Ophthalic

Ophthalic is a historical or less common term with two main senses. In ophthalmology, it is an archaic adjective meaning relating to the eye; modern medical usage generally prefers ophthalmic to describe eye-related conditions, drugs, or procedures. The term can still appear in older texts or in certain chemical nomenclature contexts, where it may cause confusion with ophthalmic.

In chemistry, ophthalic has been used to refer to the ortho isomer of phthalic acid, that is, ortho-phthalic acid (also called o-phthalic acid). This is benzene-1,2-dicarboxylic acid, with the two carboxyl groups adjacent on the ring. The meta and para isomers are known as isophthalic and terephthalic acids, respectively. Historically, derivatives of ophthalic acid were described using the same prefix, but modern nomenclature prefers ortho-, meta-, and para- designations. The corresponding anhydride of the ortho isomer is commonly called phthalic anhydride in contemporary usage, though older literature may refer to it as ophthalic anhydride. Phthalic anhydride is a major industrial chemical used in the production of alkyd resins, plasticizers, and certain polyesters.

Overall, while ophthalic appears in some chemical and older medical writings, it is largely superseded by ortho-phthalic for the acid and by ophthalmic or related terms for eye-related matters. Modern references typically use ortho-phthalic acid and phthalic anhydride, aligning with current systematic naming and industry practice.