Combined Atropine With Orthokeratology in Childhood Myopia Control (AOK) -A Randomized Controlled Trial

Overview

This study aims to compare effects in retardation of myopia progression of combined ortho-k and 0.01% atropine therapy with those of ortho-k alone.Myopia control methods mainly focus on optical and pharmaceutical interventions . Currently, overnight-wear orthokeratology (ortho-k), is used extensively in Hong Kong with approximately 50% retardation effect. Pharmaceutical methods have focused on the use of atropine eye drops to slow myopic progression.The use of 1% atropine was limited by the manifestation of side effects and rebound effect.However, both side effect and rebound effect was minimal with 0.01% atropine.It was suggested that 0.01% was the optimum concentration for controlling myopia.The mechanisms of neither ortho-k nor atropine in myopia control are fully understood.It is believed that ortho-k and atropine act via different mechanisms.It is possible that by combining these two methods, additional retardation of myopia progression could be achieved.

Although it is believed that myopia is the result of an interplay between genetic and environmental factors and its progression has been attributed to the lack of outdoor activities and intensive school work, myopia control methods mainly focus on optical and pharmaceutical interventions. Use of bifocal and multifocal lenses have been shown to be ineffective in myopia control. Specially designed soft contact lenses for myopia control have recently been launched, but their effectiveness has yet to be confirmed. Currently, overnight-wear orthokeratology (ortho-k), which involves reshaping the cornea by overnight wear allowing for improved, frequently unaided, vision during the day, is used extensively in Hong Kong. Approximately 50% retardation in axial length elongation was observed in studies of patients receiving ortho-k (LORIC study, 46%, ROMIO study,43%, and TO-SEE study, 52%). Pharmaceutical methods have focused on the use of atropine eye drops to slow myopic progression. The use of 1% atropine was first suggested in the 1990's, but its application was limited by the manifestation of side effects such as pupil dilatation and loss of accommodation. The effectiveness of lower concentrations (0.5%, 0.1% and 0.01%) have been evaluated in a recent five-year randomized clinical trial, where the authors reported that 0.01% atropine once daily was effective resulting in about 50% of spherical equivalent reduction. However, this was as a result of one year (3rd year) discontinuation of atropine in the five-year study. Rebound effect was minimal with 0.01% atropine and higher dosages were associated with more manifest rebound effects, which appeared to negate former myopia retardation effects. Only 24% of those receiving 0.01% progressed 0.50D or more after discontinuation for one year. By contrast, proportion of children progressed 0.50D or more in 0.5% and 0.1% groups were 59% and 68% respectively. Moreover, use of 0.01% atropine showed sustained myopia reduction with clinically negligible effects on pupil dilatation and loss of accommodation. The authors suggested the use of 0.01% as the optimum concentration for controlling myopia. The mechanisms of neither ortho-k nor atropine in myopia control are fully understood. It is believed that ortho-k and atropine act via different mechanisms, with ortho-k slowing myopia progression by reducing peripheral hyperopic defocus, while atropine exerts effects on anti-muscarinic receptors of the retina and sclera. However, some subjects respond poorly to either atropine or ortho-k, as demonstrated in clinical trials, suggesting that a single treatment may be not enough. It is possible that by combining these two methods, additional retardation of myopia progression could be achieved. In this randomized trial, we will explore the effectiveness of combination of ortho-k and atropine therapy, and evaluate additional effects by comparing the combination with ortho-k treatment alone.