The aim of a soft contact lens is not only to restore visual acuity but also to obtain a better quality of vision. In bright light conditions, the contact lens does not affect visual function due to its transparency, but scattering causes deterioration of vision . The advanced design of a contact lens with photochromic additive, which filters in a dose-dependent manner depending on the intensity and wavelength of light, has been created for improving vision in such circumstances. The photochromic contact lenses would be expected to change optical density, and the lens had an optical density of about 0.20 in the activated state .
Even though previous studies have highlighted its visual performance, there have been no reports about the corneal wavefront aberrations of the photochromatic contact lenses in the literature. In this study, we evaluated the corneal wavefront aberrations of the photochromic contact lenses in both inactivated and activated states.
Renzi-Hammond et al.  measured photostress recovery, glare disability, glare discomfort, chromatic contrast, and vernier acuity. There was a beneficial influence on visual function with the photochromic contact lens, except vernier acuity. In a study by Buch et al. , its visual and driving performance were compared. Research showed that the photochromic soft contact lens was no different to non-photochromic soft contact lens or photochromic spectacles in both daytime and nighttime lighting under real-world conditions. According to the results of this study, the wavefront aberrations are consistent with the currently available literature regarding the photochromic soft contact lenses. These lenses may improve the visual performance via the dynamic photochromic balance between how dark the lens gets outdoor and the acceptability of the aberration profile.
HOAs have a noticeable influence on vision not correctable by glasses or contact lenses. Correcting refractive power and astigmatism, as well as HOAs induced by various contact lens designs, are the significant factors about the visual quality . Numerous contact lenses related factors have been reported for the variability of HOAs, including lens design, lens material, position and movement of lenses on the eye [2, 11, 12]. Moreover, there are also variations in ocular surface-related HOA, such as fluctuations in the tear film .
The general population has positive spherical aberration , and most of the commercially available single vision contact lenses are primarily intended to reduce this. Multiple contact lens manufacturers’ lenses include aspheric designed optics, which provide much more precise light guidance. McAlinden et al.  reported that the aspheric front surface design of Balafilcon A and Comfilcon A might have caused an increase in some aberrations. However, these increases were not clinically meaningful when the clinically significant change in magnitude was considered to be 0.1 µm. Efron et al.  found that the fitting of aspheric design soft contact lenses did not result in superior aberration control compared with equivalent spherical design soft contact lenses. These aberrations did not alter the daily performance of soft contact lenses. Even though the photochromic soft contact lenses had a spheric design, the average corneal aberrations were not affected in the current study.
The clinical relevance of aspheric over spheric contact lens remained controversial. Theoretical calculations have been demonstrated that spherical contact lenses induced HOA and reduced overall optical performance . Roberts et al.  suggested that soft spherical contact lenses for myopia increased HOA compared to not wearing a contact lens. However, the alterations were not statistically significant when individually evaluated. Jiang et al.  examined three different types of soft spherical contact lens and reported that the differences in aberrations could be attributed to the variation in the manufacturing. Neverthless, lens material and design could not be excluded. Our findings seem to support that the photochromic spherical contact lenses did not induce HOAs, especially under changing light conditions. When we compared HOAs in both inactivated and activated states, we did not observe any difference. The findings of this study may be associated with the photochromic additive part as the differences in the methods of manufacture.
Previous studies reported that spherical aberration induced by contact lens depends on lens power [19, 20]. We found no significant correlations between all aberrations with the contact lens spere power in both inactivated and activated states. The refraction of the enrolled patients was a variation between − 1.00 D and − 5.25 D. Also, the age distribution was limited in the range of 19 to 39 years to minimize the variation of aberration. Further studies will elucidate the impact of lens power on HOA in the population with different powers.
This study aimed to interpret the effect of the photochromic contact lens on wavefront aberrations in daily conditions. Therefore, the aberrations in inactivated and activated states were reported. There will be other approaches to determine the specific aberrations, but our study was mainly interested in the clinical performance of photochromic lenses. The photochromic filter always adapts to the changing light conditions, both indoors and outdoors conditions. Our study suggested that the adaptation did not increase corneal wavefront aberrations. Accordingly, these lenses could be offered to patients bothered by light to provide all-day vision. Photochromic contact lenses reduce the visual discomfort caused by aberration and might be helpful for performing outdoor activities such as sports.
One of the limitations was the relatively small sample size. Also, there was a limitation due to using a single type of contact lens and a single type of aberrometer. Moreover, the aberrometer used in this study was the Sirius Scheimpflug Placido Topography System. If a different measurement principle based aberrometers were chosen, results would be different due to aberrometer inconsistency. Another limitation was the patients who comprised young adults and habitual contact lens wearers. The broader heterogeneous adult population should be included in further studies to confirm our findings.
In summary, the characteristics of the photochromic contact lens on wavefront aberration did not change in both inactivated and activated states. These lenses may enhance visual performance by adapting to changing light conditions with a stable aberration profile in outdoor activities. Further investigations of aberration differences caused by lens design are necessary.