So long as you're making under the current SGA (Significant Gainful Activity) level, which is currently $1010 for 2012, you may be eligible for SSDI. If your employment and medical records show that you have been forced to reduce your hours due to your disability, you may be able to qualify.
Be careful not to lower your benefits by waiting too long to apply if your health continues to decline, if you were making better money and working longer hours in the past few years. In fact, should you decide to file, research the rules for the Onset Date you'll claim.
Factors such as your age, education, and the severity of your disability will all play a role in SS's decision. It is a complex medical legal evaluation.
You will want to discuss with your docs if they would be supportive of your SSDI application.