Various
corneal diseases, such as
hereditary corneal dystrophies, corneal
infection, and bullous keratopathy, cause
corneal opacity,
scarring, and
edema, leading to severely decreased visual acuity and loss of vision. These diseases were regarded as
corneal opacity diseases, and the decreased visual acuity was considered to be predominantly caused by
corneal opacity. The influence of corneal irregular
astigmatism on vision has been poorly understood to date, mainly because accurate quantification of irregular
astigmatism has been technically challenging. We have performed detailed analyses of the corneal higher-order aberrations (HOAs) of the anterior and posterior surfaces and total cornea in
corneal diseases, using an anterior segment imaging system combined with a ray-tracing method. Subsequently, we conducted correlation analyses between corneal HOAs and visual acuities and characterized the typical
HOA patterns in the
corneal diseases. Our recent studies demonstrated that corneal HOAs directly degrade visual acuity in eyes with mild-to-moderate
corneal opacities, such as
corneal dystrophies, corneal
scarring, and bullous keratopathy. The findings also suggested that correction of corneal HOAs using rigid gas-permeable
contact lenses is effective in eyes with a smooth posterior surface and useful in certain patients with corneal
scarring to some extent. Our data will be useful for decision making regarding surgical interventions, based on the amount of corneal HOAs. Our results further indicate the clinical relevance of irregular
astigmatism in the posterior surfaces in assessing the visual function of eyes with various
corneal diseases.