To answer a door bell, one has to hear the sound. If hearing is a challenge, one could rely on the vision sense to know that somebody is at the door.
The following deign provides a solution that would require little modification to the existing bell system to make it work for both senses: hearing and seeing.
A circuit switch will allow one to alternate between the 2 modes. Electric wiring was attached in paralell to the existing wires. A low voltage light bulb (12-16 Volts) was attached to the circuit.
The whole operation to modify the existing bell system would take close to 15 minutes to complete. The total cost is less than $5.0 (including the switch, electrin wires, and low voltage light bulb). Anybody with minimum knowledge of basic electric circuitry can complete the new design.