Hello, For The Past 6 To 9 Months Or So

Hello, for the past 6 to 9 months or so I have woken up 4 times with either no vision in one eye or dimmed vision. This has switched from one eye to the other. It doesn't last very long maybe a few seconds to 20 minutes at the longest. This seems to be happening more frequently. I visited my ophthalmologist a few times but we still don't have any answers. He has consulted with 3 different neurologist and they have no answers. He took a blood test and ruled out an eye stroke. It only happens in the morning. I am 48 years old and severely overweight. I have sleep apnea and sleep with a CPAP machine. I have slightly high blood pressure but is treated with medication. I also have ocular rosacea in both eyes. Any ideas on what cause the temporary blindness and what to do to treat it would be most appreciated. thank you.