Retrobulbar is a form of optic neuritis actually it just specifies where the inflammation is. Retro (behind) the bulbar (eye ball) so the inflamation is between the eye ball and the brain. The other form of optic neuritis is “papillitis” where the inflammation is at the nerve head - where it leaves the eye. the only real difference is that papillitis is one of the rare situations (only I think) where nerve inflamation can be seen.
Optic neuritis usually goes into remission and sight returns often nearly as good as is was. Often only a line or two above where you could get on an acuity test chart at the optomerist (with glasses if you use them). Some clour blindness usually remains and a bit of contrast problem. Actally there is almost always some field of vision defect but usually only detected by a test and not noticeable otherwise.
If they use eye drops to dilate the pupils that is usually so they can look in your eye to check for anomallies - if it is papillitis the nerve head can usually be seen to be swollen but the appearnce of the retiina can be checked. Also they can check if the fluid in the eye is cloudy and I guess other things. Dilating the pupils means the pupils can’t regulate how much light gets in, meaning glare can be a big problem - so a problem for driving.
Pupils are also dilated to enable the pressure in the eye to be measured - same as the puff of air at an optometrist but apparenly more accurate.
They’ll probably do eye chart tests or if can you count fingers if sight is that bad. Colour tests are usually done if you can see well enough and shing a light in your eyes to see how the pupils react (indicating how much signal is getting to the brain (a very simple VEP test).
You should go so progress in recovery can be monitored.
Hope it goes well.