Fijoya and your health plan are entirely independent of each other.
Eligibility for and utilization of a specific service on your health plan (chiropractic services, for example, or eyecare) do not prevent you from accessing a similar service through Fijoya.
The only things that matter when it comes to eligibility for a product or service from Fijoya is whether it is available on Fijoya, and whether your Fijoya allowance covers the cost.
So if you really want two pairs of prescription eyeglasses, one through your health plan (if you have coverage for that) and one through Fijoya (if available), go for it!