Astigmatism

Astigmatism text blur[1]

Astigmatism is a common, mild and generally easily treatable optical defect.

Presentation

The first symptom of astigmatism is a complaint of blurred vision. People generally complain of double vision that affects only a single eye. Few of them suffering from astigmatism develop eyestrain, squinting and even migraine headaches [5] as a result of straining to focus on objects.

In children who are born with astigmatism, it remains undiagnosed till the time they start attending school or they learn to read. Some people complain of difficulty in seeing one colour in contrast with another or can have distorted images like they see that the lines lean on one side. Severe astigmatism can also lead to double vision.

Eyes
  • Blurred Vision Both the types of astigmatism cause blurred vision[source] The first symptom of astigmatism is a complaint of blurred vision[source] Main objective of the treatment is to correct the uneven surface curvature of the lens/cornea that's leading to the blurred vision and improve the vision. [source]
  • Vision Disorder From treating vision disorders in all age groups to diagnosing ocular diseases or performing sophisticated eye surgery, MPOMG has a team of trusted specialists who make sure that you and your family receive the best eye care on the Peninsula. [source] From treating vision disorders in all age groups to diagnosing ocular diseases or performing sophisticated eye surgery, MPOMG has a team of trusted specialists who make sure that you and your family receive the best eye care on the Peninsula. [source]
  • more...

Workup

The ophthalmologists and optometrists use various tests to diagnose astigmatism and to determine the amount and axis of deviation in the optic curvature.

Vision test: A Snellen’s or Jaeger’s chart or other eye charts are used to determine the visual acuity. One is asked to read from these charts to determine the visual acuity.

Test to determine the curvature of your cornea: A keratometer is used to identify which are the flattest/steepest curvatures of the anterior corneal surface. A keratometer measures the light reflected off from the surface of the cornea. This test is called keratometry. Another test called Corneal topography may also be performed to obtain more accurate measurements of the variations in corneal surface curvature.

Test to measure light focus: In order to know how the eyes focus light, the physician places various lenses in front of the eyes by using a device called a phoropter. Using Jackson cross cylinders in a phoropter helps in measuring the refractive error of the eyes [6] [7] [8].

The physician can also use a retinoscope that will help to know how the eye focuses light. Here, a ray of light is focused on the retina and recordings are obtained regarding how the retina focused on the light beam.

Treatment

Astigmatism can be corrected with the help of eyeglasses, contact lenses, or refractive surgery. Main objective of the treatment is to correct the uneven surface curvature of the lens/cornea that's leading to the blurred vision and improve the vision.

  • Eyeglasses. Eyeglasses can be fitted with special lenses to help compensate for the uneven contours of the eye. Along with correcting astigmatism, eyeglasses also correct other refractive errors, like myopia (nearsightedness) or hyperopia (farsightedness).
  • Contact lenses. Contact lenses can also correct astigmatism like the eyeglasses. Depending on the type that is best suited to an individual, one can use hard, soft, rigid, disposable ones etc. to correct the error. But wearing contact lenses for long time at a stretch increases the risk of infection. Contact lenses can be used for orthokeratology wherein a rigid contact lens may be worn for many hours a day till the eye curvature improves. Later on it may be worn for shorter durations of time to maintain the shape. It the lens is completely discontinued, the eye will return to the original shape.
  • Refractive surgeries. This treatment method corrects the problem by modifying the surface of the eye. These surgical methods are as follows:

    • LASIK surgery. Laser Assisted In Situ Keratomileusis or LASIK is a surgical procedure where the ophthalmologist makes a measured thin, circular cut into the cornea by using an instrument called a keratome. The surgeon picks up this flap and using an excimer laser resculpts the cornea beneath the flap. An excimer laser is distinct as it does not produce heat. It is seen that LASIK is not much effective in correcting astigmatism in the internal optics [9] where as it is highly effective in correcting the astigmatism on the anterior corneal surface [10].
    • Photorefractive keratectomy (PRK). In PRK, the surgeon first removes the outer, self-replacing, epithelial layer of the cornea before using an excimer laser to reshape the faulty curvature of the cornea.
    • LASEK surgery. In laser-assisted subepithelial keratomileusis (LASEK) a far thinner layer of cornea is cut and folded, because of which the eyes are at lesser risk of any damage. LASEK is a better option if there is a thin cornea or if there is a higher risk of eye injury at work or while playing sports.

Prognosis

Astigmatism is generally a stable condition. It can be corrected using eyeglasses, contact lenses or refractive surgery. Occasionally, astigmatism can be the result of other medical conditions, especially those causing inflammation of the eyelids.

Astigmatism can worsen over a period of time and can lead to a condition known as keratoconus. Keratoconus affects the cornea such that it becomes progressively thinner in one area and starts bulging out. These conditions need more precise treatment and more supervision by a doctor than simple astigmatism.

Complications

  • Cataract Learn more Start planning your cataract procedure Planning for your cataract surgery can help you feel confident about this new vision decision. [source] See the difference correcting cataracts and astigmatism can make What you might see after you correct your cataracts What you might see after you correct both eye conditions The simulated images above are for illustration purposes only. [source] Like all technologies, there are specific brands designed to help you see clearer after cataract surgery. [source]
  • more...

Etiology

Astigmatism is commonly present at birth but it can occur due to an injury, scar or any kind of operation to the eye, that results into the damage of corneal surface. It can also occur as a result of anything pressing continuously on the surface of the cornea.

Astigmatism may run in families and is commonly seen in premature or low birth weight babies, this might be seen because sometimes the cornea does not get adequate time to develop appropriately.

Often problems with the corneal structure can result in astigmatism, some of which are present from birth. Probability of people suffering from Down’s syndrome is 1 in 5 in people who have astigmatism.

Epidemiology

Astigmatism is a common refractive error that accounts for around 13% of all the refractive errors [1]. The incidence changes with age, with increased incidence in first months of life as the curvature of cornea is very steep [2].

Prevalence of astigmatism varies according to the races too. It is more commonly seen in East Asian people followed by Chinese and Singaporean. It has been speculated that hereditary and nutritional factors affect the incidence of astigmatism. Other ethnic groups at high risk for astigmatism are those of Hispanic origin and the natives of Brazil [3] [4].

Sex distribution
Age distribution

Pathophysiology

The cornea and the lens are the two parts of our eyes that play an important role in focusing the images. In a perfectly normal eye, both these focusing elements have a perfect smooth curvature that can be compared to the surface of a smooth ball.

The cornea or the lens with such a smooth surface curvature can bend (refract) all the light rays that enter it equally to create a sharp, focused image at the back of the eye i.e. on the retina. But in case the cornea or lens is not evenly and smoothly curved, then the light rays will be focused unevenly. This leads to a refractive error and astigmatism is the result.

Astigmatism occurs when the cornea or lens is curved more in one direction and remains normal or less curved in the other directions. Depending on the affected part you will have either corneal astigmatism, if the cornea is affected or lenticular astigmatism, if the lens is affected. Both the types of astigmatism cause blurred vision. Blurring of vision can be more in one direction that can be either diagonally, horizontally or vertically. Astigmatism can be present along with other refractive errors.

Prevention

Astigmatism cannot be prevented. It runs in families and many a times present from birth. Chances of astigmatism can be reduced by taking optimal measures of eye safety while playing sports.

Summary

Astigmatism is defect in the vision such that it is blurred due to the incapability of the eye to focus at a point into a focused image on the retina. This can be because of an irregular curvature or toric curvature of either the cornea or the lens or both.

Patient Information

Astigmatism is a refractive error affecting the eyes. It is generally present from the time of birth or can be acquired later in life. Often injury to the lens or cornea or repeated infections of the eyes can lead to this condition. Astigmatism can affect both children and adults.

Those suffering from slight astigmatism won’t see much change in their vision. Thus, each child must have regular eye checkups to detect any eye abnormality at its earliest and intervene aggressively. Since it cannot be prevented, prompt treatment of the condition once diagnosed helps in preventing it from worsening.

Blurring of vision is the commonest symptom of astigmatism. There are various treatment options that are available to correct this condition. Selecting the best treatment depends on the condition of your eyes, the refractive status and your lifestyle requirements.

Self-assessment

References

  1. Porter J, Guirao A, Cox IG, et al. Monochromatic aberrations of the human eye in a large population. J Opt Soc Am A Opt Image Sci Vis. 2001 Aug;18(8):1793-1803.
  2. Howland HC, Sayles N. Photokeratometric and photorefractive measurements of astigmatism in infants and young children. Vision Res. 1985;25:73-81.
  3. Harvey EM, Dobson V, Miller JM. Prevalence of high astigmatism, eyeglass wear, and poor visual acuity among Native American grade school children. Optom Vis Sci. 2006 Apr;83(4):206-212.
  4. Kleinstein RN, Jones LA, Hullett S, et al. Refractive error and ethnicity in children. Arch Ophthalmol. 2003 Aug;121(8):1141-1147.
  5. Harle DE, Evans BJW. The Correlation Between Migraine Headache and Refractive Errors. Opt Vis Sci. 2006 Feb;83 (2): 82–7.
  6. Graff T. Control of the determination of astigmatism with the Jackson cross cylinder. [ Article in german]. Klin Monblr Augenheilkd Augenarztl Fortbild. 1962 Jun; 140: 702–8. 
  7. Del Priore LV, Guyton DL. The Jackson cross cylinder. A reappraisal. Ophthalmology. 1986 Nov; 93 (11): 1461–5.
  8. Brookman KE. The Jackson crossed cylinder: Historical perspective. J Am Optom Assoc. 1993 May; 64 (5): 329–31.
  9. Qian YS, Huang J, Liu R, Chu RY et al. Influence of internal optical astigmatism on the correction of myopic astigmatism by LASIK. J Refract Surg. 2011 Dec; 37 (12): 863–8.
  10. Kugler L, Cohen L, Haddad W, Wang MX. Efficacy of laser in situ keratomileusis in correcting anterior and non-anterior corneal astigmatism: comparative study. J Cataract Refract Surg. 2010 Oct; 36 (10): 1745–52.



Media References

  1. Astigmatism text blur, BSD

Languages