The relation between corneal and total astigmatism

• Published in: Optometry and vision science Vol. 73; no. 2; pp. 86 - 91
• Main Authors: KELLER, P. R, COLLINS, M. J, CARNEY, L. G, DAVIS, B. A, VAN SAARLOOS, P. P
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 01.02.1996
• Subjects: Adult; Astigmatism - pathology; Astigmatism - physiopathology; Biological and medical sciences; Cornea - pathology; Cornea - physiopathology; Female; Humans; Image Processing, Computer-Assisted; Male; Medical sciences; Microscopy, Video; Ophthalmology; Refraction, Ocular; Regression Analysis; Vision disorders; Human; Eye disease; Cornea; Vision disorder; Refractive error; Measurement method; Diameter; Astigmatism
• ISSN: 1040-5488; 1538-9235
• DOI: 10.1097/00006324-199602000-00003

Using computer-assisted videokeratoscopy we measured corneal astigmatism and compared these results over a range of corneal zone diameters with total ocular astigmatism derived by subjective refraction. Videokeratoscopes permit a more detailed analysis of the power distribution within a given corneal surface area, enabling comparison to the total astigmatism for equivalent aperture sizes. Although there were significant individual variations, the group average data supports the traditional view of a linear relation between corneal and total astigmatism. This was true across the range of apertures tested from 2 to 7 mm, with the coordinates of the relation being consistent with that of the modified Javal's rule; namely a slope of 1 and an intercept of approximately 0.50 D against-the-rule residual astigmatism.