Effects of yellow optical filters on contrast sensitivity function of albino patients.

BACKGROUND: Yellow ophthalmic filters are often prescribed for albino patients in an effort to enhance visual performance. The effects of a moderate- and a high-excitation purity yellow filter on the contrast sensitivity function (CSF) of ten albino patients were investigated. Hue discrimination loss induced by each filter was also evaluated. METHODS: Three monocular CSF curves (best-corrected eye) were determined for each subject: one while viewing through a #3 Kodak Wratten filter, one through a #12 filter, and one used no filter. Panel D-15 color tests were administered to five albino patients viewing through each filter. RESULTS: Using an analysis of variance (ANOVA) and a Student-Newman-Keuls Analysis, no statistical difference at the 0.05 levels of confidence was found between using no filter, the #3 filter, or the #12 filter CSF curves. A statistically significant blue-yellow hue confusion was induced by the #12 filter. CONCLUSIONS: While neither filter was shown to enhance nor degrade the CSF among these subjects, a more extensive investigation may reveal that subtle but real contrast enhancement occurs with yellow filter use. High-purity filters should be avoided to minimize hue recognition losses.

Yellow lens effects upon visual acquisition performance.

Twenty subjects made a total of 400 threshold visual acquisitions of T-38 aircraft approaching from 9 miles out. Half of the acquisitions were made with the subjects wearing yellow ophthalmic filters, and the other half without filters. No overall statistically significant difference in acquisition performance due to the use of yellow filters was found.

Contact lens wear at altitude: subcontact lens bubble formation.

A concern in the past regarding contact lens wear in aviation has been the fear of subcontact lens bubble formation. Previous reports have documented the occurrence of bubbles with hard (PMMA) lenses. Reported here are the results of contact lens bubble studies with soft hydrophilic and rigid gas-permeable lenses. Testing was accomplished in hypobaric chambers and onboard USAF transport aircraft. Hypobaric chamber flights were of three types: high-altitude flights up to 7,620 m (25,000 ft); explosive rapid decompressions from 2,438.4 m (8,000 ft) to 7,620 m (25,000 ft); and 4-h flights at 3,048 m (10,000 ft). Flights aboard transport aircraft typically had cabin pressures equivalent to 1,524-2,438.4 m (5,000-8,000 ft), and ranged in duration from 3 to 10 h. For subjects wearing rigid gas-permeable lenses, central bubbles were detected in 2 of 10 eyes and occurred at altitudes greater than 6,096 m (20,000 ft). With soft contact lenses, bubble formation was detected in approximately 24% (22 of 92 eyes) of the eyes tested, sometimes occurring at altitudes as low as 1,828.8 m (6,000 ft). Soft lens bubbles were always located at the limbus and were without sequela to vision or corneal epithelial integrity. Bubbles under the rigid lenses were primarily central, with potential adverse effects on vision and the corneal epithelium.

Effect of positive acceleration (+Gz) on soft contact lens wear.

The effects of positive acceleration on soft contact lens wear were tested on a human centrifuge to +8 Gz. There were 11 subjects who participated in this study; 5 were myopic subjects fit with low-, medium-, and high-water-content spherical soft lenses; 3 were astigmatic subjects fit with various designs of toric soft lenses and 3 were emmetropic control subjects. As an additional control, the contact lens subjects were tested with spectacles for comparison. Video photography was used to monitor lens position during the centrifuge rides and visual acuity was checked at +1, +2, +4, +6, and +8 Gz with a reduced Snellen eye chart. Each lens type and control run was evaluated in straight-ahead, lateral, and vertical gaze. No visually significant decentration was noted for any of the lens types tested up to the maximum level of +8 Gz. Visual acuity was reduced at the higher +Gz levels for contact lenses, and spectacle trials, and with the emmetropic controls--all to similar levels. Contact lens wear did not produce any corneal insult due to the +Gz exposure.

The incidence of refractive anomalies in the USAF rated population.

A field survey was conducted to determine the percentage of U.S. Air Force pilots and navigators required to wear corrective lenses. A random sample survey stratified by major air commands (MAJCOMS) was designed to retrieve the data. Data requested included initial (entry) visual acuity and refractive error, and current visual acuity and prescription if glasses were required. Of 2,383 forms sent, 2,183 were returned completed. Analysis indicated that almost 20% of pilots and 50% of navigators are required to wear corrective lenses while flying. The percentages are rather consistent among MAJCOMS. Aircrew members who enter undergraduate pilot training with minus or plano refractive values are much more susceptible to develop myopia during their flying careers than those with plus refractive values.

Vertical prism disparity in aircraft windshields.

A current method of quantifying optical distortion in F/FB-111 aircraft windshields is by a technique of displacement grading. It has been hypothesized that varying magnitudes of displacement grading result in corresponding magnitudes of vertical prism disparity, potentially inducing binocular stress. In order to test this hypothesis, three F/FB-111 windshields of varying displacement grading values were evaluated for vertical prism disparity. The hypothesis was borne out by the results. If a binocular design specification for U.S. military aircraft windshields is appropriate, a maximum vertical prism disparity value would appear to be most meaningful.

Visual performance through a sample windshield segment of the B-1 aircraft.

The stereopsis performance of 16 subjects was measured on an automated Howard-Dolman apparatus and compared with their performance through a sample segment of a proposed B-1 aircraft windshield. Recognition visual acuity was determined for 15 subjects using a low-contrast Landolt C target viewed with and without the segment. When the task was performed through the windshield segment, a statistically significant loss in stereopsis resulted, but no significant loss in visual acuity.