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At least 829 records · Page 46Linked to original sources
PubMed1999

[Minimizing induction of astigmatism in preoperative spherical cornea a. by mini-incision surgery with foldable IOL and b. by corneal tunnel incision with limbal relaxing incision].

BACKGROUND: In case of a spheric cornea preoperatively the refractive effect of a clear corneal cataract incision is undesirable. We studied two actual techniques to minimize the surgically induced astigmatism. PATIENTS AND METHODS: Temporal clear corneal incision was performed in 77 patients with practically spherical cornea (0.2 +/- 0.1 D). 27 patients with 4.1-mm clear corneal stretch incision and 5 mm PMMA lens implantation served as control. 25 further patients were operated on with the same technique, but 2 additional limbal relaxing incisions (LRI) of 0.55-mm depth and 8 mm length at 6 and 12 o'clock were performed. In 25 patients a foldable acrylic lens (Acrysof) was implanted through a 3.2-mm temporal clear corneal incision. Corneal topography results were evaluated in all patients by the Jaffe and the Holladay analysis. RESULTS: The surgically induced astigmatism of 0.8 +/- 0.5 dpt in the control group was reduced to 0.4 +/- 0.3 dpt by LRI and by reduction of the incision size as well in the treatment groups. With-the-wound-change (WTW) in the Holladay analysis was 0.6 +/- 0.7 dpt in the control group and around 0 in the groups with astigmatism reducing techniques. CONCLUSION: To preserve a spherical cornea in clear corneal-tunnel incision, compensating limbal relaxing incisions (LRI) or ultra-small incisions with foldable lens implantation should be performed.

Astigmatism↗
PubMed1992

[The unsolved problem of transplant astigmatism].

Irregularities of the trephine margins, donor/recipient thickness disparity and irregular suture technique are the important factors for high astigmatism after penetrating keratoplasty. A combined suture technique using eight interrupted 11-0 Mersilene sutures and a single continuous 10-0 nylon suture enables to control and to remedy the final postkeratoplasty astigmatism. In 35 patients with a corneal graft a final astigmatism of 2.9 diopters was reached after removal of the continuous suture and partial leaving in place of single interrupted Mersilene sutures.

Astigmatism↗
PubMed1986

[Corneal astigmatism following cataract operations].

Following a description of the surgical technique of wound opening and closure for planned extracapsular cataract extraction (ECCE) and posterior chamber lens implantation, the results, with regard to postoperative corneal astigmatism, are analyzed and discussed. In a prospective study a total of 720 cases was divided into 2 groups; the Terry surgical keratometer was used in Group I, while in Group II no postoperative measurements were performed. The results achieved in the two groups by 3 experienced surgeons were compared. Only one surgeon achieved keratometer readings which were statistically significantly lower in the early and late postoperative periods in Group I as compared to Group II. The percentage of cases with final corneal astigmatism of 2 D or less in the early and late postoperative period was higher in Group I - in which the Terry keratometer was used - than in Group II. The numerous factors influencing final postoperative corneal astigmatism are discussed.

Astigmatism↗
PubMed1981

[Myopic astigmatism for increased depth of focus in pseudophakia (author's transl)].

The optimal refraction after lens implantation is a slight simple myopic astigmatism for patients wishing to see without glasses. The depth of focus is increased in myopic astigmatism because the shape, rather than the size, of the blurred retinal image changes as Sturm's conoid moves over the retina. Such a refraction can be obtained in pseudophakia if the corneal power change induced by surgery is taken into consideration when the intraocular lens. The induced corneal ametropia is a spherocylinder with a very low equivalent power. The results in a series of 50 successive implants employing these principles are described. The depth of fucus is best in simple myopic astigmatism.

Accommodation, Ocular↗
PubMed2001

Comparison of measured astigmatic retinoscopies from different lid specula.

PURPOSE: We wanted to study the effects of different lid specula on retinoscopy readings in the pediatric population. METHODS: We prospectively enrolled 29 patients from the Eye Clinic at The Children's Hospital of Denver who were being examined under anesthesia and met the inclusion criteria for the study. Any patient with ocular pathology that could affect the pliability of the sclera of both eyes was excluded. Patients with preexisting lid abnormalities or adnexal masses were also excluded. Cycloplegic retinoscopies were performed under anesthesia with the Barraquer wire and the Lancaster solid-blade specula. The amounts and the axes of the astigmatism were tabulated and statistically analyzed with the paired t test. RESULTS: A statistically significant difference occurred in the retinoscopies obtained from the 2 lid specula. The Barraquer lid speculum seemed to induce the least amount of astigmatism (P =.0001). CONCLUSIONS: There was a statistically significant difference in the amount of astigmatism found with each lid speculum. The choice of lid speculum in performing retinoscopies on the pediatric population can influence the final refraction and may have implications for visual outcome.

Adolescent↗
PubMed2005

Comparison of endothelial cell loss and surgically induced astigmatism following conventional extracapsular cataract surgery, manual small-incision surgery and phacoemulsification.

PURPOSE: To compare the surgically induced astigmatism (SIA) and endothelial cell loss following conventional extracapsular cataract surgery (ECCE), manual small-incision cataract surgery (Blumenthal technique)(SICS) and phacoemulsification (PE) with non-foldable intraocular lens implantation. METHODS: 186 cataractous eyes with nuclear sclerosis grade 3 or less were randomized to undergo ECCE, SICS or PE with intraocular lens (non-foldable) implantation after a detailed pre-operative assessment. Keratometry and specular microscopy were performed pre-operatively and 6 weeks postoperatively. Surgically induced astigmatism was calculated using the rectangular coordinate method (Holladay et al.). RESULTS: Mean endothelial cell loss was similar for all three groups (p = 0.855); ECCE induced a loss of 4.72% (SD: 13.07); SICS 4.21% (SD: 10.29) and PE 5.41% (SD: 10.99). Mean SIA was 1.77D (1.61D) for the ECCE group, 1.17D (0.95D) for the SICS group and 0.77D (0.65D) for the PE group (p = 0.001). The magnitude of the difference between the SICS and the PE group was 0.4D. CONCLUSION: PE induced less astigmatism than SICS and ECCE in this study but the magnitude of the difference between SICS and PE was small. There was no significant difference in endothelial cell loss between the three groups.

Astigmatism↗
PubMed1998

Inheritance of astigmatism: evidence for a major autosomal dominant locus.

Although astigmatism is a frequent refractive error, its mode of inheritance remains uncertain. Complex segregation analysis was performed, by the POINTER and COMDS programs, with data from a geographically well-defined sample of 125 nuclear families of individuals affected by astigmatism. POINTER could not distinguish between alternative genetic models, and only the hypothesis of no familial transmission could be rejected. After inclusion of the severity parameter, COMDS results defined a genetic model for corneal astigmatism and provided evidence for single-major-locus inheritance. These results suggest that genetic linkage studies could be implemented and that they should be limited to multiplex families with severely affected individuals.

Adult↗
PubMed1987

Oval host wounds and postkeratoplasty astigmatism.

Penetrating keratoplasty frequently results in postoperative astigmatism. A rabbit model was used to investigate the relationship between the ovality of the recipient bed and the resulting postoperative astigmatism as measured by keratometry. Animals were grouped based on the extent that the recipient bed deviated from a 7.25-mm diameter circle (ovality of bed). All animals received a round 7.75-mm donor corneal button. With increasing ovality of the recipient bed, there was a corresponding increase in the postoperative astigmatism at 3 months after all sutures were removed.

Animals↗
PubMed1993

Control of astigmatism aided by intraoperative keratometry.

An evaluation of the final "sutures out" postoperative astigmatism in two groups of keratoconus patients undergoing penetrating keratoplasty is presented. Group I consists of a retrospective evaluation of keratoconus patients who underwent penetrating keratoplasty without using the Troutman Keratometer prior to suturing the button into position. Group II patients had their donor button rotated in the recipient bed until approximate sphericity was indicated by a circular reflex from the Troutman Keratometer before suturing into position. The mean final astigmatism with all sutures removed from Group I was 4.64, SD 1.89, and for Group II 2.27, SD 1.27. Selective positioning of the donor button using the Troutman Keratometer leads to a significant reduction in the final sutures out astigmatism in patients undergoing penetrating keratoplasty for keratoconus.

Astigmatism↗
PubMed1998

Photorefractive keratectomy using the summit SVS Apex laser with or without astigmatic keratotomy.

PURPOSE: The purpose of this study was to evaluate the results of myopic photorefractive keratectomy (PRK) with or without astigmatic keratotomy (AK) for different levels of intended correction by using the SVS Apex laser. METHODS: This is a retrospective cohort study of 226 eyes that had PRK for myopia ranging from -1.0 to -7.6 diopters and 6 months of follow-up. In addition, 64 of these eyes had AK for naturally occurring or laser-induced astigmatism. Uncorrected visual acuity, spectacle-corrected visual acuity, and corneal topography with quantitative descriptors of surface regularity (SRI) and surface asymmetry (SAI) were used to monitor the results of PRK with or without AK. RESULTS: At 6 months, 95.6% eyes had an uncorrected visual acuity of 20/40 or better, 90% eyes were within +/-1.0 diopter of emmetropia, and 3.1% eyes lost two lines of best-corrected vision. No eyes lost more than two lines of best-corrected vision. Mean refractive astigmatism was reduced, but mean SAI and SRI were increased, 6 months after PRK. Uncorrected vision, best-corrected vision, and predictability decreased, whereas SAI and SRI increased, with increasing attempted correction. CONCLUSION: PRK, with or without AK, effectively reduced myopia in all eyes by 6 months after surgery. Predictability tended to decrease with increasing attempted correction, even for eyes with relatively low to moderate myopia. PRK may induce surface asymmetry and irregularity at 6 months, and these alterations tend to be greater as the attempted correction increases.

Astigmatism↗
PubMed1978

Etiology of astigmatism.

A large amount of evidence suggests that astigmatism is hereditary. Other evidence indicates that the prevalence of astigmatism varies widely between and within racial groups and that both the direction and the amount of astigmatism tend to vary as a function of age and in response to environmental influences.

Adolescent↗
PubMed1987

Flexure and residual astigmatism with Paraperm O2 and Boston II lenses on toric corneas.

It has been shown previously that thin polymethyl methacrylate (PMMA), cellulose acetate butyrate (CAB), and Polycon I contact lenses flex on toric corneas. We investigated the flexure and induced residual astigmatism of two gas permeable contact lens materials, Paraperm O2 and Boston II, and compared the results with those of other materials. Six subjects (12 eyes) with corneal toricities ranging from 1.75 to 3.25 D wore five Paraperm O2 lenses and five Boston II lenses with center thicknesses ranging from 0.10 to 0.20 mm. Flexure and induced residual astigmatism were measured on all corneas wearing all lenses in a double-masked fashion. All lenses studied showed flexure and induced residual astigmatism, which increased as center thickness decreased. For both lens types, lenses thinner than 0.15 mm flexed significantly more than thicker lenses. This critical center thickness should be considered when fitting these lens types on toric corneas.

Adult↗
PubMed1993

Optical aspects of tolerances to uncorrected ocular astigmatism.

We approached the question of the visual tolerance to uncorrected astigmatism by exploring the changes in the retinal diffraction images brought about by astigmatism, as a function of spherical focus. Consideration of the Rayleigh and Maréchal wavefront criteria and of the changes in ocular modulation transfer function (MTF) broadly supports a value of 0.25 DC as a practical tolerance limit for uncorrected astigmatism. This study underlines the limitations of a geometrical optical approach to this problem in particular, and shows that the concept of the circle of least confusion may be misleading.

Astigmatism↗
PubMed1993

Astigmatic optical systems with separated and prismatic or noncoaxial elements: system matrices and system vectors.

A general system of noncoaxial separated astigmatic optical elements is examined. Allowance is made for prismatic elements including decentered lenses and refracting surfaces, prisms, and plane interfaces. The directions and positions of a ray entering and emerging from the system are related by a system matrix and a system vector. Given an incident ray one can readily obtain the emergent ray. The analysis is of fundamental importance for visual optics. Two numerical examples are presented. One is a model eye with astigmatic and obliquely crossing astigmatic and decentered surfaces.

Astigmatism↗
PubMed1997

Oblique (off-axis) astigmatism of the reduced schematic eye with elliptical refracting surface.

The oblique (off-axis) astigmatism of the Indiana Eye, an aspheric reduced-eye model of ocular chromatic aberration and spherical aberration, is computed across the visual field by using Coddington's equations for nonspherical surfaces of revolution. Our results show that the amount of astigmatism varies significantly with the shape of the refracting surface and with the axial location of the pupil. For a pupil located 1.91 mm from the apex of the refracting surface (as originally specified for the model), the calculated Sturm's interval was larger than that reported in the literature. However, by moving the model's pupil 0.84 mm axially away from the apex toward the nodal point, a close match was achieved between Sturm's interval of the model eye and published data from human eyes for eccentricities up to 60 degrees. These results demonstrate that the aspheric reduced-eye model is capable of simultaneously accounting for the chromatic, spherical, and oblique astigmatic aberrations typically found in human eyes.

Astigmatism↗
PubMed2004

Comparison of spherical equivalent refraction and astigmatism measured with three different models of autorefractors.

PURPOSE: The purpose of this study was to compare refractions measured with three different autorefractors. METHODS: The refractive error of each eye of 50 adults aged 17 to 59 years (mean, 30.5 years) was measured without cycloplegia using the Canon R-1 and two newer instruments, the Grand Seiko WR-5100K and the Nidek ARK 700-A. For the first two, an isolated line of 20/100 letters on an ETDRS chart at 4.0 m served as a target, whereas for the Nidek, the subject looked at a picture of a balloon in the instrument. Five readings were taken for each eye, and the data (sphere, negative cylinder power, and axis) were analyzed using Fourier decomposition of the power profile. Each reading was broken down into the spherical equivalent (M) and two Jackson crossed-cylinder vectors, J0 and J45. Right-eye results are reported. RESULTS: The mean spherical equivalent refraction measured by the Canon R-1 was -2.44 D. Measurements from the Grand Seiko were more hyperopic (mean M, -2.01 D), whereas those from the Nidek were more myopic (mean M, -2.66 D). Correlation of M for each pair of autorefractors was 0.99. For J0, the Canon was more minus than the other two instruments by 0.15 D compared with the Nidek and 0.13 D with the Grand Seiko, and on this component, the correlation of the Canon with each of the other two was 0.87. Mean J0 values for the Nidek and Grand Seiko were similar, 0.05 D and 0.03 D, respectively, and mean J45 values were 0.04 D for both instruments. Correlations were 0.97 between these two autorefractors for each of the two components. J45 measured by the Canon was more positive than the other two by 0.06 D. For J45, the correlation of the Canon with the Grand Seiko was 0.40 and with the Nidek was 0.38. In 92% of the eyes, the absolute difference in cylinder power between the Grand Seiko and the Nidek was < or =0.25 D. Only 42% of the differences between the Canon and the Grand Seiko and 40% of the differences between the Canon and the Nidek were this small. CONCLUSIONS: The Canon provided more myopic readings than the Grand Seiko and more hyperopic readings than the Nidek. The Canon measured more astigmatism that did not correlate well with the other instruments, whereas measurements of astigmatism taken by the Nidek and the Grand Seiko showed good agreement. If the Grand Seiko is used in place of the older Canon, the differences in spherical equivalent and astigmatism must be considered.

Adolescent↗
PubMed1987

Corneal astigmatic changes after pars plana vitrectomy.

The authors prospectively studied 67 eyes of 64 patients undergoing pars plana vitrectomy without a scleral buckle to determine the effect of surgery on postoperative corneal curvature. An average of 1 D of against-the-rule astigmatism was induced in the immediate postoperative period. This astigmatic change spontaneously regressed to less than 0.15 D by the 7th postoperative week. Pars plana vitrectomy does not induce clinically significant corneal astigmatism.

Astigmatism↗
PubMed1996

Methods to control astigmatism in cataract surgery.

The correction of astigmatism during cataract surgery has evolved due to recent basic and clinical studies. To control surgically induced astigmatism, the surgeon has many options, including varying incision parameters, astigmatic keratotomy, scleral flap recession and resection, toric intraocular lens implantation, and modifying postoperative medical treatment. The recent literature is reviewed, and our current approach for cataract surgery is discussed.

Astigmatism↗