The depth of focus of the human eye.

Purpose: To measure the subjective depth of focus (DOF) in keratoconic eyes andcompare it to that of normal eyes. Methods: We measured the subjective DOF in two groups of subjects with a dual-Badal-channel optical system. The first group consisted of 10 normal subjects and the secondgroup consisted of 5 keratoconic subjects. We measured DOF of the normal subjectsunder conditions both with and without cycloplegia, whereas for the keratoconics,measurements were performed on both eyes without cycloplegia. The wavefrontaberrations and corneal topography were also collected for the keratoconic subjects.From the topography files, we calculated the physical dimensions of the keratoconic coneincluding its distance to the pupil centre and volume. Results: When comparing the subjective DOF and higher order aberration (HOA)measured in the control group with and without cycloplegia, the results were highlycorrelated and no statistically significant difference was found (p>0.05). It was found thatthe subjective DOF measured in the keratoconic eyes (0.90 ± 0.21 D) was significantlylarger than that in normal eyes (0.73±0.09 D). The keratoconic group showed a meanvalue of HOA RMS approximately three times larger than that in the control group, withhigh levels of coma. However, there was no significant correlation between the largerHOA RMS and DOF of keratoconics (Pearson‟s r=0.31, p>0.05). Significant correlationwas found between keratoconic DOF and the HOA RMS contributed by the anteriorcornea (Pearson‟s r=0.67, p<0.05), and moderate correlation was found between DOFand the cone location, and between DOF and cone volume (r=-0.59, 0.58 and p=0.07,0.08 respectively). Analysis was also performed between the two eyes of eachkeratoconic subject to identify the optical factors causing the difference of DOF betweenthe two eyes. Strong correlation was found between the difference of DOF and the RMSvalue of symmetrical aberrations (r=0.96, p<0.01), and between the difference of DOFand the difference of cone dimensions (r=-0.95 and 0.92, both p<0.05). Conclusion: By using a dual-Badal-channel optical system, we can reliably measure thesubjective DOF without cycloplegia. The DOF measured in keratoconic eyes wassignificantly larger than that in normal eyes. However there was not a strong correlationbetween the large amount of HOA RMS and DOF in keratoconic eyes.