most of the existing molecules – including organic and inorganic. In April 2010 the CAS registered, in all, more than 61 million substances. Among these, more than 25,000 irritant and corrosive chemicals were identified as having the potential to cause burns [1].

In Europe, 100,204 commercial chemical substances have been recognized and numbered under EINECS (European INventory of Existing Commercial chemical Substances) by the European Chemical Bureau (ECB) System. Another 4,381 “new” substances are classifiedunderELINCSInformationSystem(European LIst of Notified Chemical Substances) since May 11, 1981. Among these, In Europe 1,230 chemical substances are officially identified as irritant or corrosive with Xi and C pictograms and risk sentences.

Among all the chemical products, the American EPA (Environmental Protection Agency) has estimated that there are approximately 100,000 chemicals in commercial use in the USA. So the same amount of identified irritant and corrosive could be expected to be found in the USA than in Europe.

Considering the high frequency of potential chemical risk and the wide diversity of the substances that might be involved, it is important to better understand the deep mechanisms of the chemical reactivity of irritants and corrosives on the eye. This will help to optimize the management of eye chemical projections. Besides, we have learned by experience that the rapidity and efficiency of the emergency decontamination are decisive parameters in order to prevent the development of potentially severe lesions and after-effects due to the chemical eye burn.

We will develop the following points:

1.The chemical agent, its nature, and the intensity of its reactivity

2.The mechanisms of the chemical burn during the contact between the aggressor and the eye

3.The practical conclusions for an optimal management of the eye chemical decontamination

intensity of this reactivity according to electronic rules involving either simple connections bonds (inductive effect) or double connections bonds (mesomeric effect).

Six elementary types of chemical reactivity are listed as follows:

•Acid–base reaction

•Reduction/oxidation (or redox)

•Chelation

•Addition

•Substitution

•Solvation

From a fundamental point of view, the strength of each of these reactions can be conceptualized on a scale of energy. This scale is defined by the reactional Dg, which is the free enthalpy.

This one, in practice, can be specifically declined for every type of elementary reactivity:

•The pK scale for acid–base reactions

•The potential scale for oxidants and reducing agents

•The complexation constant for chelating agents

•DG (the Gibbs function = reactional energy) for alkylating agents

•Partition coefficient for solvents

The energy scale is based on the notion of strength and weakness. There is a specific scale for each kind of reactivity. It is then essential to study what makes a molecule active or not and what are the parameters influencing the strength of reactivity of a molecule. The fine distinction between an irritant and a corrosive substance appeals to this principle of scale and energy level. The strength of reactivity directly conditions the speed of appearance of the reaction of the tissues, the constitution of more or less important lesions, and their more or less irreversible characteristics. We can so connect the chemical reactivity and the severeness of the chemical burn lesions.

3.2  The Chemical Agent

The chemical agent is made of a molecular skeleton on which are connected some functional groups responsible for the expression of various kinds of reactivity. The presence of modulator groups enables to vary the

3.2.1  Molecular Structure of an Irritant

or a Corrosive

Literally, a molecule is a compound of atoms connected to each other by various kinds of bonds.