Prevalence and characteristics of oblique astigmatism

Abstract

Objective: To examine the incidence and characteristics of eyes with oblique astigmatism stratified by meridian, age, sex, and eye side (left to right).

Methods: One thousand eyes of 1000 patients with oblique corneal astigmatism underwent videokeratographic examination and was classified into 4 meridian categories: (1) 31°-45°, (2) 46°-59°, (3) 121°-135°, and (4) 136°-149°. Amounts of regular and irregular astigmatism, and the vertical/horizontal (Rx) and oblique astigmatism components (Ry) decomposed using vector analysis were compared among the 4 categories and age groups, and between sexes and eye sides.

Results: Incidences of the 4 meridian categories were similar and did not differ significantly among age groups or between sexes. The incidence was significantly greater in eyes in meridian categories 1 and 2 in the left eye and categories 3 and 4 in the right eye, and significantly greater in men in their 40 s and 50 s and in women in their 70 s and 80 s (P < 0.0001). The mean regular astigmatism, asymmetry and higher-order irregularity components, and Rx and absolute Ry significantly increased with age (P ≤ 0.0372). The mean regular and irregular astigmatism, and absolute Rx and Ry did not differ significantly among the 4 categories, or between sexes or left and right eyes.

Conclusions: The incidence of oblique astigmatism was significantly greater in the temporal side meridians, and the incidence in women increased with age. The degree of oblique astigmatism increased with age, with an increase in irregular astigmatism.

Fig. 1. Schema of the 4 meridian categories of oblique astigmatism and comparison of the incidence of eyes with oblique astigmatism among the 4 meridian categories.

Oblique astigmatism is classified into 4 meridian categories: (1) 31°–45° (category 1); (2) 46°–59° (category 2); (3) 121°–135° (category 3); and (4) 136°–149° (category 4). The incidence of eyes with oblique astigmatism was significantly greater in meridian categories 1 and 2 in left eyes and in meridian categories 3 and 4 in right eyes. *Statistically significant difference among the 4 meridian categories, †Statistically significant difference between each meridian category pair.

Fig. 2. Comparison of magnitude of regular astigmatism, and asymmetry and higher-order irregularity astigmatism components among the 5 age groups.

Both the mean amounts of asymmetry and higher-order irregularity components significantly increased with advancing age. *Statistically significant difference among age groups, †Statistically significant difference between age group pairs.

Fig. 3. Comparison of vertical/horizontal astigmatism components (Rx; A) and absolute value of oblique astigmatism components (Absolute Ry; B) among the 5 age groups.

A The mean Rx significantly increased from a negative to a positive value with age, with no significant difference between each age group pair. *Statistically significant difference/ among the 5 age groups. B The mean absolute Ry value increased with age, with significant differences between patients in their 40 s or 50 s and those in their 80 s. *Statistically significant difference among the 5 age groups, †Statistically significant difference between age group pairs.

Fig. 4. Double-angle plot analysis of the change in the oblique and vertical/horizontal astigmatism components with age.

The oblique astigmatism component markedly increased with advancing age, with only a slight change toward ATR astigmatism. The 95% confidence ellipse of the data is indicated by the dotted line.

Fig. 5. Comparison of the ratio of eyes with oblique astigmatism between men and women among the 5 age groups.

The ratio of eyes with oblique astigmatism between men and women significantly changed with age; the incidence was greater in men in their 40 s and 50 s and in women in their 70 s and 80 s. *Statistically significant difference among the 5 age groups, †Statistically significant difference between age group pairs.