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Results for “ASTIGMATISM”

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At least 37 records · Page 2Linked to original sources

PubMed1999

Effect of astigmatic keratotomy on spherical equivalent: results of the Astigmatism Reduction Clinical Trial.

PURPOSE: To determine the effect of astigmatic keratotomy on spherical equivalent, as measured by the coupling ratio and a new quantity, coupling constant. METHODS: In a prospective multicenter study, subjects underwent arcuate keratotomy at a 7-mm optical zone by means of the Lindstrom nomogram for correction of astigmatism. One hundred fifty-seven eyes of 95 patients who had a follow-up examination 1 month postoperatively were studied. Mean preoperative refractive cylinder +/- SEM was 2.82 +/- 1.17 diopters. Coupling ratio was defined as the ratio of the flattening of the incised meridian to the steepening of the opposite meridian. Coupling constant was defined as the ratio of the change in spherical equivalent to the magnitude of the vector change in astigmatism. Coupling ratio, coupling constant, and change in spherical equivalent were calculated on the basis of change in refraction and keratometry. RESULTS: On the basis of change in refraction, coupling ratio was 0.95 +/- 0.10 (mean +/- SEM) and coupling constant was -0.01 +/- 0.03, consistent with a minor shift in the spherical equivalent of -0.03 +/- 0.07 diopter. On the basis of change in keratometry, coupling ratio was 0.84 +/- 0.05 and coupling constant was -0.04 +/- 0.02, consistent with minor postoperative keratometric steepening of -0.10 +/- 0.04 diopter. Coupling ratio based on change in refraction was not statistically different from the coupling ratio predicted by the Gauss' law for inelastic domes (P = .370). Incision length and number, amount of achieved cylinder correction, age, and sex had no statistically significant effect on coupling ratio, coupling constant, and change in spherical equivalent. CONCLUSIONS: Cornea behaved as an inelastic surface in response to arcuate keratotomy performed with the Astigmatism Reduction Clinical Trial study nomogram. On average, astigmatic keratotomy had a minimal effect on spherical equivalent refraction. There was variability, however, in coupling ratio, coupling constant, and change in spherical equivalent from eye to eye after astigmatic keratotomy. Caution is therefore advised when simultaneous correction of cylinder and spherical equivalent is planned.

Adolescent↗

PubMed1998

Relationship between preoperative axis of astigmatism and postoperative astigmatic change after superior scleral incision phacoemulsification.

PURPOSE: To evaluate the effect of the preoperative axis of astigmatism on the outcome of corneal astigmatism after sutured 5.2 to 5.7 mm superior incision phacoemulsification. SETTING: Departments of Opthalmology, Odense and Vejle Hospitals, Denmark. METHODS: Seventy-three consecutive patients with preoperative corneal astigmatism of 2.0 diopters (D) or less, axial length between 20.0 and 25.5 mm, and no eye disease except cataract were grouped according to preoperative with-the-rule (WTR) or against-the-rule (ATR) astigmatism. The keratometric cylinder, induced keratometric cylinder (subtraction), and induced cylinder (Jaffe) were measured and calculated 10 to 12 months postoperatively. RESULTS: The postoperative keratometric cylinder and induced keratometric cylinder were significantly higher in the ATR group (P < .00001; mean difference [95% confidence limits]: 0.76 D [0.54; 0.98] and 0.69 D [0.46; 0.92], respectively). There was no significant difference between groups in induced cylinder (Jaffe). CONCLUSION: The estimated differences were significantly in favor of patients with preoperative WTR astigmatism. The findings support using temporal incision in cases with a preoperative ATR axis of astigmatism.

Aged↗

PubMed2002

An assessment of the orthogonal astigmatism test for the subjective measurement of astigmatism.

The orthogonal astigmatism test (OAT) is a newly developed method for assessing ocular astigmatism. This study compares the OAT with the Jackson crossed-cylinder (JCC), Raubitschek arrow (RA) and the fan and block (FB) (fan chart). Fifty emmetropes or corrected spherical ametropes (<0.25 DC of astigmatism) were recruited, with a visual acuity of at least 6/5 in both eyes. Pseudo-astigmatism was induced by placing a +0.75 DC lens in front of the right eye at a random axis. With the left eye occluded, each subjective test was performed in a random order and the correcting lens power and axis noted. No significant difference was found in the ability of the OAT to locate the power and axis of the induced astigmatism over the JCC, RA and FB. In conclusion, the OAT offers the clinician an alternative method for locating and correcting ocular astigmatism. It has a similar but not superior accuracy to the other three subjective tests assessed.

Adult↗

PubMedDate not supplied

Arcuate transverse keratotomy for astigmatism followed by subsequent radial or transverse keratotomy. ARC-T Study Group. Astigmatism Reduction Clinical Trial.

BACKGROUND: We studied the safety and efficacy of arcuate transverse keratotomy performed for the primary correction of naturally occurring corneal astigmatism. METHODS: A multicenter, prospective evaluation of one-stage arcuate transverse keratotomy was conducted in 160 eyes with 1.00 to 6.00 diopters (D) of naturally occurring astigmatism. Vector analysis was used. After 1 month, those eyes that needed further refractive surgery received radial keratotomy for myopia and second-stage arcuate transverse keratotomy for residual astigmatism. RESULTS: Mean preoperative refractive cylinder was 2.80 D. At 1 month, the vector-corrected change was 2.30 D. Eighty-eight (61%) eyes had at least 1.00 D of residual refractive cylinder and 24 (17%) had at least 2.00 D. Eyes undergoing a second surgery averaged 1.60 D of vector-corrected effect, for a total effect of 2.90 D from both surgeries, indicating the astigmatic refractive effects were not additive. Eyes that had radial keratotomy alone as the second surgery demonstrated a similar change in refractive cylinder as eyes that had both radial and transverse keratotomies. Two eyes lost two lines of spectacle-corrected visual acuity, 29 eyes lost one line, 84 showed no change, and 26 eyes improved one line. CONCLUSION: Arcuate transverse keratotomy reduced refractive astigmatism. Both overcorrection and undercorrection were common. Complications were infrequent but occasionally caused significant irregular astigmatism. Arcuate transverse keratotomy appears to be a safe procedure with few complications.

Adolescent↗

PubMedDate not supplied

[Correction of high astigmatism and astigmatic anisometropia by intrastromal photokerato-ablation in children and adolescents].

A total of 151 photorefraction operations for correction of medium and high astigmatism in 38 children (9-15 years) and 47 adolescents (16-17 years) carried out by LASIK method are analyzed. The operations were performed under local anesthesia with EC-5000 eximer laser (Nidek) and Hansatome microkeratome (B & L). Complicated and common myopic astigmatism (2.07 +/- 0.89 to 2.91 +/- 0.63 diopters) was decreased by 61.2% in children and by 62.2% in adolescents. Visual acuity without correction increased by 0.58 +/- 01.2. Correction of astigmatic anisometropia resulted in its decrease to 0.75-1.5 diopters in 77.9% children and 62.8% adolescents. Hypermetropic astigmatism decreased by 64.9% of its initial value in children and by 56.9% in adolescents. Mixed astigmatism decreased by 62.7% of its initial value. The resultant visual acuity without correction was 0.39 +/- 0.13 in children and 0.47 +/- 0.17 in adolescents. According to questionnaires distributed among parents, 13.5% patients studied better at school after the operation and 19.2% went in for sports in athletic sections. The main causes for the intervention were limitations in choice of profession (for 49.6%) and desire to practice modern athletics (in 13.8%). Photorefraction correction of astigmatism in children and adolescents brings about an effective stable result decreasing refraction amblyopia and improving the quality of life.

Adolescent↗

PubMed1995

Fourier analysis of video-keratographic data. A tool for separation of spherical, regular astigmatic and irregular astigmatic corneal power components.

Topographic analysis of the cornea and computation of changes in corneal topography is difficult because of the lack of a standardized concept for analysing topographic information. We have used Fourier series harmonic analysis to decompose the often very complex information given in topographic images (TMS-1 video-keratograph). The polar data values arising from each mire were separated into spherical (average power), regular astigmatic (2' harmonic) and non-regular astigmatic components. The non-regular astigmatic components were further divided into a decentration component (1' harmonic) and a higher order irregular refractive component (root mean square (r.m.s.) of the residual between original data and the sum of spherical, 1' and 2' order components). Algorithms for utilizing the Fourier analysis technique on subjective refractive and on keratometric changes in regular astigmatism were also derived. Averages of the separate refractive components were calculated for groups of normal (right and left eye of 25 patients), keratoconic (13 eyes), and transplanted eyes (20 eyes), and average topographic maps were reconstructed and imaged. Changes in the separate topographic refractive components were compared with subjective refractive changes in eyes that had undergone combined myopic-astigmatic excimer laser ablation (8 eyes). Fourier series analysis was found superior to conventional keratometry in predicting spherical and regular astigmatic changes in subjective refraction. Fourier series analysis seems to be a powerful tool to decompose the information of complex topographic corneal images into rational optical components.

Algorithms↗

PubMed1998

Combined astigmatic keratotomy with corneal valvular incision in the treatment of high surgical astigmatism.

BACKGROUND: Astigmatic keratotomy is used conventionally to correct moderate surgical astigmatism. However, cases with very high surgical astigmatism due to wound compression can show a dramatic response to relaxing keratotomies made in the steeper meridian. The effect obtained cannot be predicted pre-operatively by using standard nomograms. METHODS: Coupled arcuate keratotomies combined with corneal valvular incisions were performed in a case of high astigmatism post-cataract surgery. RESULTS/CONCLUSION: Coupled arcuate keratotomies were combined with a corneal valvular incision enabled a surgical correction of nearly 9 D of astigmatism.

Astigmatism↗

PubMedDate not supplied

Astigmatic keratotomy followed by photorefractive keratectomy in the treatment of compound myopic astigmatism.

Eleven eyes of 9 patients that had compound myopic astigmatism were treated by astigmatic keratotomy followed 1 month later by photorefractive keratectomy (PRK). In 9 eyes arcuate incisions were performed, in 1 eye a modified Ruiz procedure was performed, and in 1 eye radial T cuts were done. The mean spherical equivalent was -8.26 +/- 2.51 diopters (D) after the astigmatic keratotomy but before photorefractive keratectomy, and -0.36 +/- 0.93 D after photorefractive keratectomy. The mean cylinder was -3.11 +/- 1.16 D preoperatively, and -0.14 +/- 0.9 D postoperatively. Combined astigmatic keratotomy and photorefractive keratectomy are effective treatments for compound myopic astigmatism.

Adult↗

PubMed1989

Astigmatism control for the cataract surgeon: a comprehensive review of surgically tailored astigmatism reduction (STAR).

It is increasingly possible for the cataract surgeon to control astigmatism. Based on a review of 4,000 consecutive patients, three categories of astigmatism and cataract patients are identified. A specific approach to astigmatism control for each category is discussed. Preliminary results on the use of astigmatic keratotomy in conjunction with cataract surgery are presented.

Aged↗

PubMed1981

A longitudinal study of corneal astigmatism and total astigmatism.

Cross-sectional studies indicate that mean total astigmatism changes with age; varying from as much as 0.62 D with-the-rule during youth to as much as 0.37 D against-the-rule in samples of elderly patients. The present study involves the examination of adult patients who were seen regularly for a period of at least 40 years. Data are analyzed to determine whether the change in corneal astigmatism accounts for the total astigmatic change, and the magnitude of change with age at each of the principal corneal meridians. Results indicate that steepening of the cornea in the horizontal meridian accounts for a major portion of the increase in against-the-rule total astigmatism among older patients.

Adolescent↗

PubMed1989

Irregular astigmatism after radial and astigmatic keratotomy.

Eleven eyes of six patients, who had been referred for management of irregular astigmatism after receiving crossed incisions for myopic astigmatism, had moderate to marked irregular corneal astigmatism with marked flattening in the meridians of intersecting incisions. All six patients had a decrease in best-corrected visual acuity with spectacles after surgery. Visual acuity with spectacles was 20/40 in five of 11 eyes; with contact lenses it reached 20/40 in ten of 11 eyes. However, two patients could not wear the contact lenses because of lens decentration caused by the marked distortion in corneal topography. Even with contact lenses, visual acuity could only be improved to 20/25 or better in six of 11 eyes.

Astigmatism↗

PubMed2002

Comparison of photorefractive keratectomy, astigmatic PRK, laser in situ keratomileusis, and astigmatic LASIK in the treatment of myopia.

PURPOSE: To determine factors affecting refractive and visual outcomes in patients treated with astigmatic and spherical photorefractive keratectomy (A-PRK and PRK) and laser in situ keratomileusis (A-LASIK and LASIK). SETTING: University referral refractive surgery clinic. METHODS: Refractive and visual acuity results in 619 eyes of 388 consecutive patients having refractive surgery over a 2-year period by a single surgeon were retrospectively analyzed. Patients were divided into mild-to-moderate myopia (spherical equivalent [SE] less than -6.12 diopters [D]) and high myopia (SE -6.12 D or higher). Multivariate and logistic regression analyses were performed. RESULTS: Refractive results in flap-based and PRK-based procedures were comparable in mild-to-moderate myopia patients but were significantly better in high-myopia patients having flap-based procedures. Refractive stability was greater in flap-based procedures than in PRK-based procedures. Elliptical ablations yielded a marked reduction in the astigmatic cylinder in patients having A-LASIK and A-PRK, while spherical PRK induced small amounts of with-the-rule astigmatism. Complications were uncommon in both groups, consisting primarily of epithelial ingrowth in flap-based procedures and haze in PRK-based procedures. Multivariate regression identified the preoperative SE as a significant determinant of PRK outcomes (with higher success for lower myopia) and intraocular pressure as a minor determinant of outcomes in PRK-based and flap-based procedures. Logistic regression suggested that only the preoperative SE was a significant factor in predicting the likelihood of poor outcomes in PRK patients. CONCLUSIONS: Refractive outcomes were almost identical in patients having elliptical or spherical ablations with flap-based or PRK-based procedures. In eyes with mild-to-moderate myopia, there was little difference in refractive or visual outcomes between flap-based and PRK-based procedures; in eyes with high myopia, flap-based procedures offered more predictable refractive outcomes and better visual outcomes.

Adult↗

PubMed1981

A system matrix for astigmatic optical systems: II. Corrected systems including an astigmatic eye.

The 4 x 4 system matrix is applied to corrected astigmatic systems including a schematic eye in which each surface is astigmatic at a different axis. In addition to representing the eye, the 4 x 4 system generates 2 x 2 magnification matrices which describe the meridional magnifications that occur in the presence of astigmatism including the magnifications that occur with bitoric eikonic correcting lenses, or other meridional magnifying systems.

Astigmatism↗

PubMed1956