External ocular hyperemia: a quantifiable indicator of spacecraft air quality

Eye irritation consistently ranks as a top astronaut complaint but is difficult to measure. Exposure to internal air pollution hypothetically disrupts the eye's tear film, thereby exposing the crewmembers' conjunctivae to the irritating effects of the recirculated, contaminant-laden atmosphere of the space vehicle. Causes elude engineers and toxicologists, who report that measured irritants remain below established Spacecraft Maximum Allowable Concentrations. Lack of objective ocular endpoints stymies efforts to identify etiologies.

Computers offer a practical means of analyzing ocular hyperemia in space.

We use computer analysis to quantify redness and blood vessels of digitized images of bulbar conjunctivae in near real time. Custom software masks artifacts, lids and lashes for each photographic or telemedicine ocular image, Algorithms then generate semi-independent measurements of hyperemia. Computed difference scores between 34 pairs of images were compared with subjective difference scores as voted on by a panel of ophthalmology residents.

Objective data were reliably extracted from ocular images and significantly correlated (r = 0.583, p < 0.05) with subjective scores.

This ground-based methodology generates accurate and reliable ocular endpoint data without mass, volume, or power penalty. To assist in identifying and eliminating onboard ocular irritants, these objective data can be regressed against independent variables such as mission elapsed time, subjective astronaut complaints, levels of chemical and electromagnetic contaminants, nephthelometric and barothermal data. As missions lengthen, sensitive tools such as hyperemia quantification will become increasingly important for assessing and optimizing spacecraft environments.