Influence of different types of astigmatism on visual acuity.
PURPOSE
To 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.


METHODS
The 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).


RESULTS
LogMAR 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.


CONCLUSIONS
VA 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.
['Remón|Laura|L|', 'Monsoriu|Juan A|JA|', 'Furlan|Walter D|WD|']
D000065:Accommodation, Ocular D000328:Adult D001251:Astigmatism D005139:Eyeglasses D005260:Female D006801:Humans D008297:Male D011932:Reading D014792:Visual Acuity
Astigmatism Visual acuity Spherical defocus Axis Accommodation state Agudeza visual Astigmatismo Defecto esférico Eje Estado de acomodación