Beyond 20/20: new clinical methods to quantify vision performance.

OBJECTIVE: To describe the design, the sensitivity, and the application of new methods to quantify visual performance. METHODS: The super vision test-night vision goggle (SVT-NVG) is a new clinical letter chart that measures high- and low-contrast vision under daytime and simulated night conditions. The cone contrast test (CCT) is a computer-based color test that readily diagnoses type and severity of color deficiency. RESULTS: The SVT-NVG reveals subtle decrements from normal not detected by standard visual acuity. The CCT shows 100% sensitivity for the detection of hereditary red or green color deficiency and reveals acquired deficiency as an early sign of disease. CONCLUSIONS: The SVT-NVG and CCT provide rapid, sensitive indices of color and spatial vision potentially linkable to real-world operational demands.

Rapid quantification of color vision: the cone contrast test.

PURPOSE: To describe the design, specificity, and sensitivity of the cone contrast test (CCT), a computer-based, cone-specific (L, M, S) contrast sensitivity test for diagnosing type and severity of color vision deficiency (CVD). METHODS: The CCT presents a randomized series of colored letters visible only to L, M or S cones in decreasing steps of cone contrast to determine L, M, and S letter-recognition thresholds. Sensitivity and specificity were determined by retrospective comparison of CCT scores to anomaloscope and pseudoisochromatic plate (PIP) results in 1446 applicants for pilot training. RESULTS: CVD was detected in 49 (3.4%) of 1446 applicants with hereditary red-green (protan or deutan) CVD detected in 47 (3.5%) of 1359 men and blue-yellow (tritan) in 2 of 1446. In agreement with the anomaloscope, the CCT showed 100% sensitivity for detection and categorization of CVD (40 deutan, 7 protan, 2 tritan). PIP testing showed lower sensitivity (80% detected; 20% missed) due in part to the applicant's prior experience and/or pretest preparation. CCT specificity for confirming normal color vision was 100% for L and M cone tests and 99.8% for S cones. CONCLUSIONS: The CCT has sensitivity and specificity comparable to anomaloscope testing and exceeds PIP sensitivity in practiced observers. The CCT provides a rapid (6 minutes), clinically expedient, measure of color vision for quantifying normal color performance, diagnosing type and severity of hereditary deficiency, and detection of acquired sensitivity loss due to ocular, neurologic, and/or systemic disease, as well as injury and physiological stressors, such as altitude and fatigue.

Permanent grounding of a USAF pilot following photorefractive keratectomy.

INTRODUCTION: Photorefractive keratectomy (PRK) has been extensively studied in the literature and its potential application in aircrew has not gone unnoticed. Complication rates following corneal refractive surgery (CRS), including PRK and laser in-situ keratomileusis (LASIK), remain low, with most patients achieving improved uncorrected visual acuity and reduced spectacle dependence. Overall, predictability, low complication rates, high rate of success, stability, and safety have all been cited as instrumental in the adoption of PRK in aviators. Consequently, the U.S. Air Force (USAF) approved PRK for aviators in August 2000. However, quality of vision outcomes following CRS remain a concern given the unique visual performance requirements in military aircrew, especially in austere operational environments. CASE REPORT: This paper will present a recent case of steroid-induced ocular hypertension that is believed to have precipitated non-arteritic anterior ischemic optic neuropathy (NA-AION) associated with reduced visual performance following PRK that resulted in the first permanent grounding of a USAF pilot following CRS. DISCUSSION: CRS has radically widened the aircrew applicant pool and has decreased spectacle dependence in war-fighters. Despite the low-risk profile of modern CRS, this case demonstrates the potential for poor outcomes from such elective surgery. Understanding these rare, but potentially devastating complications and the unique aeromedical risk factors in aircrew is paramount when considering elective vision-enhancing surgery.

Corrective lens use and refractive error among United States Air Force aircrew.

Corrective lens use by military aviators is an important consideration in the design of head-mounted equipment. The United States Air Force (USAF) has periodically monitored lens use by aviators; however, it has been over a decade since the last study. We provide an update on the prevalence of corrective lenses and refractive error among USAF aircrew based on eyeglass orders processed through the Spectacle Request Transmission System (SRTS). Currently, 41% of active duty USAF pilots and 54% of other aircrew require corrective lenses to perform flight duties. Refractive errors are characterized by low to moderate levels of myopia with a mean spherical equivalent power of -1.01 diopters (D) for pilots and -1.68 D for others. Contact lenses, and more recently refractive surgery, reduce the number of aircrew that must rely on spectacles when flying; however, spectacle compatibility remains an important consideration in the cockpit.

Using the Freiburg Acuity and Contrast Test to measure visual performance in USAF personnel after PRK.

PURPOSE: Photorefractive keratectomy (PRK) may be an alternative to spectacle and contact lens wear for United States Air Force (USAF) aircrew and may offer some distinct advantages in operational situations. However, any residual corneal haze or scar formation from PRK could exacerbate the disabling effects of a bright glare source on a complex visual task. The USAF recently completed a longitudinal clinical evaluation of the long-term effects of PRK on visual performance, including the experiment described herein. METHODS: After baseline data were collected, 20 nonflying active duty USAF personnel underwent PRK. Visual performance was then measured at 6, 12, and 24 months after PRK. Visual acuity (VA) and contrast sensitivity (CS) data were collected by using the Freiburg Acuity and Contrast Test (FrACT), with the subject viewing half of the runs through a polycarbonate windscreen. Experimental runs were completed under 3 glare conditions: no glare source and with either a broadband or a green laser (532-nm) glare annulus (luminance approximately 6090 cd/m) surrounding the Landolt C stimulus. RESULTS: Systematic effects of PRK on VA relative to baseline were not identified. However, VA was almost 2 full Snellen lines worse with the laser glare source in place versus the broadband glare source. A significant drop-off was observed in CS performance after PRK under conditions of no glare and broadband glare; this was the case both with and without the windscreen. As with VA, laser glare disrupted CS performance significantly and more than broadband glare did. CONCLUSIONS: PRK does not appear to have affected VA, but the changes in CS might represent a true decline in visual performance. The greater disruptive effects from laser versus broadband glare may be a result of increased masking from coherent spatial noise (speckle) surrounding the laser stimulus.

Intraocular lens and corneal status following aircraft ejection by a USAF aviator.

Prior to 1967, military aviators who developed visually significant cataracts that affected visual performance were grounded. Those that ultimately required surgical removal were permanently grounded because of significant optical effects post-operatively. With the advent of contact lenses, a limited number of aircrew were returned to the cockpit because of improved optical factors provided by contacts post-cataract surgery. However, development of the intraocular lens (IOL) in the 1970s marked a major technological breakthrough that provided the potential to restore post-cataract surgical vision to near normal conditions. This case report is the first known occurrence of ejection from a high performance militaryaircraft by an aviator with an IOL. The success and stability of the IOL through this event provided additional clinical and operational information relative to the overall USAF experience with certain types of IOL approved for use in USAF aircrew. The aviator also sustained unexpected corneal foreign bodies due to the canopy fragmentation system.