From the Guidelines
Astigmatism is a refractive error that can be effectively managed with corrective eyewear or refractive surgery, and regular eye examinations are crucial for monitoring changes and adjusting prescriptions. According to the refractive errors preferred practice pattern 1, astigmatism occurs when incident light rays do not converge at a single focal point, and it can be divided into corneal, lenticular, and retinal astigmatism. The most common type is corneal astigmatism, which can be further classified into regular and irregular astigmatism. Regular corneal astigmatism is characterized by a uniform curvature in each meridian, while irregular corneal astigmatism has varying magnitude and axis of astigmatism in different points of the cornea.
Some key points to consider in managing astigmatism include:
- The definition of low to moderate refractive errors, which includes less than 3.00 D of regular astigmatism 1
- The importance of distinguishing between regular and irregular astigmatism, as irregular astigmatism can be clinically significant in conditions such as keratoconus and other corneal ectasias 1
- The role of higher order aberrations (HOAs) in affecting visual quality, which cannot be fully corrected by spherocylindrical corrective lenses 1
- The various treatment options available, including corrective eyewear, toric contact lenses, and refractive surgeries like LASIK, PRK, or SMILE
In terms of treatment, corrective eyewear and refractive surgery are effective options for managing astigmatism, and the choice of treatment depends on the severity of the condition and the patient's individual needs. Regular eye examinations are essential for monitoring changes and adjusting prescriptions, and most people with astigmatism can achieve clear vision with appropriate correction 1.
From the Research
Definition and Prevalence of Astigmatism
- Astigmatism is the most frequent refractive error worldwide, followed by hyperopia and myopia 2
- Corneal astigmatism is common, with more than 40% of patients undergoing cataract surgery having 1 diopter (D) power or more of astigmatism, which left untreated is visually significant 3
Types of Astigmatism
- Internal astigmatism has to be differentiated from external astigmatism 2
- External astigmatism can be divided into "with the rule", "against the rule" and "oblique" 2
- The summation of internal and external astigmatism results in the refractive cylinder 2
Treatment Options for Astigmatism
- Multiple options exist for treatment of astigmatism, including conservative approaches such as eyeglasses or toric contact lenses 2
- Surgical procedures, such as photorefractive keratectomy, femtosecond laser-assisted keratotomy, laser in-situ keratomileusis, small incision lenticule extraction and toric intraocular lens implantation, are also available 2
- Toric intraocular lenses (IOLs) are available and can improve uncorrected visual acuity in patients undergoing cataract surgery 3
Challenges in Treating Astigmatism
- Patients with prior refractive surgery presenting for cataract surgery pose unique challenges, including recognition of the specific type of prior surgery and use of appropriate intraocular lens (IOL) power calculation formulas 4
- Accuracy and predictability of refractive outcomes remain inferior to eyes that undergo cataract surgery without a history of corneal refractive surgery 4