International eye news

In recent years, the incidence rate of myopia, especially high myopia, has risen significantly. It has become a major public health problem in the world. In East Asia, children's incidence rate is as high as 60-90%[1-3]. The younger the initial onset age of myopia, the higher the risk of blindness such as glaucoma, choroidal atrophy and retinal detachment. Therefore, it is urgent to prevent and delay the progression of myopia. A large number of studies have shown that overnight wearing orthokeratology lenses (OK lenses) can effectively delay the progression of myopia [4-8]. Professor Takahiro Hiraoka, from Tsukuba University, Ibaraki Prefecture, Japan, shared with us the five-year follow-up results of orthokeratology in adults and children at the 16th International Conference on ophthalmology and the 16th International Conference on Optometry (cooc2016) In an interview with international eye news, Professor Hiraoka analyzed the long-term clinical observation of orthokeratology.

Summary of long-term follow-up results

In order to study the effect of overnight orthokeratology on delaying axial elongation in myopic children, Professor Takahiro Hiraoka conducted a prospective study on myopic children. A total of 59 myopic children were included in the OK lens group and the control group with frame lens correction respectively. There was no significant difference in baseline data between the two groups. The axial length was measured regularly. After 5 years of follow-up, the axial length was 0.99 ± 0.47mm in the OK group and 1.41 ± 0.68mm in the control group (P = 0.0236). There were significant differences between the two groups in the first year (P = 0.0002), the second year (P = 0.0476) and the third year (P = 0.0385), but there was no significant difference in the fourth year (P = 0.0938) and the fifth year (P = 0.8633). No serious complications were found during the follow-up period. The results of five years follow-up showed that orthokeratology could significantly inhibit axial elongation in myopic children. [7] Professor Takahiro Hiraoka has also applied orthokeratology in adults. Through long-term follow-up observation, it is found that the results are very good in adults and children, with good safety and effectiveness. Orthokeratology can effectively delay the progress of myopia [4]. The satisfaction of the patients was investigated. The patients' satisfaction score ranged from 0 (not satisfied) to 10 (very satisfied), and the average score was 7.8 ± 1.8, with higher satisfaction. The better uncorrected visual acuity after treatment, the higher the satisfaction; the higher the myopia degree before treatment, the lower the satisfaction [8].

According to Professor Takahiro Hiraoka, about seven years ago, the Japanese government approved the use of orthokeratology lenses. At that time, the Japanese corneal contact lens Association developed clinical guidelines for orthokeratology. The Association recommended that adults older than 20 years old should use orthokeratology lenses. Until now, Japanese clinicians do not often regulate the use of orthokeratology lenses for children. In Japan, half of the people who use orthokeratology lenses are adults and half are children.

Orthokeratology lens can effectively delay the progression of myopia, and we can see from the literature that low dose atropine is also very promising for myopia control. We do not have data on the use of low-dose atropine, so we can not directly compare the results of the two. In Japan, a prospective study on low concentration atropine is being conducted, mainly for children, and a multi center randomized controlled study is conducted by seven universities.

Research on visual quality

Professor Takahiro Hiraoka has conducted an in-depth study on the visual quality of overnight orthokeratology. In order to study the influence of ocular optical factors on axial length of children wearing orthokeratology lenses overnight for myopia correction, 59 children aged 7-12 years were selected. The axial length and wavefront aberrations at baseline and 1 year after wearing orthokeratology lens were measured. The results showed that the axial length increased from 24.20 mm to 24.43 mm after 1 year. Multiple linear regression showed that the axial extension had the highest correlation with coma It has correlation with C20, spherical aberration, second-order phase difference and total high-order phase difference. It shows that the asymmetric corneal morphology, rather than the central and radial symmetry, has a certain effect on delaying the axial elongation, indicating that the inhibitory effect of orthokeratology lens is through mechanical action rather than reducing peripheral hyperopia defocus [6]. When the degree of myopia correction is higher, the decrease of contrast sensitivity is more significant, and this effect is caused by the increase of higher-order difference [9]. When the orthokeratology lens was 0.85 ± 0.51 mm off center, it was followed up for 3 months after wearing overnight. The results showed that coma increased, spherical aberration increased and contrast sensitivity decreased. At the same time, the contrast sensitivity was also related to the degree of myopia correction, spherical aberration and coma. Multivariate analysis showed that the degree of off center was the only effective explanation for the change of contrast sensitivity. Therefore, the off center induction therapy of orthokeratology will lead to the decrease of contrast sensitivity, which indicates the importance of centering of orthokeratology lens for good visual quality [10].

Prevention and treatment of complications

Professor Takahiro Hiraoka said that the application of orthokeratology lens is generally safe and effective, with few complications. The most common complication is corneal infection. Especially for children, we need to pay attention to it. The study shows that wearing orthokeratology glasses overnight will weaken the corneal perception, which is not related to the degree of myopia correction. Although there is no clinically significant perceptual change, doctors need to consider this factor [11]. When prescribing orthokeratology lens, if the myopia degree reaches - 5D, - 6D or higher, especially when prescribing for children, close follow-up, early detection of complications and corresponding treatment are needed.