Refractive error has become a global public health problem in recent years, with a growing incidence [1,2,3]. By 2050, there are expected to be 4.758 billion people with myopia around the world, or 49.5% of the worldwide population [4]. China is one of the countries with a high prevalence of myopia. According to the 2018 national myopia survey, the myopia rate among children and adolescents aged 6 to 18 in China is 53.6%, with approximately 100 million sufferers. Myopia not only affects daily activities, academic performance, and professional advancement but also causes amblyopia, fundus lesions, and even blindness when it develops into high myopia [5,6,7,8]. The continued growth of the myopia population will have an impact on both social selection and economic development [9]. Therefore, extensive vision screening is an important task for the whole society, and the medical and health institutions play a key role in this respect [10,11,12,13,14,15]. Only through a large-scale refractive screening can we find high-risk children in advance, and primary prevention measures such as increasing outdoor time can be implemented timely [16,17,18,19]. Early screening of myopia children and subsequent clinical intervention with low concentration atropine, orthokeratology lenses, and other secondary preventive measures can effectively slow down the progression of myopia and lower the incidence of high myopia [20,21,22,23].

Cycloplegia retinoscopy (CR) is considered to be the gold standard method for measuring refractive error [24, 25], which inhibits ciliary muscle accommodation and detects real refractive error. However, there are some limitations to CR, including the fact that the operators must receive professional and technical clinical ophthalmology training, and patients may experience a number of temporary side effects, such as blurred vision and photophobia [26, 27]. Cycloplegic drops like tropicamide take 30–40 min to take effect, and parents and kids need longer or additional appointment times [28], so the method of CR is not suitable for large-scale screening. Autorefractors, including hand-held and table-top autorefractors, play an essential role in detecting refractive error through screening [29]. Previous studies have demonstrated that the majority of current autorefractors are reliable and accurate compared to subjective refraction [30, 31]. Although these devices may rapidly test and report refractive errors, they are heavy, non-portable, and easily affected by the accommodation of children and adolescents, the operation technology of the examiner, and the cooperation of the examinee [27].

At present, the common refractive screening instruments have the advantages of compactness, good portability, and fast measurement speed, such as the Welch Allyn SureSight Vision Screener, PlusoptiX Photoscreener, Retinomax Autorefractor, Spot Photoscreener, and more [32,33,34,35,36]. Even though numerous studies have found that most of them can be used for refractive screening, their accuracy is easily affected by the accommodation of children's eyes and the influence of the detection environment and distance [37, 38]. China has a sizable population but a relative lack of medical personnel and supplies. Automatic screening equipment can effectively improve the effectiveness of eye care [14]. Therefore, it is great significance to further improve the screening performance and detection efficiency of refractive screening instruments.

The new self-contained darkroom refractive screener (YD-SX-A, Guangxi Nanning Gardener Medical Instrument Co., Ltd., China) is a binocular photoscreener with built-in 1 m long cylindrical darkroom. The upper part is shaped to fit the features of a human face, while the lower portion includes a foundation that can be securely put on the ground. When it is time to move, it may be folded and placed in a trunk or backpack. Because it is battery powered, that is no need to plug it in when using it. The operation interface and test results can be displayed on the screen of an external tablet or mobile phone that is linked through WiFi and has the instrument-specific APP downloaded beforehand. The examinees need simply come close to the upper detection place, fully open their eyes during the detection to look at the infrared emission location at the bottom, and the binocular diopter can be measured in 2 to 5 s. The instrument will automatically detect three times and then display the average diopter value. The YD-SX-A’s dark room causes the pupil to enlarge during the detection of refractive error, and it used an infrared camera to take and analyze pictures of the red pupil reflex in order to assess the alignment of both eyes and calculate the refractive error. The diopter results are acquired by automatically measuring three times and obtaining the average value. It is similar with some photoscreener such as PlusoptiX Photoscreener, Spot Photoscreener, but the difference is that YD-SX-A has a fixed detection distance and dark room environment [32]. The YD-SX-A has the advantages of simple operation, convenience and cooperation, making it practical and appropriate for infants and children who find it difficult to cooperate with table-top autorefractors.

The purpose of this study was to compare refractive measurements taken in children and adolescents using the YD-SX-A, Topcon KR8800 and CR to evaluate the performance of the YD-SX-A in detecting refractive error.