[In vitro and in vivo investigations on the treatment of presbyopia using femtosecond lasers]. / In-vitro- und In-vivo-Untersuchungen zur Presbyopiebehandlung mit Femtosekundenlasern.

BACKGROUND: Ultrashort (femtosecond) laser pulses can generate precise cuts in biological tissue without damaging the surface. The application of femtosecond laser technology at the lens was evaluated with respect to a possible treatment of presbyopia. MATERIALS AND METHODS: Femtosecond laser lentotomy was performed on 150 pig lenses in vitro. Cutting geometry and laser settings were optimized to generate smooth cuts with a minimum of produced gas bubbles. Four rabbit lenses were treated afterwards in vivo and were controlled for 3 months post-treatment. The lenses were then extracted and evaluated. RESULTS: With suitable laser settings, light scattering due to residual gas bubbles could be almost completely avoided in pig lenses. A pulse energy of less than 1.2 microJ and a cutting geometry with spot separations of more than 5 microm are important. The rabbit lenses stayed macroscopically clear for 3 months in vivo. Only the cell structures directly adjacent to the laser focus were cut; structures 5-10 microm away appeared to be intact. No cataract formation occurred during this time. CONCLUSION: Femtosecond laser application allows precise and smooth cuts inside pig and rabbit lenses without damage to adjacent tissue.

Experimental increase in accommodative potential after neodymium: yttrium-aluminum-garnet laser photodisruption of paired cadaver lenses.

PURPOSE: Loss of lens elasticity is one of several proposed mechanisms responsible for the decline in accommodation with age and is the most accepted explanation for presbyopia. We wish to confirm the lens elasticity premise and attempt to experimentally reverse the age-dependent loss of accommodative potential as measured by polar strain. DESIGN: Experimental human autopsy eye study. PARTICIPANTS AND CONTROLS: Thirty-six cadaver lenses were tested to determine the age-dependent polar strain. Eleven lens pairs were then tested with one lens treated with neodymium:yttrium-aluminum-garnet (Nd:YAG) laser and the other left untreated before rotation as an age control. TESTING: Using a custom-made rotational apparatus (described by Fisher, 1971), freshly excised cadaver lenses (<48 hours postmortem) were rotated at 1000 rpm on a 9-mm diameter pedestal to simulate the physiologic pull of the zonules. Lenses were initially tested to determine the age-dependent polar strain. One lens in a pair was then treated with an Nd:YAG laser and the other left untreated before testing. Treatment consisted of 100 suprathreshold pulse placed in a central annular pattern of 2- to 4-mm diameter. Treatment energies varied from 2.5 to 7.0 mJ/pulse, depending on the relative clarity of the lenses. Polar strain was both microscopically measured and calculated from projected photographs before and after rotation of both lased and unlased lenses. Statistically significant differences were determined by paired t test. MAIN OUTCOME MEASURES: Polar strain (decrease in axial thickness with rotation) of the lens. RESULTS: An age-dependent decrease in polar strain was observed that paralleled the findings of Fisher. Both measured and projected polar strain were greater in the lased than unlased lens, and this difference was highly significant by paired t test (P = 0.001 and P = 0.004, respectively). CONCLUSIONS: Age-dependent loss of lens elasticity (polar strain) can be experimentally reversed (increased) by selective intralenticular photodisruption.

Photorefractive keratectomy for hyperopia in 800 eyes with the Meditec MEL 60 laser.

PURPOSE: To evaluate the refractive results of 800 hyperopic eyes undergoing PRK treatment. METHODS: Eight hundred hyperopic eyes were treated with PRK. An Aesculap-Meditec MEL 60 scanning ArF excimer laser used. Treatment Group 1 consisted of eyes with a preoperative refractive error of +3.50 D or less (n = 482) and Group 2, of +3.75 D or more (n = 318). RESULTS: Preoperatively, Group 1 required an average correction of +2.88+/-1.34 D and Group 2 required +5.64+/-2.96 D. One year after PRK, average residual correction was +1.26+/-1.24 D in Group 1, and in Group 2, +2.46+/-1.84 D. In Group 1, uncorrected visual acuity (UCVA) was 20/40 or better in 88.4% (426/482); 20/20 or better in 75.7% (365); 2.1% (10/482) of eyes lost 2 lines, 2.1% (10/482) gained 2 lines; 3.1% (15/482) gained 2 or more lines of BSCVA; 74.4% (359/482) of eyes were within +/-0.50 D of target correction and 84.8% (408/482) were within +/-1.00 D. In Group 2, 47.5% (151/318) had UCVA of 20/40 or better; 34.2% (109/318) saw 20/20 or better uncorrected; 19.1% (61/318) lost 2 lines; 11.6% (37/318) lost 3 lines; none of the eyes gained 2 or more lines of BSCVA; 22.3% (71/318) were within +/-0.50 D and 46.8% (149/318) were within +/-1.00 D of target correction. Refractive stability was achieved after 6 months; a slight regression after 6 months was still observed. In Group 1, 10.5% (42/482) and in Group 2, 21.6% (69/318) complained of problems with daytime vision (glare and ghost image); during night-driving in Group 1, 17.6% (85/482) and in Group 2, 40.5% (129/318) had problems. CONCLUSION: PRK with the Aesculap-Meditec MEL 60 scanning ArF excimer laser offered the best long-term results with +3.50 D or less preoperative refractive error. With higher corrections, regression, decrease in BSCVA, and daytime visual problems were encountered.

Highlights of the 1st International Congress of Wavefront Sensing and Aberration-free Refractive Correction.

As we review the many new and evolving techniques for treating patients with customized ablation, it is obvious that there is a rapid evolution of technology and thought. Newly refined diagnostic technology, such as wavefront sensing, and more sophisticated spot laser delivery systems with eye tracking gives the refractive surgical team greater flexibility in tackling challenging optical abnormalities. These highlights of the 2000 Congress now set the stage for further development, outlined in the following selected papers from the 2001 Congress.

Treatment of intraocular pressure elevation after photorefractive keratectomy.

PURPOSE: To study the effect of timolol maleate, dorzolamide, or a combination of both in post photorefractive keratectomy (PRK) eyes with an elevated intraocular pressure (IOP) after topical steroid administration. SETTING: Refractive Surgery Outpatient Department, 1st Department of Ophthalmology, Semmelweis University, Budapest, Hungary. METHODS: Forty-five patients with elevated IOP were randomly enrolled in 3 groups: Group 1 received timolol maleate 0.5% twice a day; Group 2 received timolol maleate 0.5% twice a day and dorzolamide 2% 3 times a day; and Group 3 received only topical dorzolamide 2% 3 times a day. Intraocular pressure was measured 3 days and 1, 3, and 6 weeks after the antiglaucoma medication was started. RESULTS: The mean preoperative IOP was 15.25 mm Hg +/- 1.28 (SD). Following administration of topical fluorometholone, the IOP increased a mean of 27.39 +/- 2.88 mm Hg. Six weeks after the antiglaucoma therapy was started, the mean IOP reduction was 6.6 mm Hg in Group 1, 8.86 mm Hg in Group 2, and 4.64 mm Hg in Group 3. CONCLUSIONS: A combination therapy of timolol 0.5% and dorzolamide 2% was most effective in treating secondary IOP elevation after PRK. Dorzolamide alone did not adequately control secondary post-PRK IOP elevation.

Photorefractive keratectomy for astigmatism with the Meditec MEL 60 laser.

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) in eyes treated with astigmatic refractive errors. METHODS: Nine hundred forty eyes were treated with the Aesculap Meditec MEL 60 ArF excimer laser. Treatment groups were: Group 1 (n=746) eyes with compound myopic astigmatism, Group 2 (n=104) eyes with compound hyperopic astigmatism, Group 3 (n=75) eyes treated for mixed astigmatism, and Group 4 (n=15) eyes with simple myopic astigmatism (negative cylinder). RESULTS: In Group 1, the preoperative spherical equivalent refraction of -6.10 D with an average of -1.50 D cylinder decreased to -0.95 D with -0.13 D cylinder; uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 86% (642/746 eyes); 20/20 or better in 58% (433/746 eyes); 0.8% (6/746 eyes) lost two lines of spectacle-corrected visual acuity (SCVA); 74% (552/746 eyes) were within +/-0.50 D and 93% (694/746 eyes) were within +/-1.00 D of target refraction. In Group 2, preoperative mean +4.57 D spherical equivalent refraction with an average of +1.57 D cylinder decreased to +1.13 D with +0.38 D cylinder; UCVA of 20/40 or better was achieved in 84% (87/104 eyes); 20/20 or better in 46% (48/104 eyes); 14,4% (15/104 eyes) lost two or more lines of SCVA; 52% (54/104 eyes) were within +/-0.50 D and 82% (85/104 eyes) were within +/-1.00 D of target refraction. In Group 3, mean preoperative -4.20 D cylinder and +3.00 D spherical equivalent refraction decreased to -0.50 D cylinder and -0.50 D spherical equivalent refraction; UCVA of 20/40 or better was achieved in 83% (62/75 eyes); 20/20 or better in 32% (24/75 eyes); 13.3% (10/75 eyes) lost two or more lines of SCVA. In Group 4, mean preoperative -3.98 D cylinder decreased to -0.62 D cylinder; UCVA of 20/40 or better was achieved in 60% (9/15 eyes); none of the eyes achieved 20/20 or better; SCVA remained stable in 6.6% (1/15 eyes) and decreased two or more lines in 20.0% (3/15 eyes); 20% (3/15 eyes) were within +/-0.50 D and 53.3% (8/15 eyes) were within +/-1.00 D of target refraction. CONCLUSION: PRK with the Meditec MEL 60 laser produced the best results in eyes with compound myopic astigmatism (Group 1). In all other groups, results were less predictable.

Postoperative complications of excimer laser photorefractive keratectomy for myopia.

Excimer laser photorefractive keratectomy has become an increasingly popular surgical treatment for the correction of myopia. Unfortunately, no surgical technique can be entirely without complications. This article discusses the problems encountered following PRK for myopia in two main sections: those primarily refractive or optical in nature and those causing medical problems.

Stress wave amplitudes during laser surgery of the cornea.

PURPOSE: To determine the stress wave amplitudes generated during photoablation of the cornea using an argon fluoride excimer laser. DESIGN: Experimental study using porcine eyes. METHODS: Profiles of the stress wave amplitudes and enucleated human eyes along the axis of symmetry of porcine eyes and enucleated human eyes were measured using a miniature piezoelectric transducer. The ablation parameters, fluence, and ablation diameters were varied within the range of clinical application. MAIN OUTCOME MEASURES: Stress wave amplitudes generated during photoablation. RESULTS: The stress waves pass through a pressure focus located in the posterior lens and anterior vitreous, where amplitudes of up to 100 atm were measured with a 6-mm or larger ablation zone. Posterior to this focus, the stress wave amplitudes rapidly decrease to less than 10 atm at the retinal site. Small diameter excimer laser spots (< or =1.5 mm) produce a declining stress wave with no pressure focus at the lens and anterior vitreous. CONCLUSIONS: Stress waves may be potentially hazardous to anterior structures of the human eye, including the corneal endothelium, lens and anterior vitreous face. They peak at the lens and vitreous with a broad beam, but not with small spot laser ablation. At posterior retinal and subretinal structures, they may be considered harmless.

Understanding refraction and accommodation through "retinal imaging" aberrometry: a case report.

PURPOSE: A new form of aberrometry based on Tscherning optics has been proposed that captures the refraction and high-order aberrations of the eye with and without accommodation. DESIGN: Experimental clinical optics study. METHOD: A green neodymium:yttrium-aluminum-garnet laser grid pattern is projected into the eye and viewed on the retina through a narrow, collimated aperture of 1 mm. The resulting aberrated pattern is photographically recorded in a normal eye in the unaccommodated and accommodated state through a pharmacologically dilated pupil without cycloplegia. MAIN OUTCOME MEASURES: Detection of pupil-dependent refraction and high-order optical aberration with and without accommodation. RESULTS: Subtle pupil-dependent errors in refraction and high-order aberrations (spherical aberrations and coma) are demonstrated in the unaccommodated normal eye. Accommodation reveals slightly more spherical power through the central 3-mm zone than through a 6.5-mm pupil without significant increase in aberration. CONCLUSIONS: Tscherning aberrometry based on 'retinal imaging' is useful in defining the refraction and optical aberrations in a normal eye. Accommodation increases spherical refractive power with only small aberration changes, including negative asphericity.

Surgically-induced astigmatism after laser in situ keratomileusis for spherical myopia.

PURPOSE: To characterize the surgically-induced-astigmatism (SIA) associated with spherical LASIK. METHODS: Refractive outcomes in 70 eyes that underwent primary myopic LASIK with purely spherical ablation were analyzed. The Summit Apex Plus excimer laser was used. The Bausch & Lomb Hansatome with the 180-microm plate was used to produce superiorly hinged flaps. The relationship between refractive astigmatism and corneal topographic astigmatism was analyzed using linear regression and vector analysis. RESULTS: There was a statistically significant negative correlation (slope = -0.21) between refractive surgically-induced astigmatism and preoperative topographic cylinder. A 0.24-D with-the-rule shift was also found. Surgically-induced astigmatism was not correlated with the magnitude of laser ablation. CONCLUSION: The lamellar keratotomy portion of LASIK reduces pre-existing corneal astigmatism and produces a relative steepening of the hinge meridian.

Agreement and repeatability of pupillometry using videokeratography and infrared devices.

PURPOSE: To evaluate the accuracy and repeatability of the pupil-measuring modules of several corneal topography devices. SETTING: Department of Ophthalmology, Saint Louis University Eye Institute, St. Louis, Missouri, USA. METHODS: In 14 eyes of 7 healthy myopic patients, pupillometry was performed with 3 corneal topography devices and with an infrared pupillometer under luminance-matched conditions for the Placido projection of the topography devices. Pupils were also measured under a mesopic condition. Outcomes were pupil diameters, limits of agreement, and coefficient of repeatability of the topography devices. RESULTS: Mean pupil diameter measurements with the Technomed C-Scan, Humphrey Masterview, Alcon EyeMap, and under a mesopic condition were 3.35 mm, 2.96 mm, 2.34 mm, and 5.94 mm, respectively. All pupil diameter measurements differed significantly from one another except those by the Masterview and C-Scan devices. The mean difference between the C-Scan and luminance-matched infrared measurements was 0.74 mm and between the Masterview and luminance-matched infrared measurements, 0.27 mm. The limits of agreement +/- 2 standard deviations was 4.12 mm and 1.56 mm for the C-Scan and Masterview devices, respectively. Coefficients of repeatability were 0.56 mm, 0.46 mm, and 0.44 mm for the C-Scan, Masterview, and EyeMap devices, respectively. CONCLUSIONS: Although topography pupillometry was repeatable, it underestimated the largest natural pupil diameter because of the luminance of the Placido rings. The difference in limits of agreement between the C-Scan and Masterview devices may be explained by pupil physiology and the static nature of videokeratoscopy. These results have implications when topography pupillometry is used to assess pupil diameters prior to refractive surgery. We do not recommend using pupil diameters measured by topography to preoperatively determine halo-related safety.

Improvement of visual function with glare testing after photorefractive keratectomy and radial keratotomy.

PURPOSE: To evaluate the effect of a glare source on visual function in patients after photorefractive keratectomy and radial keratotomy. METHODS: Thirteen patients (22 eyes) who underwent photorefractive keratectomy and 20 patients (40 eyes) who underwent radial keratotomy were evaluated in this cross-sectional study. LogMAR visual acuity and contrast sensitivity were measured. Pupils were measured with the Rosenbaum card. A halogen/tungsten glare source approximated the luminance of headlights of an oncoming car at 100 feet. RESULTS: In the photorefractive keratectomy and radial keratotomy groups, pupils were significantly smaller (P<.01) and the pupillary clearance of the ablation zone in photorefractive keratectomy and the clear zone in radial keratotomy were significantly larger under the glare condition (P<.01). In the photorefractive keratectomy group, visual acuity and contrast sensitivity under the glare condition were significantly higher than in the no-glare condition (P = .02). In the radial keratotomy group, contrast sensitivity under the glare condition was significantly higher than under the no-glare condition (P = .001 to .003). CONCLUSIONS: After photorefractive keratectomy or radial keratotomy, the traditional glare source constricted the pupil and partially masked the optical aberrations, which resulted in an improvement in visual function. A "pupil-sparing" aberration test is needed for evaluation of visual function after refractive surgery.

Central bump-like opacity as a complication of high hyperopic photorefractive keratectomy.

PURPOSE: A new complication is reported in association with high hyperopic excimer laser photorefractive keratectomy. METHODS: One thousand consecutive eyes were treated with a Meditec MEL-60 excimer laser (Meditec Inc, Heroldsberg, Germany) for hyperopic refractive error between +1 diopters and +7 diopters. RESULTS: Three eyes with high hyperopic corrections between +5 and +6 diopters had a central, round bump-like subepithelial scar develop 1 month after hyperopic photorefractive keratectomy, which reduced the uncorrected and spectacle-corrected visual acuity. CONCLUSION: Central bump-like opacity is a new, visually significant complication of unknown origin associated with high hyperopic photorefractive keratectomy. Possible causes of this complication include drying and edema of the cornea as a result of prolonged exposure, interruption of the peripheral superficial nerve plexus affecting the central anterior stroma, and abnormal epithelial or tear film function resulting from excessive central steeping.

Photorefractive keratectomy for low-to-moderate myopia and astigmatism with a small-beam, tracker-directed excimer laser.

OBJECTIVE: To assess the safety and effectiveness of the Autonomous Technologies Corporation LADARVision excimer laser system for photorefractive keratectomy correction of myopia and astigmatism. DESIGN: A multicenter, prospective, noncomparative case series. PARTICIPANTS: The cohort consisted of 467 eyes corrected for spherical myopia and 211 eyes corrected for myopia with astigmatism. INTERVENTION: Treatments were performed at six sites in the United States using a 6-mm ablation zone for spherical myopes and a 5.5-mm zone with a 1.0-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, corneal haze, intraocular pressure, complications, adverse reactions, patient satisfaction, and corneal endothelial changes. RESULTS: Twelve-month follow-up was available on 414 spherical eyes and 175 astigmatic eyes. The results for spherical eyes with correction between -1 and -5.99 diopters (D) were: uncorrected visual acuity (UCVA) of 20/40 or better achieved by 98.1%, 20/20 or better by 72%, 1.8% lost 2 lines and 0.3% lost greater than 2 lines of best spectacle-corrected visual acuity (BSCVA); 76.4% were within 0.50 D of the target correction and 94.4% were within 1.00 D. The results for myopia with astigmatism with spherical equivalent correction between -1 and -5.99 D were: UCVA of 20/40 or better in 97.4%, 20/20 or better in 61.7%, 2.5% lost 2 lines and no eyes lost greater than 2 lines BSCVA; 73.9% were within 0.50 D of the target correction and 95% were within 1.00 D. For spherical myopes combined with myopic astigmats corrected for 6 to 10 D, results were: UCVA of 20/40 or better in 93.4%, 20/20 or better in 61.2%, 2.3% lost 2 lines and no eyes lost greater than 2 lines of BSCVA; 67.2% were within 0.50 D of the desired correction and 87.8% were within 1.00 D. Refractive stability was achieved between 3 and 6 months for the spherical and astigmatic groups. No eyes had corneal haze graded as moderate or greater, and there was no significant decrease in endothelial cell density. CONCLUSIONS: Patients treated for 1 to 10 D of spherical equivalent myopia, with or without astigmatism, showed early refractive stability, excellent UCVA, no significant loss of BSCVA, no loss of endothelial cell density, and very low levels of corneal haze to 12 months after surgery.

Comparison of contrast sensitivity in different soft contact lenses and spectacles.

PURPOSE: To compare the visual performance of soft contact lenses and spectacles. METHODS: Twenty eyes of ten patients were examined. Each patient was fit with Acuvue, Cibasoft, and Biomedics contact lenses in random order. LogMar visual acuity and contrast sensitivity using the VectorVision CSV-1000 were measured. RESULTS: There was no significant difference in visual acuity between any contact lenses (P=.15). Contrast sensitivity at 12 cycles/degree was significantly lower for the Cibasoft lens compared to spectacles (P=.04). There was no significant difference between spectacles and contact lenses for remaining spatial frequencies (P=.07-.35). CONCLUSIONS: Visual acuity appears to be an insensitive method for evaluating soft contact lenses. The lathe-cut manufacturing process may be responsible for reduced visual function compared to cast-molded lenses. Further study in this area is needed.