Optimisation of corneal biomechanical characteristics in orthokeratology for myopia control

The rapid increase in myopia prevalence has escalated a wealth of research interest in the prevention mechanisms of myopia. Orthokeratology (ortho-k) is among the most promising approaches. A reluctance to employ this modality has been observed, owing to the selective treatment outcome and the long-term effects to the corneal tissue. This thesis investigates the attitudes of clinicians towards various myopia control interventions, including ortho-k within a cross-sectional internet-based survey; long-term effects of ortho-k lens wear on corneal biomechanical properties in myopic school-children over a two year period; short-term corneal biomechanical changes over the first 7 nights of lens wear; and the influence of factors (age, ethnicity, eye/body size and nutrition) on corneal biomechanical properties in healthy adults. The aim of this thesis is to aid a deeper understanding of the role of corneal biomechanical properties in ortho-k lens wear,specifically for myopia control. The findings within the thesis demonstrate that surveyed eye-care practitioners are aware of the scientific findings within the field of myopia control; two thirds would still prescribe single vision glasses to their patients, owing to a lack of clear guidelines and the selective treatment outcome. Results of the ortho-k studies suggest that the corneal biomechanical characteristics are affected by long term ortho-k wear, having a stabilising effect to the components of the anterior eye in progressing myopia. Short term ortho- k lens wear study reveals marked changes in corneal biomechanical parameters within the first seven nights of lens wear. Ortho-k itself and the anterior segment changes observed cannot explain all the variation in treatment response. The final study demonstrates the relationship between corneal biomechanical parameters and nutrition, ocular biometry and body size, suggesting that individual factors, although non-substantially, contribute towards the treatment outcome. It, is therefore, suggested to establish an internationally acknowledged guideline for myopia control. Further studies should be designed to understand the complex mechanisms underlying ortho-k in myopia control

A Surgical Cryoprobe for Targeted Transcorneal Freezing and Endothelial Cell Removal

PURPOSE: To examine the effects of transcorneal freezing using a new cryoprobe designed for corneal endothelial surgery. METHODS: A freezing console employing nitrous oxide as a cryogen was used to cool a series of different cryoprobe tip designs made of silver for high thermal conductivity. In vitro studies were conducted on 426 porcine corneas, followed by preliminary in vivo investigations on three rabbit corneas. RESULTS: The corneal epithelium was destroyed by transcorneal freezing, as expected; however, the epithelial basement membrane remained intact. Reproducible endothelial damage was optimally achieved using a 3.4 mm diameter cryoprobe with a concave tip profile. Stromal edema was seen in the pre-Descemet's area 24 hrs postfreeze injury, but this had been resolved by 10 days postfreeze. A normal collagen fibril structure was seen 1 month postfreeze, concurrent with endothelial cell repopulation. CONCLUSIONS: Transcorneal freezing induces transient posterior stromal edema and some residual deep stromal haze but leaves the epithelial basement membrane intact, which is likely to be important for corneal re-epithelialization. Localized destruction of the endothelial monolayer was achieved in a consistent manner with a 3.4 mm diameter/concave profile cryoprobe and represents a potentially useful approach to remove dysfunctional corneal endothelial cells from corneas with endothelial dysfunction

Global trends in myopia management attitudes and strategies in clinical practice

PURPOSE: Myopia is a global public health issue; however, no information exists as to how potential myopia retardation strategies are being adopted globally. METHODS: A self-administrated, internet-based questionnaire was distributed in six languages, through professional bodies to eye care practitioners globally. The questions examined: awareness of increasing myopia prevalence, perceived efficacy and adoption of available strategies, and reasons for not adopting specific strategies. RESULTS: Of the 971 respondents, concern was higher (median 9/10) in Asia than in any other continent (7/10, p<0.001) and they considered themselves more active in implementing myopia control strategies (8/10) than Australasia and Europe (7/10), with North (4/10) and South America (5/10) being least proactive (p<0.001). Orthokeratology was perceived to be the most effective method of myopia control, followed by increased time outdoors and pharmaceutical approaches, with under-correction and single vision spectacles felt to be the least effective (p<0.05). Although significant intra-regional differences existed, overall most practitioners 67.5 (±37.8)% prescribed single vision spectacles or contact lenses as the primary mode of correction for myopic patients. The main justifications for their reluctance to prescribe alternatives to single vision refractive corrections were increased cost (35.6%), inadequate information (33.3%) and the unpredictability of outcomes (28.2%). CONCLUSIONS: Regardless of practitioners' awareness of the efficacy of myopia control techniques, the vast majority still prescribe single vision interventions to young myopes. In view of the increasing prevalence of myopia and existing evidence for interventions to slow myopia progression, clear guidelines for myopia management need to be established

IMI : global trends in myopia management attitudes and strategies in clinical practice : 2022 update

PURPOSE. Surveys in 2015 and 2019 identified a high level of eye care practitioner concern/activity about myopia, but the majority still prescribed single vision interventions to young myopes. This research aimed to provide updated information. METHODS. A self-administered, internet-based questionnaire was distributed in 13 languages, through professional bodies to eye care practitioners globally. The questions examined awareness of increasing myopia prevalence, perceived efficacy and adoption of available strategies, and reasons for not adopting specific strategies. RESULTS. Of the 3195 respondents, practitioners’ concern about the increasing frequency of pediatric myopia in their practices differed between continents (P < 0.001), being significantly higher in Asia (9.0 ± 1.5 of 10) than other continents (range 7.7–8.2; P ≤ 0.001). Overall, combination therapy was perceived by practitioners to be the most effective method of myopia control, followed by orthokeratology and pharmaceutical approaches. The least effective perceived methods were single vision distance undercorrection, spectacles and contact lenses, as well as bifocal spectacles. Practitioners rated their activity in myopia control between (6.6 ± 2.9 in South America to 7.9 ± 1.2/2.2 in Australasia and Asia). Single-vision spectacles are still the most prescribed option for progressing young myopia (32.2%), but this has decreased since 2019, and myopia control spectacles (15.2%), myopia control contact lenses (8.7%) and combination therapy (4.0%) are growing in popularity. CONCLUSIONS. More practitioners across the globe are practicing myopia control, but there are still significant differences between and within continents. Practitioners reported that embracing myopia control enhanced patient loyalty, increasing practice revenue and improving job satisfaction