In modern society, the number of people who become blind due to the removal of visual organs is rapidly increasing due to trauma to the eye, tumors, or diseases. Recently, a type of artificial implant has been designed to restore the shape of the eye to enable normal daily activities and social function. These eye implants involve an artificial eye. They are used to repair cosmetic problems or restore the natural appearance of patients. Currently, there is no objective and standardized technique, and the process can be expensive and time consuming. Therefore, many people with visual impairment can experience social discomfort because they do not wear an artificial eye due to economic costs, or because they wear low-quality artificial eyes or artificial eyes that are not suitable for them. To reduce the time and cost of the manufacturing process, studies on artificial eye fabrication using advanced equipment, such as 3D printers have been actively conducted. In 2013, the fripp design company in the UK worked with Manchester Metropolitan University to successfully produce artificial eyes of color with 3D printing, reducing both the time and money required for the fabrication process. Design work on the shape, color, and blood vessel distribution is required to make an artificial eye using this automated equipment. Therefore, there is a need to develop a standardization model before automated artificial eyes can be produced on a wider scale. Currently, most artificial eyes are made by hand, but standardization of iris color is essential to make artificial eyes using advanced equipment, such as 3D printers.
Since the iris is the part of the eye that is colored, visual judgment is an important step in making an artificial eye. The iris consists of layers, including the anterior border layer, stroma, sphincter and dilator muscle fibers, and the posterior pigment epithelium. The anterior layer and stroma are the most important parts in terms of the color of the eye [
1]. Wielgus and Sarna [
2] showed that the color of the iris results from the amount of melanin and that brown eyes have 40% more melanin than other eye colors. The iris has several structural layers, and the iris color and pattern are generated according to the shape of the pigment and the structures of each layer [
3]. Attempts to classify iris colors date back to 1843 in the work by Petrequin [
4]. Thereafter, a genetic approach was used to increase the number of iris color categories from 3 to 8 [
56]. The first attempt to standardize artificial eyes by classifying iris colors was made by Rudolf Martin [
7], who made 16 glass eyes. However, lightness, chroma, hue, and color attributes were not defined, so there were limitations in the use of the original iris color classification as a diagnostic kit. In a previous study in the Netherlands, 24 iris colors were classified using 67 eye images [
8]. In addition, two skilled separators studied iris photography to develop a classification method based on 5 iris colors [
9]. The 5 colors of the iris are blue, gray, green, light brown, and brown. Therefore, this 5 color system cannot be applied to the classification of the iris color of Koreans, whose eyes are homogeneously colored brown. Research has been conducted in the United States to digitize and analyze iris color information obtained from photographs [
10]. In previous studies [
1112], we investigated the distribution of iris colors by comparing the color of a sample with the color of the standard color table developed by Kim et al. [
11], who investigated the relationship between iris coloration and skin color by analyzing photographs of patients with skin-related diseases. Park [
13] introduced an iridescent coloration table for the manufacture of artificial eye using 9.03YR, 2.06Y, and lightness 3.11, based on iris colorimetry of Koreans [
14]. It is known that iris formation tissues change through a random process for the first year or two after birth so that each person has a unique iris pattern, while the iris pattern is maintained after these early years in most individuals. The purpose of this study was to classify the color and pattern of the iris in Koreans using a colorimetric photographic technique based on the measurement of iris color using digital image analysis to obtain iris images of Korean eyes.