Though it is recommended, if you do not have the time for that here are some tips to help you make the right decision.
Know what you are looking for in the goggles.
Most goggles in the market are suitable for myopia, hyperopia, astigmatism, and prism.
Lots of swimming goggles for sale are pre-made and offer a "round up" prescription.
Looking into goggles that are fully customizable is the way to go.
Tailored to you goggles are great because they allow you to have the best possible sight. Some places even allow you to fabricate each individual lens (left & right) to your exact prescription.
Each brand has their own range of Rx they cater for.
But if you have a stronger prescription, you should look into a brand that specializes in difficult prescriptions.
Prescription swimming goggles can also have features like UV protection, tinted and transition lenses. Lenses can also come with special coatings, like Anti-Fog, Anti-Scratch, and Anti-Glare coatings.
Keep in mind that custom prescription swim goggles will cost more than off the shelf goggles. They will also take longer to manufacture and ship.