Open Globe Injury — Classification

The BETT System

The Birmingham Eye Trauma Terminology (BETT) system is the standardized classification used internationally to describe mechanical eye injuries. It exists because "ruptured globe," "penetrating injury," and "perforating injury" used to mean different things to different clinicians and different studies — BETT fixes the vocabulary so injury descriptions, treatment decisions, and outcome data can actually be compared across centers.

Under BETT, an open globe injury is defined as any full-thickness wound of the corneoscleral eye wall — the cornea, the sclera, or both. This is the fundamental split in ocular trauma: a closed globe injury leaves the eye wall intact (contusions, lamellar lacerations, superficial foreign bodies), while an open globe injury means the wall itself has been breached and intraocular contents are potentially exposed to the outside world. That distinction drives essentially every downstream decision, from what the examiner is and isn't allowed to do on exam to how urgently the patient needs the operating room.

Mechanism: Rupture vs. Laceration

Once an injury is confirmed open globe, BETT further classifies it by the mechanism that opened the wall — and this split matters clinically, not just semantically, because rupture and laceration wounds tend to look and behave differently in the operating room.

A globe rupture is the closed-globe-equivalent mechanism under BETT: it results from blunt trauma, not a sharp object. A blunt impact transiently spikes intraocular pressure until the eye wall fails at its weakest point, producing a full-thickness wound that blows outward from the inside — an "inside-out" wound. Rupture classically occurs at the limbus or under the rectus muscle insertions, where the sclera is thinnest, and the wound edges are often irregular and difficult to appose compared to a clean sharp laceration.

A laceration, by contrast, is caused directly by a sharp object entering the eye wall — a clean, "outside-in" full-thickness wound at the point of entry.

Laceration Subtypes

BETT further divides lacerations by how many full-thickness wounds the sharp object leaves behind:

Penetrating Injury

A penetrating injury is a single full-thickness entrance wound caused by a sharp object, with no corresponding exit wound — the object enters the eye wall and stops (or remains lodged) inside, without passing all the way through and out the other side.

Perforating Injury

A perforating injury has both an entrance and an exit full-thickness wound, caused by the same sharp object passing completely through the globe. Two wounds from one object is the key distinguishing feature from a penetrating injury's single entrance wound — and a perforating mechanism carries independent prognostic weight, since it's one of the variables scored by the Ocular Trauma Score.

Mixed Mechanism

When a single traumatic event produces more than one distinct BETT mechanism in the same eye — for example, a blunt rupture in one location combined with a separate sharp laceration elsewhere — the injury is classified as mixed mechanism. This isn't just a fallback label for an ambiguous exam; it's used specifically when two genuinely different mechanisms are identified in the same globe.

Intraocular foreign body injury is sometimes described alongside these subtypes as well — a penetrating wound with a retained fragment left inside the eye rather than an object that entered and exited cleanly.

Anatomic Zone Classification

Separately from the mechanism (rupture vs. laceration), open globe injuries are also classified by where along the eye wall the wound sits — the anatomic zone system, which helps predict visual prognosis since posterior wounds tend to involve more visually critical structures and are harder to repair.

• Zone I — limited to the cornea and the corneoscleral limbus.
• Zone II — extends from the limbus to 5 mm posterior into the sclera.
• Zone III — extends posterior to 5 mm from the limbus, often involving posterior structures such as the optic nerve and macula, and generally carries the worst visual prognosis of the three zones.

Mechanism-of-Injury Risk Factors

The history obtained at triage can be as diagnostic as the exam itself. Hammering metal-on-metal work and other high-velocity projectile mechanisms are classic causes of penetrating injury with an intraocular foreign body — a small metal fragment moving fast enough can create a corneal or scleral wound so small it's easy to miss on a cursory exam, while still fully breaching the eye wall. A construction or machining history with a small corneal wound and an irregular pupil should be triaged as an open globe with a suspected intraocular foreign body until proven otherwise, since it warrants emergent imaging and surgical evaluation rather than treatment as a simple corneal abrasion.

High-Yield Pearls

BETT terminology shows up constantly in trauma questions precisely because the words sound similar but mean specific, non-interchangeable things — "penetrating" and "perforating" are not synonyms under this system, and mixing them up is one of the most common exam traps in this subtopic.

Related Topics

Continue exploring Ocular Trauma: