Vision Problem at age of 21, unknown to ophthalmologist?

I'm 21, and having trouble seeing out of my right eye. Its like spots of darkness cloud my vision. Opthamologist ruled out retinal detachment, pvd and any kind of macular degeneration. He said it looked like a pigment change in the tissue near the retina. I'd like to know what else it could be since most eye problems i've been researching only occur in people 50+ yrs old. Thank you.