What is Dysthyroid Optic Neuropathy?

Dysthyroid optic neuropathy (DON) is a severe side effect of thyroid eye disease (TED), which is one of the most common autoimmune diseases affecting the area around the eyes. DON, which was previously known as crowded orbital apex syndrome, can cause severe loss of vision because it damages the optic nerve due to issues related to the thyroid.

The European Group on Graves Orbitopathy (EUGOGO) grades the seriousness of TED into three levels: mild, moderate-severe, or sight-threatening. The sight-threatening level, which includes DON or an eye condition called keratopathy, requires immediate medical attention.

Diagnosing DON can be very difficult due to several factors. It doesn’t show symptoms in the early stage, there are other factors that can complicate the diagnosis and there can be other reasons for visual impairment in TED cases. A detailed evaluation of DON and prompt treatment are crucial to prevent permanent blindness in patients with TED.

What Causes Dysthyroid Optic Neuropathy?

Several factors are thought to influence the advancement of Thyroid Eye Disease (TED), which could also potentially relate to Dysthyroid Optic Neuropathy (DON). One significant factor associated with this is problems with the thyroid gland. In most instances, DON is linked to hyperthyroidism, an overactive thyroid, because this condition is the most common thyroid issue seen in TED.

However, it’s worth mentioning that other thyroid conditions like hypothyroidism (an underactive thyroid), autoimmune thyroiditis (inflammation of the thyroid), or even a normally functioning thyroid can also be associated with DON.

Additionally, a treatment known as Radioactive Iodine therapy, a known risk factor for TED progression, might increase the chances of developing DON, although solid evidence for this is yet to be confirmed.

Studies have found that smoking is a changeable risk factor for developing DON. Recent studies have revealed a connection between early onset DON and the presence of thyroid-stimulating antibodies in the blood.

Patients with diabetes-related blood vessel disease, particularly those using insulin injections, are found to be at risk of their optic nerve not getting enough oxygen, which could then lead to nerve damage. If these patients also have TED, they should be closely monitored for potential optic nerve issues.

Past studies have associated numerous genes with the development of TED; however, no specific genes have been identified in its relation to DON so far.

Risk Factors and Frequency for Dysthyroid Optic Neuropathy

TED, or thyroid eye disease, can lead to optic neuropathy, which threatens one’s ability to see. This serious condition affects about 5 out of 100 people with TED. It’s less common in younger people and more common as you get older. In fact, with each 10-year increase in age, there’s roughly a 60% higher chance of developing this condition. It’s worth noting that if you’re older when you’re diagnosed, the outcomes are generally worse.

About 5 out of every 100 patients with TED will develop optic neuropathy.
The risk of this condition increases by about 60% with each 10-year increase in age.
Older age at diagnosis can lead to worse long-term outcomes.

Interestingly, while TED is more common in women in the white race population, optic neuropathy is more common in men. This means that older men are much more likely to develop this condition than younger women.

Signs and Symptoms of Dysthyroid Optic Neuropathy

Thyroid eye disease (TED) often presents with different symptoms that might include blurred vision or difficulty seeing colors properly. Some people may not have noticeable symptoms when the disease is in its early stages. Checking for thyroid eye disease usually involves a thorough examination that might reveal the following:

A decrease in the ability to see clearly even with the best possible corrective lenses
One pupil responding differently to light than the other, especially in cases affecting only one eye or affecting the eyes unequally
Swelling and excessive blood flow in the optic disk (acute form)
Damage to the optic nerve (chronic form)
Restrictions in eye movements
Eye protrusion
Eye misalignment
Possibly a drooping eyelid.

This may or may not be accompanied by an active disease state, as determined by a Clinical Activity Score of more than 2 out of 7, according to EUGOGO 2016 guidelines.

Testing for Dysthyroid Optic Neuropathy

Dysthyroid optic neuropathy (DON) may appear complicated, but it boils down to a few key details. Currently, there’s some confusion around DON. It isn’t fully understood, and the criteria for diagnosing it have yet to be fully fleshed out. There are a few telltale signs of early onset DON, though. A change in color vision, or a change in sensitivity to contrast, could signal the early stages of DON. Further signs include a type of blind spot which is either central or slightly off-center or various other visual defects.

When these symptoms are present, it can be useful to take a test that examines the nerve fibers in the back of the eye and the macular ganglion cells. This test, known as optical coherent tomography, is becoming a popular choice because it is non-intrusive and extremely accurate. To better understand the health of the optic nerve, tests including visual evoked potential signals can be run. They evaluate electrical signals created by visual stimuli. Any changes in the expected results could mean something is amiss.

To investigate further, radiology techniques like CT and MRI scans are often employed. They can reveal various factors or changes that might signal DON. These include crowded area at the apex of the eye socket, orbital fat that is slipping through the superior orbital fissure into an abnormal position, swelling in certain muscles near the optic nerve, or an enlarged superior ophthalmic vein.

There are a number of metrics, like Barrett’s Muscle Index, Extra-ocular Muscle Volume/Orbital Volume, and Crowding Index, that have proven to be good indicators of DON. It’s also important to note that another supportive measuring technique, color Doppler ultrasonography, has proven helpful in detecting early-onset DON by monitoring changes in blood flow inside the eye socket.

However, none of these metrics or tests can provide a definite diagnosis of DON on their own. That’s why in 2007, Dayan and Dayan proposed a helpful diagnostic algorithm or sequence of steps to guide doctors. This sequence hinges on the presence of TED-like symptoms or damage to visual functionalities. If these symptoms are present, doctors need to rule out other causes of vision loss. If no other causes are found, AND there’s radiological evidence supporting compression, DON is “likely”. However, if radiological evidence is lacking, DON is “possible”. It’s important to remember though that even if an alternative cause for vision impairment is found and there’s no compressive features detected on imaging, DON is still “possible”.

This scenario highlights the fact that DON diagnosis is a complex process and in certain cases, like those with subclinical stage, euthyroid presentation, and bilaterally symmetric DON, the results can be quite confusing. So, it’s essential to always be vigilant and maintain a high level of suspicion.

Treatment Options for Dysthyroid Optic Neuropathy

Treating complications of TED (thyroid eye disease) with DON (dysthyroid optic neuropathy) require careful attention and can involve a range of treatments including medication, radiation and surgery. Each case is unique, so sometimes a combination of these treatments may be recommended. The first treatment usually tried is corticosteroid therapy, with a medication called intravenous methylprednisolone (IVMP) commonly used. Patients will typically receive this medication intravenously daily for three days, possibly repeated after a week. If improvement is seen after two weeks, the dosage may be reduced or taken orally. This therapy has resulted in complete vision recovery in almost half of all cases. However, this medication is potent and the dose must not exceed a certain limit to avoid serious side effects such as heart or liver failure, and even sudden death.

Before starting corticosteroid treatment, the doctor will conduct a full body examination and several tests such as blood sugar level and liver function tests, electrocardiography (measuring the electrical activity of the heart), chest x-ray and blood pressure check. If after two weeks of IVMP therapy there are no improvements, surgical decompression of the orbit (the eye socket) may be necessary. This surgery can result in visual improvement in 70-85% of cases. Different types of surgical decompression methods are used and chosen based on the condition of the patient.

The post-surgical period can have complications such as a high rate of double vision, numbness in the alveolar nerve, leakage of cerebrospinal fluid, and entropion (turning in of the eyelid). There are also different surgical approaches, with some resulting in scarring or potential damage to the tear duct system. Targeted surgical approaches can reduce the chance of double vision after surgery, and in some complicated cases of TED with DON, removing fat alone can relieve pressure.

Another novel surgical approach involving the endoscopic removal of both medial orbital wall and orbital fat has shown lower rates of postoperative double vision. Radiotherapy is an option for patients who don’t respond to medication and surgery or those with certain additional health conditions, though the evidence supporting its use in treating DON is not definitive. The use of other medications which suppress the immune system is still being explored.

The process of diagnosing Dysthyroid Optic Neuropathy (DON) involves considering other potential causes that could lead to severe Thyroid Eye Disease (TED). These can include different diseases affecting the eye’s surface. Additionally, it’s important to exclude other reasons for damage to the optic nerve, especially those linked to harmful substances or nutritional issues. This is particularly crucial when there are specific types of blind spots present.

An enlarged blind spot, along with certain changes detected through electrophysiological tests, might also suggest Optic Neuritis, which is an inflammation of the optic nerve. In some cases of TED, secondary Glaucoma can occur, leading to changes in visual sharpness, specific field defects, defects in the retinal nerve fiber layer, and changes in the blood flow within the eye.

A detailed patient history, careful clinical assessment, and thorough tests can help distinguish DON from these other conditions.

What to expect with Dysthyroid Optic Neuropathy

The outcome of DON, or Descending Necrotizing Mediastinitis, heavily relies on when treatment was received and how advanced the disease was at that time. If treatment is given promptly, it can save the patient’s vision, with approximately 70% of people recovering fully. Some positive factors that can increase the chances of a good outcome include being younger in age and having a high Clinical Activity Score.

Possible Complications When Diagnosed with Dysthyroid Optic Neuropathy

Thyroid eye disease (TED) can lead to a severe complication known as Dysthyroid optic neuropathy (DON). If not correctly diagnosed or treated, DON can cause permanent loss of vision. Beyond causing vision loss, it can also result in significant emotional and social distress.

Preventing Dysthyroid Optic Neuropathy

It’s crucial for everyone with Thyroid Eye Disease (TED) to focus on reducing changeable risk factors and promptly returning to a normal thyroid hormone level. If the disease advances to the stage of Dysthyroid Optic Neuropathy (DON), patients should be advised to seek treatment right away after understanding the pros and cons. In order to increase chances of a good outcome, patients should take steps to manage their metabolism and participate in regular eye and overall health check-ups.