I break bad news every day. "You have cataracts." AMD, a hemorrhage in the eye, disk swelling, possibility of glaucoma, etc... I just tell them. Sometimes if you're TOO empathetic it makes the patient even more anxious. It's a thin line that takes practice.
Cataracts are easy. They always ask "how long will it be until they need to be removed" and so I include that time in the break the news part. "You have mild cataracts and it will take about 20 years until they need to be addressed." Easy. Then answer questions.
AMD is more scary. For mild cases I'll say, "You have some deposits called drusen which put you at-risk for developing macular degeneration." Then I give them vitamins, usually AREDS or Ocuvite 50+, given there's no medical or medicinal contraindication. You say, "The vitamins won't improve the vision but they will help keep the condition stable or from worsening. You will need to take them indefinitely." (But hey, everyone should be taking a supplement with our nutrient-poor American diet). Give them an Amsler grid, too.
If you think the patient has a brain tumor and you need to run a field, you say, "I want to run an additional test to see if there's anything behind the eye that I can't see that's interfering with the signal between the eye and the brain." The really smart ones will figure out you're looking for a tumor, aneurysm, lesion etc... and they'll ask more questions. The the rest of the patients will nod and then will schedule the field and let YOU figure it out.
Occasionally, I'll be able to map a visual field defect with confrontation fields and when the defect is deep enough to do that, the patient will KNOW there's something wrong. In those cases, you try to calm them down, take it one step at a time. Once, I sent a patient straight to the ER for an MRI because we didn't want to wait around for a referral from their PCP.
It's really rare for a patient to undergo a complete meltdown in the office and so you just go with the flow and break it to them as compassionately as possible, but also as truthfully as possible.