Astigmatism Review: Regular vs Irregular; Correction; Magnitude & Population Data

A set of practice flashcards covering regular vs irregular astigmatism, symmetry, vector planning, orientation (with-the-rule, against-the-rule, oblique), correction options, pediatric vs elderly prevalence, magnitudes considered significant, and population-based study findings from the notes.

How is regular astigmatism distinguished from irregular astigmatism in terms of symmetry and corneal topography?

Regular astigmatism is symmetric around the visual axis and typically shows a bow-tie pattern on corneal topography; irregular astigmatism lacks symmetry or does not follow a geometric pattern.

What topographic pattern is classically associated with regular astigmatism?

A bow-tie pattern on corneal topography.

In regular astigmatism, how are the powers of the two meridians arranged as the meridians traverse 180 degrees?

The powers of the two meridians are successive as the meridians traverse 180 degrees.

What planning approach allows separate treatment considerations for each corneal meridional division in bow-tie irregular astigmatism?

A vector planning approach, enabling separate planning for each corneal meridional division (MA division).

How are astigmatism orientations defined as with the rule (WTR), against the rule (ATR), and oblique?

With the rule: greatest power in the vertical meridian (flat along the horizontal axis); Against the rule: greatest power in the horizontal meridian; Oblique: major meridians at intermediate axes (roughly 30–60° and 120–150°).

What are the common methods listed for correcting astigmatism?

Eyeglasses, contact lenses, or refractive surgery.

Regarding Chapter 2, why are glasses often insufficient for irregular astigmatism, and what is commonly prescribed instead?

Glasses do not adequately correct irregular astigmatism; rigid contact lenses are often prescribed.

What age-related prevalence pattern is described for with-the-rule versus against-the-rule astigmatism?

With-the-rule astigmatism is more common in children; against-the-rule astigmatism is more common in the elderly; overall, with-the-rule is more common than against-the-rule, while oblique is least favorable.

What is javal’s rule, and when was it published?

Preference for with-the-rule astigmatism in distant vision; published in 1890.

What is considered a significant magnitude of astigmatism, and what prevalence is noted among cataract patients?

Typically 1 diopter or greater is significant; about 20% of eyes with cataract have at least 1.5 diopters of corneal astigmatism.

Which population-based study is highlighted in Chapter 3, and what were its key findings for adults 20 or older?

The 2008 NHANES study (12,010 participants); 36.2% had astigmatism of ≥1 diopter, with 95% CI 34.9%–37.5%.

What measurement method is commonly used in population-based studies of refractive error, as mentioned in the notes?

Manifest refraction.

What vision distortions can astigmatism cause besides blur, according to the notes?

Streaks of light in dark conditions and tilting of the image.

What percentage of eyes with cataract are reported to have at least 1.5 diopters of corneal astigmatism in the notes?

As many as 20%.