**The effects of aberrations on image quality and the objectively assessed depth of focus (DoF) were studied. Aberrometry data from 80 young subjects with a range of refractive errors was used for computing the visual Strehl ratio based on the optical transfer function (VSOTF), and then, through-focus simulations were performed in order to calculate the objective DoF (using two different relative thresholds of 50% and 80%; and two different pupil diameters) and the image quality (the peak VSOTF). Both lower order astigmatism and higher order aberration (HOA) terms up to the fifth radial order were considered. The results revealed that, of the HOAs, the comatic terms (third and fifth order) explained most of the variations of the DoF and the image quality in this population of subjects. Furthermore, computer simulations demonstrated that the removal of these terms also had a significant impact on both DoF and the peak VSOTF. Knowledge about the relationship between aberrations, DoF, image quality, and their interactions is essential in optical designs aiming to produce large values of DoF while maintaining an acceptable level of image quality. Comatic aberration terms appear to contribute strongly towards the configuration of both of these visually important parameters.**

*SD*= 22.9 ± 3.5 years) previously collected as part of a study conducted at the School of Optometry & Vision Science, Queensland University of Technology, were analyzed in this study. All participants gave written informed consent, and were treated in accordance with the tenets of the Declaration of Helsinki. A noncycloplegic subjective refraction performed on all subjects revealed spherical refractive errors ranging from −7.25 to +0.75 D (mean ±

*SD*= −0.80 ± 1.68 D), with no subject exhibiting astigmatism greater than 0.5 D (mean ±

*SD*cylinder magnitude = −0.17 ± 0.11 D, mean axis 1.4° ± 19.0°). All subjects exhibited best corrected visual acuity of logMAR 0.00 or better. Subjects were divided into three groups, based on their spherical refractive error: mild hyperopia to emmetropia (+0.75 D to 0.00 D), mild myopia (ranging from −0.25 to −1.50 D), and moderate to high myopia (with myopia greater than −1.5 D). Table 1 shows a summary of the main characteristics of each group. The three groups did not exhibit significant differences in terms of mean age (

*p*= 0.875) or pupil diameter (

*p*= 0.108).

*c*

_{22}) root mean square (RMS), third order trefoil RMS (

*c*

_{33}), third order coma-like RMS (

*c*

_{31}), fourth order tetrafoil RMS (

*c*

_{44}), fourth order astigmatism RMS (

*c*

_{42}), spherical-like RMS (

*c*

_{460}, taking into account fourth and sixth Zernike radial orders), and fifth order coma RMS (

*c*

_{51}) were considered. These aberrations terms are related to the OSA standards for reporting aberrations of the eye (Thibos, Applegate, Schwiegerling, & Webb, 2002) as follows:

*c*

_{22}corresponds to

*c*

_{33}is

*c*

_{31}is

*c*

_{44}is

*c*

_{42}is

*c*

_{460}is

*c*

_{51}is

*c*

_{22}and ending with

*c*

_{51}. This method performs a multilinear regression and keeps the statistically significant (

*p*< 0.05) variables within the model, while the nonsignificant (

*p*> 0.05) variables are rejected sequentially and do not appear in the final linear model. Therefore, this analysis provides a suitable way to explain the DoF and the Peak VSOTF by means of the aberrations that play the most significant role in the calculation of these parameters.

*p*> 0.056). The ANOVA was repeated for the other two conditions (only HOAs and HOAs minus third order aberrations), which also showed no differences associated with refractive group. Given the lack of statistically significant differences in astigmatism and HOAs among the refractive groups for these values, all subjects were grouped together to form a single population for the remaining calculations. A posthoc power analysis revealed the sample size used had 95% power to detect a 0.005-micrometer difference in HOAs. A summary with the DoF and Peak VSOTF mean values (along with standard deviation) for the different conditions and pupil diameters is shown in Table 2, when the data from all refractive groups were pooled.

*p*< 0.001). The equation from the stepwise linear regression to predict the DoF50 in diopters, for a 3.6 mm pupil diameter was: where

*c*

_{22}is the second order astigmatism RMS in micrometers. For DoF80, the aberration terms found to significantly contribute to the final model was fourth order astigmatism. In this case, the DoF80 (in diopters) can be obtained using the equation: Repeating the same, but using the 4.6 mm pupil diameter, the equation obtained for the DoF50 was with

*p*values of 0.010 for the spherical-like RMS (

*R*

^{2}= 0.086), and 0.036 for the second order astigmatism (

*R*

^{2}increase = 0.053). For DoF80, the result was Correlations between the calculated values and those predicted by each of the linear models are shown in Figure 4. It is interesting to note that the predicted DoF values are not close to the calculated ones, which means the models in these particular cases are generally poor.

*p*< 0.05 in all cases). Trefoil RMS was additionally included in the model for the 4.6 mm of pupil size. Correlations between the calculated values and those predicted by each one of the linear models are shown in the lower panel of Figure 4. The order in which these predictors were added for the smaller pupil was

*c*

_{22}(

*R*

^{2}= 0.577),

*c*

_{31}(

*R*

^{2}increase = 0.081),

*c*

_{42}(

*R*

^{2}increase = 0.029), and

*c*

_{460}(

*R*

^{2}increase = 0.022). For the larger pupil, the order was

*c*

_{22}(

*R*

^{2}= 0.424),

*c*

_{460}(

*R*

^{2}increase = 0.066),

*c*

_{31}(

*R*

^{2}increase = 0.058),

*c*

_{42}(

*R*

^{2}= 0.026), and

*c*

_{33}(

*R*

^{2}increase = 0.024). It was observed that when the pupil size increases, the linear model is weaker, and therefore the predictions are worse.

*p*values of < 0.001 for the third order coma (

*R*

^{2}= 0.627), and 0.007 for the fifth order coma (

*R*

^{2}increase = 0.035). For the 80 % threshold, the result was Correlations between the calculated values and those predicted by each of the linear models are shown in Figure 5. In this case, more than 80% of the variance in DoF50 is explained using only the third order coma RMS at a 3.6 mm pupil. As the pupil size and the selected threshold increase, the linear models are weaker (lower

*R*

^{2}), giving as a result poorer predictions.

*c*

_{31}(

*R*

^{2}= 0.780;

*p*< 0.001),

*c*

_{51}(

*R*

^{2}increase = 0.035;

*p*< 0.001),

*c*

_{33}(

*R*

^{2}increase = 0.035;

*p*< 0.001), and

*c*

_{460}(

*R*

^{2}increase = 0.026;

*p*< 0.001). In the larger pupil case, the terms selected were

*c*

_{31}(

*R*

^{2}= 0.563;

*p*< 0.001),

*c*

_{51}(

*R*

^{2}increase = 0.071;

*p*< 0.001),

*c*

_{460}(

*R*

^{2}increase = 0.068;

*p*< 0.001), and

*c*

_{33}(

*R*

^{2}increase = 0.017;

*p*= 0.038).

*p*values of < 0.001 for the fifth order coma (

*R*

^{2}= 0.485),

*p*< 0.001 for the spherical-like RMS (

*R*

^{2}increase = 0.220), and 0.030 for the fourth order astigmatism term (

*R*

^{2}increase = 0.018). with

*p*values of < 0.001 for the fifth order coma (

*R*

^{2}= 0.523),

*p*< 0.001 for the spherical-like RMS (

*R*

^{2}increase = 0.252), and

*p*< 0.001 for the fourth order astigmatism term (

*R*

^{2}increase = 0.032).

*p*values of < 0.001 for the spherical-like term (

*R*

^{2}= 0.708), and

*p*< 0.001 for the fifth order coma (

*R*

^{2}increase = 0.089). The result obtained for the 80% threshold was The order in this case was spherical-like term (

*R*

^{2}= 0.582;

*p*< 0.001) and the fifth order coma (

*R*

^{2}increase = 0.042;

*p*= 0.005).

*c*

_{460}(

*R*

^{2}= 0.550;

*p*< 0.001),

*c*

_{51}(

*R*

^{2}increase = 0.273;

*p*< 0.001),

*c*

_{42}(

*R*

^{2}increase = 0.083;

*p*< 0.001), and

*c*

_{44}(

*R*

^{2}increase = 0.028;

*p*< 0.001). For the larger pupil, the terms selected were

*c*

_{460}(

*R*

^{2}= 0.582;

*p*< 0.001),

*c*

_{51}(

*R*

^{2}increase = 0.210;

*p*< 0.001),

*c*

_{42}(

*R*

^{2}increase = 0.084;

*p*< 0.001) and

*c*

_{44}(

*R*

^{2}increase = 0.044;

*p*< 0.001). The correlations between the calculated values and those predicted by each of the linear models are illustrated in Figure 6. In this case, almost all the predictions are very good, since there are less aberration terms and their magnitude is smaller and less variable between subjects.

*R*

^{2}> 0.97 for both pupil sizes and thresholds), as seen in the bottom row of Figure 7. This result highlights the trade-off that exists between optical quality and DoF. It is interesting to note that while removal of second order astigmatism resulted in an improvement in image quality, its removal also resulted on average in an increase in DoF whereas the removal of each of the other terms resulted in an improvement in image quality and a reduction in DoF. The aberration that had the largest impact on both parameters (DoF and Peak VSOTF) was the third order coma. This impact was larger than that caused by the second order astigmatism. For small pupils, the differences in the impact of the correction of several aberrations using the two different thresholds was minimal, whereas for larger pupils, small variations start to appear between thresholds, mainly from the correction of the spherical-like aberrations. It is also noticeable that for larger pupil diameters, the correction of aberrations with greater radial order, like the fifth order coma and the spherical-like aberrations has a larger impact on the optical quality of the eye compared to the smaller pupil analysis.

*c*

_{22}which ranged between 42% and 67% for the 3.6 mm pupil, and from 14% to 67% for the larger pupil size. Regarding the Peak VSOTF, the standard deviation values grow with the removal of successive terms, reaching values up to 140% for the small pupil size, and up to 220% for the larger pupil, which emphasizes the high variability among subjects.

*R*

^{2}values reaching up to ∼0.8 for analyses considering HOAs only). However, poorer models were obtained for DoF when astigmatism was included in the calculations (

*R*

^{2}values < 0.3). This is likely due to the fact that astigmatism was the aberration that presented the larger variation among subjects, and these larger interindividual differences may reduce the reliability of the linear predictions. Another trend that can be observed in the linear models is that they tend to become poorer when the pupil diameter increased. This trend likely occurs due to the fact that the magnitude of the aberrations and their variability among subjects increases with pupil size, which may result in a worsening of the outcomes from the linear models.

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