Why Doesn’t the Eye’s Blind Spot Look Like a Hole?

Each eye really does have a normal physiological blind spot. Photoreceptors in the retina convert light into neural signals, but the optic nerve must leave through the back of the eye. The optic disc at that exit contains no rods or cones, so an image falling there is not recorded.

We usually see no black hole partly because the visual fields of the two eyes overlap extensively. Information missing from one eye is normally available to the other. Even with one eye closed, the visual system fills in continuity from the colours, lines and textures surrounding the blind spot. It does not recover lost detail; it constructs the most likely seamless surface from nearby structure.

Draw a cross and a dot on paper, about a handspan apart. Close your left eye, fix your right eye on the cross, and slowly move the paper towards or away from you. At one distance the dot disappears, yet the white background still looks continuous. The dot's image has fallen on the optic disc, where no signal is available, while the surrounding white is perceptually extended across the gap.

The blind spot therefore shows that vision is not a pixel-for-pixel copy of the world. The eyes provide limited signals with gaps, and binocular redundancy plus neural organisation produces a stable visual field. Filling-in preserves continuity, but it cannot reveal content that was never sampled.

https://openstax.org/books/anatomy-and-physiology-2e/pages/14-1-sensory-perception
https://pubmed.ncbi.nlm.nih.gov/?term=On+the+filling+in+of+the+visual+blind+spot