8721
PURPOSE : To introduce an image analysis of the cornea in photorefractive keratectomy ( PRK ) for preoperative and early postoperative determination of changes in the condition of the cornea .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
 Entities:  
Answer:
 None