal flap: Chiron Automated Corneal Shaper (ACS), Baush and Lomb Surgical Hansatome, and Nidek MK 2000 microkeratomes. The same surgeon performed all procedures on the right eye first and then on the left eye using the same blade and the same surgical technique. RESULTS: Mean corneal flap thickness created by the ACS (160-μm depth setting) microkeratome was 128.30 ′ 12.57 μm in the right eye and 122.96 ′ 13.30 μm in the left eye. The Hansatome (160-μm depth plate) microkeratome created a flap of mean 141.16 ′ 20.11 μm in the right eye and 120.95 ′ 26.95 μm in the left eye, and the Nidek MK 2000 (130-μm depth plate) microkeratome created a flap of 127.25 ′ 4.12 μm in the right eye and 127.54 ′ 3.7 μm in the left eye. CONCLUSION: Corneal flap thickness tended to be considerably thinner than expected on both eyes using the ACS and Hansatome. With the ACS and Hansatome, the difference in corneal flap thickness between the first and second operated eye was statistically significant. With the Nidek MK 2000 microkeratome, there was no statistically significant difference between the first and second operated eye and measurements were close to desired corneal flap thickness. Intraoperative pachymetry is recommended for every LASIK procedure.

Early onset ectasia following laser in situ keratomileusus: case report and literature review.

Abstract: Purpose Laser in situ keratomileusis (LASIK) has been associated with the development of postoperative corneal ectasia. We present a case of early onset ectasia after LASIK, review known risk factors in development, and discuss possible strategies for prevention. Methods A 39-year-old man underwent bilateral LASIK for moderate myopia. Preoperative cycloplegic refractions were -9.00 + 0.25 x 140 degrees OD and -7.75 sphere OS. Corneal topography demonstrated mild inferior steepening bilaterally although definite evidence of keratoconus by either the Klyce/Maeda and Smolek/Klyce keratoconus screening tests was not present. Following the creation of flaps with 160-microm plates, ablations of 93 microm OD and 80 microm OS were performed, estimated to leave residual stromal beds of at least 314 microm OD and 330 microm OS. Results On the first postoperative day, uncorrected visual acuities were 20/400 OD and 20/40 OS. On the fifth postoperative day, the patient's uncorrected visual acuity was 20/400 OD, and 20/300 OS. Corneal topography of the right eye showed profound inferior steepening with an apical corneal power in excess of 57 D; topography of the left eye showed mild inferior steepening. Eighteen months after surgery best corrected visual acuity was 20/40 OD and 20/30 OS with rigid gas permeable contact lenses. Conclusions This case highlights the need for a high index of suspicion when one notes an asymmetric bow-tie pattern on preoperative LASIK corneal topography, despite seemingly safe estimates of residual stromal bed thickness.

Adaptive optics visual simulator.

Abstract: PURPOSE: To develop a prototype instrument that uses adaptive optics to introduce virtually any desired aberration profile in a subject’s eye. At the same time, the instrument could be used to evaluate the subject’s spatial vision for each controlled aberration profile. This “aberration testing station” or “visual simulator” allows us to study the relationship between specific aberrations and visual quality. METHODS: The apparatus uses infrared light to measure the wavefront aberration of the system plus the eye with a Hartmann-Shack wavefront sensor. Defocus is added (or removed) with a computer-controlled, motorized optometer, while higher order aberrations are introduced by a 37-channel membrane deformable mirror. A parallel viewing channel is used for visual testing with the instrument. Visual acuity, contrast sensitivity, and other visual tests are performed under normal viewing for each desired aberration profile. RESULTS: The range of defocus that can be added is nearly unlimited, while the maximum amount of other aberration modes is restricted to approximately 0.5 µm, depending on mode. Pure modes or any selected combination of modes can be produced with high repeatability and precision (usually better than 0.05 µm), and the system works for pupil diameters up to 6 mm (with a natural pupil). CONCLUSIONS: The adaptive optics visual simulator is a powerful, non-invasive tool to evaluate how aberrations affect vision. In addition, it can be used for the interactive design and testing of new ophthalmic devices, and for the simulation of visual outcomes in customized refractive surgery. [J Refract Surg 2002;18:S634-S638]

Effect of aging on ocular light scatter and higher order aberrations.

Abstract: Purpose To study the effect of aging on ocular light scatter and higher order aberrations in humans. Methods Seventy-six eyes of 76 normal subjects who had refractive errors but no ocular disease were studied. Their age ranged from 4 to 69 years (mean 34.8 +/- 5.8 yr). Both light scatter and total higher order aberrations were simultaneously and quantitatively measured by a Hartmann-Shack sensor for the central 4-mm-diameter pupil. Higher order aberrations were calculated from the Zernike polynomials up to the 4th order. The amount of light scatter was estimated by using the diameter of the point spread functions (PSFs) of the Hartmann images. A correction was made for the effect of the aberrations on the width of the images. Linear regression analysis was performed to investigate the effect of aging on light scatter and total higher order aberrations. Results A significant correlation was found between scatter and age (Spearman rank correlation coefficient, r = 0.501, P = .001). Also, the total higher order aberrations increased significantly with age (r = 0.323, P = .005). The total higher order aberration and scatter index were not statistically significantly correlated (r = 0.184, P = .112). Conclusions These results indicate that scatter was better correlated with age than higher order aberrations.

Aberration generation by contact lenses with aspheric and asymmetric surfaces.

Abstract: Purpose We explored the potential of aberration correction in the human eye by using a new generation of soft contact lenses with aspheric and asymmetric surfaces. Methods Soft contact lens samples were designed with one asymmetrical surface (front) and one spherical (back) to produce predetermined amounts of desired pure defocus, astigmatism, trefoil, coma, and spherical aberration. Contact lens wavefront aberrations were measured ex vivo using a Fizeau-Tolanski interferometer and compared with the in vivo wavefronts obtained by subtracting the aberrations of the eye with and without the contact lenses. These second set of measurements were obtained using a Shack-Hartmann sensor. Results We found that an aberration-free contact lens sample induced in the eye a small amount of residual aberration. We obtained a good match between the ex vivo and in vivo wavefront measurements for most of the samples of the contact lenses. Conclusions The aberrations generated by soft contact lenses on the eye were predictable. Rotations and translations of the contact lenses with respect to correct position on the eye were, however, the main limitation for precise correction of the ocular aberrations.

Comparison of TGF-β1 in Tears Following Laser Subepithelial Keratomileusis and Photorefractive Keratectomy

Abstract: PURPOSE: To compare the release of tear fluid transforming growth factor-beta1 (TGF-beta1) of 15 patients who underwent photorefractive keratectomy (PRK) in one eye and laser subepithelial keratomileusis (LASEK) in the other eye. METHODS: Tear fluid samples were collected with scaled microcapillary tubes preoperatively (day 0) and on the first, second, and seventh postoperative days. We calculated the release of TGF-beta1 (tear fluid flow-corrected concentrations of TGF-beta1) by multiplying the concentration by capillary tear fluid flow and also evaluated corneal haze at 1, 3, and 6 months after PRK or LASEK. RESULTS: The median TGF-beta1 release values were: Day 0: 50.6 pg/min (range 0 to 101.6 pg/min) for PRK and 56.7 pg/min (range 0 to 121.8 pg/min) for LASEK (P=.496); Day 1: 240.6 pg/min (range 56.6 to 1120.2 pg/min) for PRK and 155.2 pg/min (range 45.1 to 480.4 pg/min) for LASEK, which showed a significant difference between the two procedures (P=.041); Day 2: 395.7 pg/min (range 92.3 to 1150.7 pg/min) for PRK and 185.2 pg/min (range 41.4 to 872.5 pg/min) for LASEK (P=.004); and Day 7: 91.3 pg/min (range 0 to 225.4 pg/min) for PRK and 74.3 pg/min (range 0 to 187.1 pg/min) for LASEK, (P=.244). The mean corneal haze score at 1 month after PRK was 0.88 +/- 0.50 and 0.53 +/- 0.29 after LASEK, and a statistically significant difference was noted between the two groups (P=.005). At 3 months (P=.083) and 6 months (P=.157) after the procedures, there were no statistically significant differences. CONCLUSIONS: A lower amount of tear fluid transforming growth factor-beta1 was released in the early postoperative days following LASEK than in PRK. The lower grade of corneal haze seen in LASEK than PRK in the early postoperative period may come from a decreased release of TGF-beta1, which may have a role in wound healing.

Mesopic contrast sensitivity function after excimer laser photorefractive keratectomy.

Abstract: PURPOSE To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. METHODS Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes. RESULTS Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P .01 for all frequencies). CONCLUSION Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.

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

Abstract: Purpose To clarify the feasibility of aberration-sensing and wavefront-guided laser in situ keratomileusis (LASIK) to manage grossly decentered ablation and to discuss the limitations of the technology. Methods Three patients with previous decentrations of the ablation zone between 1.5 to 2.0 mm were scheduled for wavefront-guided LASIK. All patients reported monocular diplopia and halos. Wavefront aberrations were measured with a Tscherning-type aberrometer. Laser ablation was done with a WaveLight Allegretto in a one-step procedure with ablation profiles calculated only from the individual wavefront map. Decentrations were determined from corneal topography. Results Three months after surgery, patient WM and patient SU had gained uncorrected and best spectacle-corrected visual acuity. The root mean square-wavefront error decreased up to 61% and 33%, respectively, for total and higher order aberrations (Zernike modes of 3rd order and higher). There was significant enlargement of the optical zone determined by corneal topography, and both patients no longer reported diplopia and halos at 3 months postoperatively. The optical aberration of the third patient (RE), after a 5.00-D overcorrection with a 2-mm decentration, was too high for aberration-sensing; retinal images obtained from the wavefront device were too smeared and not of sufficient contrast. In addition, this patient had a residual corneal thickness of 416 microm and thus wavefront-guided LASIK was not done. Conclusions Wavefront-guided LASIK offers a new way of managing grossly decentered laser ablations. Unfortunately, there are still patients who have aberrations too large for wavefront sensing or with other clinical limitations such as a residual corneal thickness too thin for further treatment.

Microbial keratitis after laser in situ keratomileusis

Abstract: PURPOSE AND METHOD: To review the literature on microbial keratitis reported after laser in situ keratomileusis (LASIK). RESULTS: Forty-one eyes have been reported to have microbial keratitis after LASIK. The causative organisms vary from gram positive bacteria to atypical mycobacteria, fungal, and viral pathogens. The infection is usually acquired intraoperatively, but may also be caused by postoperative contamination. A majority of the patients present within 72 hours of the surgery with an acute onset of symptoms. Management of microbial keratitis after LASIK includes aggressive topical fortified antibiotic therapy, irrigation of stromal bed with antibiotic solution after lifting the flap, and sending the scraping of the infiltrate for microbiological evaluation. The keratitis heals with scarring and a best spectacle-corrected visual acuity of 20/40 or better can be obtained in the majority of the patients. CONCLUSION: Microbial keratitis is a sight-threatening complication of LASIK.

Comparison of wavefront-guided customized ablation vs. conventional ablation in laser in situ keratomileusis.

Abstract: PURPOSE: To compare visual outcome after applying wavefront-guided customized ablation with conventional ablation in laser in situ keratomileusis (LASIK) patients. METHODS: We performed a prospective, randomized controlled study that included 22 eyes of 11 patients who were treated with LASIK using the Nidek EC-5000 excimer laser system. We applied wavefront-guided customized ablation (study group) in the first eye of each patient. The conventional ablation (control group) was performed in the other eye of the same patient. Best spectacle-corrected visual acuity (BSCVA), spherical equivalent refraction, and high-order aberrations were evaluated preoperatively and at 1 month. High-order aberrations were measured using the Nidek OPD-Scan. RESULTS: Preoperative and 1-month postoperative BSCVA were better than 20/40 (100%) after LASIK with both conventional ablation (control) and wavefront-guided customized ablation. Preoperatively, mean high-order aberrations in the control group were 0.572 and in the study group, 0.428 (Zernike coefficient unit). One-month after LASIK, mean high-order aberrations in the control group were 0.496 and in the study group, 0.476 (Zernike coefficient unit). We found no statistically significant difference between preoperative and 1-month postoperative high-order aberrations in either group. CONCLUSION: LASIK with both conventional ablation and wavefront-guided customized ablation resulted in the same BSCVA 1 month after LASIK. Preoperative and 1-month postoperative high-order aberrations were not statistically different following LASIK between ablation types.

Factors that affect corneal flap thickness with the Hansatome microkeratome

Abstract: PURPOSE To evaluate factors that influence corneal flap thickness with the Hansatome microkeratome. METHODS One hundred thirty-two eyes of 70 patients underwent laser in situ keratomileusis (LASIK). Corneal flap thickness was measured by subtracting the intraoperative corneal bed pachymetry measurement from intraoperative total corneal pachymetry. Variables examined included plate thickness, ring size, blade use, temperature, humidity, barometric pressure, age, average keratometric power, and preoperative corneal thickness. RESULTS Mean flap thickness using a 180-microm plate was 143 +/- 19 microm (range 61 to 207 microm). Mean flap thickness using a 160-microm plate was 119 +/- 20 microm (range 83 to 159 microm). The difference was statistically significant (P < .05). Mean flap thickness using a 180-microm plate and the same blade on the right and left eye was 151 +/- 21 microm (range 113 to 200 microm) and 137 +/- 21 microm (range 91 to 191 microm), respectively. The 14-microm difference was statistically significant (P < .001). There was a slight negative correlation of flap thickness with humidity. There was a positive correlation with preoperative corneal thickness (pachymetry). CONCLUSION The Hansatome tended to cut thinner flaps than anticipated based on the plate used. Flaps cut on the first eye were thicker than the second eye using the same blade. Thicker corneas tended to lead to thicker flaps. There was no correlation between flap thickness and microkeratome ring size, temperature, barometric pressure, patient age, or average keratometric power.

Changes in intraocular pressure after laser in situ keratomileusis for myopia, hyperopia, and astigmatism.

Abstract: PURPOSE Reports have shown that photorefractive keratectomy changes intraocular pressure (IOP) in myopic eyes by changing the thickness and curvature of the cornea Changes in intraocular pressure after laser in situ keratomileusis (LASIK) for hyperopia led the authors to evaluate IOP after LASIK for various refractive errors METHODS The measurement of intraocular pressure with a Goldman applanometer in the central cornea was evaluated before and 3 months after LASIK in 100 eyes of 55 patients with various refractive errors Corneal thickness (pachymetry) and corneal topography were evaluated RESULTS After LASIK, a significant decrease of intraocular pressure was observed in most eyes: mean 119 +/- 32 mmHg before and 98 +/- 26 mmHg at 3 months after surgery (P < 001) Mean decrease in IOP was 275 +/- 33 mmHg (P < 0001) for myopic eyes, 228 +/- 243 mmHg (P < 001) for hyperopic eyes, and 147 +/- 25 mmHg (P < 0012) for astigmatic eyes IOP reduction was not significantly correlated to the amount of ablation (r = 005) or to corneal thickness CONCLUSION Intraocular pressure decreased in myopic, hyperopic, and astigmatic eyes after LASIK The reduction was not correlated to the amount of tissue removed or to flattening or steepening of the central cornea

Phakic intraocular lens to correct high myopic amblyopia in children.

Abstract: PURPOSE: In a clinical investigation, we evaluated anatomical and functional outcomes of posterior phakic chamber lens (ICL) implantation for correction of high myopia with amblyopia in children. METHODS: Twelve eyes of 11 children, age 3 to 16 years, with high myopic amblyopia were operated with implantation of a Staar Surgical ICL. In these patients, conventional therapy with spectacles or contact lenses was unsuccessful. Mean preoperative spherical equivalent refraction was -12.70 D (range -8.00 to -18.00 D) and best spectacle-corrected visual acuity ranged from count fingers to 20/63. Mean follow-up was 20.5 months (range 3 to 48 mo) Preoperative and postoperative anatomical and functional outcomes were compared. RESULTS: We noted good tolerance of ICLs without inflammatory reactions or secondary capsular opacity, stable intraocular pressure, and good ICL position in all eyes. Predictability was +0.71 D (range -0.75 to +2.00 D). Mean postoperative best spectacle-corrected visual acuity was 20/63. Recovery of binocular vision was achieved in six patients and orthotropic position in seven patients. Quality of life was improved in all patients. CONCLUSION: The Staar Surgical phakic ICL appeared to be an effective method to treat high myopia in children with amblyopia. Good results with high satisfaction were noted.

Flap measurements with the Hansatome microkeratome.

Abstract: PURPOSE: To evaluate flap thickness, flap diameter, and hinge length during laser in situ keratomileusis (LASIK) and to correlate these measurements with preoperative keratometric power, central corneal thickness, and patient refraction, gender, and age. METHODS: In this prospective study of 50 eyes of 28 patients (mean age 31 +/- 6.6 yr; range, 24 to 43 yr) results of LASIK for myopia were analyzed (mean spherical equivalent refraction of -7.16 +/- 1.69 D; range, -2.75 to -13.50 D). Corneal flaps were created using the Hansatome microkeratome (Baush & Lomb Surgical) with a 160-microm plate and a 9.5-mm suction ring. Corneal thickness was evaluated using an ultrasonic 50-MHz pachymeter (Sonogage Corneo Gage Plus) and the mean keratometric power was measured with a Corneal Analysis System videokeratographic unit (EyeSys). Data were analyzed using t-test, Pearson product moment correlation coefficient, and Spearman's rho non-parametric correlation coefficients. RESULTS: Mean corneal flap thickness was 142.6 +/- 20.8 microm (range, 107 to 177 microm), mean flap diameter was 9.9 +/- 0.3 mm (range, 9.2 to 10.5 mm), and mean hinge length was 6.2 +/- 0.4 mm (range, 5.2 to 7 mm). Statistically significant correlations (P<.05) were found between mean keratometric power and flap hinge length, mean keratometric power and flap diameter, preoperative spherical equivalent refraction and flap diameter, corneal thickness and flap hinge length, as well as patient age and corneal thickness. CONCLUSIONS: The Hansatome microkeratome was an effective and safe instrument in the creation of corneal flaps for LASIK. Consideration of preoperative keratometric power and corneal thickness may help to reduce or avoid complications.

Laser epithelial keratomileusis for myopia with the autonomous laser.

Abstract: Purpose To describe the refractive outcome, objective clinical data, and subjective patient experiences after laser epithelial keratomileusis (LASEK) at 1, 3, and 6 months after surgery. Methods This was a retrospective, nonrandomized, comparative study of 58 LASEK-treated eyes (36 patients) with myopia (with and without astigmatism) between -1.50 and -14.75 D (mean -7.80 +/- 2.90 D, median -7.90 D). Refractive surgery was performed using the Alcon Summit Autonomous LADAR Vision excimer laser. Manifest refraction, best-spectacle and uncorrected Snellen visual acuity, stability of refraction, and corneal haze were evaluated before surgery and up to 6 months after surgery. A group of randomly selected LASIK-treated eyes were compared at each time point. Results Patients who opted for monovision (n=12) were excluded. In the emmetropia targeted eyes (n=46), 45%, 83%, 85%, and 89% achieved 20/40 or better uncorrected Snellen visual acuity (UCVA) at 1 day, 1 week, 2 weeks, and 1 month respectively. At 6 months, 73% (n=28) of eyes treated achieved UCVA 20/20 with 97% achieving 20/40 or better (mean, -0.51 D). At 3 and 6 months, 71% (n=46) and 68% (n=28) were within +/- 0.50 D of emmetropia. The percentage of eyes that achieved UCVA 20/40 or better at 6 months was 97% (n=28). Visually significant corneal haze was evident in two LASEK-treated patients (four eyes) at 6 months. No eyes lost two or more lines of best spectacle-corrected Snellen visual acuity. Conclusions Preliminary data suggest that LASEK appears to be a safe, effective, and comparable alternative to LASIK, even for higher amounts of myopia. A prospective, randomized clinical trial is needed to better define the role of LASEK as it compares to other refractive procedures, specifically LASIK and PRK.

Latrogenic keratectasia following laser in situ keratomileusis.

Abstract: PURPOSE To evaluate keratectasia after laser in situ keratomileusis (LASIK) for high myopia. METHODS A 49-year-old male patient with myopia of -23.50 D in both eyes underwent LASIK with a Summit Technology Apex Plus excimer laser. A Moria manually-guided MDSC microkeratome was used. Preoperative corneal topography in both eyes did not reveal underlying or fruste form of keratoconus. Four months after LASIK, a progressive keratectasia occurred in right eye and after 12 months, in left eye. Corneal transplantation was performed in both eyes. RESULTS Histological and ultrastructural examinations were performed on one corneal button. The analysis showed regular stromal morphology and cellularity, with no sign of inflammation. The morphometric analysis showed an overall thickness of 334 microm, with a flap of 262 microm and a stromal residual bed of 72 microm, in the center of the button. CONCLUSION A LASIK corneal flap made with a planned 120-microm plate turned out histologically to be approximately 260 microm thick, in an eye with a refractive correction of -23.50 D. The excessive flap thickness and excessive ablation produced progressive keratectasia requiring a penetrating keratoplasty.