Effect of Lithotomy Position on Optic Nerve Sheath Diameter

This study is looking at whether the position used during a common kidney stone procedure (lithotomy position, where legs are elevated) raises pressure around the optic nerve — potentially affecting eye health. Researchers will measure the nerve using ultrasound. **You may be eligible if...** - You are between 18 and 65 years old - You are scheduled for a kidney stone procedure called retrograde intrarenal surgery - You are alert and cooperative - Your health classification is ASA I or II (generally healthy or with mild systemic disease) **You may NOT be eligible if...** - Your BMI is over 30 - You have had prior brain or eye surgery - You are allergic to any medications used in the study Talk to your doctor to see if this trial is right for you.