An orbital decompression operation is a surgical procedure undertaken to create more space in the orbit. There are a number of indications for orbital decompression:

1. Compressive optic neuropathy
   This is the main indication for this type of surgery. Compressive optic neuropathy refers to visual loss due to compression or stretching of the optic nerve at the back of the orbit. The optic nerve is compressed by swollen muscles at the apex of the orbit where there is a confined space. An orbital decompression may be considered as the main management of this problem or it may be used for patients in whom alternative treatments as steroids and radiotherapy have failed or have caused intolerable side effects.
   
   
2. Exposure keratopathy
   This refers to a situation where the cornea is exposed due to severe proptosis (protrusion of the eye) with poor closure of the eye, resulting in drying of the cornea and even ulceration and scarring in advanced cases.
   
   
3. Chronic pain
   Some patients have constant aching orbital pain due to congestion of the orbital tissues which can be relieved by a decompression procedure.
   
   
4. Subluxation of the eye
   This distressing, most painful and dangerous situation is where the eyes are so protrusive that they may prolapse out of the orbit, especially on attempting to look up. The eyelids may close behind the eye. Subluxation of an eye should be considered an emergency.
   
   
5. Patients undergoing eye muscle surgery
   In some patients whose eyes are quite protrusive, the eyes may become even more protrusive following eye muscle surgery to improve double vision. In such patients decompressive surgery may be considered desirable prior to such eye muscle surgery. By own experience we recommend an orbital decompression in significant exophthalmos (>22mm) before squint surgery for biomechanical reasons.
   
   
6. Severe eyelid retraction
   In some patients, a satisfactory result cannot be obtained by eyelid lengthening procedures alone as extreme protrusion of the eyes is the main cause of the lid retraction. Such patients require an orbital decompression.
   
   
7. Cosmetic deformity
   Decompressive surgery is being requested more and more frequently to improve the cosmetic appearance of patients as the surgical results and safety of the surgery have improved considerably over recent years. Most orbital surgeons would regard such surgery as rehabilitative (as opposed to «cosmetic») with an attempt being made to restore a patient's appearance to that which existed prior to the onset of this disease process. However, such goals are rarely achieved completely, but very good results are possible in most cases.

The choice of the stage an orbital decompression is performed depends on individual circumstances, the stage and the activity of the disease. If it is to be performed, it is usually performed before any surgery is advised for double vision or for eyelid retraction. Ideally the type of orbital decompression performed should be tailored to the individual presentation and anatomical situation, as well as to the requirements of the patient and the experience of the surgeon.
There are basically 2 types of surgical decompression procedure which can be used separately or in combination:

• Removal of orbital fat
• Removal of bone from two or more walls of the orbit

A removal of orbital fat depends on the findings on preoperative assessment. If a patient has involvement of the fat behind the eye as opposed to enlargement of the eye muscles, the fat itself can be debulked. This can be performed alone or it can be used to gain additional decompressive effect in patients undergoing a bony decompression. The incisions for such surgery are usually made in the conjunctiva (as in squint surgery) and/or in the eyelids. In a bony decompression, the medial (inner) wall and the floor is usually removed along with the lateral (outer) wall of the orbit to create a «balanced» decompression. Parts of the floor (inferomedial orbital strut) are usually left intact unless there is an extreme degree of protrusion of the eye.
The bony walls can be approached in a variety of ways:

• Via a simple incision in the lower eyelids beneath the lashes
• an incision in the conjunctiva on the inside of the eyelid with a small skin incision at the outer aspect of the eyelids (a swinging eyelid approach)
• a large scalp incision behind the hairline (a bi-coronal approach)
• Via the nose using an endoscope (an endoscopic approach)
• an incision in the mouth above the upper teeth
• an incision on the side of the nose in the inner corner of the eye (transcaruncular approach)
• an incision in the conjunctiva (transconjunctival approach)

Each of these approaches has its advantages and disadvantages. The endoscopic approach avoids the need for any skin incisions and is excellent for emergency access to the apex of the orbit in patients who are losing vision due to compression of the optic nerve from enlarged eye muscles. It does not, however, allow the additional safe removal of orbital fat. It does not allow a simultaneous removal of the lateral wall which is commonly advocated to balance the decompression to avoid the chances of postoperative double vision. If the lateral wall is decompressed at the same time a skin incision is required. A bicoronal approach is a much more invasive operation which, in an era of small incision surgery, does not have many firm indications. It requires a greater amount of theatre and anaesthetic time. It requires a much longer inpatient stay placing pressure on inpatient beds. It commits the surgeon to performing a bilateral operation which runs a risk, albeit small, of visual loss. It is commonly associated with a large area of transient loss of sensation in the forehead and scalp. In bold male patients this approach should not be used due to visible scar formation in the bold scalp. On the other hand a bicoronal approach allows for osteotomies and osteosynthesis with lateral and anterior placement of the bony orbital rim to further reduce exophthalmos in very severe cases or in patients with shallow orbits and midface hypoplasias. The incision on the side of the nose is favoured by some surgeons but leaves a very visible scar. The approach via the mouth is favoured by some ENT surgeons but again does not permit the safe removal of orbital fat. It is uncomfortable for the patient.
The swinging eyelid approach leaves a cosmetically excellent, barely visible scar and permits access to the inner and outer walls of the orbit and the floor of the orbit. (If necessary, it can be used in conjunction with an endoscope to gain an excellent view of the apex of the medial wall.) Orbital fat can be safely removed via this approach. These approaches rely on good postoperative compliance on the part of the patient who is instructed to massage the eyelids to prevent any contraction of the wound. Patients undergoing such surgery are usually in hospital for only one night.
At present a number of different types of surgeons perform orbital decompressions:

• Orbital surgeons
• Maxillo-facial surgeons
• Plastic surgeons
• ENT surgeons
• Neurosurgeons

In the past there have been too few orbital surgeons available to undertake many of these operations. This situation has now changed with the appointment around the country of ophthalmic surgeons who have been suitably trained to undertake such orbital surgery. An orbital surgeon has an appreciation of the complexities of thyroid eye disease and is aware of the treatment options and of the goals of decompressive surgery. He/she can perform orbital fat excision safely and can protect the eye during surgery.