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F. Yi, D. R. Iskander, M. J. Collins; Subjective Measurement of Depth of Focus in Keratoconus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4971.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the subjective depth of focus (DOF) in keratoconic eyes and compare it to that of normal eyes.
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 second group consisted of 5 keratoconic subjects. We measured DOF of the normal subjects under conditions both with and without cycloplegia, whereas for the keratoconics, measurements were performed on both eyes without cycloplegia. The wavefront aberrations and corneal topography were also collected for the keratoconic subjects. From the topography files, we calculated the physical dimensions of the keratoconic cone including its distance to the pupil centre and volume.
When comparing the subjective DOF and higher order aberration (HOA) measured in the control group with and without cycloplegia, the results were highly correlated and no statistically significant difference was found (p>0.05). It was found that the subjective DOF measured in the keratoconic eyes (0.90 ± 0.21 D) was significantly larger than that in normal eyes (0.73±0.09 D). The keratoconic group showed a mean value of HOA RMS approximately three times larger than that in the control group, with high levels of coma. However, there was no significant correlation between the larger HOA RMS and DOF of keratoconics (Pearson’s r=0.31, p>0.05). Significant correlation was found between keratoconic DOF and the HOA RMS contributed by the anterior cornea (Pearson’s r=0.67, p<0.05), and moderate correlation was found between DOF and 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 each keratoconic subject to identify the optical factors causing the difference of DOF between the two eyes. Strong correlation was found between the difference of DOF and the RMS value of symmetrical aberrations (r=0.96, p<0.01), and between the difference of DOF and the difference of cone dimensions (r=-0.95 and 0.92, both p<0.05).
By using a dual-Badal-channel optical system, we can reliably measure the subjective DOF without cycloplegia. The DOF measured in keratoconic eyes was significantly larger than that in normal eyes. However there was not a strong correlation between the large amount of HOA RMS and DOF in keratoconic eyes.Keywords: depth of focus, keratoconus, cycloplegia.
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