Irregular astigmatism

Astigmatism is normally caused by the cornea being more curved in one direction than another. Fortunately, the maximum and minimum curves are normally at right angles to one another, resulting in a surface rather like that of a rugby football. Irregular astigmatism is normally the result of injury or keratoconus and occurs when the cornea is pulled into a distorted shape, due to scarring or the progression of a cone in keratoconus. 

The resulting shape cannot be catered for by spectacle lenses or regular soft contact lenses that mould themselves around the shape. Instead, rigid gas permeable lenses or scleral lenses may be used. These will not flex around the distortion, and the liquid reservoir that forms behind each lens becomes a “tear lens”, which corrects the irregularity and restores clear vision.

Some speciality soft and hybrid lenses are also available to correct irregular astigmatism.

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