Astigmatism is a reflective error of the eye and many people in the world have it, without even knowing it!
But do you know exactly what it is?
- Astigmatism is a type of refractive error in which the eye does not focus light evenly on the retina
- This results in distorted or blurred vision at all distances
- Other symptoms can include eyestrain, headaches, and trouble driving at night
- If it occurs early in life it can result in amblyopia
- The cause of astigmatism is unclear
- It is believed to be partly related to genetic factors
- The underlying mechanism involves an irregular curvature of the cornea or abnormalities in the lens of the eye
- Diagnosis is by an eye exam
- Three options exist for the treatment: glasses, contact lenses, and surgery
- Glasses are the simplest
- Contact lenses can provide a wider field of vision
- Refractive surgery permanently changes the shape of the eye
- In Europe and Asia astigmatism affects between 30 and 60% of adults
- People of all ages can be affected
- Astigmatism was first reported by Thomas Young in 1801
- Although astigmatism may be asymptomatic
- Higher degrees of astigmatism may cause symptoms such as blurry vision, double vision, squinting, eye strain, fatigue, or headaches
- Some research has pointed to the link between astigmatism and higher prevalence of migraine headaches
- There are several kinds of astigmatism
- Regular astigmatism- principal meridians are perpendicular
- The steepest and flattest meridians of the eye are called principal meridians
- With-the-rule astigmatism- the vertical meridian is steepest
- A rugby ball or American football lying on its side
- Against-the-rule astigmatism- the horizontal meridian is steepest
- A rugby ball or American football standing on its end
- Oblique astigmatism- the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees
- Irregular astigmatism- principal meridians are not perpendicular
- Astigmatism, whether it is regular or irregular, is caused by some combination of external and internal optical properties
- In some people, the external optics may have the greater influence
- And in other people, the internal optics may predominate
- Importantly, the axes and magnitudes of external and internal astigmatism do not necessarily coincide
- But it is the combination of the two that by definition determines the overall optics of the eye
- The overall optics of the eye are typically expressed by a person’s refraction
- A number of tests are used during eye examinations to determine the presence of astigmatism and to quantify its amount and axis
- A Snellen chart or other eye charts may initially reveal reduced visual acuity
- A keratometer may be used to measure the curvature of the steepest and flattest meridians in the cornea’s front surface
- Corneal topography may also be used to obtain a more accurate representation of the cornea’s shape
- An autorefractor or retinoscopy may provide an objective estimate of the eye’s refractive error
- And the use of Jackson cross cylinders in a phoropter or trial frame may be used to subjectively refine those measurements
- An alternative technique with the phoropter requires the use of a “clock dial” or “sunburst” chart to determine the astigmatic axis and power
- A keratometer may also be used to estimate astigmatism by finding the difference in power between the two primary meridians of the cornea
- Javal’s rule can then be used to compute the estimate of astigmatism
- A method of astigmatism analysis by Alpins may be used to determine both how much surgical change of the cornea is needed
- And after surgery to determine how close treatment was to the goal
- Another rarely used refraction technique involves the use of a stenopaeic slit
- Where the refraction is determined in specific meridians
- This technique is particularly useful in cases where the patient has a high degree of astigmatism
- Or in refracting patients with irregular astigmatism
- There are three primary types of astigmatism: myopic astigmatism, hyperopic astigmatism, and mixed astigmatism
- Astigmatism may be corrected with eyeglasses, contact lenses, or refractive surgery
- Various considerations involving eye health, refractive status, and lifestyle determine whether one option may be better than another
- In those with keratoconus, certain contact lenses often enable patients to achieve better visual acuity than eyeglasses
- Once only available in a rigid, gas-permeable form, toric lenses are now available also as soft lenses
- Laser eye surgery is successful in treating astigmatism
- According to an American study nearly three in 10 children (28.4%) between the ages of five and 17 have astigmatism
- A recent Brazilian study found that 34% of the students in one city were astigmatic
- Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatism
- A Polish study published in 2005 revealed “with-the-rule astigmatism” may lead to the onset of myopia
- A number of studies have found the prevalence of astigmatism increases with age
- As a student, Thomas Young discovered that he had problems with one eye in 1793
- In the following years he did research on his vision problems
- He presented his findings in a Bakerian Lecture in 1801
- Independent from Young, George Biddell Airy discovered the phenomenon of astigmatism on his own eye
- Airy presented his observations on his own eye in February 1825 at the Cambridge Philosophical Society
- Airy produced lenses to correct his vision problems by 1825
- While other sources put this into 1827
- When Airy obtained cylindrical lenses from an optician from Ipswich
- The name for the condition was not given by Airy
- But from William Whewell
- By the 1860s astigmatism was a well established concept in ophthalmology, and chapters in books described the discovery of astigmatism
