PhD programs in medical schools are organized by laboratories headed by principal investigators who write grants and obtain funding to conduct research which often includes funding the tuition and stipends of doctoral students (including MD/PhD students) who chose/are chosen to work in that lab and do their dissertation based on research being conducted in that lab.
What is "eye research"? Do you have something like this research in mice in mind, "Metabolic Deregulation of the Blood-Outer Retinal Barrier in Retinitis Pigmentosa"
Do you have any lab skills? Have you presented at a meeting or published? That's the coin of the realm when it comes to getting a coveted slot in a MD/PhD program. The expectation, too, is that you will be 20% clinical/80% research when you are ready to practice so if that is not for you, then the MD/PhD will not be a good fit.