Purchase this article with an account.
C.D. Coe, L.N. Thibos, A. Bradley; Predicting Depth of Focus from Wavefront Aberrations . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1500.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To account for the subjective depth–of–focus (DoF) using image quality (IQ) metrics derived from wavefront aberration measurements.
Subjective DoF was determined psychophysically with a monochromatic Badal optometer for both a 3mm and 8mm pupil using a criterion of just–noticeable–blur. The Badal target consisted of a high–contrast logMAR letter–chart illuminated with 579nm light. Wavefront aberrations were measured for 10 subjects at 843nm under cycloplegia with a clinical aberrometer (COAS, Wavefront Sciences Inc) and converted to 579nm using the IndianaEye model of ocular chromatic aberration. Optimum focus of the eye was determined from the wavefront by adding a series of spherical wavefronts to find the one that maximized each of 30 different metrics of IQ. These same through–focus computations also determined the IQ associated with extremes of the subjective DoF interval. Using correlation analysis and paired samples T–tests, we evaluated the hypotheses that blur is detected when one of the following quantities falls to some fixed threshold: IQ, (IQmax– IQ), or (IQmax– IQ)/IQmax.
The quantity (IQmax– IQ)/IQmax (i.e. Weber’s fraction for IQ) accounted best for the subjective depth of focus. This quantity was independent of pupil size for 8 of 30 metrics of IQ.
We have identified 8 different metrics of IQ that account for the subjective detection of blur, and the corresponding DoF interval, based on the rule "blur is detected when (IQmax– IQ)/IQmax (i.e. Weber’s fraction for IQ) falls to some fixed threshold level. This result may prove useful for objectively assessing the accuracy and efficacy of refractive therapy.
This PDF is available to Subscribers Only