PRK and Use of Night Vision Goggles

A study conducted by the Ophthalmology Service and the Center for Refractive Surgery at Walter Reed Army Medical Center, Washington, DC, shows that soldiers who have undergone photorefractive keratectomy (PRK) show no significant loss of visual acuity postoperatively and no change in best-corrected visual resolution using night vision goggles (NVGs). Uncorrected visual resolution was significantly enhanced compared with preoperative levels. These findings may translate into better function for soldiers who are unable to or choose not to use optical correction in operational environments.

In the nonrandomized, comparative self-controlled trial, researchers measured visual acuity with best optical correction preoperatively and 3 months postoperatively in 19 patients (38 eyes) of active-duty U.S. Army Special Forces soldiers who underwent PRK for myopia and astigmatism. They used acuity charts of various contrast (100, 10, 2.5, 1.25 percent). They assessed preoperative and postoperative (3-month) uncorrected and best-corrected visual resolutions through NVGs using a high-contrast tribar chart presented at four light levels (3.44 x 10^-3, 1.08 x 10^-3, 1.04 x 10^-4, 1.09 x 10^-5 foot-Lamberts) simulating a range of night sky conditions. Subjects were trained before testing.

Results showed no significant loss of visual acuity across a range of contrast levels 3 months postoperatively: Uncorrected visual acuity at the 3-month assessment was >/= 20/20 in 33 (86.8 percent) of 38 eyes. No eyes lost 2 or more lines of best spectacle-corrected visual acuity. Preoperative and 3-month postoperative best-corrected low-contrast acuity measurements showed no significant differences at all levels of resolution.

Researchers also observed no change in best-corrected NVG visual resolution postoperatively. Preoperative visual resolution through NVGs decreased systematically with decreasing night sky conditions, while visual acuities before PRK were reduced without optical correction. Postoperative visual performance with NVGs (without optical correction) equaled or exceeded performance preoperatively with best correction.

SOURCE: Subramanian PS, O'Kane B, Stefanik R, et al. Visual performance with night vision goggles after photorefractive keratectomy for myopia. Ophthalmol 2003;110(3):525-30.