A retinal detachment occurs when the clear gel (vitreous humor) inside the eyeball cavity pulls away from its attachment to the retina (the nerve layer that lines the inside of the eyeball and transmits images to the brain). When the vitreous gel pulls hard enough to create a tear in the retina in one or more places, fluid can pass through the tear and underneath the retina, causing the retina to become detached from the eyewall.