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Cristina Pacheco Del Valle; A mathematical model for corneal posterior astigmatism calculus based on corneal anterior astigmatism.. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2148.
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© ARVO (1962-2015); The Authors (2016-present)
To asses the posterior corneal astigmatism with a mathematical model based on the anterior corneal astigmatism measurement.
Retrospective study in which the corneal characteristics were measured with a Scheimpflug camera (Pentacam®HR): keratometries (K1 and K2), anterior corneal astigmatism (CAant), total corneal astigmatism (TCP) and posterior corneal astigmatism (CApost) and astigmatism axis. Demographic data was collected (gender and age). Eyes with any kind of irregularity on symmetry indexes (vertical or horizontal) and any keratometry greater than 47D were excluded. Descriptive statistics were used. Pearson’s correlation coefficient was used to evaluate the astigmatism anterior chamber and posterior chamber relationship. Lineal regression was used for all quantitative variables.
One thousand one hundred and twenty-two eyes were included. All the data were extracted from 4 different topography devices, all of them were Pentacam ® HR. Statistic analysis was made with STATA 15® sofware, values were expressed as mean (min and max). Mean age 36.4 yo (9-82), TCP 1.31 (0-4.7D), CAnt 0.55 (0-0-19D) and CApost-0.42(-1.3 –0D). The entire population was divided per astigmatism axes. The most frequent were anterior and posterior-vertical (n=915 eyes). These were employed for mathematical modelling. Pearson’s correlation coefficient was R2 = 0.465A simple linear regression was used to predict the posterior astigmatism value based on the anterior astigmatism value. We employed the following formula: y=mx + b where m= 0.1417, x=anterior astigmatism known value and b=-0.2442.We found correlation In those cases, in which the keratometry was less than 47D and both anterior and posterior axes were vertical, there is a correlation between CA ant and CApost.
The toric intraocular lens and refractive results calculation require to know the CApost value. This parameter helps us to anticipate its own effect on refractive outcomes, never the less, not all the available devices (topographs) are capable to measure this parameter so, its estimation by this mathematical formula we propose, may help to predict this parameter knowing only the anterior corneal astigmatism.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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