How can I be sure that I don't have glaucoma without going to the doctor?

You cant. Sorry, an exam of the optic nerves by a Eye MD is the only recommended way to establish the diagnosis of glaucoma. Ancillary testing can help, but interpretation of the tests and correlation of the results to the eye examination is essential. This particularly important in families with higher risk: Aftican-American or Hispanic, positive family history, over 60, eye injury, steroid use, diabetes..
You can't be sure. It is important to see an eyemd to evaluate you for glaucoma. While gross loss of visual fields may be detected by a person doing a self exam, subtle loss would likely go unnoticed.
You can't! Only an eye pressure test and dilated exam to look at the optic nerve can rule out the disease.
Silent. Glaucoma if undetected and untreated can progressively damage the optic nerve and eventually resulting in irreversible visual field loss. This is why it important to have a dilated retinal examination and intraocular pressure check, especially after 50 years old.