An orbital decompression operation is a surgical procedure undertaken to create more space in the orbit. This is usually performed for the management of a patient with thyroid eye disease.

There are a number of indications. These are:

1. Compressive optic neuropathy.
   
   This is the main indication for this type of surgery. Compressive optic neuropathy refers to visual loss due to compression of the optic nerve at the back of the orbit. Occasionally it is due to extreme stretching of the optic nerve. 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 e.g. steroids, 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 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 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.
   
   
5. Patients undergoing eye muscle surgery.
   
   In some patients whose eyes are quite protrusive, the eyes may become more protrusive following eye muscle surgery to improve double vision. In such patients a decompression operation may be considered desirable prior to such eye muscle surgery.
   
   
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.

This very much depends on individual circumstances, the stage and activity of the disease. If it is to be performed (only a small proportion of patients with thyroid eye disease undergo such surgery), it is usually performed before any surgery is advised for double vision or for eyelid retraction.

Patient with thyroid eye disease with proptosis and eyelid retraction	Same patient 3 months following a right 2-wall orbital decompression with removal of orbital fat and 2 weeks following the same procedure on the left side

How is a surgical decompression performed?

This depends on a number of factors, including:

• The indication(s) for the surgery
• The relative expertise of the surgeon

Ideally the type of orbital decompression performed should be tailored to the individual requirements of the patient.

There are basically 2 types of surgical decompression procedure which can be used separately or in combination:

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

A removal of fat depends on the findings on preoperative scans (a CT scan usually). 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 operations) and/or in the eyelids.

In a bony decompression, the medial (inner) wall is usually removed along with the lateral (outer) wall of the orbit to create a "balanced" decompression. The floor of the orbit is usually left intact unless there is an extreme degree of protrusion of the eye.

The bony walls can be accessed in a variety of ways. Each of these approaches has its advantages and disadvantages.

• Via a simple incision in the lower eyelids beneath the lashes
• Via 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 flap approach)
• Via a large scalp incision behind the hairline (a bi-coronal flap approach)
• Via the nose using an endoscope (an endoscopic approach)
• Via an incision in the mouth above the upper teeth
• Via an incision on the side of the nose in the inner corner of the eye

The endoscopic approach avoids the need for any skin incisions and is excellent for 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 and removes this advantage of the use of an endoscope.

A bicoronal flap 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 (a precious resource in the modern health service). 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. The alternative approaches permit one orbit to be decompressed at a time. In addition it runs the risk of creating a permanent palsy of one or both eyebrows. It is commonly associated with a large area of loss of sensation in the forehead and scalp. In male patients, loss of hair leaves a large visible scar.

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 flap approach leaves a cosmetically excellent 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 surgeon 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.

Serious complications from decompressive surgery e.g. loss of vision, are extremely rare. The major potential complication which must be considered is postoperative double vision. The incidence of this complication varies considerably from centre to centre. It is much more of a problem in patients who have some double vision prior to surgery with a risk of up to 30% that this may be worse postoperatively. In patients with no pre-existing double vision, the risk is considerably reduced (<5%). It is rare for any patients who suffer this complication to be left with a significant problem following corrective eye muscle surgery. This risk must, however, be considered very carefully in a patient who wishes to improve cosmesis as this has implications for driving. It may be necessary to wait for some months before muscle surgery can be undertaken to improve double vision. In some patients temporary prisms can be fitted to glasses to improve double vision.

Other potential complications which should be considered:

• Bleeding
• Infection
• Loss of sensation in the cheek, side of the nose and front teeth
• Retraction of the lower and/or upper eyelid

No. The outcome of surgery is dependent on a number of factors. For this reason it is not always helpful for patients to meet patients who have undergone such surgery as direct comparisons cannot be made and expectations may be raised to a level which cannot be achieved. The variables include:

1. The stage of the disease. Patients with chronic disease tend to have scarring within the orbital fat which does not prolapse into the spaces created by the surgery. Such fat may also be difficult to remove.
   
   
2. The size of the eye muscles. It is difficult to gain good cosmetic results for patients who have massively enlarged eye muscles.
   
   
3. The size of the bony orbit. Some patients have shallow orbits which are difficult to enlarge.
   
   
4. The size of the eye. Short-sighted (myopic) patients tend to have large eyes compounding the problem of protrusive eyes and create problems in achieving good results from cosmetic decompressive surgery.
   
   
5. The size of the sinuses adjacent to the orbit. Some patients have under-developed sinuses which do not permit a great deal of soft tissue prolapse from the orbit.

You will visit the hospital a few weeks before the date of your surgery, to have a preoperative consultation with your surgeon. He will ask you questions about your current and past health, and will need to know about any allergies you may have, medications you are taking (including over the counter products e.g. aspirin, indomethacin or vitamin supplements), previous surgery, and whether you smoke. You may also be required to have a physical examination of your heart and lungs by your GP to make sure it is safe for you to have an anaesthetic. You may need to have some routine laboratory tests, such as urinalysis (tests of your urine), chest x- rays, or complete blood cell counts. These should reveal potential problems that might complicate the surgery if not detected and treated early. It is very important for the anaesthetist to have an up-to-date thyroid function test result.

Please answer all questions completely and honestly as they are asked only for your own wellbeing, so that your surgery can be planned as carefully as possible. If you are unsure of the names of any medications, bring them with you. You will be told whether or not to stop any medications at this preoperative clinic visit. For example, if you are taking aspirin-containing medicines or anticoagulants, they may need to be temporarily withdrawn or reduced in dose for two weeks before the procedure. If you can, try to stop smoking at least six to eight weeks prior to surgery.

It can be extremely difficult to explain the complexities surrounding decompressive surgery to patients in the relatively short time available in consultations. In my practice I have found it extremely helpful to be able to advise the patient to contact the Thyroid Eye Disease Society, frequently in advance of their consultation (their details and a leaflet can be obtained by contacting my secretary at the address below). Many patients then arrive in clinic well informed about their disease making a consultation a much more fruitful exercise for the patient as well as the surgeon.

Unless you have been told otherwise please do not use aspirin or any anti-inflammatory agents for at least 3 weeks prior to the surgery. This may include a number of arthritis medications. If in doubt please ask.

Please Note:

If you are insured it is important that you clarify in advance with your insurance company the level of reimbursement they will allow for this surgery. Unfortunately, some insurance companies grossly under-estimate the expertise and time required for this type of treatment and leave patients with a shortfall. We will be happy to provide your insurance company with details of your proposed treatment along with a quote of the costs.