Abstract
Progressive axial myopia is a developmental refractive eye condition predicted to become the next world-wide pandemic, with significant prevalence in far Eastern countries presently. Current myopia management interventions (MMI) (contact lenses (CLs) of various types (multifocal (MF); MiSight; OrthoK), and glasses lenses (Miyosmart; Stellest))are designed to reduce axial eye length growth and slow progression. In literature, the success rate with these interventions in reducing the progression reportedly ranges from a mean value of 20 to 79% (percentage reduction in SER/AL). As such, the exact mechanism, or factors determining intervention success likelihood remain unclear, thus this thesis investigates the effect of myopia, and its management interventions, on the oculomotor responses of the human eye.Current literature limits our understanding of the oculomotor responses of the eye when viewing through myopia management optical devices, due to un-natural conditions in which lab-based accommodation and oculomotor response experiments are conducted. Chapter 4 includes a series of experiments that verify various aspects of the equipment and set-up of a novel head mounted binocular recording device.
The dynamic accommodation response (AR) is utilised by living humans in everyday life. This accommodation step response allows humans to make fast accommodative movements when looking at various distances, ranging in various step sizes. In Chapter 5, a 2.75D step response was recorded whilst subjects viewed a Maltese cross target. This target alternated, with near-far and far-near step directions. This data was measured in myopes and emmetropes, when looking through single vision (SV) CLs and MFCLs. This experiment concluded that subjects appear to derive the defocus error required for accommodation control from elsewhere other than solely the distance zone of the MFCL. A reduced performance in response to abruptly changing vergence stimuli has been found, although this deterioration in dynamic performance is small and unlikely to have an impact on everyday visual tasks.
To further investigate the amount of near zone utilised by the eye in MFCL wear and its effect on the AR of the eye, Chapter 6 used pinhole (PH) apertures (3-6mm) to alter the amount of the various zones of the MFCL available for the eye to utilise when viewing a distance or near Maltese cross target. ARs, and microfluctuations of the AR were analysed finding no overall effect of increasing PH size on either type of AR. Myopic subjects exerted significantly less accommodation at near through MFCLs compared with emmetropes, with no such effect on microfluctuations.
Whilst there is a large amount of literature reporting on ARs in adults, there is limited insight into the ARs in the children who wear current MMIs, and whom experience a variation of success rates. To investigate, accommodation responses were measured in children with their worn and adapted MMI, and through SVCLs in Chapter 7. This data was obtained via autorefraction and dynamic retinoscopy (DR), as a means to investigate measurement method comparibility. Accommodation stimulus-response curves were 2generated to report ARs through MFCLs, MiSight and OrthoK. DR can be used as an alternative method to autorefraction when measuring retinal defocus at 4D. Measurements are in less agreement at further working distances (2D). Regardless of MMI type, the magnitude of the myopic defocus experience through the distance zone of each lens type is not dependent on viewing distance. Further, retinal defocus experienced through the near zone of the MMIs differs significantly with OK lenses experiencing the more protective myopic defocus through the near zone compared to MiSight lenses. No difference was found between any other MMI type. This suggests that wearing orthoK lenses and undertaking distance viewing may produce the most favourable conditions for reducing myopia progression.
Furthermore, light levels in Scottish classrooms, and naturalistic pupil diameters in Scottish school children were reported for the first time in Chapter 8. Classrooms in central Scotland are found to generally experience light levels ranging from 2580 to 58 lux (average: 566.03 ± 594.95) indoors and 104300 to 798 lux (average: 23751.55 ± 29279.89) is experienced outdoors during breaks. This is above recommended levels. Pupil diameters in Scottish children are largest indoors whilst distance viewing. With increasing age between 7 to 12 years, the pupil diameter decreases when indoors and during outdoors distance viewing tasks. The potential for children to utilise the transition and near zones of a myopia interventions is therefore greatest at younger ages.
| Date of Award | 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Sponsors | College of Optometrists |
| Supervisor | Mhairi Day (Supervisor), Dirk Seidel (Supervisor) & Lorraine Cameron (Supervisor) |