This is a combination review of a handful of preservative free eye drops. This is by no means extensive nor thorough. There are many others on the market that I have yet to try, but these were the ones I believed to be most relevant to my needs, which consist of relief after PRK surgery.Drops reviewed:Refresh Relieva for contactsSystane Gel DropsSystane Hydration PFBiotrueSystane Ultra PFOasis Tears PlusI will cross post this on each of the other drops' pages. I will review the drops based on relief, perceived longevity, consistency, ease of use, and relevant features. At the time of this review, I am at exactly one month post surgery. I will be rating each of these drops 5 stars on their relevant pages because they all do exactly what they're designed to do and don't have any glaring issues that warrants fewer than 5 stars. The in-post reviews are relevant to comparing between these drops.Refresh Relieva (5 stars):These drops are fantastic. I find that I want to reach for these the most often when I'm looking for good eye lubrication. These drops spread over my eye very quickly without feeling like they stick to the edges of my eyes or eyelashes. Out of all the drops other than the gel, these drops feel like they last the longest in between drops. I use this the least often and find great relief for about half an hour before I want to use them again. These drops feel less slimy than the other drops except for Biotrue. Out of all of the other bottles, it's the most traditional dropper and easiest to use, but due to the design, it may be most susceptible to contaminants and early expiration. It's the only bottle that I'm able to fit my nanodropper onto and that will potentially mitigate the potential contamination and as a result, will prevent early expiration as well as extend the number of drops due to the smaller drops the nanodropper creates. Overall, these are my favorites drops.Systane Gel (3 stars):Out of all of the drops, I reach for these least often. I thought I might try them to see if they last longer and provide the longest lasting relief. If that's what you're looking for, these drops are great, except there are drawbacks that cause me to not use them. They're sticky. If I fall asleep with them in, my eyelids get a little glued together and I sometimes have to pick the gel out of my eyelashes and that can be very uncomfortable. They provide a great deal of relief for the longest period of time and that's the saving grace for these drops, but I'd rather not deal with the slime I get all over my face when I inevitably rub my eyes due to the uncomfortable residue that sits on the edges of my eyes and eyelashes. This dropper is very easy to use and on par with the Refresh dropper. I have no complaints about the amount it drops and the ease of use.Systane Hydration (5 stars):These drops are a very close second to Refresh overall. The relief is only noticeably less than Refresh because the Refresh feels so good. These are exactly what I would expect from a high quality drop and would not be disappointed if these were the only drops available to me. They last about 20-30 minutes and are easy to use. The consistency of these drops is pretty thin. They're only ever so slightly thicker than Biotrue, Ultra, and Refresh. The dropper produces a slight bit of waste if you don't stop squeezing at the right moment but is otherwise very easy to use. Overall, my second favorite drops to use.Biotrue (4 stars):The relief that these drops provide are comparable to Refresh except they don't last as long. I end up having to use these fairly frequently because they don't last very long. I've been using these drops just to get through the bottle. These drops just feel slightly inferior to Systane Hydration in almost every aspect. They go on very nicely and don't stick to my eyelashes or the edges of my eyes as much as Systane, but they don't last as long, provide comparable relief, and the bottle is far more difficult to use. The consistency is the thinnest out of all these drops. This bottle has a special technology that requires a great deal of force to squeeze out a drop. Despite that, the bottle creates a significant amount of waste no matter how you squeeze it, and you have to squeeze it pretty hard. This bottle is my least favorite to use even if the drops are pretty decent. Overall, these are my second to last choice only beating the gels.Systane Ultra PF (5 stars):I think that if I had gotten these in a bottle, they'd be my second favorite to use. They're my go-to for when I'm on the go and need portable drops. They provide a great deal of relief and give about 30 minutes of lubrication. I almost always grab a few of these if I'm going to be out of the house for an extended period of time. The consistency is thin and far less slimy than Hydration. I find that they coat my eye very well and don't stick to my eyelashes and the edges of my eyes. My only issue with these is that they create a significant amount of waste compared to the bottles. I also end up dropping them or losing them when they drop out of my pockets, but they serve a purpose. There's always some product that gets stuck in the twist off cap, so that's a problem too. They're great for transport though, and if I had a bottle, I'd probably prefer it over Hydration. Overall, I really like these drops but I feel bad about the waste.Oasis Tears Plus (3 stars):I feel like these drops are the standard for high quality drops. They provide a fair amount of relief, they last a fair amount of time (roughly 20 minutes), and they're the second most thick drops only less thick than the gel. I don't think I'd get these drops again with these other options. I don't dislike them, but they just don't provide the same amount of relief and longevity as some of the other options. It's also smaller than the Ultra so I get fewer drops out of them. They seem to be smaller so they produce less waste, but not by much. They're very easy to use, but all of these disposable drops produce waste of materials and some product gets stuck in the twist cap, so there's always waste there as well. The Ultra is no different. Overall, I'd probably never use these unless they serve a particular purpose that I'm unaware of.