Management of Irregular Astigmatism

Introduction to Irregular Astigmatism

Irregular astigmatism is a refractive error where the magnitude and axis of astigmatism vary in different points of the cornea, causing light rays to not converge at a single focal point, resulting in distorted vision that cannot be fully corrected with standard spherocylindrical lenses 1
It can be quantified using methods like Zernike and Fourier reconstruction algorithms, producing higher order aberrations (HOAs) such as coma, spherical aberration, and trefoil 1
Irregular astigmatism is clinically significant in several conditions, including keratoconus and other corneal ectasias, corneal epithelial basement membrane and stromal dystrophies, corneal scarring, post-surgical corneas, trauma, and infections 1, 2

Wavefront analysis measures higher-order aberrations, with vertical coma being the dominant aberration in keratoconus 2
Anterior segment optical coherence tomography provides imaging of retrocorneal structures and can assess LASIK flap thickness in post-refractive ectasia 2
Corneal biomechanical assessment, including parameters like corneal hysteresis and corneal resistance factor, may help detect early or subclinical disease 2
Corneal topography/tomography is essential for assessing irregular astigmatism, determining management options, and identifying patterns, as recommended by the American Academy of Ophthalmology 3

Rigid gas-permeable (RGP) lenses are a first-line option for most cases, offering advantages such as masking corneal irregularities and providing superior visual outcomes, with 93% of patients achieving BCVA of 20/30 or better in the DUSKS study 2, 4, 1
Scleral lenses are effective for severe irregular astigmatism, offering advantages such as not contacting the cornea, especially with anisometropia, as suggested by the American Academy of Ophthalmology 1
Hybrid contact lenses combine a rigid center with a soft skirt, providing good centration and comfort, while piggyback systems are useful when other options fail or for improved comfort, particularly for high astigmatism or postoperative refractive error 1
Topography-guided ablation and wavefront-guided ablation are useful for treating specific patterns of irregular astigmatism, reducing pre-existing higher-order aberrations, according to the American Academy of Ophthalmology 4
Corneal cross-linking (CXL) is primarily used for preventing progression in ectatic disorders like keratoconus, most effective when applied early in the disease process, as recommended by the American Academy of Ophthalmology 2

SADs can cause significant side effects including reduced contrast sensitivity, decreased night vision, visual disturbances like glare and halos, and potential loss of best-corrected visual acuity 4
Glare and halos, especially at night, can be caused by SADs, with symptoms similar to those seen with other refractive procedures but may be more pronounced due to the aperture restriction 4
Potential for inducing new or worsening existing irregular astigmatism if device placement is suboptimal, which can result from decentration of the small aperture 4
Risk of permanent reduction in best-corrected visual acuity (BCVA) due to complications with device placement or tissue response 4

Careful patient counseling is essential regarding potential complications, such as darkened vision, floaters, and realistic expectations about visual improvement, with approximately 27.3% of patients reporting unsatisfactory visual outcomes in one study 4
Patients should be advised to halt eye rubbing, which has been associated with disease progression, as recommended by the American Academy of Ophthalmology 2
Contact lens wear requires careful monitoring for complications, such as hypoxia, neovascularization, and infection, with daily disposable lenses causing less damage to the ocular surface, as noted by the American Academy of Ophthalmology 1
Patients should be informed about the potential for night vision problems with any correction method, and for patients considering refractive surgery, careful evaluation with corneal topography/tomography is essential, as recommended by the American Academy of Ophthalmology 4

The American Academy of Ophthalmology recommends thorough evaluation with corneal topography/tomography before any keratorefractive surgery, with a strength of evidence level of high 4
For mild to moderate irregular astigmatism, the American Academy of Ophthalmology suggests starting with RGP contact lenses, and if intolerant, trying hybrid lenses or piggyback systems, with a strength of evidence level of moderate 3
For severe irregular astigmatism, the American Academy of Ophthalmology recommends beginning with scleral lenses, and if unsuccessful, considering surgical options based on etiology, with a strength of evidence level of high 3