Visual Effects Accompanying TEPP

Pilots and others have long recognized the miosis which is frequently a consequence of spraying tetraethylpyrophosphate (TEPP) dust by aircraft. This effect of TEPP often occurs without symptoms referable to any part of the body except the eyes. Parathion (O,O-diethyl O-para-nitrophenyl thiophosphate) may also produce miosis, but it does so less frequently, and when it does the eye signs and symptoms are usually accompanied by general, systemic illness. The reason for the difference in clinical effect is not entirely clear but probably involves, among other things, the difference in molecular weight and vapor pressure of the two compounds. Various flying accidents have been blamed on the effects of organic phosphates on pilots.* Two complaints which are occasionally made by the pilots themselves involve an inability to judge distance and a sensation that things are darker than the time of day, the season, and the weather justify. A study in 1953 of the visual fields of 15 pilots and 2 other persons before, during, and after occupational exposure to TEPP did not reveal any meaningful change. However, only one pilot in this series was available for study of visual fields at a time when he actually had miosis. A much greater diversity of tests conducted during miosis seemed to be required to explain the reported disturbances of function. The dosage level in the eye required to contract the pupil to 1 mm. diameter was worked out in an intensive study of one volunteer at three dosage levels. The study served to establish techniques for conducting a battery of ophthalmological tests. Instillation of 1 drop (about 0.01 cc.) of 0.0125% TEPP and later of 1 drop of 0.05% TEPP produced no measurable effect. Instillation of 2 drops (about 0.02 cc.) of 0.05% TEPP produced slight miosis and a slight increase of near accommodation. Maximal miosis was produced by 2 drops of 0.1% TEPP, the pupils being fixed at 1 mm. diameter. A fourth drop did not cause further miosis or other observed change. Visual acuity (Snellen), peripheral fields (Ferree-Rand simplified