@Tito: how close to the top of your cage/bulb is the plant? You said your temp is 90F, I'm hoping that is at the highest part of the cage under the basking spot? You didn't tell us what kind of chameleon you have or what its age is, but 90F is likely slightly hot for some species as well....just in case you might want to fill out the "Help form" and we can look over your whole setup to let you know if its all good or not
are leaves falling off on other parts of it or only the parts near the light?
this may seem stupid, but are you watering it enough? I found that I ended up neglecting my chameleon plants the most because I was assuming the misting was watering them enough; in my case (handmisting) it wasn't! My ficus was having the same problems until I started watering it directly and it popped right back.
EDIT:
Leaves will grow back if the conditions become appropriate; but the leaves aren't falling off on their own, there is most likely something "killing" them and until you fix that they probably won't come back.
HERE IS THE HELP FORM:
Chameleon Info:
Your Chameleon - The species, sex, and age of your chameleon. How long has it been in your care?
Handling - How often do you handle your chameleon?
Feeding - What are you feeding your cham? What amount? What is the schedule? How are you gut-loading your feeders?
Supplements - What brand and type of calcium and vitamin products are you dusting your feeders with and what is the schedule?
Watering - What kind of watering technique do you use? How often and how long to you mist? Do you see your chameleon drinking?
Fecal Description - Briefly note colors and consistency from recent droppings. Has this chameleon ever been tested for parasites?
History - Any previous information about your cham that might be useful to others when trying to help you.
Cage Info:
Cage Type - Describe your cage (Glass, Screen, Combo?) What are the dimensions?
Lighting - What brand, model, and types of lighting are you using? What is your daily lighting schedule?
Temperature - What temp range have you created (cage floor to basking spot)? Lowest overnight temp? How do you measure these temps?
Humidity - What are your humidity levels? How are you creating and maintaining these levels? What do you use to measure humidity?
Plants - Are you using live plants? If so, what kind?
Placement - Where is your cage located? Is it near any fans, air vents, or high traffic areas? At what height is the top of the cage relative to your room floor?
Location - Where are you geographically located?
Current Problem - The current problem you are concerned about.
A picture of your setup will help a lot too