The clinical diagnosis of Acanthamoeba keratitis is mainly based on the following aspects: 1. Risk factors: common risk factors include agricultural trauma, corneal contact lenses wear, splashing of foreign matters or small insects, etc. 2. Onset time: the disease gradually progresses in 3–7 days after being affected by one or more risk factors. 3. Characteristics of the corneal signs (Fig. 5.1a–d): (a) Typical corneal ring infiltration (b) Ditch-shaped melting at the edge of corneal ulcer (c) Crude salt-like granular dense infiltration (d) Radial keratoneuritis