Long standing prone position could affect vision or optic nerve. To measure the optic nerve sheath diameter using ultrasound is quick and useful assessments of patients.

This study will look at the change of optic nerve sheath diameters of patients undergoing surgery in prone position

Inclusion Criteria:

• Patients undergoing surgery in prone position

Exclusion Criteria:

• Patients who did not agree to participate in the study
• Patients has ophthalmic diseases
• Patients has previous history of ophthalmic surgery.
• Patients has neurological disorders.
• Patients has history of head surgery.
• Severe anaphylactic allergy to ultrasound gel or Tegaderm

Patients undergoing prone position surgery in out institute.