Astigmatism is the condition where the refractive power of the cornea (it’s anterior or front surface primarily but also it’s back surface) and even one’s own natural lens or intraocular implant do not allow incoming light to hit the macula (the key part of the retina we see the world) uniformly across all meridians.
Source: Uday Devgan, MD
If you have astigmatism, light entering the eye may be focused more strongly along the vertical meridian than along the horizontal meridian. This difference in refractive power causes images to be smudgy, smeared, and blurry along the longer optical axis, resulting in less than perfect 20/20 vision.
The cause of astigmatism is not fully understood, but genetics and mechanical interactions between the cornea, eyelids, and extraocular muscles may affect its development.
If left uncorrected, even small amount of astigmatism caused significant blurry vision, double vision, glare, haloes, ghosting, and/or asthenopia (ie eye discomfort of strained, tired, uncomfortable eyes).
A dry tear film or significant meibomian gland atrophy can also cause astigmatism measurements and symptoms to be more pronounced.
Of note, when the principal meridians of astigmatism (the highest and lowest refractive powers) are perpendicular or orthogonal to each other and refractive power is uniform across each meridian, the astigmatism is considered regular. Typically, regular astigmatism can be corrected with glasses or contact lenses. When the principal meridians are not orthogonal or the refractive power varies along a given meridian, the astigmatism is considered irregular, which is harder to treat.
Nearly 50% of individuals worldwide have more than 0.50 D of astigmatism.
No matter how perfect your cataract surgery is, even with the use of Femtosecond lasers and Toric intraocular implants, the astigmatism can return with aging. This is a frustration to patients and surgeons alike. The below paper is a good review. Most patients tolerate the return of astigmatism well, but some patients will still need glasses even after state of the art cataract surgery, to correct astigmatism.
Good review on astigmatism.
Impact of small incision sutureless cataract surgery on the natural course of astigmatism in 10 to 20 years
- Abstract
Purpose:
To retrospectively assess astigmatic changes over 10- and 20-years after small incision cataract surgery.
Setting:
Five ophthalmic surgical sites in Japan.
Design:
Retrospective case series.
Methods:
Data were collected from patients who had undergone phacoemulsification and implantation of an intraocular lens (IOL) through a 2.2- to 2.4-mm incision. Preoperative corneal and postoperative manifest astigmatism were converted to power vector notations: horizontal/vertical (J0) and oblique (J45) astigmatism components.
Results:
In 422 eyes of 422 patients who were followed up for 10 years, data before and at 1 month, and 1, 3, 5, 8, and 10 years after surgery were analysed. The mean J0 decreased significantly (p<0.001, repeated measures analysis of variance) with an against-the-rule (ATR) shift of 0.363 ± 0.433 D over 10 years, but the mean J45 did not change significantly (p=0.150). Double-angle plot analyses also showed similar ATR shifts in all astigmatism groups. In the subgroup analysis conducted in 34 patients who were followed up for 20 years, J0 declined significantly (p<0.001) by 0.649 ± 0.576 D over 20-year follow-up, while J45 did not (p=0.516). The postoperative changes in J0 and J45 were not significantly different between eyes with preoperative with-the-rule, ATR, or oblique astigmatism.
Conclusions:
Postoperative astigmatism continued to shift towards ATR during the follow-up period of 20 years after small incision cataract surgery, which appears to reflect the natural course of corneal astigmatic changes that commonly occur with aging. ATR astigmatic shifts were similar in both pattern and magnitude regardless of the type of preoperative astigmatism.
https://www.healio.com/news/ophthalmology/20170919/astigmatic-effect-from-phaco-incision-placement
https://crstodayeurope.com/articles/2017-oct/what-is-astigmatism-anyway/
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