During the operation on Jonas, the neurosurgeon is wearing only protective goggles over her eyes and she is always standing fully upright. In delicate surgery, such as that on Jonas, the surgeon would have been much closer and would have had magnifying lenses, looking like miniature telescopes, attached to the goggles.
A more modern setup would have had a powerful microscope above the site of the surgery where both the operating surgeon and Frasier could see in very close detail.
At one point, when Dr Fraser is shining a light into Jonas Quinn's eyes she has a sticking plaster on her pinkie. The plaster looks as though it has been on for some time. (The edges are quite frayed). A real doctor would have covered this with a glove before any contact with a patient, in order to prevent any cross-contamination.
While operating on Jonas the neurosurgeon says that the tumor in his brain is an astrocytoma and that it is unusual and shouldn't exist because it is not malignant. Astrocytomata are the second most common type of brain tumor. Of the four different sub-types of astrocytoma tumors, two of them are benign (non-malignant) and make up about 10-15% of astrocytoma cases. So while a benign astrocytoma is not all that common it is not impossible or even unusual.
However, the neurosurgeon may have meant that this *particular* astrocytoma was benign.