Mr. Monk Is Up All Night - S6-E9
Factual error: [SPOILER ALERT] At the end of the episode, it is revealed that the mysterious cab driver had corneal transplants to repair damage to her vision from Retinitis Pigmentosa. RP is a defect of the retina, in the back of the eye, which accumulates pigment, losing its photoreceptivity, resulting in vision loss. A corneal transplant will not restore vision to someone with RP.
Answer: Notice also that in the opening credits scene when he is touching parking meters her also wipes his hand on his clothes each time he does it.