Quantification of sphero‐cylindrical defocus using refractive data

Abstract

Abstract Purpose To compare various indices calculated using refractive data to quantify defocus. Methods Subjective refraction, pupil diameter (Colvard) and asphericity (Orbscan) were prospectively recorded in 200 healthy eyes (including ametropia) of 121 patients. Refractive data were expressed by a sinusoidal curve in one plane (power / meridian) and by a vector in a 3D dioptric power space. The three Cartesian coordinates of the vector respectively represented the spherical equivalent, WTR/ATR component (0°/90° Jackson), and oblique component (45°/135° Jackson). The defocus was quantified by the root‐mean‐square (RMS) value of the power curve and the length of the vector. Correlations between uncorrected visual acuity (UCVA) in LogMAR units and principal parameters including defocus indices and refractive parameters were analyzed. Results The length of the power vector and the RMS index provided the highest correlation with UCVA (rs=0.90 p<0.001 and rs=0.88 p<0.001, respectively), whereas the correlation was less strong for subjective spherical equivalent (rs=0.70 p<0.001) and subjective cylinder (rs=0.30 p<0.001). Correlation was poor for the pupil diameter (rs=0.20, p<0.001); sex and asphericity coefficient showed no significant correlation (rs<0.08 p>0.20) with UCVA. Conclusion The length of the sphero‐cylindrical vector is clinically relevant to quantify the defocus with the aid of a single index using both spherical and astigmatic components of refraction. The UCVA is mainly explained by the ametropia.