Medical Investigations for Optometrists

Optometrists and ophthalmologists are often drawn to the apparent certainty of a blood test result or scan report. However investigations should be used thoughtfully, to confirm a diagnosis already suspected from the history and examination, occasionally to exclude rare but serious conditions or to help grade a condition. Unnecessary investigations can cause problems, not least unjustified anxiety and cost.
Diplopia has many causes, some of which require systemic investigation. An acute third cranial nerve palsy associated with pain and pupil involvement has to be assumed to be due to an intracranial aneurysm until a scan of the head is able to prove otherwise. Any isolated cranial nerve palsy may be due to giant cell arteritis. An interesting scenario is that of a sixth cranial nerve palsy as a ‘false localizing sign’ of raised intracranial pressure, something to consider especially if there is bilateral optic disc swelling. Another cause of diplopia that merits urgent investigation is thyroid eye disease with optic nerve compromise.
Isolated iritis does not need investigated, but uveitis should prompt a search for systemic associations if it is bilateral, severe, unusual, intermediate, posterior. For example both sarcoidosis and tuberculosis can manifest as uveitis, both having characteristic chest x-ray changes.
There are many causes of optic disc swelling. Giant cell arteritis (GCA) should never be missed, and two blood tests can be used to confirm the suspicion of GCA (erythrocyte sedimentation rate and C-reactive protein). Optic neuritis raises interesting issues about whether to request an MRI head, as it may be associated with multiple sclerosis.
Systemic investigations however can be very simple: monitoring blood glucose and blood pressure in patients with diabetes mellitus have a direct visual benefit in the long term. Optometrists and medics need to learn from each other about what is best for our patients.