Usually the optometrist is basing their opinion on automated perimetry. They should send you a copy of the visual field printout. Look to see if it is neurological (e.g., a hemianopia obeying the midline in each eye) or glaucomatous (usually arcuate – arcing around the centre of the plot). Make sure there is no obvious cause for the defect; e.g., a previous occipital infarct or a retinal scar. If the optician is querying glaucoma then there should be supporting features such as raised IOP and optic disc changes. Patients should generally be referred routinely. If the patient has a bitemporal hemianopia, referral should be soon via letter as they may have a pituitary compression.