UPSC IES eyesight requirements for distant vision are:

• Minimum acceptable vision in better eye: 6/9
• No specific mention of the vision requirement for the weaker eye

Based on the information provided (vision in better eye 6/6), you seem to meet the criteria for the better eye. However, there is no clear official guidance on the minimum acceptable vision for the weaker eye.

• Even if you meet the minimum requirements, the medical board might conduct a further assessment to determine your fitness for the Indian Engineering Services based on your vision in both eyes.
  
  
• Good depth perception and binocular vision are crucial for many engineering fields.
  
  https://competition.careers360.com/exams/upsc-ies-iss
  
  I hope it helps!