Posterior corneal astigmatism | 合法醫療器材資訊網

Astigmatism is a prevalent optical disorder that affects different visual functions, for instance, visual acuity and sensitivity to the intensity of darkness and brightness of the contrast. It can cause some problems such as reduced vision, and causing some symptoms for the patients such as epiphora, unilateral diplopia, asthenopia and distortion.1–3 The treatment of astigmatism is more difficult than other types of refractive errors due to making some distortions after correction.4 These problems are posing a challenge for the patient and the physician.3,5 Some studies have shown that age, sex, environment and genetic factors are important points that affect type and amount of astigmatism.3,6 Studies estimated that the prevalence of astigmatism is 10–13 percent of the refractive errors.3,7

The optical surface of the cornea is the first and the most important optical surface of the eye and its center thickness is about 550 μm, its vertical diameter is abou...