Patent ID: 8835484

Claim:
A method of dying ophthalmic tissue for use in a surgical treatment or a diagnostic method comprising contacting said tissue with a contrast agent of Formula (I), wherein X 1 and X 2 are independently selected from 1 to 12 CH 2 units, one or more of which may be independently substituted by a carbonyl group, an oxygen atom, a sulfur atom, a cis- or trans-CH═CH— group, wherein a CH— unit may also be substituted by a nitrogen atom, an acetylenic C≡C— group, a divalent phenyl, pyridine, or thiophene radical, a divalent naphthalene radical, wherein one or two CH— groups may be substituted by nitrogen atoms, a divalent anthracene radical, wherein one or two CH— groups may be substituted by nitrogen atoms, and wherein up to 12 individual hydrogen atoms of the CH 2 units may each independently from each other, and also on the same C atom, be substituted by the halogens fluorine, chlorine, bromine, or iodine, or a cyano group, or by a linear alkyl chain with up to 18 C atoms, wherein 1 to 6 CH 2 units may each independently be substituted by a carbonyl group, an oxygen atom, a sulfur atom, a cis- or trans-CH═CH— group, wherein a CH— unit may also be substituted by a nitrogen atom, an acetylenic C≡C— group, a divalent phenyl, pyridine, or thiophene radical, a divalent naphthalene radical, wherein one or two CH— groups may be substituted by nitrogen atoms, or a divalent anthracene radical, wherein one or two CH— groups may be substituted by nitrogen atoms; R 1 and R 2 are independently selected from a carboxylic acid group (—COOH), a carboxylic acid ester group, a sulfonic acid group (—SO 3 H) or a halogen atom; R 3 , R 4 , R 5 and R 6 are independently selected from hydrogen and C 1 -C 6 alkyl; and A − represents an optional anion that is capable of balancing the formal charge of a positively charged nitrogen atom.