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Refraction in keratoconus: how could topo-aberrometry help us?

Poster Details

First Author: R.Fasciani ITALY

Co Author(s):    E. Mandarà   R. Gori   S. Ambrogio   A. Caristia   A. Caporossi  

Abstract Details


Main aim of the study is to investigate the relationship between subjective refractive cylinder power and axis and objective topo-aberrometric parameters in keratoconus eyes.Refraction in keratoconus patients is often a challenge. Although spectacles and contact lenses represent the best aids to improve vision in patients not eligible for surgery, there are no clinical guidelines in Literature helping ophthalmologists and opticians to find the best spectacle correction in those patients.


Ophthalmic Institute, Catholic University of Sacro Cuore, Rome, Italy


125 keratoconus patients, 218 eyes, attending to our Cornea Service for medical or surgical consultation between 2006/2013 were enrolled in the study. Exclusion criteria were keratoplasty or other surgeries for advanced keratoconus; fruste keratoconus with aberrometric RMS less than 0.30 micron and absence of subjective astigmatism. All the enrolled patients were submitted to subjective refraction (uncorrected visual acuity and best spectacle corrected visual acuity), corneal topography using tangential map and corneal aberrometry (CSO, Firenze Italy) analyzing aberrometric astigmatism power and axis and coma axis. We divided all the eyes in 3 groups: A, 101 eyes, 'with the rule topographic astigmatism' (axis range between 61° and 120°), B, 52 eyes, 'against the rule topographic astigmatism' (axis range between 0°-30° and 151°-180°) and C, 65 eyes, 'oblique topographic astigmatism' (axis range between 31°- 60° and 121°-150°). Statistical analysis was performed using Proven Probability, Analisys of Means and Dispersion Analysis (i.e. variance, standard deviation and interquartile range).


The subjective refractive astigmatism power is better related with the topographic astigmatism power (77% of eyes) than aberrometric astigmatism power (53%). The subjective astigmatism axis depends on the steepest meridian localization : in A group, the most accurate index is the coma axis (89% of eyes); in B group, coma becomes less specific (50% of eyes), and the aberrometric astigmatism axis and topographic axis resulted equally useful (87% and 82% respectively); in the C group, coma results the less specific index (12% of eyes) and none of instrumental indexes seems to be accurate in determining refractive astigmatism (43-50%).


In conclusion we can state that corneal topography represents the gold standard exam for the detection of subjective refractive astigmatism power, while for the astigmatism refractive axis it's mandatory to consider the steepest meridian localization as the major determinant in indexes reliability. In particular, corneal aberrometry, expecially coma evaluation, results useful in the majority of keratoconic patients. These tips could facilitate keratoconus refractive best spectacle correction in daily clinical practice. FINANCIAL INTEREST: NONE

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