Isso é explicado em Memória Alfa :
The VISOR detected electromagnetic signals across the entire EM spectrum between 1 Hz and 100,000 THz and transmitted those signals to the brain through neural implants in the temples of the individual via delta-compressed wavelengths. (TNG: "The Masterpiece Society") The result was a vastly different visual acuity, with VISOR-wearers able to see in the infrared and ultraviolet ranges and beyond.
Isso também foi confirmado no TNG: The Mind's Eye
When Romulans kidnapped La Forge in 2367, they were able to use his existing neural implants to tap directly into his visual cortex and secretly brainwash him.
Então, ele basicamente age como um olho biônico aprimorado que ele usa por cima de seus olhos. Isso, então, conecta-se a implantes neurais no lado de sua cabeça (foto abaixo - observe os pequenos 'pontos vermelhos' no lado de sua cabeça) que transmitem essa informação visual para seu córtex visual!
Os sinais são transmitidos via comprimentos de onda comprimidos:
The VISOR sensed signals across the entire electromagnetic spectrum, and transmitted them to the sensory centers of user's brain via delta-compressed wavelengths ("transmitting the electromagnetic spectrum electronically to the brain"). (TNG episode: "The Naked Now", TNG episode: "The Enemy", TNG video game: The Transinium Challenge)
( Fonte )
Quanto ao que Geordi realmente vê, aqui estão algumas fotos:
Ten Forward seen through Geordi La Forge's VISOR. Includes examples of the written Romulan language. (TNG: "The Mind's Eye")
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Data as seen through Geordi La Forge's VISOR with the visual acuity transmitter. (TNG-R: "Heart of Glory")
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