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At least 1,531 records · Page 85Linked to original sources
PubMed1999

Very high-frequency ultrasound corneal analysis identifies anatomic correlates of optical complications of lamellar refractive surgery: anatomic diagnosis in lamellar surgery.

OBJECTIVE: To examine the utility of very high-frequency (VHF) ultrasound scanning in determining the anatomic changes and correlates of optical complications in lamellar refractive surgery. STUDY DESIGN: Case series. PARTICIPANTS: Cases analyzed included marked asymmetric astigmatism postautomated lamellar keratoplasty (ALK), image ghosting despite normal videokeratography post-ALK, uncomplicated myopic laser in situ keratomileusis (LASIK), and hyperopic LASIK with regression. METHODS: A prototype VHF ultrasound scanner (50 MHz) was used to obtain sequences of parallel B-scans of the cornea. Digital signal processing techniques were used to measure epithelial, stromal, and flap thickness values in a grid encompassing the central 4 to 5 mm of the cornea, enabling pachymetric mapping of each layer with 2-micron precision. MAIN OUTCOME MEASURE: The appearance of the corneas in VHF ultrasound images and thickness values of individual corneal layers determined from VHF ultrasound data. RESULTS: VHF ultrasound resolved the epithelial, stromal cap, or flap and residual stromal layers 1 year after lamellar surgery. Asymmetric stromal tissue removal was differentiated from stromal cap irregularity. Epithelium acted to compensate for asymmetry of the stromal surface about the visual axis and for localized surface irregularities. Irregularities in the epithelial-stromal interface accounted for image ghosting present despite apparently normal videokeratography. Epithelial thickening was shown after uncomplicated myopic LASIK. Hyperopic LASIK demonstrated relative epithelial thickening localized to the region of ablation accounting for refractive regression. CONCLUSIONS: VHF ultrasound shows promise as a sensitive method of determining the anatomic correlates of optical complications in lamellar refractive surgery.

Adult↗
PubMed2004

[Particular clinical situations in the glaucoma patient. True or false deterioration of the visual field?].

Measurement errors, correction errors, head position errors, changes in strategy, fluctuations. There are many parameters influencing the results of visual field measurement. When in doubt, it is indispensable to repeat the examination before concluding that the results have deteriorated. In addition to the qualitative assessment, the analysis of global indices can pinpoint the degree of visual field deterioration.

Algorithms↗
PubMed2005

[Refractive phakic IOLs: three different models and contact with the crystalline lens. An AC-OCT study].

Three patients received three different models of phakic implants. With the usual slit-lamp examination method, we were not able to establish whether there was contact between the implants and the natural crystalline lens. Using the anterior chamber optical coherence tomography scanner (AC-OCT), we were able to demonstrate that there was direct contact between the natural crystalline lens and the three different phakic implants. A dynamic study of these contacts was carried out during accommodation. These observations show that examination of the anterior segment with the optical coherence tomography scanner is essential in refractive surgery.

Accommodation, Ocular↗
PubMed2005

[Pigment dispersion and Artisan implants: crystalline lens rise as a safety criterion].

PURPOSE: To validate the theoretical notion of a crystalline lens rise as a safety criterion for ARTISAN implants in order to prevent the development of pigment dispersion in the implanted eye. MATERIAL AND METHOD: Crystalline lens rise is defined by the distance between the crystalline lens's anterior pole and the horizontal plane joining the opposite iridocorneal recesses. We analyzed the biometric measurements of 87 eyes with an Artisan implant. A comparative analysis of the crystalline lens rise was carried out on the nine eyes having developed pigment dispersion and 78 eyes with no problems. Among the modern anterior segment imaging devices (Artemis, Scheimpflug photography, optical coherence tomography, radiology exploration, magnetic resonance imaging, TDM), an anterior chamber optical coherence tomography (AC-OCT) prototype was used. RESULTS: This working hypothesis was confirmed by this study: the crystalline lens rise must be considered as a new safety criterion for implanting Artisan phakic lenses. Indeed, the higher the crystalline lens's rise, the greater the risk of developing pigment dispersion in the pupil area. This complication is more frequent in hyperopes than in myopes. We can consider that there is little or no risk of pigment dispersion if the rise is below 600 microm; however, at 600 microm or greater, there is a 67% rate of pupillary pigment dispersion. In certain cases, when the implant was loosely fixed, there was no traction on the iris root. This is a complication that can be avoided or delayed. CONCLUSIONS: The crystalline lens rise must be part of new safety criteria to be taken into consideration when inserting an Artisan implant. This notion must also be applied to other types of phakic implants. The distance remaining between the crystalline lens rise and a 600-micromm theoretical safety level allows one to calculate a safety time interval.

Adolescent↗
PubMed2000

Hyperopic photorefractive keratectomy with the erodible mask and axicon system: two year follow-up.

PURPOSE: To evaluate efficacy and long-term stability of hyperopic photorefractive keratectomy (H-PRK) using the erodible mask and Axicon system. SETTING: Department of Ophthalmology, St. Thomas' Hospital, London, England. METHODS: Forty-three patients (43 eyes), with a mean preoperative refraction (spherical equivalent) of +4.54 diopters (D) (range +1.75 to +7.50 D), were treated using an Apex Plus(R) excimer laser (Summit Technology). This uses an erodible mask to ablate a 6. 50 mm diameter hyperopic correction and an Axicon to fashion a 1.50 mm blend zone around the correction. The overall ablation diameter was 9.50 mm. Follow-up was 2 years. RESULTS: At 2 years, the mean manifest refraction was +0.16 D (range +4.125 to -4.000 D), with the induced correction appearing stable after 9 months. Based on the Munnerlyn algorithm, predictability was acceptable for corrections up to +4.50 D, with 68% of eyes within +/-1.00 D of the predicted correction. It was poorer for +6.00 D corrections, with 33% of eyes within +/-1.00 D of that expected. Patient satisfaction was high. Forty eyes (93%) had an improvement in uncorrected near visual acuity and 37 (86%), an improvement in uncorrected distance acuity. A peripheral ring of haze, 6.5 mm in diameter, appeared in all eyes 1 month postoperatively. Its intensity was maximal at 3 to 9 months and then diminished over time. There were no significant differences in measurements of the central corneal transparency at 12 and 24 months and those preoperatively. Measurements of flicker contrast sensitivity, forward light scatter (glare), and scotopic halos showed no significant differences between preoperative values and those measured after 6 months. CONCLUSIONS: Achieved H-PRK corrections with the erodible mask and Axicon system agreed closely with the Munnerlyn algorithm, with refractive stability after 9 months. Predictability was acceptable for corrections up to +4.50 D. Axial corneal transparency was not compromised and visual performance, in terms of best spectacle-corrected visual acuity, forward light scatter, and night halos, was not impaired.

Adult↗
PubMed2000

Theoretical analysis of ablation depths and profiles in laser in situ keratomileusis for compound hyperopic and mixed astigmatism.

PURPOSE: To compare the theoretical ablation depths and profiles of 4 treatment strategies for compound hyperopic and mixed astigmatism. SETTING: Theoretical analysis. METHODS: Corneal contour drawings of theoretical corneal ablation profiles during laser in situ keratomileusis (LASIK) and photoastigmatic refractive keratectomy were made. The depths of tissue ablation in 4 treatment strategies for compound hyperopic astigmatism (Groups 1 to 4) and for mixed astigmatism (Groups 5 to 8) were compared: (1) combined hyperopic spherical and myopic cylindrical treatments (Groups 1 and 5); (2) combined spherical and hyperopic cylindrical treatments (Groups 2 and 6); (3) combined cylindrical treatments (Groups 3 and 7); (4) combined cross-cylinder and spherical equivalent treatments (Groups 4 and 8). RESULTS: In compound hyperopic astigmatism, the 4 approaches resulted in identical final curvatures, but the ablation depths were greatest in Group 1 (combined hyperopic spherical and myopic cylindrical treatments). The smallest amount of ablation occurred in Group 2 (combined hyperopic spherical and hyperopic cylindrical treatments) and Group 3 (combined hyperopic cylindrical treatments), which had similar tissue ablation patterns. In mixed astigmatism, the greatest ablation depth was in Group 5, followed by Group 8, and Groups 6 and 7. The tissue ablation depths and profiles were similar in Groups 6 and 7. CONCLUSION: The treatment approaches in Groups 2, 3, 6, and 7 (which avoided the use of minus cylinder) resulted in the smallest degree of stromal ablation. Patients with compound hyperopic or mixed astigmatism may benefit from reduced ablation depths by deferring treatment until hyperopic cylindrical and/or combined cylindrical treatments are available.

Astigmatism↗
PubMed2001

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.

Adult↗
PubMed2001

Laser in situ keratomileusis to correct hyperopic shift after radial keratotomy.

PURPOSE: To assess the safety and efficacy of excimer laser in situ keratomileusis (LASIK) to correct hyperopic shift following radial keratotomy (RK). SETTING: Ophthalmic Health Center, Tel Aviv, Israel. METHODS: The study comprised 15 eyes of 12 patients who had uneventful RK and subsequently developed a hyperopic shift. Laser in situ keratomileusis was performed using the Chiron Automated Corneal Shaper and the Nidek EC-5000 excimer laser with 5.5 mm central and 7.5 mm peripheral ablation zones. The corneal flap was 160 microm in thickness and 8.5 mm in diameter. The refractive correction corresponded to the patients' refractive errors. RESULTS: The mean time after RK was 10.46 years +/- 2.21 (SD) and the mean follow-up after LASIK, 7.3 months (range 1 to 42 months). The mean spherical equivalent refraction was corrected from +3.08 +/- 1.02 diopters (D) to -0.16 +/- 0.73 D after LASIK. At the last examination, 12 eyes (80%) had a refractive error within +/-1.00 D of emmetropia and an uncorrected visual acuity of 20/40 or better. No wound dehiscence, epithelial ingrowth, or other significant complication developed in any eye. CONCLUSIONS: Early postoperative results of the correction by LASIK of a hyperopic shift after RK are encouraging, but long-term studies of a larger population group are required to evaluate the method's clinical value.

Adult↗
PubMed2001

Piggyback implantation using the AMO array multifocal intraocular lens.

Piggyback intraocular lens (IOL) implantation allows refractive correction in cases in which the IOL power requirement exceeds that of the available lenses. By combining a piggyback technique with the use of a multifocal IOL, one can obtain the optical advantages of both, achieving high-quality visual acuity for distance and near vision and reducing the optical aberrations of extremely high-powered single IOLs. We report 5 hyperopic patients (6 eyes) who had phacoemulsification and in-the-bag implantation of 2 foldable IOLs in the bag, a silicone multifocal IOL placed in front of a silicone monofocal IOL. Good results were obtained in near and distance uncorrected visual acuities, and patient satisfaction was excellent in all cases. However, in 2 cases, the anteriorly placed IOL was exchanged because of incorrect power calculation. Piggyback IOL implantation with a multifocal lens appears to be a safe, efficient procedure and a good refractive solution.

Adult↗
PubMed2001

Changes in measured intraocular pressure after hyperopic photorefractive keratectomy.

PURPOSE: To investigate the effect of hyperopic photorefractive keratectomy (PRK) on intraocular pressure (IOP) measurements. SETTING: University of Ottawa Eye Institute, Ottawa Hospital, Ottawa, Canada. METHODS: In this retrospective cohort study, IOP and central corneal thickness (CCT) were measured preoperatively and at 1, 2, 3, 6, 12, 18, and 24 months in 191 eyes that had hyperopic PRK with the VISX Star excimer laser. All corrections applied were between +1.00 and +6.50 diopters (D) of sphere and less than 3.75 D of cylinder. RESULTS: At all postoperative examinations, the mean IOP in the hyperopic PRK group was 1.0 to 1.8 mm Hg lower than the preoperative IOP (P <.001). A large range of IOP changes was found across the population; eg, at 6 months, 49% of the eyes had a change in IOP from baseline of at least +/-3 mm Hg. A mean reduction of 19 microm of CCT was found with pachymetry after surgery (P < .001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or applied correction. Changes in IOP were strongly correlated with preoperative IOP at all time points and with preoperative CCT at 18 and 24 months (P < .001). After hyperopic PRK, the measured IOP was more likely to increase in patients with preoperative IOPs less than 14.5 mm Hg and more likely to decrease in patients with preoperative IOPs above 14.5 mm Hg. CONCLUSION: Changes in IOP after hyperopic PRK were similar to changes after myopic PRK, despite only minimal changes in the CCT. This suggests that hyperopic PRK results in biomechanical effects that modify the elastic properties of the cornea beyond the changes in rigidity expected from central corneal thinning. There was a strong negative correlation between the measured preoperative IOP and the change in IOP postoperatively that was likely the result of regression of the mean effect.

Cohort Studies↗
PubMed2001

Effect of high-altitude exposure on myopic laser in situ keratomileusis.

PURPOSE: To study the effect of high-altitude exposure on visual acuity after myopic laser in situ keratomileusis (LASIK). SETTING: Aconcagua, Mendoza, Argentina. METHODS: In the early postoperative period after uneventful myopic LASIK, 2 physicians prospectively assessed their visual acuity during an ascent of Aconcagua (22841 feet). The distance uncorrected visual acuity (UCVA) and peripheral oxygenation were measured at approximately every 2000 feet of altitude. RESULTS: Both climbers developed a moderate loss of distance UCVA but described normal near and pinhole acuity consistent with a myopic shift. The distance UCVA diminished to 20/100 in the right eye and 20/125 in the left eye of Climber A and to 20/160 and 20/30, respectively, of Climber B. The vision loss worsened with increased altitude, duration of exposure, and decreased peripheral oxygenation. One week after the climb, the manifest refraction demonstrated a small myopic shift in both eyes of Climber A; these subsequently resolved. CONCLUSIONS: Two climbers, 8 and 14 weeks after myopic LASIK, experienced vision loss consistent with a temporary myopic shift in the refractive error with ascent to high altitude. Climbers who have LASIK, particularly those in the early postoperative period, should be prepared for visual acuity fluctuations with high-altitude exposure.

Adult↗
PubMed2002

Implantation of spheric phakic posterior chamber intraocular lenses in astigmatic eyes.

PURPOSE: To evaluate the simultaneous correction of spherical and cylindrical ametropia through implantation of phakic posterior chamber (PC) intraocular lenses (IOLs) combined with a limbal incision. SETTING: Eye Department, Schlosspark-Klinik, Charité University Berlin, Berlin, Germany. METHODS: In 5 hyperopic and 7 myopic eyes with varying astigmatic measurements, a refractive correction was achieved by implanting phakic PC IOLs (Staar Surgical Co.) and performing limbal incisions of different lengths. The incisions were placed approximately 1.0 mm from the limbus with a mean depth of 600 microm and a length of 6.0 mm +/- 0.9 (SD). The phakic PC IOLs were implanted after the limbal incisions were placed. RESULTS: In the 5 hyperopic eyes, the astigmatism decreased from 2.7 diopters (D) preoperatively to 0.5 D at a mean of 7.5 +/- 1.7 months without alteration of the axis of highest bowing. In the 7 myopic eyes, it decreased from 2.2 D preoperatively to 0.7 D at 7.2 +/- 2.6 months. In 3 hyperopic eyes and 1 myopic eye, the limbal incisions were repeated. CONCLUSIONS: The observed mean postoperative spherical equivalent was close to emmetropia. Repeat incisions were necessary in eyes exhibiting astigmatism greater than 2.5 D. The advantage of limbal incisions in combination with phakic PC IOL implantation is demonstrated not only by the astigmatic reduction but also by the axis stability. It will be interesting to see whether toric phakic lenses can achieve the same postoperative results, especially in axis stability and reduction of higher degrees of astigmatism.

Adult↗
PubMed2002

Analysis of anterior and posterior corneal curvature changes using Orbscan technology in radial keratotomy eyes exposed to hypoxia.

PURPOSE: To study the changes in anterior and posterior corneal curvatures in radial keratotomy (RK) and normal eyes exposed to hypoxia using Orbscan (Bausch & Lomb) technology. SETTING: Department of Ophthalmology, Madigan Army Medical Center, Tacoma, Washington, USA. METHODS: At sea level, 11 RK subjects and 10 control subjects were exposed to ocular surface hypoxia in 1 eye by filtering humidified, compressed 100% nitrogen (0% oxygen) through an airtight goggle system for 2 hours. The contralateral eye was exposed to humidified, compressed air (21% oxygen) simultaneously through the airtight goggle system. Orbscan analysis was performed in each subject before and immediately after gas exposure. This analysis included measurement of the anterior axial and posterior axial corneal curvatures as well as corneal pachymetry. RESULTS: In the RK eyes exposed to 100% nitrogen gas, there was a statistically significant flattening in the anterior axial corneal curvature (P = .0012) and in the posterior axial corneal curvature (P = .0067). Radial keratotomy and control eyes exposed to air and control eyes exposed to 100% nitrogen gas demonstrated no statistically significant change in the anterior axial or posterior axial corneal curvature. CONCLUSIONS: Corneal hypoxia induced a statistically significant flattening in the anterior axial and posterior axial corneal curvatures in eyes that had had RK. There was no significant change in these curvatures in RK eyes exposed to air and in control eyes exposed to air or 100% nitrogen gas.

Adolescent↗