If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Lens optical design can affect accommodative micro-fluctuation during reading.
•
Aspheric lens reduced accommodative micro-fluctuations compared to spherical lens.
•
Less change in accommodative micro-fluctuations shows reduced ciliary muscle stress.
•
Aspheric lens design may help to reduce eye strain when viewing digital devices.
Abstract
Purpose
Accommodative micro-fluctuations (AMF) are small dioptric changes during accommodation. The aim of this study was to evaluate and compare changes in AMF when wearing silicone hydrogel contact lenses of two different optical designs.
Methods
A multi-centre, randomised, cross-over, non-dispensing study was conducted on 68 adapted contact lens wearers aged 25–35 years to compare AMF responses to a spherical and aspheric silicone hydrogel (comfilcon A) lens designs. A Righton Speedy “i” series Auto Refractometer in accommodation analyser mode was utilized before and after reading a standard text in font size 8 on an iPhone 5 for 20 min at a 25 cm viewing distance. Phone screen brightness was set by automatic adjustment mode and ambient illumination was controlled at all sites.
Results
Mean ± SD AMF change from before to after the reading task was 2.25 ± 5.6 and 0.13 ± 5.7 (relative values) for the spherical and aspheric lens designs, respectively. The difference was statistically significant (P = 0.017, Paired t-test).
Conclusions
The smaller change in AMF when using an aspheric lens design suggests reduced ciliary muscle stress when reading print on a smart phone at a close distance for short periods (20 min). Contact lens wearers who frequently use digital devices and are experiencing eye strain may benefit from switching from a spherical design to one that incorporates aspheric optics.
] and is mostly associated with near vision tasks. In the last decade, there has been a resurgence of awareness and concern because the condition seems to be aggravated by computer use [
]. The assumption is that this condition is more prevalent in people who have a reduced accommodative amplitude, even though near addition lenses are commonly prescribed for loss of accommodation. Sheedy et al. categorized asthenopia into two groups: that caused by stress of the accommodative and convergence mechanisms, and that caused by dryness and irritation of the ocular surface [
]. A term now commonly used to describe the condition is ‘digital eye fatigue’ or ‘digital eye strain’, since almost everyone uses digital devices such as smartphones and tablets in addition to computers. According to a study that examined the health impact of participation in competitive electronic sports, eye fatigue was the most frequently reported complaint amongst elite players at 52 % [
]. In 2018, adult Americans spent an average of 6.3 h per day viewing digital media using smartphones and tablets (3.6 h), computers (2.0 h), and other devices (0.7 h) [
Accommodative micro-fluctuations (AMF) are tremors or states of temporal ocular instability due to spasms of the ciliary muscle when viewing a near target [
]. AMF can be measured as changes in the refractive power of the eye over time with high-speed infra-red optometers or auto-refractors. Campbell et al. were the first to notice the small fluctuations in refractive power during accommodation [
]. The investigators used an infrared optometer as an objective measure of AMF in subjects who were asthenopic and non-asthenopic. In their small sample, Kajita et al. demonstrated that the asthenopic group had higher AMF responses. Therefore, reducing AMF response may help to alleviate symptoms of eye strain.
Contact lenses with innovative optical designs may help to reduce AMF and, thus, minimize digital eye strain. Biofinity® Energys (comfilcon A, CooperVision, Inc.) uses aspheric curves across the front-surface of the optical zone to ease asthenopia without impacting distance vision. The aspheric power profile provides a slight positive power at the centre of the lens. Biofinity® Energys is also designed to aid the wearer’s visual transition from on-screen to off-screen viewing. The objective of this study was to determine whether the AMF response differed when wearing spherical and aspheric lens designs (of the same material and back surface design) after subjects performed a 20-minute reading task.
2. Methods
This was a prospective, multi-centre (9 sites in Japan), randomized, cross-over, subject-masked, bilateral wear, non-dispensing study. The study conformed with the tenets of the Declaration of Helsinki. Prior informed consent was obtained from all participants. The research was reviewed and approved by an Independent Ethics Committee prior to commencement.
Seventy-seven adapted soft (37 silicone hydrogel and 31 hydrogel) contact lenses wearers were enrolled in the study. Their age ranged from 20 to 35 years (mean, SD 26.4 ± 4.6). The inclusion criteria were spherical prescription in the range of −0.25 to −6.00 DS (inclusive) and no greater than 0.75 DC of astigmatism. Subjects had to have been successfully wearing their lenses for a minimum of 8 h per day and 5 days per week and have at least 20/20 distance visual acuity in each eye. The exclusion criteria were any type of ocular or systemic disease, greater than 2.00 D of anisometropia, pregnancy, and previous corneal refractive surgery.
The study lenses were all made of Biofinity® comfilcon A silicone hydrogel material (CooperVision Inc.) in either a spherical lens design (CASD) or a multiple aspheric curve lens design (CADZO). Other than the front surface design, the two types of study lenses were identical (Table 1).
The subjects arrived at the respective clinics during the morning and were screened according to the inclusion and exclusion criteria. After eligibility confirmation, the subjects read and signed informed consent forms. The study lenses were fitted, either sphere or aspheric, on a randomized basis. The lens power for the first set of lenses was selected by determining the lowest minus power to give best visual acuity; the second set of lenses were prescribed at the same power as the first. AMF measurements were recorded without lenses for each eye, both at baseline (before study lenses were fitted) and again after subjects wore lenses for a reading task. AMF was measured within 1 min of removing the lenses.
Subjects completed a 10-minute lens-settling period before performing a 20-minute reading task on an iPhone 5 (Apple) at a viewing distance of 25 cm (Fig. 1). A standard text was displayed in Meirvo (font size 8), phone screen brightness was set by automatic adjustment mode, and ambient illumination was controlled at all sites. After a wash-out period of 1 day, AMF measurements were conducted with the second set of lenses using exactly the same procedure. In total, there were four sets of AMF measurements for each subject: Day 1 before and after the reading task, and Day 2 before and after the reading task.
Fig. 1Reading distance controls used for all subjects.
AMF measurements were conducted using a Speedy “i” series (Righton, Tokyo) Auto Refractometer in accommodation analyser mode. Speedy series is an infrared optometer with a spectral power calculation program, using the Short-time Fourier Transform method to analyse the non-stationary spectrum of accommodative micro-fluctuations. AMF was measured in the dominant eye first (monocular sighting dominance). AMF – caused by movement of the crystalline lens due to ciliary muscle oscillation during accommodation – was recorded as the dioptric change waveform when a subject viewed the fixation target for 20 s. For the AMF measurements, subjects were instructed to look clearly at the fixation target with minimal, quick blinks. The accommodative stimuli of the fixation targets were set from +0.50 D to −3.00 D in 0.50 D steps, giving eight accommodative stimuli.
The waveforms were analysed and the spectral power of accommodative micro-fluctuation was calculated as follows. Waveform noise caused by blinking was removed from the waveform, which was then fixed using cubic spline interpolation. Next, 8 s of waveform was extracted from the total 20 s of waveform, and the sample dots were increased from 250 to 1024 by cubic spline interpolation. Then, to simplify calculations, the waveform was shifted to make the average refractive power zero before using Hann window and Fast Fourier Transform to calculate the spectral power. This was then transferred to a logarithmic scale. Lastly, AMF high frequency component (HFC) was determined by integral calculus for the range 1–2.3 Hz.
For measurements at each fixation target, 11 HFCs were found by repeating the waveform analysis from the 1 s waveform through to the 11 s waveform. The 11 HFCs were found in order to compensate for missing data due to blinks or temporary eye closure during measurement. In the data analysis, HFC −1.00 D (fixation target at 100 cm), which represents the resting/steady sate of accommodation, was used because this state is the most sensitive to small changes in AMF-HFC.
The statistical analysis was undertaken for 68 subjects because of protocol deviations among nine subjects; the data of three subjects were lost (not recorded in the database) and incorrect lens powers were prescribed for six subjects. A paired t-test was used to determine the statistical significance of the difference between lens types for the mean change in AMF values from before and after the iPhone reading task.
3. Results
Among the 68 subjects who completed the study per protocol, the mean (±SD) change in the spectral power of AMF (at 1–2.3 Hz) after the reading task was 0.13 (±5.6) for CADZO and 2.25 (±5.5) for CASD. Table 2 summarizes the AMF values before and after the reading task, and Fig. 2 displays the changes in AMF. The difference between lens types in the change of AMF was statistically significant (P = 0.017).
Table 2Summary of AMF Results among 68 Per-Protocol Subjects.
Fig. 2Mean + SD change in high frequency component (HFC) of AMF (before and after reading on a smartphone) for two optical contact lens designs among 68 per-protocol subjects (P = 0.017).
The AMF response to a 20-min reading task differed significantly when subjects wore spherical and aspheric lens designs. The aspheric lens design resulted in a significantly smaller change in AMF than did the spherical lens design.
The findings suggest that the aspheric design (Digital Zone Optics) of the comfilcon A, Biofinity® Energys lens reduced the accommodative load on the eyes of subjects to a greater extent than did the spherical design of the Biofinity® sphere. Given the association between AMF and asthenopia – AMF is sometimes used as an objective measure of asthenopia –, Biofinity® Energys would be expected to reduce subjective symptoms of eye strain [
]. The only difference between the two lens types used in this study was their front-surface optical designs, showing that the aspheric design of Biofinity® Energys reduced the accommodative load presented to the ciliary muscles by the reading task.
A number of studies have used AMF as an objective measure of eye strain [
], including studies that investigated AMF associated with vision correction. In a randomized cross-over study, Kajita et al. compared AMF between wear of 2-weekly replacement Menicon DUO and ACUVUE® 2 (etafilcon A) contact lenses [
]. Nineteen subjects wore each test lens for two weeks with a 1-week wash-out between wear periods. Investigators measured the high-frequency component of AMF in the morning and in the early or late afternoon. Overall, AMF did not significantly change after wearing the lenses. Nonetheless, among a subset of seven subjects for whom measurements were made in the late afternoon, AMF was better with Menicon DUO than with ACUVUE® 2 lenses. Kajita et al. concluded that Menicon DUO lenses helped to relieve the accommodative strain caused by near work.
The current study compared changes in AMF after a reading task between contact lenses of different optical designs but identical material, diameter, and base curve. The fact that the lens materials were identical is important given that AMF may be induced by tear film instability [
]. Both Biofinity® Energys and Biofinity® sphere contact lenses feature Aquaform® Technology, which attracts and binds water throughout the lens.
The main limitation of this study is that the clinical significance of the results is unknown. Nonetheless, the study confirms that lens design can influence accommodative load during a near-vision task. Future studies should further examine the relationship between changes in AMF and symptoms of digital eye fatigue, such as tiredness. Additionally, future studies could include a longer follow-up in order to investigate how AMF changes over time and could examine AMF under real-world conditions, which has various tasks and viewing circumstances.
Lens selection should take digital lifestyle and complaints of eye strain into account, with an appropriate lens design being selected accordingly. Many cases of severe eye strain could be avoided by using vision correction appropriate for common viewing distances [
]. For example, eye strain can be prevented in the early stages of presbyopia with correction that alleviates the burden on ciliary muscles at the frequent viewing distance of approximately 1 m [
]. For those patients who frequently use digital devices and are experiencing eye strain, Biofinity® Energys may provide an alternative to spherical contact lenses by helping to ease accommodative effort.
5. Conclusion
This study shows that lens optical design can affect the accommodative micro-fluctuation (AMF) response that occurs when reading a digital device. Compared with the equivalent spherical design, Biofinity® Energys reduces the change in AMF that occurs due to reading a smartphone. This reduction in AMF indicates that Biofinity® Energys can help reduce stress to the ciliary muscle during digital device use. Contact lens patients who frequently use digital devices and are experiencing eye strain may benefit from switching their spherical lens designs for Biofinity® Energys.
Disclosure
Masayoshi Kajita is Tokyo Medical and Dental University Clinical Professor; Taku Muraoka is Executive Senior Consultant at CooperVision Japan; Gary Orsborn is Vice President of Global Professional & Clinical Affairs at CooperVision.
Funding
This work was supported by CooperVision Inc.
Acknowledgements
Thanks to Nathan Greenaway (Visioncare Research Ltd) for his help in preparing this manuscript.
References
Riva M.A.
Arpa C.
Gioco M.
Dante and asthenopia: a modern visual problem described during the middle ages.
30046-1&id=gr1.jpg){kind=link}
30046-1&id=gr2.jpg){kind=link}