A chemical burn can be conceived only between two chemical entities in interaction with each other, one acting as the “donor” the other one as the “acceptor.” It is the strength of the corrosive aggressor that affects the weakness of its biochemical target, until it consumes it completely. Then, the aggressor attacks the species of hardly superior energy level and so on until exhaustion of its own concentration (Fig. 3.58).

For example, a strong acid can only act on a weak base. If the base was stronger than the acid, the base would react by consuming the acid. An acid of given energy level (pK) is going to consume all the bases of weaker energy level (pK of a bigger value) beginning with the most remote level. Lobes represent the concentration involved by the aggressor on one hand and by the potential biochemical targets on the other hand (Fig. 3.59).

For a corrosive attack of the cornea, the biological targets will be among others the residues of the amino acids of the tissues proteins.

In summary, in order to understand the mechanism of chemical burns, it is necessary to be able to integrate all the previously detailed data, the interaction of which is summed up in the following plan (Fig. 3.60).

The general structure of a molecule is, most of the time, carbon. It can be considered as a main structure

The energy

Fig. 3.60  Structure and function relationship

on which are “connected” one or several functional groups. These groups are responsible for the type of chemical reactivity of the substance: acid, basic, oxidizing, reducing.

The level of expression of the intensity of this reactivity can be increased or decreased by one or several atoms or groups of atoms called “modulators.”

3.4.3  Key Parameters of Chemical Burns

Some of these fundamental notions will be also summed up in Chap. 6 under the more applied perspective of the pathophysiological mechanisms of chemical eye burns.

In the case of total consumption of the acid

Consumed base

Conjugated base of the attacking acid

pK of the attacking

acid Acid

Fig. 3.59  Donor–acceptor

Conjugated acid of attacked bases

Donor entity

3.4.3.1  Danger Resulting of the Nature

of the Involved Chemical

Solid Form

During an eye projection of a solid chemical, there is a double effect:

•Physical aggression, which is translated by an erosion of the surface of the cornea

•Chemical aggression, which is translated by a cellular necrosis

The following experiment illustrates this problem. It shows the time that is necessary for the dissolution of a soda pellet in water during the simulation of a simple wash (with a 150 mL/min debit). These observations show that it takes 2 min and 30 s so that the soda pellet dissolves completely during a continuous wash with the excitement of a stirring magnet. Without stirring, it takes 3 min and 30 s. Knowing that some solid particles dissolve more or less quickly, it will then be necessary to prolong the wash and to examine attentively the conjunctival sacs and the surface of the cornea with a slitlamp to make sure that any particle was well eliminated.

The pH curve shows a weak evolution. It’s the same with the temperature curve (Fig. 3.61).

Viscosity

The viscosity is responsible for a covering effect, which makes the simple passive wash more difficult, because the product sticks on the contact area (Figs. 3.62 and 3.63).

Washing solution (500 mL a 150 mL/min)

Substance to be tested

(0.1 mL) Watch glass

Substance carried away by the washing flood

Waste container

Fig. 3.62  Viscosity measurement schema

Water T°(°C) (no stirring)

21

Time (s)