Evaluation of relationships among refractive and topographic parameters

Abstract

As the degree of myopia and negative asphericity increased, the corneal radius of curvature decreased. Corneal Q-values less than -0.3 were associated with reduced optical performance of the cornea.

Anterior Segment Eye Assessment of Refractive Surgery Candidates in the Southeast of Iran

“…The present study agrees with the majority of researches (Carney, Mainstone, & Henderson, 1997;Budak, Khater, Friedman, Holladay, & Koch, 1999;Hashemi et al, 2013) that on average corneal power in myopia is about 1.0 D greater than in hyperopia.…”

Relationship between anterior corneal asphericity and refractive variables

“…When compared using the Student's t-test, this mean differed significantly with respect to previously reported means [14,26]. Table 2 shows the mean keratometry, Q and astigmatism measurements obtained using the Atlas videokeratoscope according to manifest refraction.…”

“…A negative Q is obtained for the most common corneal shape (prolate ellipse), and our values are in the range of previously reported measurements for normal eyes: −0.01 to −0.81 [11], −0.01 to −0.64 [12], −0.20 to −0.40 [29], −0.04 to −0.72 [30] and −0.11 to −0.26 [13]. The most accepted Q-values are the figures of −0.26 reported by Budak et al [26] or −0.23 for Caucasian subjects quoted by Yebra-Pimentel et al [14]. Our figures (mean −0.35) were significantly (p=0.05) more negative than reported values as indicated by the Student's t-test.…”

“…Mainstone et al [25] reported similar findings in 25 hyperopes and ten emmetropes. Budak et al [26] detected no correlation between asphericity and refractive error. However, Q-values were more positive in moderate myopia (−2 to −6 diopters, D) than in hyperopia, although the trend was not seen in high myopia or emmetropia.…”

Measuring higher order optical aberrations of the human eye: techniques and applications

“…The photographic cameras were replaced by modern semiconductor charge coupling devices (CCD) and the tiresome analysis of the Plácido images was replaced by fast and semiautomated image processing algorithms (12,13) and sophisticated mathematical models of the human cornea (14,15). Nowadays the whole process of corneal analysis takes only a few seconds and at the end the eye-care professional may have a multitude of visualization options at a click of the mouse, with the aid of special tools, such as indexes for keratoconus screening (16,17), contact lens fitting modules (18) and special displays of corneal parameters (19). These displays may go from simple corneal slices, difference maps for pre-and postsurgical analysis, up to rotating three-dimensional corneal maps.…”