The drops that they use are intended to dilate the pupils so that they can get clearer images at the back of the eye. The only drawback is that the drops take a few hours to wear off during which time your eyes will find it difficult to accomodate to light and your vision will be blurred. The only recomendation is that you do not drive, but your vision will still allow you to use public transport. If you feel more comfortable having someone go with you then by all means take someone. This may also help alleviate your anxiety as well.
I am due to have the eye test next months but had to have the drops as a child for many years. Just thinking about it is making my eyes water. Good luck with the eye test
regards
Mart