Influence of different types of astigmatism on visual acuity

Abstract

PurposeTo investigate the change in visual acuity (VA) produced by different types of astigmatism (on the basis of the refractive power and position of the principal meridians) on normal accommodating eyes.MethodsThe lens induced method was employed to simulate a set of 28 astigmatic blur conditions on different healthy emmetropic eyes. Additionally, 24 values of spherical defocus were also simulated on the same eyes for comparison. VA was measured in each case and the results, expressed in logMAR units, were represented against of the modulus of the dioptric power vector (blur strength).ResultsLogMAR VA varies in a linear fashion with increasing astigmatic blur, being the slope of the line dependent on the accommodative demand in each type of astigmatism. However, in each case, we found no statistically significant differences between the three axes investigated (0°, 45°, 90°). Non-statistically significant differences were found either for the VA achieved with spherical myopic defocus (MD) and mixed astigmatism (MA). VA with simple hyperopic astigmatism (SHA) was higher than with simple myopic astigmatism (SMA), however, in this case non conclusive results were obtained in terms of statistical significance. The VA achieved with imposed compound hyperopic astigmatism (CHA) was highly influenced by the eye's accommodative response.ConclusionsVA is correlated with the blur strength in a different way for each type of astigmatism, depending on the accommodative demand. VA is better when one of the focal lines lie on the retina irrespective of the axis orientation; accommodation favors this situation.

Prediction of distance visual acuity in presbyopic astigmatic subjects

“…We used the SEVA for the assessment of visual performance in astigmatic eyes, when the least circle of confusion is focused on the retina in the current study, in order to precisely investigate the effect of the amount of astigmatism on visual acuity. Remón et al also evaluated the SEVA when the least circle of confusion is focused on the retina in astigmatic eyes, but the subject age was much younger (25 to 32 years) 10 . To the best of our knowledge, this is the first study to assess the relationship between astigmatism and visual acuity in both phakic and pseudophakic elderly subjects, and to establish a prediction formula of distance visual acuity according to the amount of astigmatism in a large cohort of such subjects.…”

Effect of incision on visual outcomes after implantation of a trifocal diffractive IOL

“…This finding was consistent with Cui Y’s [ 18 , 19 ] studies, which showed the same phenomenon after cataract surgery. However, the impact of the astigmatic axial on visual acuity was oblique> ATR > WTR astigmatism [ 20 ]. In our study, a higher percentage of oblique astigmatism but a much lower percentage of WTR astigmatism was found postoperatively in group B 2 compared with those in group A 2 .…”

<p>Effect of cylinder power and axis changes on vision in astigmatic participants: a comment [Letter]</p>

“…Finally, it is important to note that, like happens for the HCVA,4 the rate of change of the other visual parameters with the blur strength may depend on the type of residual astigmatism, and also on the amplitude of accommodation of the participants. This may be one of the reasons for the different slopes in the data corresponding to undercorrection by 0.75 DC in the above-mentioned Figure 2 (dotted line).…”

“…However, it is well known that cylinder power and axis are not independent variables; in fact, astigmatism is a vector magnitude. Several studies2,4 use vector formalism to quantify the blur strength produced by astigmatism. Even in previous literature,1 the authors show the power vector components ( M, J 0 , J 45 ) in Table 1, for the different groups in which the sample is divided.…”