Considering even emmetropic eyes elongate, what are the limits of myopia control efficacy? This novel analysis explores the absolute axial elongation of treated and untreated myopes in the MiSight 3-year clinical trial in comparison to previously published models of myopic and emmetropic eye growth. The results indicate a potential limit to the short-term percentage efficacy of myopia control treatments.
Previous multi-ethnicity studies have shown ‘normal’ axial elongation in emmetropic children to be around 0.1mm / year. In this study, 700 Chinese schoolchildren with stable emmetropia showed 0.2mm per year axial elongation from age 7-11, which reduced with age and ceased at age 15. This appears higher than measured in Singaporean Chinese children in the SCORM study, 20 years ago.
Total spherical-like higher-order aberrations (HOA) increased by more than double in the distance-centred +2.50 Add compared to +1.50 Add, with total coma-like HOA increasing further. Since orthokeratology studies have reported an association between more change in HOAs and better myopia control efficacy, this could indicate a mechanism of action in multifocal contact lens myopia control.
Young adults wearing the spectacle-mounted Clouclip device to measure viewing behaviour and light exposure also kept an activity diary. Mean daily near work and outdoor time were subjectively reported at about 150% of the objectively measured hours. This indicates the value of objective measures in research, as well as for clinical education and behaviour modification tools in future.
A sample of slow and fast progressors in prior 24 month orthokeratology clinical trials were found to have the same baseline refraction and axial length. The slow progressors were older, and showed 0.5mm smaller treatment zone diameters (TZDs), but no difference in induced peripheral myopic shift. There was also no direct correlation between TZD and axial elongation, indicating an intriguing but not yet defined relationship.
Young adults fit with CooperVision Proclear multifocal contact lenses showed no loss of peripheral vision detection ability compared to single vision contact lenses. The near add was chosen to generate +0.50 or +1.00 of peripheral blur, confirmed by peripheral refraction measurement. This is a positive indication that fitting MFCLs in young wearers doesn’t impact peripheral visual performance.
Light-emitting glasses worn by young adults for 1-2 hours reduced axial length and increased choroidal thickness by around 20 microns compared to darkness. The study participants viewed a colour-muted television at 5m while indoors, and the changes regressed within 30 minutes. A future myopia treatment to increase ‘outdoor’ time?
After the 3-year MiSight 1 day clinical trial, the control group children were switched to MiSight. A ‘virtual control group’ mathematical model, previously published, was utilized to demonstrate a continued myopia control effect across six years, plus effectiveness of treatment for children who commenced wear at age 11-15 years.