Green’s Dictionary of Slang

(US) used of a personal inspection or eyewitness account.

1960		J. Brosnan Long Season 16: [A]nxious for an eyeball report of the student technician with the good hands and the high bust.
1984		J. Ellroy Because the Night 190: Lloyd waited, keeping a sustained eyeball fix on 4109.
1988		T. Harris Silence of the Lambs (1991) 108: The other vehicle, an ‘eyeball van’ with one-way glass and surveillance equipment.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 112: Eyeball witnesses ID’d them as driving a 1948 to 1950 Mercury coupe.
2002		Simon & Burns ‘The Wire’ Wire ser. 1 ep. 6 [TV script] ‘What would be enough?’ ‘Eyeball witness. Some kid of corroboration for what youre telling me’.