Normally the cavity(excavation) of the eyeball is occupied by vitreous body, gelatinous, colorless and transparent mass as the white of raw egg. Vitreous body adheres to the retina; with the age, it tends to collapse, to curl up on him even, where from its separation with the retina.
The nearsightedness(myopia) stresses this tendency(propensity) to retract.
Sometimes this separation with the retina is not complete, bridges persist between retina and vitreous body, where from possible gnawing pains of vitreous body on the retina, going until the detachment of the retina of its position, where from surgical urgency(emergency).
We can visualize relationships between retina and vitreous body with the ultrasound, or the tomography (OCT or optic coherence tomography) and study especially if it exist bridles between both formations, bridles which can be at the origin of a retinal tear and afterward of a detachment of retina.