Uptake of soft toric contact lenses
The use of soft toric contact lenses is widespread in a number of countries, including the United Kingdom but this is not a universal trend. Previous work has shown that around 45% of people require an astigmatic correction of 0.75DC (ie a clinically significant amount) in one or both eyes2 and when soft lens fits are scrutinised in the UK, the fitting rate is at about this level.3-5
This is not the case worldwide4 and it seems that these variations are unlikely to be attributable to ethnic differences in the level of astigmatism.6,7 A range of factors could account for reduced rates of soft toric lens prescribing, including the clinical competence, educational background and communication skills of the prescribing practitioner.
One historic belief – that extra chair time is needed for fitting with modern soft toric lenses compared with spherical lenses – has recently been addressed and rebutted.8 However, another possibility is the potential impact of the higher cost of soft toric vs soft spherical contact lenses,9 and how this might influence practitioner prescribing and patient purchasing. In short, are soft toric contact lenses ‘worth it’ and how can this be evaluated?
Willingness to Pay
One method to assist understanding the likelihood of a price of a product to act as a barrier (or an incentive) to its adoption is to measure the Willingness to Pay (WTP) of a consumer for that product. This is an especially useful measure. It provides a monetary estimate of how beneficial an item is to a person, and can be applied to leisure pursuits, consumer items, healthcare products and indeed a wide range of products and services.
One of its advantages is that it allows human experiences to be placed on the same scale, a monetary one, which is generally understandable by all. If someone believes that the enjoyment of a day at a nearby beach with their family is worth £10 or £100 or £1,000 to them, then it is possible to compare this person to others or indeed the value of a day at the local beach compared to the experience of visiting a more distant town or a short trip overseas.
Although WTP is used widely in many fields, it has been used only sparingly in optometry and related areas. It has been adopted previously to determine the utility of spectacles, especially in developing nations.10-13 Estimating WTP is potentially especially useful to understand the benefits of different contact lens designs, including soft toric lenses, particularly in people with low and moderate levels of astigmatism.
This is because while it might be expected an astigmat prefers to be corrected with toric lenses than with spheres, the experiential differences may be difficult for the wearer to explain in conventional terms, especially in a quantitative manner.
A two-part study was designed to investigate this rationale, where first low astigmats scored the relative performance of spherical and toric contact lenses in terms of comfort and vision, followed by a detailed WTP experiment on this same clinical group and then online with a much larger group of contact lens wearers.
Clinical study
The norm in studies of WTP is to capture online responses from thousands of people to allow for detailed and sophisticated analysis; however, a critical part of the work is to accurately describe the performance of the item under evaluation.
This is not straightforward in contact lens studies because describing differences between lenses is difficult and in some cases, not well understood, so to help accurately describe relative lens performance in low and moderate astigmats, a clinical study was first executed to capture this, ahead of economics evaluations on both the small clinical group and a much wider, online cohort.
In the initial clinical study, subjects aged 18-45 years with refractive astigmatism in both eyes between -0.75DC and -1.50DC, a spherical refractive correction of -0.50DS to -6.50DS and with no noteworthy ophthalmic history were recruited and consented. Subjects were fitted with pairs of Biofinity (a spherical lens design) and Biofinity toric lenses (both CooperVision), in random order.
Subjects with no previous contact lens experience were fitted with clariti 1 day lenses (CooperVision) for one hour before the main study lenses were fitted, to allow for a short period of contact lens adaptation. After the pair of main study lenses were applied, 10 minutes of settling was allowed and then lens fit and visual acuity (high and low contrast) were evaluated.
To allow for a range of short-term experience with the applied lenses to be evaluated, subjects then spent a few minutes browsing a mobile phone (a near task), browsing web pages on a desktop computer (an intermediate task) and walking around the building while looking at signage, including a car number plate at 20m (a distance task).
After each of these experiences, subjects graded their vision and vision stability from 0 to 100 with reference to printed visual analogue scales. Ocular comfort was also assessed in the same way. After evaluation of the first lens pair was complete, the second lens pair was applied and the process was repeated.
Twenty-seven subjects (14 females and 13 males, with a mean ± standard deviation age of 28.7 ± 7.9 years) successfully completed this study. Fourteen of the subjects presented with a refractive cylindrical component in their right eye of -0.75 DC, six with -1.00DC, one with -1.25DC and six subjects with -1.50DC.
All final lens fits were considered acceptable in terms of centration, movement and coverage, and all end-of-visit biomicroscopy findings were within clinical normal limits. For the Biofinity toric lens, 96% of lenses settled within 10° of the ideal orientation
position.
Figure 1: LogMAR visual acuity showed better performance for the Biofinity toric lens compared with Biofinity sphere, for high and low contrast measures both monocularly and binocularly (n = 27). These ‘box and whisker’ plots show the distribution of the measurements recorded for visual acuity with each individual value shown as a small dot. The shaded boxes show the inter-quartile range with the upper and lower edges of boxes indicating the 75th centile and 25th centile of the dataset, respectively. The lines (whiskers) extended above and below the boxes show the full range of the measured results, and the horizontal line in the box is the median result.
Mean low and high contrast visual acuity scores are presented in figure 1. All measures were statistically significantly better with the Biofinity toric lens (all p < 0.01), with the magnitude of improvement between 0.6 and 1.1 lines of logMAR acuity.
Typical contact lens wearers would be expected to notice this degree of visual acuity difference between the two lenses because this
magnitude of improvement is similar to or greater than the test-retest variability for letter-by-letter visual acuity measurement reported to be 0.7 lines,14 0.9 lines15 and 1.0 lines16 by previous researchers.
All subjective scores for vision (table 1) numerically favoured the Biofinity toric lens. Differences for the distance (walking) task were statistically significant, and the difference between the lenses for vision stability for the intermediate task (desktop web browsing) approached the p = 0.05 threshold.
It is interesting to note that the degree of subjective improvement in vision reported with the toric lens diminished as the task distance changed from distance to intermediate to near. This seems likely to be due to the reduced need for optimum visual acuity with nearer tasks as day-to-day vision requirements are typically less demanding at near, assuming an appropriate optical correction.
That is, the angular size of a typical near object (eg a 12-point letter on a computer screen) is significantly larger than a challenging distance object (eg a car number plate at 20m). This information is likely to be helpful to eye care professionals discussing the potential benefits of a proper astigmatic correction to low and moderate astigmats.
There was no difference between the two lenses for comfort (Biofinity: 79.8 ± 19.9, Biofinity toric: 81.6 ± 16.5, F = 0.2 p = 0.68). The relative comfort of spherical and toric lenses has been considered previously and older studies tended to favour comfort with a spherical lens.17,18
However, a more recent report suggests otherwise19 and the current study also fails to support the notion that soft toric lenses are less comfortable than their spherical equivalents.
Economics study
In the first part of the economics study, subjects who had completed the clinical study were again asked about the comfort and vision they experienced for the two lens types studied; this time this was evaluated on a five-point Likert scale, with possible answers ranging from ‘much worse than spherical lenses’ to ‘much better than spherical lenses’, with the option of a neutral (‘about the same’) midpoint.
A clear majority (80% vs 12%) of subjects reported that vision with the toric lens was ‘better’ or ‘much better’ than the spherical lens (table 2) (χ2 = 12.6, p = 0.0004). Comfort preferences for the two lens types were similar (48% vs. 32%) (χ2 = 0.8, p = 0.37) (table 2).
Subjects were then asked a number of price questions to first determine how much they paid (existing wearers) or would pay (non-wearers) for a month’s supply of daily disposable spherical lenses. This was found to be a mean of £22.92, ranging from a low of £12.50 to a high of £37 across the group.
A ‘stated preference discrete choice experiment’, which is commonly used in WTP work to efficiently and accurately determine how much people will pay for an item or service, was then performed.
Essentially, the subject was presented with a range of scenarios, which varied in terms of lens comfort and vision, to determine how much less or more they would pay for a month’s supply of daily disposable soft toric lenses compared to a month’s supply of daily disposable spherical contact lenses.
Given the small number of subjects in the clinical sample, a relatively simple statistical model (a binary logit model) was estimated. Results indicated that, under the scenario where subjects found that toric lenses provided better vision and similar comfort to spherical lenses ¬ the typical response ¬ the WTP a monthly premium was an extra £13.33 [with a 95% confidence limit from £4.70 to £21.89].
In the scenario where toric lenses provided better vision but worse comfort ¬ a minority response ¬ the WTP monthly premium reduced to £4.10 [£-0.69, £8.88].
Having conducted this analysis on the clinical study subjects, an online survey was then initiated in which 413 UK contact lens wearers, of whom 264 were astigmatic, were evaluated.
In this part of the work, no contact lenses were fitted so the findings of the clinical study were outlined to the online subjects to help provide a context for the work. This group was again asked for their monthly spend on daily disposable spherical contact lenses; this was £28.37.
Another discrete choice experiment was then conducted, and established that the WTP monthly premium for soft toric lenses compared with soft spherical lenses was £16.47 [£14.20, £18.74] if vision was better and comfort was similar, the typical scenario. With better vision and worse comfort the WTP a premium fell to £11.51 [£8.64, £14.38].
The much larger online sample size had the benefit of allowing more complex econometric modelling and a ‘random parameters logit model’ was estimated on the dataset.
This analysis found that the WTP for better vision and similar comfort was a monthly premium of £15.42 [£13.86, £16.99]. With better vision but worse comfort the willingness to pay monthly premium fell to £12.65 [£10.60, £14.69].
Overall, then, three lots of WTP data were available: one estimate from the small clinical group and two measures from the larger online survey, derived from different statistical approaches. The monthly WTP premiums were between £13 and £16 when toric lens vision was better and comfort similar to spherical lenses, as we found to be generally the case.
These are the equivalent to premiums of 54 to 58% when considering the reported monthly payments for daily disposable spherical contact lenses. Interestingly, this increase in the monthly price that wearers would pay for their improved visual experience is rather greater than the price premium that is generally charged for daily disposable torics compared with spheres.
FIGURE 2: Premiums charged to wearers for various daily disposable toric contact lenses compared to their spherical equivalents for three major UK multiple suppliers. The median values of 28-33% (short red lines) are lower than the 54% to 58% (long red line) which study subjects reported they would be willing to pay for the benefits of a toric correction. Note that the two obvious outliers reflect a large increase in cost for the toric version of one lens brand for two of the suppliers. In each case, this is due to a significantly lower cost for the spherical lens compared to other spherical brands offered by the supplier
A review of the website prices for three major UK contact lens suppliers shows median premiums for toric lenses of 28%, 31% and 33% (figure 2). In other words, the clinical benefits offered to a typical astigmatic contact lens wearer are greater with toric lenses than that which would be expected by a consumer paying this increase in price. In short, it does seem that soft toric daily disposable contact lenses are indeed ‘worth it’.
Conclusions
This work is the first to have considered this economic approach to describing the wearer benefits of different contact lens designs in a low and moderate astigmatic group.1 It has demonstrated that better visual acuity was achieved with the Biofinity toric lens compared with the Biofinity spherical lens, and this was supported by improved subjective distance vision.
Comfort was similar for the two lens designs. Contact lens wearers report that the monetary benefit of toric lenses to them is much greater than the typical extra cost charged, and this insight should provide further confidence to eye care professionals to prescribe soft toric contact lenses to their patients with low or medium levels of astigmatism.
- Ash Morgan and John Whitehead are professors in the Department of Economics at Appalachian State University in Boone, North Carolina. Philip Morgan is professor of optometry at the University of Manchester.
Declaration
The clinical study, economic modelling and article were sponsored by CooperVision Inc.
References
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