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Against-the-rule astigmatism – the horizontal meridian is steepest (a rugby ball or American football standing on its end). [17] Oblique astigmatism – the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees. [17] Irregular astigmatism – principal meridians are not perpendicular.
Keratoconus. Keratoconus ( KC) is a disorder of the eye that results in progressive thinning of the cornea. [ 3] This may result in blurry vision, double vision, nearsightedness, irregular astigmatism, [ 4] and light sensitivity leading to poor quality-of-life. [ 3][ 5] Usually both eyes are affected. [ 3] In more severe cases a scarring or a ...
Pellucid marginal degeneration ( PMD) is a degenerative corneal condition, often confused with keratoconus. It typically presents with painless vision loss affecting both eyes. Rarely, it may cause acute vision loss with severe pain due to perforation of the cornea. It is typically characterized by a clear, bilateral thinning ( ectasia) in the ...
Aberrations of the eye. The eye, like any other optical system, suffers from a number of specific optical aberrations. The optical quality of the eye is limited by optical aberrations, diffraction and scatter. [1] Correction of spherocylindrical refractive errors has been possible for nearly two centuries following Airy's development of methods ...
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- ( a-) meaning "without" and ...
Treatment options include contact lenses and intrastromal corneal ring segments for correcting refractive errors caused by irregular corneal surface, [7] [8] corneal collagen cross-linking to strengthen a weak and ectatic cornea, [9] or corneal transplant for advanced cases.
Other symptoms may include double vision, headaches, and eye strain. [1] Near-sightedness is due to the length of the eyeball being too long, far-sightedness the eyeball too short, astigmatism, the cornea being the wrong shape, and presbyopia aging of the lens of the eye such that it cannot change shape sufficiently. [1]
Central serous chorioretinopathy ( CSC or CSCR ), also known as central serous retinopathy ( CSR ), is an eye disease that causes visual impairment, often temporary, usually in one eye. [ 1][ 2] When the disorder is active it is characterized by leakage of fluid under the retina that has a propensity to accumulate under the central macula.