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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 -
Eye & Contact Lens Sep 2018Within the last 200 years, the perception of astigmatism has evolved from that of an infrequent and peculiar defect of the eye to a distortion almost as common as... (Review)
Review
Within the last 200 years, the perception of astigmatism has evolved from that of an infrequent and peculiar defect of the eye to a distortion almost as common as spherical refractive errors. Most of the significant findings on this condition were made in the 19th century, including the first description by Thomas Young (1773-1829) and the introduction of the treatment methods used today. The purpose of this study was to investigate the milestones in the understanding and management of astigmatism that occurred up to the year 1900. This fascinating history illustrates how knowledge evolves across time, geographical areas, and interdisciplinary boundaries. The first article looking at the use of a cylindrical lens to correct astigmatism was written by George Airy (1801-1892) in 1825. The term "astigmatism" was introduced in by William Whewell (1794-1866) in 1846. Methods for subjective and objective evaluation were subsequently established, including the introduction of a cross cylinder, keratoscope, astigmatic dial, and the development of retinoscopy and ophthalmoscopy. In the last two decades of the 19th century, the first attempt to alter the refraction in astigmatic patients by changing the shape of the cornea was made. It must be noted that diverse challenges were encountered in this field on the way to the development of a treatment, including the technical manufacture of a lens, the precise measurement of the refractive error, and understanding the optical properties of the eye. The importance of the 19th century was that interdisciplinary cooperation, such as that seen in this study, between physicists and astronomers, and mathematicians and physicians, led to the development of comprehensive knowledge on astigmatism.
Topics: Astigmatism; History, 19th Century; Humans; Ophthalmology
PubMed: 29140824
DOI: 10.1097/ICL.0000000000000449 -
Survey of Ophthalmology 1987With the numerous significant advances in surgical methodology--e.g., microinstrumentation, the operating microscope, the surgical keratometer, and intraocular... (Review)
Review
With the numerous significant advances in surgical methodology--e.g., microinstrumentation, the operating microscope, the surgical keratometer, and intraocular lenses--that have been developed over the past two decades, both surgeons and patients have become increasingly aware of the final optic result of any surgical intervention. This is especially so since the development of refractive surgery, where good uncorrected vision is frequently the final arbiter of success. We have progressed to the stage where the optic manipulation of the cornea, whether intentional or otherwise, can be understood in terms of a number of variables. These include the preparation and closure of the surgical wound, the choice of suture material, and both intraoperative and postoperative manipulations. Where these have failed and postoperative astigmatism still occurs, a number of surgical procedures are available to reduce the astigmatic error to an acceptable level.
Topics: Astigmatism; Cataract Extraction; Cornea; Corneal Transplantation; Humans; Postoperative Complications; Retina
PubMed: 3554571
DOI: 10.1016/0039-6257(87)90023-3 -
Journal Francais D'ophtalmologie Mar 2012Excimer laser is the best and the more used technique for Astigmatism correction. Lasik is generally preferred to PRK and must be the choice for hyperopic and mix... (Review)
Review
Excimer laser is the best and the more used technique for Astigmatism correction. Lasik is generally preferred to PRK and must be the choice for hyperopic and mix astigmatisms. Myopic astigmatisms are the easier cases to treat: the length of the photoablation is placed on the flat meridian. Hyperopic and mix astigmatisms are more difficult to correct because they are more technically demanding and because the optical zone of the photoablation must be large. Flying spots lasers are the best for these cases. The most important point is to trace the photoablation very precisely on the astigmatism axis. The use of eye trackers with iris recognition or a preoperative marking of the reference axis avoid cyclotorsion or a wrong position of the head. Irregular astigmatism are better corrected with topoguided or wavefront guided photoablations.
Topics: Astigmatism; Corneal Topography; Humans; Keratomileusis, Laser In Situ; Lasers, Excimer; Photorefractive Keratectomy; Refractive Surgical Procedures; Treatment Outcome
PubMed: 22386997
DOI: 10.1016/j.jfo.2011.12.001 -
Journal Francais D'ophtalmologie Mar 2012Through the creation of astigmatic keratotomies, femtosecond laser can correct congenital or post-surgical astigmatism. We have been using an optimized treatment... (Review)
Review
Through the creation of astigmatic keratotomies, femtosecond laser can correct congenital or post-surgical astigmatism. We have been using an optimized treatment nomogram, which offers superior and more predictable results than manual incisional techniques. Femtosecond arcuate incisions allow a reduction of over 50% of the preoperative astigmatism. Nonetheless, the efficacy can likely be improved further by refining these nomograms specific to the femtosecond laser.
Topics: Astigmatism; Corneal Surgery, Laser; Corneal Topography; Humans; Lasers; Postoperative Complications; Refractive Surgical Procedures
PubMed: 22245056
DOI: 10.1016/j.jfo.2011.10.001 -
Contact Lens & Anterior Eye : the... Oct 2022Astigmatism is a highly prevalent refractive error and while studies typically focus to describe the axis symmetry between eyes, little is known about the refractive...
PURPOSE
Astigmatism is a highly prevalent refractive error and while studies typically focus to describe the axis symmetry between eyes, little is known about the refractive symmetry. Therefore, this study determined the astigmatic power symmetry between eyes in a large clinic population.
METHODS
A clinical chart review was conducted at three optometric practices in the United States, the United Kingdom and Canada and subjective refraction data from 88,891 patients 14-70 years of age who presented with at least -0.25DC refractive astigmatism in at least one eye were included in the analysis. Data were obtained at these practices between January 2014 and March 2017. The overall distribution (%) and magnitude (DC) of astigmatism was determined and refractive differences between eyes were identified.
RESULTS
The mean age of the patients was 42.1 ± 15.9 years and included 51,685 (58%) female and 37,206 (42%) male patients. In this data pool of 177,782 eyes, 10.9% required zero astigmatic correction, while 56.2% had astigmatism of -0.25 to -0.75DC. In total 23.9% of patients presented with astigmatism of at least -0.75DC in only one eye, while the other eye had 0 to -0.50DC. Overall, the difference in astigmatism between eyes was less than -0.75DC for 82.1% of astigmatic patients. For patients who presented with astigmatism of -1.00DC in the right eye, 80.8% of them had an astigmatic prescription of -1.00 ± 0.50DC in the left eye. For an astigmatic prescription of -4.00DC in the right eye, only 40.6% of patients exhibited astigmatism of -4.00DC ± 0.50DC in the left eye.
CONCLUSIONS
The majority of patients exhibited a difference in astigmatism between eyes of less than -0.75DC, however the refractive cylinder power symmetry was significantly lower in patients with higher refractive astigmatism.
Topics: Adult; Astigmatism; Female; Humans; Male; Middle Aged; Prescriptions; Refraction, Ocular; Refractive Errors; Vision Tests
PubMed: 34507898
DOI: 10.1016/j.clae.2021.101510 -
Current Opinion in Ophthalmology Jan 2009There are several options for correcting astigmatism at the time of cataract surgery. They include incision placement on the steep axis of corneal astigmatism, single or... (Review)
Review
PURPOSE OF REVIEW
There are several options for correcting astigmatism at the time of cataract surgery. They include incision placement on the steep axis of corneal astigmatism, single or paired peripheral corneal relaxing incisions, and toric intraocular lens implantation. The aim of this review is to update readers on advances reported during the last year.
RECENT FINDINGS
Phacoemulsification incision placement on the steep corneal axis corrects small amounts of astigmatism and is sufficient for most eyes. Peripheral corneal relaxing incisions correct greater amounts of astigmatism. They may be necessary when implanting multifocal intraocular lenses in eyes with more than 1 diopter of astigmatism. Toric intraocular lenses are also safe and effective for treating more than 1 diopter of astigmatism, and they now have excellent rotational stability.
SUMMARY
Good uncorrected postoperative distance visual acuity can be obtained for a high percentage of cataract patients with preexisting corneal astigmatism. Postoperative keratorefractive surgery is available to enhance the condition of patients who achieve less-than-optimal astigmatic results.
Topics: Astigmatism; Cataract; Cataract Extraction; Cornea; Humans; Lens Implantation, Intraocular; Phacoemulsification; Refractive Surgical Procedures; Reoperation
PubMed: 19077825
DOI: 10.1097/ICU.0b013e328319c27a -
Ophthalmic & Physiological Optics : the... May 2014To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations... (Review)
Review
PURPOSE
To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism.
RECENT FINDINGS
The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options.
CONCLUSION
Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.
Topics: Astigmatism; Contact Lenses; Eyeglasses; Humans; Ophthalmologic Surgical Procedures; Vision Disorders
PubMed: 24635572
DOI: 10.1111/opo.12128 -
Current Opinion in Ophthalmology Aug 1998Many factors have led to the improved success rate for clear corneal grafts after penetrating keratoplasty. Unfortunately, postoperative corneal astigmatism commonly... (Review)
Review
Many factors have led to the improved success rate for clear corneal grafts after penetrating keratoplasty. Unfortunately, postoperative corneal astigmatism commonly occurs and can produce significant visual impairment. Astigmatic correction may include spectacle correction or contact lenses, but if this fails, then surgical options are considered. Refractive surgical techniques such as suture removal or adjustment, relaxing incisions, wedge resections, and photorefractive keratectomy or laser in situ keratomileusis can dramatically reduce postoperative astigmatism after penetrating keratoplasty and lead to improved, functional vision. However, significant variability between results in individual patients can occur. So although general guidelines are useful, it is important to individualize and modify the planned surgery based on qualitative keratoscopy and corneal topography for the initial and subsequent astigmatic corrections.
Topics: Astigmatism; Contact Lenses; Cornea; Corneal Topography; Eyeglasses; Humans; Keratoplasty, Penetrating; Laser Therapy; Reoperation; Treatment Outcome
PubMed: 10387463
DOI: 10.1097/00055735-199808000-00004 -
Investigative Ophthalmology & Visual... Feb 2021To determine the effects of optically imposed astigmatism on myopia development in chickens.
PURPOSE
To determine the effects of optically imposed astigmatism on myopia development in chickens.
METHODS
Chicks were randomly assigned to wear either spherical (-10D, "LIM", n = 14) or sphero-cylindrical lenses (n ≥ 19 in each group) monocularly for a week from 5 days of age. All lenses imposed the same magnitude of spherical-equivalent hyperopic defocus (-10D), with the two astigmatic magnitudes (-8D or -4D) and four axes (45°, 90°, 135°, or 180°) altered to simulate four subtypes of clinical astigmatism. At the end of the treatment, refractive state was measured for all birds, whereas ocular axial dimensions and corneal curvature were measured for subsets of birds.
RESULTS
Sphero-cylindrical lens wear produced significant impacts on nearly all refractive parameters (P < 0.001), resulting in myopic-astigmatic errors in the treated eyes. Compared to LIM, the presence of astigmatic blur induced lower myopic error (all except L180 group, P < 0.001) but with higher refractive astigmatism (all P < 0.001) in birds treated with sphero-cylindrical lenses. Distributions of the refractive, axial, and corneal shape parameters in the sphero-cylindrical lens-wear groups indicated that the astigmatic blur had directed the eye growth toward the least hyperopic image plane, with against-the-rule (ATR) and with-the-rule (WTR) astigmatisms typically inducing differential biometric changes.
CONCLUSIONS
The presence of early astigmatism predictably altered myopia development in chicks. Furthermore, the differential effects of WTR and ATR astigmatisms on anterior and posterior segment changes suggest that the eye growth mechanism is sensitive to the optical properties of astigmatism.
Topics: Animals; Astigmatism; Chickens; Disease Models, Animal; Disease Progression; Follow-Up Studies; Myopia; Optics and Photonics; Refraction, Ocular; Time Factors
PubMed: 33605983
DOI: 10.1167/iovs.62.2.27