SoftSpecialEdition is a quarterly newsletter FOR HEALTH CARE PROVIDERS that gives independent updates from the international literature on soft specialty lens-related topics. View as Webpage
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This marks the 50th edition of the Soft Special Edition newsletter and the 50th column in the 'world-wide-vision' series. As an informal and arbitrary tradition, in each decimal column, as the editor of the newsletter, I try to reflect on specialty soft lens fitting. In line with that: let’s have a chat about soft lens fitting. In fact, let’s have a ChatGPT about soft lens fitting. At the world conference of the international association of contact lens educators (WC4 IACLE) in Birmingham), recently, the lecture about 'how do we fit soft lenses' and 'how do we teach this to our students' stirred up some serious discussion. To be quite frank, it is not an easy task. If we try to explain the 'central-k and base curve' route, the students frequently tell us 'that doesn't make sense' and that it doesn't add up (quite literally). Well...these students may be smarter than we think, as they are right: it doesn't make sense and it doesn't add up. So where do we stand with soft lens fitting education? I decided to ask 'the oracle of the internet': ChatGPT. He/she/it knows everything right? Well...spoiler alert: not in this case. No matter how much I kept asking, pleading or begging to provide a basic rule for soft lens fitting, it kept telling me that 'the soft lens need to align with the ocular surface' and 'the eye care practitioner needs to determine which soft lens is most suitable for the eye'...but there was a complete absence on the 'how'. It kept telling me how the lenses can/should be applied to the eye, and how important lens care and hygiene are. Yes, dear Chat, we know that. But how on earth do we 'fit' our lenses?! See more via the link below.
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Many eye care practitioners (ECPs) use soft contact lenses as an option for myopia progression reduction in children. But what do we know about the power profiles of these lenses? Are there any differences, or are the all the same? A study performed at the University of Salento (Italy) aimed at reporting the differences in power profile (on-label/off-label) of the most common soft lenses used for myopia control to give ECPs potentially more insight into what they are fitting to children in daily practice. The power profiles of the eight lenses analyzed show interesting characteristics. First, the optical profiles indeed vary substantially among the different designs. From an educational standpoint, the eight lenses analyzed can be assigned into four main profile categories: multiconcentric, multifocal, EDOF and torus. Category 1 is the fundamenal multiconcentric category, which has sharp power changes in three rings of power surrounding the central distance zone (such as the MiSight); cateogy 2 is the ‘classic’ multifocal design, with a center-distance zone (such as Biofinity CD, Proclear CD & BYO MC); category 3 is the extended depth of focus, or EDOF, with catenary optics, such as the Bloom/NaturalVue multifocal or non-monotonic/aperiodic optics such as the 1 Day Pure EDOF/Mylo. And then there is the new kid on the block (category 4): the “torus” design (Abiliti). If a lens in a certain soft lens category does not provide satisfactory myopia management results, switching to another of the four categories as a theoretical consideration makes sense rather than trying another lens in the same category. |
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Tony Hough from the United Kingdom at the last Global Specialty Lens Symposium also presented a poster on this topic to specify the characteristic power profile of MiSight, NaturalVue and medium-add SEED EDOF soft contact lenses. The power profiles of lenses with labelled powers of -1.00D to -5.00D in 0.50D steps in each of the products were measured using a Rotlex Contest instrument. Five independent measurements were taken for each of three lenses in each of the nine labeled powers (135 independent measurements per product). This study too found that based on the results of this work, the medium- and long-term outcomes for myopia management using the various products would not be similar. Additionally, Hough determined that the quality of vision with all three products was inferior to single-vision minus-powered soft lenses. |
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BCR, OAD, SAG & Temperature |
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The mentioned Salento study did two other things: it looked at sagittal height (SAG) values among the eight multifocal lenses for myopia management that were measured, and it looked at the influence of temperature on lens parameters. The lenses tested demonstrated considerable differences in SAG values. Considering the measurement at 20°C, the highest SAG value was the 1 Day Pure EDOF 8.4, and the lowest was the Proclear CD 8.7 (delta-SAG 221µm). At 35°C, all the lenses presented a reduction of SAG compared with their SAG at 20°C. The highest value at 35°C was the 1 Day Pure EDOF 8.4, and the lowest was the Biofinity CD 8.6 (delta-SAG 307µm). As stated in the opening column, base curve is of limited value; the new Abiliti lens, with a labelled 'steep' base curve of 7.9, had an ordinary SAG value in the mid-range. It was interesting to note that all lenses showed a reduction in mean overal diameter (OAD) and base curve when going to 35°C (eye temperature compared to 20°C—e.g., soft lenses 'shrink' on the eye going from room temperature to eye temperature. This temperature change also induced changes in power profiles in some of the lenses tested, with possible effects on lens performance. The column 'Make It Count' in Contact Lens Spectrum (May 2023) by Kevin Chan from Treehouse Eyes, also anticipates on 'the how' of soft lens selection for myopia management.
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Impact of Dual-Focus Lenses on Accommodation
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How do soft multifocal lens options for myopia management work? That is still not fully understood. To study the impact of dual-focus soft contact lenses for myopia control on the dynamics of the accommodative response and facility, this study from Spain investigated 24 young adult myopes who were fitted with dual-focus soft lenses for myopia control (MiSight) and with single-vision soft contact lenses (Proclear). The study reported greater lags of accommodation with the MiSight lenses than with the Proclear lenses at near distances (40cm and 20cm), whereas a higher variability of accommodation was observed with the dual-focus than with the single-vision lenses at 500cm, 40cm, and 20cm. In conclusion, greater accommodative lags were observed at near, and a higher variability of accommodation was observed at near and far distances, when wearing the dual-focus lenses; also, the accommodative facility was quantitatively and qualitatively affected by the use of these dual-focus lenses. |
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Brett O'Connor in a Contact Lens Spectrum article tackles astigmatism in myopia management, from orthokeratology to soft lens options. Correcting astigmatism in myopia management may prove to be pivotal to the effectiveness of the therapy. Prescribing a spherical multifocal lens in addition to cylinder-correcting glasses worn over the contact lenses is considered a last resort by the author, as many soft toric lenses for myopia management are on the market now. For a full overview of availability, see the poster presented at the BCLA, in which different soft lens options are covered based on modality (daily disposable, monthly or quarterly) and on availability as a toric option. Four of the eight lenses offer a toric option; in essence, none in the daily disposable group, partial availability in the monthly replacement group and full availability in the custom-made/quarterly-replacement category (without limits).
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The Burden of Astigmatism |
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Apart from multifocal options (for different applications), toric lenses remain the biggest obstcle and opportunity in contact lens practice. A systematic literature review in Optometry & Vision Science (open access) provides an overview of this issue in a very comprehensive paper. The literature search yielded 6804 citations, of which 125 met the inclusion criteria (epidemiology, 68; patient burden, 60; economic burden, 6). Astigmatism prevalence in the general population varied from 8% to 62%, with higher rates in individuals 70 years or older. The prevalence of with-the-rule astigmatism was higher in individuals 40 years or younger, whereas rates of against-the-rule and oblique astigmatism increased with age. Astigmatic patients experienced decreased vision quality, increased glare (53% to 77%), haloes (28% to 80%), night-time driving difficulties (66%), falls, and spectacle dependence (45% to 85%). Astigmatic patients performed vision-related tasks slower (1D, 9% slower; 2D, 29% slower) and made more errors (1D, 38% more errors; 2D, 37% more errors) compared with fully corrected individuals. In conclusion, uncorrected astigmatism decreases patients' vision-related quality of life, decreases productivity among working-age adults, and poses an economic burden on patients and their families, the authors state. |
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Soft Toric Lenses for Digital Device Users
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Global dependence on digital devices is only growing. The average number of digital devices per person is expected to increase from 2.4 in 2018 to 3.6 this year. The type of digital device use also matters; tasks with increased cognitive demand are linked to decreased blink rate, and studies have demonstrated reduced blink frequency and blink amplitude associated with dry eye symptoms in digital device users. Digital device use is also associated with visual complaints, eye strain, burning, blurred vision, irritation, and meibomian gland dysfunction. A study evaluated both objective and subjective digital visual performance and comfort during near tasks in patients who had low-to-moderate astigmatism (–0.75D to –1.50D of astigmatism). They were fit randomly with either spherical or toric contact lenses. With toric contact lenses, automated visual acuity and visual acuity at near in both high and low contrast improved by 3 to 4 letters. Additionally, iPad reading speed increased. Patients with toric lenses also had improved subjective vision on the NAVQ and enhanced comfort on the CLDEQ-8. In summary: compared to spherical contact lenses, toric contact lenses improve comfort as well as objective and subjective visual performance with digital devices and other near tasks. In the April edition on the same platform and by the same author, the question of which diagnostic toric lens to select was raised, looking at sagittal height values as a potentially helpful tool.
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