In early glaucoma if there is no loss of visual function, can that mean that any loss in vision is not noticed by the patient in daily activities?

Gradual adjustment: Open angle glaucoma is a wasting disease of the optic nerves, usually associated with elevated intraocular pressure. The earliest changes of glaucomatous optic neuropathy include altered color vision and reduced contrast sensitivity, which may not interfere with your activities of daily living in the same way visual field loss and visual acuity loss do. Reduce your eye pressure with medication.

Depends: Early manifestations of glaucoma involve structural changes in the optic nerve without visual field loss. This so called "pre-perimetric" disease indicates no visual filed loss, therefore your visual field function (perimetry) is tested as "normal". You would not notice loss of your visual field. In fact, by the time a patient notices glaucomatous field loss, there is approx. 30-50% nerve damage.