Question: What components of a diagnostic glaucoma evaluation are separately billable from the E/M service? Alaska Subscriber Answer: A typical diagnostic examination for glaucoma includes measuring visual acuity, checking the intraocular pressure, gonioscopy, pupil dilation, visual field examination, and optic nerve photography (taking fundus photographs). Of these typical components of a glaucoma exam, gonioscopy, 92020 ( Some carriers only allow visual field to be billed once every six months, but this varies from carrier to carrier. Be sure to consult your carrier's local medical review policies on the frequency of billing these diagnostic tests before assuming you should report them separately.