Leopard Gecko concern!

Question
Hello. My 10 year old leopard gecko has been acting very strange. He hasn't been opening his left eye and has been showing sighns of poor coordination and falling over! Can you please help me figure out the nature of this problem and how to help him? I have him In a large cage in a woodland habitat with no light,because sunlight comes into my room. The temperature of the cage is around 80 degrees and there is no humidity in the cage. I have him on a diet of crickets nothing else.

Answer
Leopard geckos should have a 90F basking area, and while crickets are a nutritious food, they must be supplemented with a calcium supplement containing vitamin D3.  Crickets are too high in phosphorus to be a good food source without supplementation.  Additionally, in a setup with no UVB light, leopard geckos (which actually DO bask in sun in the wild), must have supplemented vitamin D.

Without calcium and D3, they will develop 'nutritional secondary hyperparathyrodism', also known as 'metabolic bone disease', or just 'hypocalcemia'.  Vitamin D3 is needed to allow proper metabolism of calcium, and when calcium intake is not sufficent as well, the body will begin to pull calcium from the bones.  Edema will be noted as well as brittle and soft bones, jaw deformity, etc...and eventually, death will occur.

If you have been giving proper supplements, then it is possible your gecko has some sort of infection.  This could cause an inner ear issue.

Regardless of the cause, he needs to see an experienced reptile veterinarian right away--no one can diagnose your pet online, and I am not a veterinarian.

At age 10, he's still young--please get treatment for him immediately.  Delaying treatment generally ensures a bad outcome when it comes to reptile medicine.  Prompt treatment is likely to be much less expensive, and have a good outcome.