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[Zhonghua Yan Ke Za Zhi] Chinese... Jan 2016Since sixty percent of ametropes obtain astigmatism, which has influence on the visual quality, correcting the astigmatism is always the focus of concerns during visual... (Review)
Review
Since sixty percent of ametropes obtain astigmatism, which has influence on the visual quality, correcting the astigmatism is always the focus of concerns during visual correction procedures especially for the corneal refractive surgery. The postoperative spherical equivalent or residual cylindrical dioptors was used as quantitative index to evaluate the correction of astigmatism previously; however, such results neglect the effect of astigmatic axis shift on the treatment. Taking astigmatism as a vector parameter could describe the magnitude and direction of astigmatism accurately, thus it was increasingly applied in the evaluation of astigmatism correction. This paper reviews the present vector analysis methods, evaluation indexes and its application for the correction of astigmatism in the corneal refractive surgery.
Topics: Astigmatism; Humans; Refractive Surgical Procedures
PubMed: 26899223
DOI: 10.3760/cma.j.issn.0412-4081.2016.01.017 -
Current Opinion in Ophthalmology Feb 2002Correcting astigmatism at the time of cataract surgery can be accomplished either by incisional techniques, such as use of a cataract incision for flattening or... (Review)
Review
Correcting astigmatism at the time of cataract surgery can be accomplished either by incisional techniques, such as use of a cataract incision for flattening or astigmatic keratotomy, or by implanting a toric intraocular lens. Both methods can reduce mild to moderate astigmatism. For correcting larger amounts of astigmatism, a combination of techniques can produce greater correction. New methods of analyzing the change induced by surgery provide a more complete understanding of the astigmatic change.
Topics: Astigmatism; Cataract; Cataract Extraction; Cornea; Humans; Lens Implantation, Intraocular; Lenses, Intraocular
PubMed: 11807381
DOI: 10.1097/00055735-200202000-00002 -
Vision Research Dec 2019We investigated the effect of induced astigmatism on subjective best focus and on visual acuity in 28 subjects of different ages (pre-presbyopic and presbyopic) and with...
We investigated the effect of induced astigmatism on subjective best focus and on visual acuity in 28 subjects of different ages (pre-presbyopic and presbyopic) and with different refractive profiles (emmetropes and astigmats). Measurements were performed using a custom-developed Adaptive Optics system, which allowed correction of high order aberrations and induction of astigmatism (0.5, 1, 1.5 and 2.0 D; axis: 180°, 45° and 22.5°). Upon induction of astigmatism, best focus shifted towards negative values in pre-presbyopic emmetropic eyes (by -0.14 D for 0.5 D and by -0.33 D for 2.0 D), while it shifted towards positive values in presbyopes, both in emmetropic presbyopes (by +0.04 D for 0.50 D and by +0.16 D for 2.0 D) and in astigmatic presbyopes (by +0.23 D for 0.50 D and by +0.40 D for 2.0 D). Also, visual acuity was most sensitive to astigmatism induction in pre-presbyopic emmetropes and least sensitive in presbyopes, particularly when high order aberrations were corrected: visual acuity ratio with/without astigmatism was: 0.74/0.85/0.98 (for astigmatism induced at 180°) and 0.68/0.73/0.86 at 45°, for pre-presbyopic emmetropes/presbyopic emmetropes/presbyopic astigmats. These findings may be connected to long term exposure to astigmatism in astigmats and corrected presbyopes.
Topics: Adult; Astigmatism; Female; Humans; Male; Middle Aged; Presbyopia; Refraction, Ocular; Vision Tests; Visual Acuity; Visual Perception; Young Adult
PubMed: 31751899
DOI: 10.1016/j.visres.2019.10.008 -
Journal of the American Optometric... Dec 1988Previous studies indicate that a number of individuals display significant differences between astigmatism measured at farpoint and nearpoint. Adventitious effects,... (Review)
Review
Previous studies indicate that a number of individuals display significant differences between astigmatism measured at farpoint and nearpoint. Adventitious effects, purposeful lenticular changes and adaptations in response to environmental forces are reviewed as possible sources of this astigmatic variability.
Topics: Accommodation, Ocular; Astigmatism; Cornea; Environment; Eyeglasses; Humans; Lens, Crystalline; Volition
PubMed: 3062058
DOI: No ID Found -
Journal of Cataract and Refractive... Jun 2022To assess the effect on visual function of different residual astigmatic situations combined with 0.50 diopters (D) negative defocus at different distances in patients...
PURPOSE
To assess the effect on visual function of different residual astigmatic situations combined with 0.50 diopters (D) negative defocus at different distances in patients with trifocal intraocular lenses (IOLs).
SETTING
Clínica Rementería, Madrid, Spain.
DESIGN
Prospective case series.
METHODS
The study included patients implanted with AcrySof IQ PanOptix IOL. Visual acuity (VA) was measured at far distance (0.00 D of vergence) and at -1.5 D, -2.5 D, and -3.0 D of vergence. Residual astigmatism was induced by adding 0.50 D and 1.00 D cylindrical lenses placed at 90 degrees (against the rule [ATR]), 45 degrees (oblique), and 180 degrees (with the rule). All measurements were made with distance correction (emmetropia as the reference situation) and with a simulated residual myopia of 0.50 D.
RESULTS
The study included 61 eyes of 61 patients. Residual astigmatism of 0.50 D and 1.0 D was induced in 28 and 33 eyes, respectively. For both groups, distance and intermediate VAs were better for the reference situation (P < .001 for all cases). With 1.0 D of cylinder (without and with induced defocus), the proportion of patients who lost ≥2 lines was higher for the ATR astigmatism. For near vision, differences were smaller for all simulated situations.
CONCLUSIONS
Residual astigmatism of up to 0.50 D, regardless of its orientation, seems to be tolerated at all distances. For astigmatisms of 1.0 D, distance and intermediate VAs decreased significantly, and ATR orientations showed worse results in a higher proportion of patients. The combination of astigmatism with residual myopia significantly decreased distance VA, whereas this negative shift affected near VA less.
Topics: Astigmatism; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Myopia; Phacoemulsification; Prospective Studies; Prosthesis Design; Refraction, Ocular
PubMed: 34508029
DOI: 10.1097/j.jcrs.0000000000000814 -
Current Opinion in Ophthalmology Feb 2003An increasingly important goal of modern cataract and implant surgery is to obtain the most desirable refractive outcome for our patients, and in so doing, decrease... (Review)
Review
An increasingly important goal of modern cataract and implant surgery is to obtain the most desirable refractive outcome for our patients, and in so doing, decrease their dependence upon spectacle correction. Refined spherical outcomes are now achieved by directing close attention to biometry technique, through the use of third generation intraocular lens (IOL) power formulae, and refinements in technology such as partial coherence interferometry. Similarly, improvements in astigmatic outcomes are now possible by focusing upon and obtaining more accurate preoperative cylinder measurements, careful surgical planning particularly in regard to incision(s) design, use of toric IOLs, and employing advanced postoperative enhancement techniques. Because of these refinements in technique and technology, the field of cataract and implant surgery has emerged as a true and recognized form of refractive surgery.
Topics: Astigmatism; Cataract; Cataract Extraction; Humans; Lens Implantation, Intraocular; Lenses, Intraocular
PubMed: 12544808
DOI: 10.1097/00055735-200302000-00006 -
Eye (London, England) May 2022To determine difference in surgically induced astigmatism (SIA), post-operative intraocular pressure (IOP) and axial length (AL) between single site and twin-site... (Randomized Controlled Trial)
Randomized Controlled Trial
PURPOSE
To determine difference in surgically induced astigmatism (SIA), post-operative intraocular pressure (IOP) and axial length (AL) between single site and twin-site phacotrabeculectomy augmented with Mitomycin C (MMC).
DESIGN
Prospective interventional randomised controlled study.
METHODS
In a prospective interventional comparative study, eligible patients were scheduled for phacotrabeculectomy. They were randomised to either group A: single site or group B: twin-site phacotrabeculectomy with MMC 0.2 mg/mL. Axial length was measured by using Zeiss IOL master I, pre-operatively and at 1, 3, 6 and 12 months post-operatively. Corneal topography was performed using Bausch and Lomb Orbscan I pre-operatively and at 3, 6 and 12 months post-operatively to analyse surgically induced astigmatism. Vector analysis was used to analyse the surgically induced astigmatism.
RESULTS
One hundred and eight eyes of which 55 patients in group A, and 53 patients in group B were enroled for vector analysis. The mean preoperative astigmatic vector power was +0.89 ± 0.4 D and +0.97 ± 0.5 D in group A and B respectively. The mean post-operative astigmatic vector power was +0.78 ± 0.4 D in group A and +0.96 ± 0.5 D in group B at the end of 12 months. Corneal topography showed post-operative superior flattening (51.8% at 3 months and 55.4% at 12 months) in group A (P = 0.072) compared to superior steepening (59.6% at 3 months and 61.5% at 12 months) in group B (P = 0.977).
CONCLUSIONS
The two commonly used techniques of combined cataract and glaucoma surgery proved to be efficacious without significant difference in surgical induced astigmatism.
Topics: Astigmatism; Corneal Topography; Humans; Mitomycin; Phacoemulsification; Prospective Studies
PubMed: 34117400
DOI: 10.1038/s41433-021-01601-2 -
Investigative Ophthalmology & Visual... Aug 2015We estimated the contribution of the gradient refractive index (GRIN) and lens surfaces to lens astigmatism and lens astigmatic angle as a function of age in human donor...
PURPOSE
We estimated the contribution of the gradient refractive index (GRIN) and lens surfaces to lens astigmatism and lens astigmatic angle as a function of age in human donor lenses.
METHODS
Human lenses were imaged, ex vivo, with 3D-spectral optical coherence tomography (OCT) and their back focal length was measured using laser ray tracing. The contribution of lens surfaces and GRIN to lens astigmatism were evaluated by computational ray tracing on the GRIN lens and a homogenous equivalent index lens. Astigmatism magnitude and relative astigmatic angle of and between lens surfaces, GRIN lens, and lens with homogeneous refractive index were evaluated, and all results were correlated with age.
RESULTS
The magnitude of astigmatism in the anterior lens surface decreased with age (slope = -0.005 diopters [D]/y; r = 0.397, P = 0.018). Posterior surface astigmatism and lens astigmatism were not age-dependent. Presence of GRIN did not alter significantly the magnitude or axis of the lens astigmatism. The astigmatism of GRIN lens and lens with homogeneous refractive index correlated with anterior lens surface astigmatism (GRIN, P = 3.9E - 6, r = 0.693; equivalent refractive index lens, P = 4.1E - 4, r = 0.565). The astigmatic angle of posterior surface, GRIN lens, and homogeneous refractive index lens did not change significantly with age.
CONCLUSIONS
The axis of lens astigmatism is close to the astigmatic axis of the anterior lens surface. Age-related changes in lens astigmatism appear to be related to changes in the anterior lens astigmatism. The influence of the GRIN on lens astigmatism and the astigmatic axis is minor.
Topics: Adult; Aged; Aging; Astigmatism; Humans; Imaging, Three-Dimensional; Lens, Crystalline; Light; Middle Aged; Photic Stimulation; Refraction, Ocular; Refractometry; Tomography, Optical Coherence; Young Adult
PubMed: 26241395
DOI: 10.1167/iovs.15-16484 -
Graefe's Archive For Clinical and... Feb 2022To examine the long-term changes in the astigmatism-correcting effect of a toric intraocular lens (IOL) after stabilization of surgically induced astigmatic changes due...
PURPOSE
To examine the long-term changes in the astigmatism-correcting effect of a toric intraocular lens (IOL) after stabilization of surgically induced astigmatic changes due to cataract surgery.
METHODS
Unilateral eyes of 120 patients that received a toric IOL for against-the-rule (ATR) or with-the-rule (WTR) astigmatism were enrolled. Manifest refractive and anterior corneal astigmatism, and ocular residual astigmatism which is mainly derived from internal optics were examined preoperatively, at approximately 2 months postoperatively (baseline) and at 5 ~ 10 years postbaseline. The astigmatism was decomposed to vertical/horizontal (Rx) and oblique components (Ry), which was compared between baseline and 5 ~ 10 years postbaseline.
RESULTS
In the eyes having ATR astigmatism, the mean Rx and Ry of the manifest refractive and corneal astigmatism significantly changed toward ATR astigmatism between the baseline and 5 ~ 10 years postbaseline (p ≤ 0.0304), but those of ocular residual astigmatism did not change significantly between the 2 time points. In the eyes having WTR astigmatism, the Rx and Ry of refractive, corneal, and ocular residual astigmatism did not change significantly between the 2 time points. Double-angle plots revealed an ATR shift in refractive and corneal astigmatism and no marked change in the ocular residual astigmatism in the eyes with ATR astigmatism, and there is no change in this astigmatism in the eyes with WTR astigmatism.
CONCLUSION
The long-term changes with age in the effect of a toric IOL significantly deteriorated due to an ATR shift of corneal astigmatism in the eyes having ATR astigmatism, while it was maintained in eyes having WTR astigmatism, suggesting that ATR astigmatism should be overcorrected.
Topics: Astigmatism; Cornea; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Phacoemulsification; Refraction, Ocular
PubMed: 34495370
DOI: 10.1007/s00417-021-05406-7 -
Journal of Cataract and Refractive... Jan 2001To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors: target...
PURPOSE
To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors: target induced astigmatism vector (TIA), surgically induced astigmatism vector, and difference vector, as described by the Alpins method.
METHODS
A data set of 100 eyes that had laser in situ keratomileusis to correct myopia and astigmatism (minimum preoperative refractive astigmatism 0.75 diopter) was analyzed. The data included preoperative and 3 month postoperative values for manifest refraction and standard keratometry. Using the ASSORT or VectrAK analysis program, individual and aggregate data analyses were performed using simple, polar, and vector analysis of astigmatism and an analysis of spherical change. Statistical analysis of the results was used for means and confidence limits, as well as to examine the differences between corneal and refractive astigmatism outcomes.
RESULTS
At an individual patient level, the angle of error was found to be significant, suggesting variable factors at work, such as healing or alignment. A systematic error of undercorrection of astigmatism is prevalent in the treatment of these 100 patients by a factor of between 15% and 30%, depending on whether refractive or corneal values are examined. Spherical correction showed systematic undercorrection of 11%, and parallel indices demonstrated it to be more effective than the astigmatic correction.
CONCLUSION
This method of astigmatism analysis enables the examination of results of astigmatism treatment measured by both refractive and corneal measurements using vector analysis. By examining individual vector relationships to the TIA (ie, the correction index, index of success, and flattening index), a comprehensive astigmatism analysis is completed. Each index provides information necessary for understanding any astigmatic change. Astigmatic outcome parameters are more favorable when measured by subjective refractive than objective corneal methods.
Topics: Astigmatism; Cornea; Diagnostic Techniques, Ophthalmological; Humans; Keratomileusis, Laser In Situ; Mathematics; Myopia; Refraction, Ocular
PubMed: 11165856
DOI: 10.1016/s0886-3350(00)00798-7