Intraocular penetration of toxic substances

ABSTRACT

PURPOSE: The seriousness of ocular alkali burns has been linked to the rapidity with which the alkali enters the eye. The authors report the results of an experimental study on intraocular ammonia penetration. MATERIALS AND METHODS: 23 eyes of New Zealand albino rabbits were burned by applying for one minute 100 ul of a solution titrating 15.3 percent of ammonia. A pH meter probe was inserted into the anterior chamber beforehand to permit pH measurements every 5 seconds. Experiments were carried out after 1,3,5,10 and 30 minutes. The ammonia concentration was measured at the end of the experiment by puncturing the anterior chamber. RESULTS: The pH increased 1 to 3 minutes after applying ammonia on the cornea, reaching a maximum (mean) of 10 five to six minutes later, before an exponential decrease. After 30 minutes, the pH was always more than the physiological pH. The penetration ratio of ammonia through the cornea is about 11 percent. At 30 minutes, the concentration of ammonia is low. The pH observed differs from the calculated pH. DISCUSSION: The difference between observed and calculated pH indicates increases with an intervening plateau, showing the existence of two successive acid-base chemical reactions between ammonia and two types of acid. In addition, the amount of protein destroyed by ammonia can be calculated. CONCLUSIONS: These data show for the time the possibility of calculating the density of proteins destroyed in vivo by a base penetrating the anterior chamber. This opens the possibilty of interesting research work, because it is possible to relate the density of proteins destroyed in the eye to the pK of this base, and to forecast the potential danger of a base of biological tissues.(AU)