with Dexter.
First... do you live in an area that is fairly populated or close to an area that is? I live in the chicago area and even here there are a lot of vets that specialize in reptiles/aviary, but that is who you REALLY need to see. I know you have spent money (and probably a fair amount) to take him to the ER vet, which is good, but I STRONGLY suggest you take him to a vet who specializes in reptiles! I have had two take care of mine. One takes care of the lizards at the Lincoln Park Zoo in Chicago, and the new one (just b/c he is closer) is also well known in the area for his knowledge.
If he has ooze coming out of his eyes, the first thing to do is make sure he only has felt, paper, or papertowel in his aquarium. With sand, etc. he is going to be rubbing his head on the ground to try and get the ooze off him and when he does this, he is going to get sand in his eyes. I know from experience. Dexter had to have his eyes flushed and then a dye put in to make sure they weren't scratched - thankfully they weren't. So first, take care of the substrate. I still keep felt in his tank to this day (the kind that have at Petsmart).
Second, do you have a UVB light in his cage? Didn't sound like it. These little guys NEED UVB!! Not just full spectrum. Very important and you can see other strings about lighting.
The eye drops that the vet prescribed to me each time was "Gentamicin Sulfate Opthalmic Solution" by Falcon. Those cleared up his eyes every time! One drop in each eye two times a day. He also has been on antibiotics. One was Enroflexacin and the other was SM2-TMP. He has been sick a couple times. The one vet said it was b/c when these guys get sick it is tough to pull them back out of it and get them back to 100%. When his system didn't seem to be responding to the two oral antibiotics any longer, she had him take some by syringe (trust me, that wasn't fun). I believe the spelling on that one is Fortez.
Without the proper lighting, he can have all sorts of issues with digestion and metabolic bone wasting disease. My second vet just gave him an xray to make sure all was fine and it was. But to make sure he is strong, he still has me giving him Neo Calglucon once a day, which is a calcium supplement. I also have had to force feed Dexter. The vet gave me some stuff from Walkabout Farms which my new vet also said was the best supplemental food to give - not baby food. Their web site is www.herpnutrition.com and the email is walkaboutf@aol.com Dexter has responded to this very well.
But as my current vet states, all lizards are individual and what works for one may not work for another. He said another great website to visit about lizard care is www.anapsid.org This is a web site by a very skilled herpetoculturist. Her focus is iguana's, but she has a lot of good lizard info too though. And www.kingsnake.com which is where you are at! 
I know this can cost money --- trust me on that.. I have spent much on Dexter... but I feel he is worth it. And I have a feeling you feel the same if you already took him to an ER vet. If you follow the vets instructions TO THE TEE, you can get them better... but you have to devote to following them. My vets have told me that they are surprised Dexter keeps on snapping back, but I tell them it is just b/c I follow their direction carefully! 
I hope this is helpful. Eve and Wwwwwells are both great resources on here... I have learned a lot from them, especially a lot of communication from Eve. 
Good luck!!
-----
JIM aka jakeleolizard
1 Collared Lizard -Dexter- DOB 4/23/03
1 Beagle/Pug mix -Teagan- DOB 11/26/03