Astigmatism

Excerpt

Astigmatism is a common refractive error, where refraction changes in different meridians of the eye. The light rays passing through the eye cannot converge at a particular focal point but form focal lines. In other words, astigmatism is a condition where parallel rays of light passing from the cornea do not converge to a point focus on the retina.

Astigmatism can be regular or irregular. The etiology of astigmatism can be corneal, lenticular, or retinal. Regular astigmatism is divided into with the rule astigmatism, against the rule astigmatism, oblique, and bi-oblique astigmatism. The principle of Sturm's conoid defines the optics of regular astigmatism.

Astigmatism can also be divided into simple, compound, and mixed astigmatism. The common symptoms of astigmatism can be asthenopia, discomfort, blurred and defective vision, elongation of objects, and accommodation problems. The signs include partial lid closure, head tilt, vertically oval or tilted optic disc, and different power in different meridians. The investigations needed include retinoscopy, slit lamp, examination, keratometry, Schiempflug imaging, astigmatic fan, and Jackson cross-cylinder evaluation.

Astigmatism can be managed with spectacles, contact lenses, and surgical correction of astigmatism through refractive surgery, toric IOL implantation, and astigmatic relaxing incisions.