The IRS allows taxpayers to claim expenses paid for a non-dependent (whose gross income exceeds $4050, which would eliminate them from being a dependent) if the taxpayer provides more than half of the person's support.
In the case of your father, that's the test: support. If you don't provide more than half -- and any medical expenses would be included in that support calculation -- then you aren't allowed to claim the medical expenses. If you do provide more than half his support, then you can.
Here's a link to IRS Publication 502, Medical Expenses, which discusses all aspects of the deduction (note the top of page 4): https://www.irs.gov/pub/irs-pdf/p502.pdf
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