The answer depends entirely on the depth of the injury. A simple surface erosion closes within one to three days; damage reaching the stroma takes weeks, sometimes months. This page sets out the real timelines, layer by layer, and explains why some wounds heal slowly.
The cornea is a transparent, blood-vessel-free tissue organised in several layers. This architecture explains very different repair speeds depending on which layer is injured. The epithelium at the surface renews continuously and repairs within days. The stroma, which makes up most of the thickness, repairs far more slowly — and final transparency depends on how it repairs. The endothelium, at the back, barely regenerates at all in adults.
| Layer involved | Usual timeframe | Effect on vision |
|---|---|---|
| Epithelium (erosion, superficial foreign body) | 24 to 72 hours | Full recovery, no sequelae |
| Basement membrane | Several weeks | Risk of recurrent erosions if reconstitution is incomplete |
| Stroma (deep ulcer, wound, surgery) | Weeks to several months | Possible, often permanent opacity (scar) |
| Endothelium | No true regeneration | Corneal oedema if the deficit is significant |
This is the most common situation: a fingernail scratch, a branch, a contact lens removed too abruptly, a superficial foreign body. Pain is sharp, often with tearing and light sensitivity, because the cornea is one of the most densely innervated tissues in the body. As soon as the epithelium closes, the pain disappears — hence the impression of sudden improvement after a day or two.
Mechanically, neighbouring epithelial cells flatten and migrate to cover the denuded area, at around 60 to 80 micrometres per hour. The surface is therefore closed well before the tissue is fully normal again: the basement membrane, which anchors the epithelium to the underlying stroma, takes several weeks to reconstitute fully. During this phase recurrent erosions may occur, typically on waking, when the still poorly anchored epithelium detaches on opening the eyes.
As soon as the injury extends beyond the epithelium, the logic changes. Stromal cells — keratocytes — transform into myofibroblasts and produce a new collagen matrix. This matrix closes the wound, but lacks the regular organisation of normal corneal collagen, the very organisation that makes the cornea transparent. Hence the possibility of a residual opacity, or scar, whose significance depends on the depth and extent of the injury.
Wound closure may take a few weeks, but remodelling — the gradual reorganisation of collagen and clearing of the opacity — spans several months, sometimes over a year. Vision may therefore continue to improve long after healing appears complete. Location matters as much as size: a small scar at the centre of the cornea, in the visual axis, is far more disabling than a larger peripheral opacity.
A persistent epithelial defect is diagnosed when a surface wound has not closed after about two weeks of appropriate treatment. This is not simply slow healing: it signals that something is preventing normal repair, and that this factor must be identified.
The most frequent causes of delay are:
Some signs should not be attributed to "normal but slow" healing:
Corneal ulceration or delayed healing, post-surgical or spontaneous.
Urgent consultation →This information is provided for educational purposes and does not replace a medical consultation. Only an ophthalmological slit-lamp examination can assess the depth of a corneal lesion and establish a prognosis.
