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Visual performance with night vision goggles after photorefractive keratectomy for myopia
Prem S Subramanian1, Barbara O'Kane, Raymond Stefanik
1Ophthalmology Service, Walter Reed Army Medical Center, Washington, DC.
Objective:
To evaluate visual performance and resolution through night vision goggles (NVG) before and after photorefractive keratectomy (PRK).
Design:
Nonrandomized, comparative (self-controlled) trial.
Participants:
Nineteen patients (38 eyes) of active-duty US Army Special Forces soldiers.
Intervention:
PRK for myopia and astigmatism.
Main Outcome Measures:
Visual acuity with best optical correction was measured preoperatively and postoperatively (3 months) using acuity charts of various contrast (100%, 10%, 2.5%, 1.25%). Preoperative and postoperative (3 month) uncorrected and best-corrected visual resolutions through NVGs were assessed 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:
Uncorrected visual acuity at the 3-month postoperative assessment was greater than or equal to 20/20 in 33 of 38 (86.8%) 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. Preoperative visual resolution through NVGs decreased systematically with decreasing night sky condition. 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.
Conclusions:
This prospective case series provides data on the safety and efficacy of PRK with respect to visual performance under night sky conditions using NVGs. There was no significant loss of visual acuity across a range of contrast levels 3 months postoperatively. There was no change in best-corrected NVG visual resolution postoperatively, whereas uncorrected visual resolution was significantly enhanced compared with preoperative levels. This improvement may translate into better function for soldiers who are unable to or choose not to use optical correction in operational environments.