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At least 937 records · Page 52Linked to original sources
PubMed1995

[Excimer laser photorefractive keratectomy in myopia and astigmatism--1 year experience].

The authors evaluate the results of photorefractive keratectomy by means of an excimer laser myopia and astigmatism in 343 eyes with a minimal follow-up period of 9 months. The value of the preoperative refractive error expressed in spherical equivalents was -1,75 to -18,5 d. In astigmatism the maximal value was -5 cyl. d. The group was divided into four sub-groups: A) -1,75 to -3,0 d., B) -3,25 to -6,0 d., C) -6,25 to -10,0 d., D) more than -10,25 d. The spherical equivalent of the refractive error 9 month after operation was -0,28 d. in group A, -0,37 d. in group B, -0,67 d. in group C and -1,82 d. in group D. Uncorrected vision, 6/12 or better, 9 mons after operation was recorded in group A in 98,1% patients, group B 95,6% group C 91,2% and in group D in 72,5% patients. The authors proved a high effectiveness, safety predictability and stability of photorefractive keratectomy by means of an excimer laser in myopia up to -10 d. Photorefractive keratectomy is a promising method which extends the possibilities of correcting myopia and astigmatism in sufficiently positively motivated and indicated patients.

Adult↗
PubMedDate not supplied

[Interlamellar sectoral keratoplasty in the surgical correction of astigmatism].

A new original method of interlamellar sectorial keratoplasty is proposed for surgical correction of astigmatism. Eleven operations were carried out in 8 patients (11 eyes) with astigmatism of 4 to 7.0 diopters. Vision acuity without correction was 0.6 to 1.0 in 5 patients (7 eyes, 63.6%). In 2 patients (2 eyes, 18.2%) vision acuity without correction was 0.3 to 0.5 diopters, and in 2 more patients (2 eyes, 18.2%) it was from 0.1 to 0.3 diopters, that is, equal to the maximal vision acuity with the optimal correction. The refraction effect stabilized in 3-4 months. The highest refraction effect attained was 7.0 diopters. The patients were followed up for 3 months to 4 years. Clinical analysis of the operations confirmed the efficacy and reliability of the method and stability of refraction. Interlamellar sectorial keratoplasty is recommended for surgical correction of astigmatism.

Adolescent↗
PubMed1997

Corneal topography after selective suture removal for astigmatism following keratoplasty.

BACKGROUND AND OBJECTIVE: The authors sought to determine whether the immediate corneal topographic changes induced by selective suture removal for astigmatism after keratoplasty were stable over time. PATIENTS AND METHODS: Computerized videokeratoscopic images were obtained prior to and immediately following suture removal in 14 patients, and then again at the next postoperative visit 4 to 6 weeks later. These images were analyzed and statistically compared for central corneal power and vector of the central 3-mm corneal astigmatism. RESULTS: Most of the topographic changes induced by suture removal occurred immediately. However, continued shifting in corneal curvature did take place over the subsequent 4 to 6 weeks. Unpredictable shifts were more pronounced in patients whose surgery had been performed more than 20 months prior to suture removal. CONCLUSION: Computerized videokeratoscopy graphically elucidates continued shifts in corneal topography following the removal of sutures for the control of astigmatism after keratoplasty.

Aged↗
PubMed1997

The annular tinted contact lens syndrome: corneal topographic analysis of ring-shaped irregular astigmatism caused by annular tinted contact lenses.

PURPOSE: Irregular corneal astigmatism has been reported in association with annular tinted hydrogel contact lenses. We report the abnormal videokeratographic findings of five patients wearing annular tinted contact lenses, who presented with bilateral blurred vision and revealed a loss of best corrected visual acuity. METHODS/RESULTS: The corneal topographic analysis revealed a previously unreported distinct ring-shaped pattern of irregular astigmatism. The topographic circular band of irregular astigmatism was further characterized by concentric areas of relative steepening, flattening, and steepening with a diameter of approximately 4 mm. This pattern suggests that forces acting at the junctional zone between the tinted area and the clear pupillary area are inducing structural abnormalities of the corneal surface. At the time of presentation, the mean surface regularity index (SRI) was 2.06 (range: 0.61-5.88). The topography and best-corrected visual acuity returned to normal within days of discontinuing annular tinted lens use, and the mean SRI decreased to 0.44 (range: 0.21-1.16). Digital imaging of lenses obtained from our patients and of identical control lenses was performed. A masked analysis suggested that the study lenses contain greater amounts of pigment compared to the control lenses. CONCLUSIONS: We present ten characteristic signs and symptoms of this condition, which we have named "the annular tinted contact lens syndrome." Corneal topographic analysis is a powerful tool for detecting specific reversible irregularities of the corneal surface associated with the use of annular tinted contact lenses.

Adolescent↗
PubMedDate not supplied

Experiences with photorefractive excimer laser treatment in compound myopic astigmatism.

The invention of excimer lasers and different masks in order to treat refractive failures has opened a new era in refractive surgery. The refractive grading, the ablation effect, which can be controlled within one micrometer, and the design of a special mask made possible so-called "corneal sculpting" in compound astigmatism. The authors evaluated their experiences on 27 myopic compound astigmatic eyes. The average age of the patients was 28.67 +/- 9.78 years and the average preoperative uncorrected visual acuity was 0.06 +/- 0.04. The spherical component averaged -6.74 +/- 2.81 D and the cylindrical component averaged -2.3 +/- 1.54 D (the preoperative correction needed to obtain the best corrected visual acuity). Postoperatively, the uncorrected visual acuity improved to 0.65 +/- 0.26. To obtain the best corrected postoperative visual acuity an average -0.51 +/- 1.06 D sph and an average -0.54 +/- 1.06 D cyl component was needed. The authors conclude that ArF excimer laser treatment is able to alter both of the spherical and cylindrical components of the eye toward emmetropia. The lower the degree of preoperative compound myopic astigmatism, the better are the chances of postoperative emmetropia. No serious complications were met during the follow-up period.

Adult↗
PubMed1976

The development of corneal astigmatism in contact lens wearers.

In this study of 131 eyes, a comparison of the corneal astigmatism present before wearing hard contact lenses was made with that found after several years of wear (mean length of time: 4.4 years). The eyes were divided into 3 groups according to their ocular rigidity measurements. Statistical analysis of these groups showed that eyes with low ocular rigidity developed a high incidence of with-the-rule astigmatism change and that, furthermore, this change was of significant amount (twice that developed by eyes in the other groups). It was notable that all of the eyes that developed more than 1 1/2 diopters of astigmatism had low ocular rigidity.

Adolescent↗
PubMed1997

[Astigmatism after penetrating keratoplasty. Videokeratoscopic analysis on a series of 60 grafts].

PURPOSE: To study the factors which induce post keratoplasty astigmatism. To assess the reliability of different methods in the astigmatism measurement and to study the visual acuity predicting factors. METHODS: We retrospectively studied the corneal topography in 60 eyes with penetrating keratoplasty after suture removal, using the CAS* (Eye Sys). The diagnosis was keratoconus in 65% of the cases and bullous keratopathy in 15% of the cases. The graft was secured with a single running suture in 38.3% of the cases, interrupted sutures in 23.3% of the cases, or a combination of both running and interrupted sutures in remaining 28.3%. RESULTS: The suture method, diagnosis and surgeon did not influence subjective refraction nor visual acuity. The topographic pattern correlated with subjective cylinder (rs = 0.52 p = 0.02). The refractive power cylinder ("Holladay diagnostic summary") correlated well with subjective cylinder (rs = 0.81 p < 0.001) and visual acuity (rs = -0.63; p < 0.001). The Javal keratometry remains the best method to measure astigmatism axis (rs = 0.58; p < 0.001). CONCLUSIONS: The Holladay diagnostic summary (refractive power) is a useful tool for evaluating qualitative outcome of corneal transplantation.

Adolescent↗
PubMed2005

Astigmatic electron diffraction imaging: a novel mode for structure determination.

In a conventional transmission electron microscope, stigmators are used to correct for the effects of axial astigmatism in the diffraction lens. It seems feasible that these same stigmators could also be used to form a series of 'astigmatic' diffraction patterns. It is shown how this series of diffraction patterns could then be used to perform exit-surface wavefunction reconstruction. This has the advantage that the diffraction patterns are not resolution limited by the objective aperture as are images when performing exit-surface wavefunction reconstruction from a focal series. A scheme for carrying out phase reconstruction from a series of astigmatic diffraction patterns in an electron microscope is presented.

Journal Article↗
PubMed1998

Astigmatic single photon emission computed tomography imaging with a displaced center of rotation.

A filtered backprojection algorithm is developed for single photon emission computed tomography (SPECT) imaging with an astigmatic collimator having a displaced center of rotation. The astigmatic collimator has two perpendicular focal lines, one that is parallel to the axis of rotation of the gamma camera and one that is perpendicular to this axis. Using SPECT simulations of projection data from a hot rod phantom and point source arrays, it is found that a lack of incorporation of the mechanical shift in the reconstruction algorithm causes errors and artifacts in reconstructed SPECT images. The collimator and acquisition parameters in the astigmatic reconstruction formula, which include focal lengths, radius of rotation, and mechanical shifts, are often partly unknown and can be determined using the projections of a point source at various projection angles. The accurate determination of these parameters by a least squares fitting technique using projection data from numerically simulated SPECT acquisitions is studied. These studies show that the accuracy of parameter determination is improved as the distance between the point source and the axis of rotation of the gamma camera is increased. The focal length of the focal line perpendicular to the axis of rotation is determined more accurately than the focal length to the focal line parallel to this axis.

Algorithms↗
PubMed2005

Propagation analysis of the Laguerre-Gaussian beam with astigmatism.

The entire range of transformations that a Laguerre-Gaussian (LG) beam with astigmatism can go through in free space is clarified. The transformations are governed by the relative phase between the astigmatic Hermite-Gaussian components. Formulas describing the behavior of this relative phase are obtained and used to classify and map the transformation patterns to initial beam parameters. The difference between an LG beam and a phase singular beam generated by a hologram under astigmatic conditions is also investigated.

Journal Article↗
PubMed2005

Focusing astigmatic Gaussian beams through optical systems with a high numerical aperture.

We theoretically derive the electric field distribution of an astigmatic Gaussian laser beam after it is focused through a high-aperture objective. We show that astigmatism values that are hard to detect in the collimated laser beam can have a large effect after diffraction-limited focusing. Such astigmatic beams may be frequently encountered in fluorescence correlation measurements and in laser-scanning confocal microscopy. We present experimental measurements of the excitation intensity distribution measured by 3D scanning of single fluorescent molecules immobilized on a glass surface.

Journal Article↗
PubMed1987

Orthogonal astigmatic axes in Chinese and Caucasian infants.

Caucasian infants are known to have a high incidence of astigmatism. The axis of greatest power is usually in the orientation orthogonal to the most common type found in Caucasian adults, with-the-rule astigmatism. We now find that Chinese infants also have a high incidence of astigmatism relative to adults, but its orientation is orthogonal to that of Caucasian infants. The source of this racial difference is not clear. It is unlikely to be due to the most obvious difference, the structure of the eyelids.

Adolescent↗
PubMed1980

Surgical correction of high postkeratoplasty astigmatism. Relaxing incisions vs wedge resection.

Improved techniques and procedures have resulted in a higher rate of clear grafts after penetrating keratoplasty. A clear graft, however, does not give a good visual result if high corneal astigmatism prevents the successful wearing of spectacles or contact lenses. This article describes the methods and results of two microsurgical techniques--the corneal wedge resection to steepen the flat meridian and relaxing incisions to flatten the steep meridian. Average reduction in corneal astigmatism was greater for the wedge resection (ten cases) (6.50 diopters as compared with 4.25 D [16 cases] for the relaxing incisions). The relaxing incisions operation was successful in 75% of cases with stabilization of corneal curvature readings in an average of three weeks and is an outpatient procedure. After a wedge resection, corneal stabilization usually takes months. We believe that wedge resection should be reserved for cases in which relaxing incisions are unsuccessful.

Astigmatism↗
PubMed1993

Keratotomy for astigmatism using an arcuate keratome.

We describe a new system for performing transverse arcuate corneal incisions for the correction of astigmatism. The instrument consists of a conical housing with suction and/or friction fixation to the limbus and two micrometric diamond knives mounted on a carrier that can be rotated by a gear mechanism. The depth, length, and location of the incisions can be predetermined. Light microscopy of donor eye corneas documented the achieved incision depth. One sweep at normal speed produced an incision depth 28% less deep than the preset depth. One sweep at low speed achieved depths of approximately 100% of the knife setting. Variability from one incision to another in the same cornea was related to blade sharpness. We report successful use of the instrument in five consecutive eyes with naturally occurring astigmatism.

Adolescent↗
PubMed1995

One-year evaluation of excimer laser photorefractive keratectomy for myopia and myopic astigmatism. Melbourne Excimer Laser Group.

OBJECTIVE: To evaluate prospectively the efficacy and safety of excimer laser photorefractive keratectomy in the treatment of myopia and myopic astigmatism. METHODS: Up to 15 diopters (D) of myopia with or without astigmatism of less than 6 D was treated with an excimer laser (VISX Twenty/Twenty). One hundred fifty procedures have been followed up for more than 12 months. RESULTS: Postoperative refractions were generally stable after 3 months without significant early overcorrection. Of those eyes treated with spherical equivalents of 5 D or less, 96% were within 1 D of the targeted refraction after photorefractive keratectomy and 88% had uncorrected visual acuities of 20/40 or better. At 12 months, 77% of all 150 eyes treated achieved an uncorrected visual acuity of 20/40 or better and 81% were within 1 D of the intended correction. Nine eyes (6%) lost 2 or more lines of best corrected visual acuity and 14 (9%) gained 2 or more lines. Adverse reactions were reported in 12 patients (8%) during the postoperative period. CONCLUSIONS: Photorefractive keratectomy is capable of correcting low and moderate myopic errors with a relatively high degree of accuracy and safety. The predictability and stability of the postoperative refraction during the first 12 months seem to be good.

Adult↗
PubMed1996

Overcorrection after excimer laser treatment of myopia and myopic astigmatism. Melbourne Excimer Laser Group.

OBJECTIVE: To study the incidence and associations of overcorrection after excimer laser treatment of myopia and myopic astigmatism. METHODS: The study cohort consisted of 645 patients who had photorefractive or photoastigmatic refractive keratectomy done by an excimer laser during a 2-year period. Patients were assessed 1,3,6, and 12 months postoperatively. The variables evaluated were visual acuity, refraction, keratometry, and corneal clarity. RESULTS: At 1 month, overcorrection of more than +1 diopter spherical equivalent (SEQ) was seen in 22% of the eyes. This progressively regressed so that only 8.6% of the 140 eyes that were overcorrected at 1 month were overcorrected at 1 year. Overall, 2.2% of eyes were overcorrected at 1 year. The magnitude of attempted correction and use of topical nonsteroidal anti-inflammatory drugs disclosed a notable association with occurrence of overcorrection at 1, 3, and 6 months. The use of bandage contact lenses also was associated with overcorrection at 1 and 3 months. After controlling for myopia and use of contact lenses, the odds of overcorrection for use of topical nonsteroidal anti-inflammatory drugs at 1,3, and 6 months were 2.21 (95% confidence limits [CL]=1.49, 3.44), 1.69 (95% CL=0.88, 3.24), and 2.01 (95% CL=0.88, 4.56), respectively. The odds of overcorrection with bandage contact lenses were 1.79 (95% CL=1.05, 3.05) at 1 month and 2.42 (95% CL=1.23, 4.75) at the end of 3 months. No associations were seen between overcorrection and age, gender, surgical technique, or simultaneous astigmatic corrections. CONCLUSIONS: Overcorrection is common during the early postlaser treatment period and is associated with degree of myopia, use of nonsteroidal anti-inflammatory drugs, and bandage contact lens wear.

Adult↗
PubMed1975

[Postoperative astigmatism after penetrating corneal grafts (author's transl)].

232 cases of penetrating grafts from 1961-1972 have been studied. 141 (60%) were evaluated for visual acuity and corneal astigmatism. Since the introduction of the running suture (1966) postoperative complications have markedly decreased, visual acuity is in the average good and even very good. Patients operated for keratokonus however show higher postoperative astigmatism than patients operatedfor other corneal diseases.

Adolescent↗
PubMed1977

A trichromatic test for spheric and astigmatic refraction.

An improved chromatic rotatable refraction test for simultaneous spheric and astigmatic refraction is described. Its new features are interposition of a bright yellow stripe between the conventional red and green fields and a pair of parallel test lines, which traverse vertically all colored fields. Thereby astigmatic errors become easily visible.

Astigmatism↗