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Clinical & Experimental Optometry Jan 2007Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various... (Review)
Review
Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.
Topics: Age Factors; Animals; Astigmatism; Cornea; Corneal Topography; Disease Progression; Humans; Prevalence; Refraction, Ocular; Risk Factors
PubMed: 17177660
DOI: 10.1111/j.1444-0938.2007.00112.x -
Clinical & Experimental Ophthalmology Jul 2022Uncorrected refractive astigmatism degrades visual acuity. Spherical intraocular lenses (IOLs) leave astigmatic errors resident in the cornea manifest in refractive... (Review)
Review
Uncorrected refractive astigmatism degrades visual acuity. Spherical intraocular lenses (IOLs) leave astigmatic errors resident in the cornea manifest in refractive astigmatism. Toric IOLs, correcting for this corneal astigmatism, contribute to spectacle-free vision in the pseudophakic eye. This review provides information to assist surgeons in a rational choice of eyes suitable for toric IOL implantation, methods of IOL cylinder power calculation, surgical techniques for toric IOLs and management of complications. With appropriate application of this information, correction of visually detrimental astigmatism can be achieved routinely.
Topics: Astigmatism; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Phacoemulsification; Refraction, Ocular
PubMed: 35584257
DOI: 10.1111/ceo.14106 -
Asia-Pacific Journal of Ophthalmology... 2019Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high... (Review)
Review
Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high efficacy and safety profile and also carries potential advantages over laser in situ keratomileusis such as a better corneal biomechanical stability, reduction in dry eyes rate, and the avoidance of flap complications. However, there have been concerns regarding the precision of astigmatism correction that undercorrection has been reported to be apparent. Various factors that affect astigmatism correction have been identified in the literature. The purpose of this review is to discuss the factors that affect astigmatism correction in SMILE and several techniques to improve the refractive outcomes.
Topics: Astigmatism; Corneal Stroma; Corneal Topography; Humans; Keratomileusis, Laser In Situ; Lasers, Excimer; Visual Acuity
PubMed: 31490198
DOI: 10.1097/01.APO.0000580140.74826.f5 -
BioMed Research International 2015Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision... (Review)
Review
Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision impairment. It affects all ethnic groups and both genders. Both environmental and genetic factors may contribute to its pathogenesis. This review is to summarize the current research development in KC epidemiology and genetic etiology. Environmental factors include but are not limited to eye rubbing, atopy, sun exposure, and geography. Genetic discoveries have been reviewed with evidence from family-based linkage analysis and fine mapping in linkage region, genome-wide association studies, and candidate genes analyses. A number of genes have been discovered at a relatively rapid pace. The detailed molecular mechanism underlying KC pathogenesis will significantly advance our understanding of KC and promote the development of potential therapies.
Topics: Astigmatism; Environmental Exposure; Genetic Linkage; Genome-Wide Association Study; Humans; Keratoconus; Myopia
PubMed: 26075261
DOI: 10.1155/2015/795738 -
Andes Pediatrica : Revista Chilena de... Dec 2021Worldwide, there is an epidemic increase in myopia. In children, the evidence points to a lack of ex posure to natural light. In Chile, the population situation of...
INTRODUCTION
Worldwide, there is an epidemic increase in myopia. In children, the evidence points to a lack of ex posure to natural light. In Chile, the population situation of myopia in children is unknown. Objec tive: To estimate the tendency of myopia and myopic astigmatism in 1st- and 6th-grade students from the public education system in Chile.
SUBJECTS AND METHOD
Ecological study based on diagnostic confirmations of the JUNAEB Medical Services Program, between 2012 and 2018. Annual country prevalence of myopia and astigmatism was estimated by region and sex. The screening evaluation included visual acuity using Snellen Eye Abbreviated chart, red reflex, Hirschberg test, Titmus test, Cover test, ocular motility, and anterior segment examination. Chi2 and logistic regression were used to assess differences and linear regression to estimate average annual change.
RESULTS
Between 2012 and 2018, myopia and myopic astigmatism had a heterogeneous geographical presentation. Myopia and myopic astigmatism ≥ 3 dioptres increased by an annual average of 0.11% (R2 0.67) and 1.21% (R2 0.90), respectively, in 1st-grade children and by 0.2% (R2 0.65) and 8.7% (R2 0.79), respectively, in 6th-grade children. Myopia < 3 dioptres decreased by 0.13% annual average (R2 0.45) in 1st-grade children and myopic astigmatism < 3 dioptres by 0.5% (R2 0.53) in 6th-grade children. High myopic astigmatism affected men more than women and myopia < 3 dioptres affected more 6th-grade females.
DISCUSSION
In schoolchildren of the public education system, myopia and myopic astigmatism > 3 dioptres tend to increase. The protective effect of natural light against myopia has been demonstrated in longitudinal and experimental studies. This evidence is to be considered in promoting children's time spent outdoors.
Topics: Astigmatism; Child; Chile; Female; Humans; Male; Myopia; Refraction, Ocular; Schools; Sunlight; Visual Acuity
PubMed: 35506801
DOI: 10.32641/andespediatr.v92i6.3527 -
Indian Journal of Ophthalmology Dec 2017Toric intraocular lenses (IOLs) are the procedure of choice to correct corneal astigmatism of 1 D or more in cases undergoing cataract surgery. Comprehensive literature... (Review)
Review
Toric intraocular lenses (IOLs) are the procedure of choice to correct corneal astigmatism of 1 D or more in cases undergoing cataract surgery. Comprehensive literature search was performed in MEDLINE using "toric intraocular lenses," "astigmatism," and "cataract surgery" as keywords. The outcomes after toric IOL implantation are influenced by numerous factors, right from the preoperative case selection and investigations to accurate intraoperative alignment and postoperative care. Enhanced accuracy of keratometry estimation may be achieved by taking multiple measurements and employing at least two separate devices based on different principles. The importance of posterior corneal curvature is increasingly being recognized in various studies, and newer investigative modalities that account for both the anterior and posterior corneal power are becoming the standard of care. An ideal IOL power calculation formula should take into account the surgically induced astigmatism, the posterior corneal curvature as well as the effective lens position. Conventional manual marking has given way to image-guided systems and intraoperative aberrometry, which provide a mark-less IOL alignment and also aid in planning the incisions, capsulorhexis size, and optimal IOL centration. Postoperative toric IOL misalignment is the major factor responsible for suboptimal visual outcomes after toric IOL implantation. Realignment of the toric IOL is needed in 0.65%-3.3% cases, with more than 10° of rotation from the target axis. Newer toric IOLs have enhanced rotational stability and provide precise visual outcomes with minimal higher order aberrations.
Topics: Astigmatism; Cataract Extraction; Humans; Lenses, Intraocular; Postoperative Complications; Refraction, Ocular; Treatment Outcome
PubMed: 29208810
DOI: 10.4103/ijo.IJO_810_17 -
Eye (London, England) Feb 2014The aim of this study was to present methods to improve the analysis of refractive data. A comparison of methods is used to analyse refractive powers using individual... (Review)
Review
The aim of this study was to present methods to improve the analysis of refractive data. A comparison of methods is used to analyse refractive powers using individual powers and aggregate data. Equations are also developed for the representation of the average power of a lens or refractive data as a univariate measure, which includes spherical, coma, and/or other aberrations. The equations provide a precise representation of refractive power, which is useful for comparing individual and aggregate data. Average lens power in the principal meridian can be adequately computed as can the average lens power through orthogonal and oblique meridians, providing a good univariate representation of astigmatism and refractive power. Although these formulae are perhaps not as easy to use as, for example, the spherical equivalent, they are more precise and superior in principle involving fewer approximations and are not subject to systematic bias. These effects are of significance when dealing with high-powered lenses such as intraocular lenses or the cornea. They need to be taken into account particularly for calculations of intraocular lens power, toric intraocular lenses, and cornea refractive surgery, especially if outcomes are to be improved. Such issues are of particular importance when dealing with aggregate data and determining statistical significance of treatment effects.
Topics: Astigmatism; Biometry; Cornea; Corneal Wavefront Aberration; Data Interpretation, Statistical; Humans; Lens, Crystalline; Refractive Errors
PubMed: 24336294
DOI: 10.1038/eye.2013.266 -
Eye (London, England) Sep 2021To characterise the posterior and total corneal astigmatism using colour point-source light-emitting diodes (LED) topography.
PURPOSE
To characterise the posterior and total corneal astigmatism using colour point-source light-emitting diodes (LED) topography.
METHODS
In a prospective case series 400 eyes from 400 patients were evaluated by colour-LED topography. Only eyes with normal topographies were considered. The following parameters were studied: magnitude and distribution of SimK and posterior corneal astigmatism, correlation between SimK and posterior corneal astigmatism, and differences in magnitude and axis between total and anterior corneal astigmatism.
RESULTS
The mean SimK corneal astigmatism was 1.21 ± 0.94 D. The mean posterior corneal astigmatism was 0.37 ± 0.24 D. Posterior astigmatism was vertically oriented in 68% of eyes. Twenty-two percent of eyes showed a posterior corneal astigmatism ≥ 0.50 D. The correlation coefficients between SimK and posterior corneal astigmatism were: r = 0.066; p = 0.371 in WTR eyes, r = 0.112; p = 0.173 in ATR eyes and r = -0.019; p = 0.879 in oblique eyes. A difference between SimK and total corneal astigmatism ≥ 0.50 D was found in 7% of eyes. A difference in axis between SimK and total corneal astigmatism ≥ 10° was found in 24% of eyes.
CONCLUSIONS
The percentage of eyes with posterior corneal astigmatism ≥ 0.50 D and the differences between anterior and total corneal astigmatism were higher than those previously reported in the literature. Therefore, this study supports the consideration of total corneal astigmatism magnitude and axis is mandatory for a precise surgical correction of astigmatism.
Topics: Astigmatism; Color; Cornea; Corneal Diseases; Corneal Topography; Humans
PubMed: 33203976
DOI: 10.1038/s41433-020-01278-z -
Optometry and Vision Science : Official... Mar 2023This is the first literature review to report the epidemiology, patient burden, and economic burden of astigmatism in the general adult population. The unmet needs of...
SIGNIFICANCE
This is the first literature review to report the epidemiology, patient burden, and economic burden of astigmatism in the general adult population. The unmet needs of astigmatism patients with coexisting ocular conditions (cataract, glaucoma, dry eye, presbyopia, or macular degeneration) and risks associated with untreated astigmatism are also reviewed and reported.
PURPOSE
This study aimed to identify, report, and summarize the published literature on epidemiology, patient burden, and economic burden of astigmatism using a systematic literature review.
METHODS
MEDLINE, EMBASE, and Cochrane Library databases were searched (January 1996 to May 2021). Search results were limited to the English language. Proceedings (2018 to 2021) from ophthalmology congresses were searched along with gray literature using the Google Scholar platform.
RESULTS
The literature search yielded 6804 citations, of which 125 met the inclusion criteria (epidemiology, 68; patient burden, 60; economic burden, 6). Astigmatism prevalence in the general population varied from 8 to 62%, with higher rates in individuals 70 years or older. The prevalence of with-the-rule astigmatism was higher in individuals 40 years or younger, whereas rates of against-the-rule and oblique astigmatism increased with age. Astigmatic patients experienced decreased vision quality, increased glare (53 to 77%), haloes (28 to 80%), night-time driving difficulties (66%), falls, and spectacle dependence (45 to 85%). Astigmatic patients performed vision-related tasks slower (1 D, 9% slower; 2 D, 29% slower) and made more errors (1 D, 38% more errors; 2 D, 370% more errors) compared with fully corrected individuals. In cataract patients with astigmatism, the annual mean per-patient productivity loss costs ranged from €55 ($71) to €84 ($108), and mean informal care costs ranged from €30 ($39) to €55 ($71) with a mean of 2.3 to 4.1 hours spent on informal care.
CONCLUSIONS
Uncorrected astigmatism decreases patients' vision-related quality of life, decreases productivity among working-age adults, and poses an economic burden on patients and their families.
Topics: Adult; Humans; Astigmatism; Visual Acuity; Quality of Life; Vision, Ocular; Cataract
PubMed: 36749017
DOI: 10.1097/OPX.0000000000001998 -
Korean Journal of Ophthalmology : KJO Dec 2004We investigated pseudophakic residual astigmatism in order to minimize postoperative refractive astigmatism. We examined 110 eyes of 87 patients who had undergone... (Comparative Study)
Comparative Study
We investigated pseudophakic residual astigmatism in order to minimize postoperative refractive astigmatism. We examined 110 eyes of 87 patients who had undergone phacoemulsification with small incision and posterior chamber intraocular lens (IOL) implantation. Corneal astigmatism was measured using an autokeratometer (RK-5, canon), refractive astigmatism by manifest refraction, and residual astigmatism by vector analysis. Mean pseudophakic residual astigmatism was +0.47 x 176 degrees, predominantly against-the-rule. Variations of pseudophakic residual astigmatism according to sex, age and IOL type were not statistically significant. When performing cataract surgery as refractive surgery, we may consider that pseudophakic residual astigmatism is approximately 0.50D against-the-rule.
Topics: Adult; Aged; Aged, 80 and over; Astigmatism; Female; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Male; Middle Aged; Phacoemulsification; Postoperative Complications; Postoperative Period; Pseudophakia; Refraction, Ocular; Retrospective Studies
PubMed: 15635824
DOI: 10.3341/kjo.2004.18.2.116