Orbital Fat Prolapse
Orbital fat prolapse consists of a benign prolapse of healthy fat tissue to a space outside it's anatomical bed, mostly towards the subconjunctival space. The diagnosis is frequently clinical but imaging can be applied to perform a correct differential diagnosis . It is usually asymptomatic but discomfort and epiphora can occur. If one of these is present or the patient finds it unaesthetic, excision can be performed.
Orbital fat prolapse consists on the extrusion of intraconal and extraconal orbital fat to a space outside it’s anatomical bed. It is a benign condition and it can happen towards the intracranial space, the infratemporal fossa or, most commonly, the subconjunctival space. Depending on the location it can have different manifestations, although most cases are asymptomatic.
The actual incidence of orbital fat prolapse is difficult to determine, although the literature describes it is a rare phenomenon that mostly affects male individuals. It occurs bilaterally in 50% of the cases with the superotemporal quadrant being the most affected (when subconjunctival prolapse is accessed). Age, trauma, surgery, obesity and thyroid orbitopathy are important risk factors.
The prolapsed material consists, as the names states, of orbital fat, specifically mature adipocytes with Lochkern cells, fibrovascular septae and an inflammatory infiltrate.
The intraconal and extraconal orbital fat consists of adipose tissue that lies inside and around the myofascial cone of the eye, giving structural support and protection to the vascular and neural structures that reach the eye from the intracranial space. It is contained by Tenon’s capsule, the periorbita and the orbital septum. When there’s weakness of the Tenon capsule (either following trauma or by dehiscence) this orbital fat is able to move anteriorly and infiltrate into the subconjunctival space. If there is a weakness in the orbital septum the fat content can also herniate towards the sub and retro orbicularis fat pads.
In other rare situations the orbital fat can herniate posteriorly through the superior orbital fissure (mostly in thyroid eye disease)  or inferiorly through the inferior orbital fissure towards the infratemporal fossa. 
The subconjunctival fat prolapse mostly occurs in the superotemporal quadrant and appears as a yellow and soft subconjunctival mass with fine blood vessels on its surface. It is usually very mobile and becomes prominent with globe retropulsion. 
The patient is usually asymptomatic and reaches for aesthetical reasons, although some might refer discomfort and in rare cases epiphora.
If the prolapse occurs through the orbital septum to the sub and retro orbicularis fat pads the patient might complain of local swelling. Posterior prolapses will manifest as optic nerve compression signs such as visual acuity decrease, visual field affection, dyschromatopsia and relative afferent pupillary defect. 
The diagnosis is usually made through clinical examination but imaging techniques such as CT and MRI can be applied when in doubt, providing information on lesion density and posterior extension.  Posterior prolapse always requires imaging and further investigation.
Differential diagnosis (of subconjunctival prolapse)
- Conjunctival lymphoma
- Lacrimal gland prolapse
- Lacrimal gland neoplasia
If the mass causes discomfort or the patient finds it aesthetically unpleasant treatment must be applied.
Conservative treatment, in cases of discomfort, can rely on lubrication with artificial tears.
The surgical approach aims to reposition or to resect the prolapsed tissue. The reposition can be achieved by posterior displacement of the fat tissue followed by conjunctival fixation to the sclera. In this procedure 2% lidocaine is injected in the subconjunctival space and a traction suture is passed to correctly position the eye. A blunt object is then used to reposition the fat prolapse posteriorly, followed by an interrupted suture of the conjunctiva to the superficial sclera. The reposition of the prolapsed tissue can also be achieved through a small incision of the conjunctiva followed by fibrin glue closure. Resection of prolapsed tissue can be performed through small or larger conjunctival incisions with self-sealing or suture closure. No technique has proven to be superior to others.
Since most cases are asymptomatic and do not require treatment, prognosis is good, with infrequent progression of the prolapse. If resection or repositioning is performed there is always a risk of recurrence, with a reintervention being a possibility.
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