Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ASTIGMATISM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62Linked to original sources
PubMed1996

Astigmatic shift following sutureless, triplanar, curvilinear, single hinge, clear corneal incision for phacoemulsification and intraocular lens implantation.

BACKGROUND AND OBJECTIVE: Questions remain regarding wound stability, in particular astigmatism and leakage, in large, sutureless, clear corneal incisions. A polymethylmethacrylate (PMMA) implant, which may be more desirable than a silicone foldable in a very young patient, can be implanted through this incision. PATIENTS AND METHODS: Twenty eyes of 19 patients underwent a 5.2-mm, temporal approach, clear corneal, sutureless phacoemulsification with intraocular lens implantation. The Langerman single hinge technique with a curvilinear groove and a triplanar, sutureless incision was used in all cases. RESULTS: The average axis-corrected induced cylinder was 1.05 D of with-the-rule change. Stromal hydration was not done and only one eye required a single suture. CONCLUSION: A 5.2-mm, clear corneal incision was self-sealing, with an acceptable induced with-the-rule astigmatism.

Adult↗
PubMed1996

Vectoranalysis of surgically induced astigmatism in small corneal and scleral cataract incisions.

Vector analysis of surgically induced astigmatism was performed on several scleral and corneal tunnel incisions (6.0-mm W; 3.5- and 2.5-mm L scleral tunnel; 4.1-mm linear and 2.5-mm L corneal tunnel). The analysis revealed a mean astigmatism between 1.18 and 0.64 D, as compared to 0.35 D in a control group of nonoperated eyes. The best results were obtained with the scleral and corneal L-shaped incisions.

Astigmatism↗
PubMed1997

[Photorefractive excimer laser keratectomy in myopia and astigmatism with a 2-year follow-up after surgery].

In a group of 1037 operated eyes the effectiveness, predictive value, stability and safety of photorefraction keratectomy by means of an excimer laser was tested in myopia (PRK) and astigmatism (PARK) with a two-year follow-up period after operation. The range of the preoperative refraction defect was -1.75 to -2.10 dpt (SE). The maximal value of the corrected cylinder in astigmatism was -6.0 cyl dpt. In the PRK group 459 operations were evaluated, in the PARK group 578 operations. Both groups are classified according to the spherical equivalent of the refractory defect into three groups. Group A is formed by myopia up to -6.0 dpt, group B myopia -6.25 to -10.0 dpt and group C above -10.25 dpt. Non-corrected visual acuity 6/12 and better was recorded in the 20th month after operation in group A in 93.4-97.6% (PARK-PRK) operated eyes, in group B 88.7-91.5% and in group C 61.2-68.4% of operated eyes. The achieved final refraction (SE) in an interval +(-1.0) dpt from the originally planned one was recorded during the 20th month after operation in group A in 92.8-96.5% (PARK-PRK) operated eyes, in group B 73.5-78.9% and in group C 59.7-63.5% operated eyes. The best corrected visual acuity (NKZO) in the whole group 20 months after operation was unaltered or better by 1 line of projected optotypes as compared with NKZO before operation in group A in 97.6%, in group B in 94.3% and in group C in 89.7% operated eyes. The analysis of results in PRK and PARK in the group with a two-year follow-up period after operation permits to evaluate the method as sufficiently effective and safe for correction of myopia up to -10.0 dpt but less predictive in myopia above -10.0 dpt.

Adult↗
PubMed1976

Use of the astigmatism correction device on the Zeiss fundus camera for peripheral retinal photography.

High quality photographs of the peripheral retina are made possible by the proper positioning of the astigmatism correction device on the Zeiss fundus camera. Using a plus cylinder, axis perpendicular or a minus cylinder, axis parallel to that around which the eye is rotated will eliminate the astigmatism induced by viewing the retina obliquely through the optical surfaces of the eye, resulting in a sharply focused image at the film plane. Proper use of this instrument can be helpful in evaluating and diagnosing retinal lesions that occur in the peripheral fundus.

Astigmatism↗
PubMed1997

[Induced astigmatism after implantation of Acrysof MA 60 BM and Hydroview H 60 M intraocular lenses].

The purpose was to find an induced corneal astigmatism after cataract surgery. Change in the keratometric cylinder was examined in two ways by the vector analysis according to Jaffe/Clayman and according to Cravy. In the majority of cases we examined excellent visual acuity in only the first week after surgery. Concerning the mean actual keratometric cylinder values for the first eight postoperative months, in both groups induced astigmatism and rotation of cylinder axis was absolutely minimalized.

Astigmatism↗
PubMed1998

Corneal scarring and irregular astigmatism following refractive surgery in a corneal transplant.

BACKGROUND: Scarring may follow refractive surgery, causing irregular astigmatism and loss of visual acuity. METHODS: A case report of scarring and irregular astigmatism occurring in a corneal transplant following photorefractive keratectomy and arcuate incisions is presented. RESULTS: Following surgical excision of the scar, unaided visual acuity improved from 1/60 to 6/12. Histopathology of the excised scar was obtained. CONCLUSIONS: Refractive surgery following corneal transplantation may produce scarring. The origin of the scar in the present case has not been established.

Adult↗
PubMedDate not supplied

[Effects of surgical wounds hermetic closure methods in cataract extraction on postoperative corneal astigmatism].

Main factors of hermetic closure of the operation wound after cataract extraction are discussed. A new method of closing the wound in this operation is described. The opposition intracorneal mattress sutures are made across the section plane. Their principal difference is that the thread is not thrown over the external edge of the section of the cornea, as in traditional suturing, and when pulled tight, the thread does not deform the external surface of the cornea in the central zone, and thus does not induce postoperative astigmatism. Eighteen patients were operated on using this technique. Opposition sutures made after the above technique involve no high postoperative astigmatism or none at all.

Aged↗
PubMed1998

[Hydrophilic toric contact lenses in the correction of astigmatism].

Technological advances in the design and manufacture of soft toric contact lenses have made it possible for most astigmatic patients to achieve successful results with current soft lenses, but a small percentage of those patients are wearing them. We present the observations on 21 subjects that requested soft toric lenses in the past year. This lenses (TP 60) offered all the comfort of soft lenses and a good vision correction for astigmatism up to 6 diopters.

Adolescent↗
PubMedDate not supplied

[Photorefractive keratectomy by excimer laser for correcting myopia and myopic astigmatism].

Photorefraction keratectomy (PRK) was carried out using Nidek EC-5000 eximer laser in patients with myopia of different degree and myopic astigmatism. After 12 months, visual acuity without correction was 0.6-1.0 diopters in all patients with slight myopia, 0.7-1.0 in 95% of patients with medium myopia, and 0.8-1.0 in 86% of patients with high myopia. A lower visual acuity in high myopia was caused by retinal complications of myopia. The results of refraction after PRK depended on the severity of myopia and patient's age. The degree of myopia regression depended on preoperative refraction and was more expressed in high myopia. Young patients developed a more expressed tendency to decrease of postoperative refraction. The results indicate that eximer laser is an effective and reliable tool for correcting myopia of different degree and myopic astigmatism.

Adolescent↗
PubMed2000

Visual acuity, lens flexure, and residual astigmatism of keratoconic eyes as a function of back optic zone radius of rigid lenses.

The purpose of this study was to determine whether the visual acuity of keratoconic eyes was affected by alteration of back optic zone radii (BOZRs) of rigid gas permeable lenses (RGP) contact lenses. Visual acuity, spherical and sphero-cylindrical over-refraction and keratometry of the front surface of the RGP lenses of nine keratoconic eyes were measured. The BOZR of the five lenses varied from steeper to flatter than that habitually worn by the subjects. The steepest lenses produced significantly greater lens flexure and residual astigmatism (P < 0.002) and worse high and low contrast visual acuity with the spherical over-refraction (P < 0.05). There was no statistical difference in visual acuity across the range of BOZR when a sphero-cylindrical over-refraction was applied. Thus reduced visual acuity in keratoconus with steep lenses is likely due to uncorrected residual astigmatism from a combination of several possible sources.

Journal Article↗
PubMed2001

An auto-tuning method for focusing and astigmatism correction in HAADF-STEM, based on the image contrast transfer function.

An auto-tuning method for high-angle annular detector dark field scanning transmission electron microscopy (HAADF-STEM) is proposed which corrects the defocus to the optimum Scherzer focus and compensates the astigmatism. Because the method is based on the image contrast transfer function formulated for the HAADF-STEM, the defocus and the astigmatism are accurately measured from input of two different defocus images. The method is designed to work independent of object function in the linear imaging model by analysing the spectral ratio between two Fourier spectra of their images, which is useful for cases where the spectrum of object function is not uniformly spread out over the reciprocal space. The method was preliminarily tested in a Hitachi HD-2000 STEM, and successful results of the auto-tunings from the viewpoint of verification of the algorithm were obtained using general specimens of Au fine particles and a thin section of a semiconductor device.

Journal Article↗
PubMed2006

Linear astigmatism of confocal off-axis reflective imaging systems and its elimination.

Linear astigmatism of a confocal off-axis reflective imaging system when the object plane is tilted and located at a finite distance from the imaging system is derived. We show that linear astigmatism can be eliminated by proper configuration of the parent mirror axes in confocal off-axis two-mirror systems. The tilt angle of the image plane is also derived. The developed theory is verified by ray-tracing analysis of an example system.

Algorithms↗
PubMed2007

Paraxial matrix description of astigmatic and cylindrical mirror resonators with twisted axes for laser spectroscopy.

A complete matrix description of ray-optic propagation in an astigmatic multipass cell is presented, with expressions for the coupling of coordinates. A pair of transforms puts the 4 x 4 paraxial system matrix into block-diagonal form, allowing a solution using Sylvester's theorem. A variation on the Jones matrix calculus is employed wherein the ray coordinates on both resonator mirrors are simultaneously represented as a single state of the system. The formulations are applicable to resonators with any degree of astigmatism and axial twist. Examples are presented of beam paths and the boundary shapes of beam spots. The shape of the pattern boundaries, as a function of the coordinate coupling coefficient, influences the practical availability of patterns.

Journal Article↗
PubMed2007

Reflection and refraction of narrow Gaussian beams with general astigmatism at tilted optical surfaces: a derivation oriented toward lens design.

The formulas for the reflection and refraction of a narrow Gaussian beam with general astigmatism at a tilted optical surface are derived by ray-tracing techniques. The propagation direction of the reflected and refracted beams is computed by tracing the central ray of the incident beam, and the characteristic parameters of the respective wavefronts are worked out by applying the formulas developed for the generalized ray tracing. Moreover, the Gaussian form of the reflected and refracted amplitude distributions along the transverse coordinates is determined by requiring the matching of the incident, reflected, and refracted light spots on the optical surface. No limiting assumptions are made regarding the form of the optical interface or the orientation of the incident astigmatic wavefront. In the end, to illustrate a simple application of these formulas, the reflection of a Gaussian beam at a conicoid is considered, and a simple property of the conicoidal mirrors is reported.

Journal Article↗
PubMed2005

Application of the fractional Fourier transformation to digital holography recorded by an elliptical, astigmatic Gaussian beam.

The authors have studied the diffraction pattern produced by a particle field illuminated by an elliptic and astigmatic Gaussian beam. They demonstrate that the bidimensional fractional Fourier transformation is a mathematically suitable tool to analyse the diffraction pattern generated not only by a collimated plane wave [J. Opt. Soc. Am A 19, 1537 (2002)], but also by an elliptic and astigmatic Gaussian beam when two different fractional orders are considered. Simulations and experimental results are presented.

Journal Article↗
PubMed1992

Focimeter measurement of the astigmatism arising from oblique central refraction.

In this article, a method for measuring the astigmatism produced by an oblique central refraction is proposed. Measurements were taken using two different values of the pantoscopic angle that can be produced by lenses mounted in frames. We show that in specific cases, and as a function of the angle and power of the lens, the resulting astigmatism can surpass the tolerance level of the eye.

Lenses↗
PubMed1989

Astigmatism shift after extracapsular surgery: Mersilene versus nylon.

Mersilene sutures are said to produce a more stable wound postoperatively than nylon. To test this 25 patients had a standard wound closure with 10-0 nylon in one eye and with 11-0 Mersilene in the other. There was no difference in the astigmatism decay over a six month period.

Astigmatism↗