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Flat Out
Getting ready to start practicing myopia management flat out? Here is a good start. Sarah McCullough and colleagues from the University of Ulster in the UK have developed a risk indicator for myopia onset and progression called PreMO. Knowing if and when to start with myopia treatment is one of the most challenging decisions to make in clinical practice. They developed two risk indicators: one for kids who are assessed for myopia at the age of 6-8 years (group 1) and one for kids 9-10 years old (group 2). After entering the age, practitioners need to know the parental history of myopia: none, one parent or two parents being myopic allocates either 0, 2 or 3 'risk points' to the indicator. Next up is cycloplegic refraction: if this is greater than +1.00D in group 1, no risk points are added; for +0.75-1.00D, there are 2 risk points added; and for less than +0.75D, 3 points are added. A similar system is available for group 2, but with different calculations. Finally, axial length (AXL) is taken into account: for group 1 kids, an AXL between 22.94 and 23.11mm adds 1 risk point, 23.12 to 23.18mm adds 2 risk points and 23.19mm or greater adds 3 risk points to the equation. Once the points are totaled, the scoring system puts these kids in the little/no-risk group (total score 0), low-risk (1-3 points), moderate-risk (4-6 points) or high-risk group (7-9 points scored). This, then, is linked to a likelihood of becoming myopic (at what age) and the suggested follow-up schedule (2-year, 1-year or 6-month interval) and advice for a myopia strategy. Flat out a good start on myopia management. But there is more: on the flatness of the cornea. See the next item.
Corneal Shape
Busted Flat
We live and breathe corneal shape in our (specialty) contact lens practices. But the link between flat corneas and axial length may be a relatively new one for some. The literature indicates that as axial length increases, the cornea tends to become flatter. Flatter corneas don’t necessarily mean longer eyes, but a flat cornea coupled with a low-hyperopic refractive error would suggest a longer eye. The mentioned PreMO indicator uses this in conjunction with cycloplegic refraction. If AXL cannot be measured, the Ulster investigators propose using a table linking average k-value of the cornea to cycloplegic refraction. Flatter eyes typically have higher risk point scores with the same refractive values in this table. For instance, a 7.7mm corneal curvature with a refraction between zero and +0.25D in the 6-8-year-old group will add 3 risk points to the total count. The rationale behind this is that flatter corneas have less refracting properties and the focal point is further away. This matches with longer eyes - e.g., longer AXLs - for a given refractive error. Measuring AXL will always be more precise, but using flatness of the cornea seems a good 'busted flat' option as an alternative, according to the investigators.
Multifocal Rigid Corneal Lenses
Adding it Up in the Zone
Muteb Alanazi et al evaluated the performance of four experimental multifocal rigid corneal lens designs and their impact on visual function in young adults. Seventeen young adults enrolled in the study, and each participant was randomly assigned to wear two of the four multifocal designs. The four lenses had various distance zone diameters (DZ) and different additions (add): design A (DZ 1.5mm/add 3.0D), B (DZ 1.5 mm/add 1.5D), C (DZ 3.0mm/add 3.0D) and D (DZ 3.0mm/add 1.5 D). Distance and near visual acuities were not significantly affected with the four designs, but the contrast sensitivity was significantly lower in design A across all measured spatial frequencies. No significant effect was observed on accommodation measured at 33cm. The authors concluded that three of the investigated multifocal lens designs preserve satisfactory visual performance; the lens design A with the higher add (3.0D) and smaller center zone diameter (1.5mm) had a negative impact on the visual performance. This contributes to evolving a better understanding of optics in multifocal lenses for both presbyopia and for myopia control purposes.
Keratoconus
Rigid Corneal Lens Research
This study aimed to assess the outcomes of treatment with aspherical and spherical multi-curve corneal lenses with flat curves in the peripheral zone for patients with keratoconus for whom vision could not be corrected with glasses, soft lenses or spherical rigid corneal lenses. Retrospectively, 78 eyes with aspherical-curve lenses and 17 eyes with multi-curve lenses were evaluated. Best-corrected visual acuities (BCVAs) significantly improved from 0.42 logMAR to 0.06 logMAR after wearing either form of lens. The Amsler-Krumeich classification showed that aspherical-curve lenses were commonly used for patients with stage 2 keratoconus, and multi-curve rigid corneal lenses were commonly used for stage 4 patients. The BCVAs were worse when the disease stage was more severe (stages 3 and 4) regardless of lens type. The mean base curve of the lenses was steeper in multi-curve lenses than in aspherical-curve lenses. The duration of lens wear significantly improved with the lenses used in this study, and corneal/conjunctival conditions of the eye improved. This study from Japan suggests that a flat peripheral curve design with aspherical-curve and multi-curve rigid lenses could be useful for patients with keratoconus, and it seems to imply that there is still room for improvement in terms of eye health, comfort and vision with rigid corneal lenses. The industry as a whole should not shy away from future research and development in the corneal lens modality.
Ocular Disease & Specialty Contact Lenses
Meibomian Glands in Sclerals
Investigators from Spain and Portugal validated an algorithm on the visibility of meibomian gland images obtained with a fundus camera. With this, they assessed the changes in meibomian glands in scleral lens wearers during one year of wear. Infrared meibography was obtained from the upper eyelid using the fundus camera. Ocular symptoms decreased with scleral lens wear statistically significantly during the scleral lens wearing period, but no significant differences were found in gland dropout percentage and gland visibility metrics. In other words, scleral lens wear appears to not adversely affect meibomian gland dropout and visibility (while that has been reported in other lens modalities, including soft and corneal rigid lenses). A previous study from Spain and Portugal looked at the influence of scleral lenses on the physiology of the eye: differences between inferior and superior bulbar conjunctiva goblet cells in scleral lens wear were investigated, but here too they found no differences in goblet cell density and in mucin cloud amplitude in the samples taken from the superior and inferior conjunctival areas. Also, they found the scleral lens wearing time to not affect the density and secretion of goblet cells. Although more studies are needed to confirm such findings, it is important to note that these 'negative' effects are important knowledge when assessing and managing scleral wearers a clinical setting.
Scleral Lenses & Scuba Diving
Call to Partake in a Patient Survey
Visser Contact Lens Practice and the Diving Alert Network (DAN) are conducting a research project to investigate scleral lens wear under scuba diving conditions. Currently, daily disposable soft lenses are the first choice to wear, but gas-permeable scleral lenses while diving are being used increasingly worldwide. How these lenses perform under scuba diving conditions has not been investigated to date, though, and the questions of whether scleral lenses are safe to use while diving and provide clear underwater vision remain unanswered. For this research, we are looking for scleral lens wearers who are involved in the act of scuba diving with scleral lenses, and we ask them to complete a questionnaire about their experiences. For this reason, this is the final call to reach out to specialty lens practitioners and ask them to approach scleral lens wearers who can partake in the questionnaire via one of the following two links below. Thank you kindly for your participation.
Conferences
International Agenda
I-site is an educational newsletter that is distributed on a monthly basis and provides an update on rigid gas permeable-related topics (scientific research, case reports and other publications worldwide). I-site is objective and non-political. Disclosure: I-site's editor Eef van der Worp, optometrist PhD FAAO FBCLA FIACLE FSLS, receives educational grants from a number of industry partners but is not related to any specific company.