To make the application of overnight orthokeratology lens in China become more appropriate and effective
With the increase of the pace of life and the pressure of the learning, the myopia rate of Chinese children has been presented a sharp rise in the recent years. Reducing and controlling the myopia progression has become a hot topic among researchers all over the world. [18–20] Overnight orthokeratology lens is an effective method in slowing down the progression of myopia. As an external object flatten the central portion of the cornea, the fitting of overnight orthokeratology lens needs the precise data of the ocular parameters of patients, especially for the juveniles who are in the period of growth and development. [21–26]
The main application market of contact lenses was for conveniently refractive correction and cosmetic reason. Therefore, the target customers of contact lens are designed for adults, the research and application of ocular parameters are also based on their data.[17] However, with the prevalence of myopia development, especially the high incidence rate of myopia in East Asia, Overnight orthokeratology lens has gradually become an effective means to control the development of myopia.[9, 27, 28]
In this study, statistical analysis was conducted in groups of different genders (males, 126 subjects with 252 eyes; females, 174 subjects with 348 eyes), simultaneously in age divided younger or equal to ten years old (180 subjects with 360 eyes) and older than ten years old (120 subjects with 240 eyes). No statistical significance was found in the above conditions.
Overnight orthokeratology lens, as a contact lens which were placed against the surface of the cornea, are worn at night and take off during the daytime. The distribution of these ocular parameters is benefit for the first best fitting of overnight orthokeratology lens. The axial elongation is an important factor for evaluating the progression of myopia, while the elongation of the AL does not mean the severity of myopia because there is also a physiological increase in adolescents.[29–32] Studying the distribution of AL in adolescents is helpful to understand the physiological axial growth.
The fitting of ortho-k lens requires accurate measurements of ocular parameters to achieve a proper lens fitting, the variation of ocular parameters was crucial for the practitioner to select the appropriate ortho-k lens. Most of the lenses now offered by manufacturers are based on the corneal profile of Caucasian adults, and repeated adjustments and lens fitting due to the improper lens would cost tremendous money and time.[9, 27, 30] Our study provides the distribution of ocular parameters in low to moderate myopic Chinese adolescents; therefore, it can provide useful information for contact lens design for Asian children.
To compare with previous studies of different race.
Although the distribution of the corneal parameters of Asians, Caucasians, Africans and Arabian have well manifested in the range of adults in the past 20 years (table 4), there was still a shortage of large sample aimed at children. The retrospective study found that Asians have smaller corneal diameter than Caucasians and Africans. The corneal diameter in our study is larger than previous study indicating there may be ocular parameters changes during the past decade. Previous studies demonstrate that Chinese children have thinner central corneal thickness than others, no conspicuous difference with the results of our study. The data of characteristics of the corneal endothelial cell density was similar with previous studies.
Table 4. The comparison of ocular parameters with previous studies of different race (see Additional table 4)