Refractive changes during 72-hour exposure to high altitude after refractive surgery

Area of Science:

• Ophthalmology
• Corneal Surgery
• High-Altitude Physiology

Background:

• Refractive surgery, including radial keratotomy (RK) and photorefractive keratectomy (PRK), alters corneal biomechanics.
• High-altitude environments present unique physiological challenges, including hypoxia, which may affect ocular tissues.

Purpose of the Study:

• To prospectively analyze refractive and pachymetric changes in patients who have undergone RK and PRK during high-altitude exposure.
• To compare these changes with those in healthy myopic individuals.

Main Methods:

• Prospective study measuring manifest refraction, cycloplegic refraction, keratometry, video keratography, and pachymetry.
• Measurements taken at sea level, during three consecutive days at 14,100 feet, and one week after return to sea level.
• Included subjects who underwent RK (11 eyes), PRK (12 eyes), and controls with myopia (17 eyes).

Main Results:

• Radial keratotomy (RK) patients showed a significant, progressive hyperopic shift (+1.52 +/- 1.01 diopters by day 3) and decreased keratometry at high altitude.
• No significant refractive changes were observed in healthy myopic subjects or those who had PRK.
• All groups exhibited significant peripheral corneal thickening by day 3, which resolved upon return to sea level.

Conclusions:

• Seventy-two-hour high-altitude exposure induces a significant, progressive, and reversible hyperopic shift in RK patients.
• Hypothesized mechanism involves increased corneal hydration at RK incision sites due to hypoxia, leading to central flattening.
• PRK patients and myopic controls are not susceptible to this altitude-induced refractive shift.