What are the treatment options for with the rule and against the rule astigmatism?

Treatment Options for With-the-Rule and Against-the-Rule Astigmatism

Full cylindrical correction with eyeglasses, toric contact lenses, or refractive surgery effectively treats both with-the-rule and against-the-rule astigmatism, though adults with previously uncorrected astigmatism may require gradual correction to improve tolerance. 1, 2

Understanding Astigmatism Orientation

• With-the-rule (WTR) astigmatism has the steepest corneal meridian oriented vertically (approximately 90 degrees), commonly seen in children and younger adults 1, 2
• Against-the-rule (ATR) astigmatism has the steepest meridian oriented horizontally (approximately 180 degrees), more prevalent in older adults and tends to remain stable over time 1, 2

Eyeglass Correction

Eyeglasses should be considered as first-line treatment before contact lenses or refractive surgery for both WTR and ATR astigmatism. 1

• Full cylindrical correction may not be needed initially, particularly for adults with regular astigmatism 1, 2
• Adults with previously uncorrected or partially corrected astigmatism poorly tolerate substantial changes in axis or power 1, 2
• High-index lenses reduce thickness and weight for higher refractive errors, improving comfort and cosmetic appearance 1
• Optimal correction for higher refractive errors requires precision in fitting, especially regarding optical center position relative to the pupil 1

Contact Lens Options

Low to Moderate Astigmatism (Less Than 3.00 D)

• Soft toric contact lenses or rigid gas-permeable (RGP) contact lenses effectively correct low to moderate astigmatism 2
• Custom-designed soft toric lenses provide good centration, flexible wear schedules, and improved comfort 2

High Astigmatism (3.00 D or More)

• Rigid gas-permeable and hybrid contact lenses are highly effective for high astigmatism 2
• Bitoric or back-surface toric designs minimize corneal bearing and improve centration for greater amounts of corneal astigmatism 2
• RGP scleral lenses (diameter >17mm) are excellent options for high and/or irregular astigmatism, particularly with anisometropia 2

Orthokeratology Considerations

• Toric orthokeratology reduces WTR astigmatism by approximately 50% on average but cannot completely eliminate pre-existing astigmatism 3
• Best suited for patients with 1.00 D to 1.50 D or less of pre-fitting astigmatism, as higher amounts show less predictable outcomes 3
• Patients may prefer toric orthokeratology subjectively despite reduced visual acuity compared to soft toric multifocal lenses 4

Surgical Correction

Refractive Surgery Planning

• Axis alignment and cyclotorsion compensation are critical for astigmatism correction, as misalignment significantly reduces treatment effectiveness 1
• Reference marks should be placed on the operative eye while the patient is seated upright before laser procedures to compensate for ocular cyclotorsion when supine 1
• Larger optical zones (6.5-6.8 mm) result in less undercorrection and fewer higher-order aberrations, particularly in high myopia, but require sufficient corneal thickness 1

Keratorefractive Lenticule Extraction (KLEx)

• Corrects astigmatism ranging from 0.25 D to 5.00 D, though higher target astigmatism shows weaker correction effects 1
• Cyclotorsion compensation significantly improves outcomes with lower residual astigmatism 1
• Low astigmatism (<2.0 D) achieves better corrective effects than high astigmatism (>2.0 D) 1

Cataract Surgery with Astigmatism Correction

The choice of astigmatism correction method during cataract surgery depends on the magnitude of astigmatism:

• Low astigmatism (1.00 D): Clear corneal incision (CCI) on the steepest meridian is effective and requires no extra skills or tools 5
• Medium astigmatism (1.00-2.00 D): Opposed clear corneal incisions (OCCI) provide greater astigmatic reduction 5
• High astigmatism (2.00-3.00 D): Toric intraocular lens implantation is superior with proper preoperative planning 5

Posterior Corneal Astigmatism Considerations

• WTR eyes: Apply a coefficient of adjustment of 0.75 to anterior corneal astigmatism values to avoid overcorrection when calculating toric IOL power (for IOL cylinders ≤2.00 D) 6
• ATR eyes: Apply a coefficient of adjustment of 1.41 to avoid undercorrection when calculating toric IOL power (for IOL cylinders ≤2.00 D) 6
• These adjustments account for the effect of posterior corneal curvature not captured by anterior measurements alone 6

Common Pitfalls

• Attempting full cylindrical correction immediately in adults with previously uncorrected astigmatism leads to poor tolerance; gradual correction is better accepted 1, 2
• Irregular astigmatism (seen in keratoconus, corneal scarring, post-surgical corneas) cannot be fully corrected with spherocylindrical lenses and requires specialty contact lenses or surgical intervention 2
• Failing to compensate for cyclotorsion during refractive surgery results in axis misalignment and reduced astigmatic correction 1
• Calculating toric IOL power based solely on anterior corneal measurements without adjusting for posterior corneal astigmatism leads to systematic overcorrection in WTR eyes and undercorrection in ATR eyes 6