What is Optic Disc Drusen?

Introduction

Optic disc drusen (ODD) refers to the build-up of fatty proteins and calcium deposits within your optic disc.1 It was originally described by Muller, where the name ‘drusen’ is derived from the old German term for rock cavities lined with crystals. These formations in the eye usually remain constant throughout a person's lifetime and rarely cause debilitating symptoms. With advancements in the field, we are gaining new insights into the eye condition, reshaping how we diagnose it, and questioning previous ideas about the development of ODD. Although ODD does not usually need treatment, it is still important to understand as it is often associated with other serious conditions that do require management. It is more commonly linked to an enlarged blind spot that isn’t noticed initially but is picked up through routine eye examinations and further investigated by trained clinicians. There is some speculation about the use of intraocular pressure-lowering medications. However, this isn’t currently offered as a first-line treatment due to the contention regarding its efficacy. While it isn't a genetic disorder, the prevalence rates increase for individuals with a family history of ODD. 

Understanding optic disc drusen

ODD refers to the abnormal build-up of calcium and proteins that accumulate within the optic nerve. This nerve is comprised of over one million nerve cells that carry visual information from the eye up to the brain, physically connecting the two. This build-up can occur in one eye but is more commonly found in both.¹ 

Generally, drusen can't be seen at birth and gradually becomes visible in the first 10 years. When having regular eye tests, the optic nerve can appear lumpy or raised and can be mistaken for a swollen nerve. This will result in the optician referring you to the hospital for closer examination. 

Prevalence and demographics of individuals affected by ODD

ODD is estimated to occur in 1-2 out of 100 people, which is considered relatively common. Many cases can go unnoticed due to the fact that a lot of people do not exhibit/notice any differences in their vision. Recent research examining 6207 cases of ODD found that the majority of cases occurred in white people assigned female at birth with both eyes affected.² 

Associated symptoms and signs

ODD typically isn't associated with any drastic changes to your vision. Peripheral vision is the most commonly affected; however, vision loss can occur so slowly that it is not noticeable. ODD is generally identified through routine eye tests rather than changes to your vision. It is estimated that approximately 9% of patients with ODD will experience changes to their visual field, which is typically an enlarged blind spot.³ 

Risk of developing more severe eye conditions

A rare complication of drusen can cause blood vessels near the optic nerve to grow abnormally, which has more serious consequences for visual impairment. People with ODD can also be at risk of developing other more serious conditions, such as:

• Nonarteritic Anterior Ischemic Optic Neuropathy (NAION) - a lack of blood flow to the optic nerve resulting in sudden vision loss 
• Vein occlusion - a sudden reduction in vision caused by a blockage in the retinal vein
• Subretinal neovascular membranes - abnormal growth of blood vessels that can accumulate until they break through the surface of the retina 

It is important to consult your healthcare provider if you suspect you might have ODD. Not only is there a risk of developing more serious conditions, but there is also an overlap in symptoms with a condition known as Papilloedema. This is a serious condition and must be treated at the earliest signs. It involves the swelling of the optic disc (anterior part of the optic nerve) and can look very similar to ODD in the underlying aetiologies. Papilloedema tends to involve little to no symptoms. However, it has been associated with headaches, transient visual obscurations, and double vision. 

Causes and risk factors

The exact causes of ODD are currently unknown. The most accepted theory to date is that the condition is caused by material being moved abnormally along the optic nerve.⁴ It is thought that this flow of important material is slowed down due to issues with the optic disc’s blood supply. When this flow is slowed, it can result in a build-up of calcified and broken-down cell parts, which creates the spot where drusen can form. This problem with blood flow is speculated to be related to inherited factors, problems in the way cells remove the broken-down cell parts, and small openings/lesions in the protective outer layer of the eye.⁵ Research suggests that while ODD isn't largely considered to be a genetic condition, it is likely that you can inherit the primary pathology of ODD. This means that your parents can pass down a susceptibility for abnormal cell growth within the optic disc and nerve, which can predispose you to develop ODD.⁶ 

Diagnosis and detection

Techniques for diagnosis

As already stated, people who have ODD may not be aware they have it due to the asymptomatic nature of the condition. Typically, someone who is carrying out a routine eye test may notice some abnormal changes to your eye and can refer you for further investigation. An ophthalmologist can use a number of diagnostic tools to look at various components of your eye for signs of ODD. Some of the imaging techniques for detecting ODD are:

Fundus photography

Taking an image of your retina with a specialised camera that can record the appearance in detail, it is commonly used in monitoring the progression of eye diseases. 

Optical coherence tomography (OCT)

This technique uses light waves to take a cross-sectional picture of your retina. It is used to look at the thickness of your retina’s layers which can help diagnose ODD in a non-invasive way. 

B-scan ultrasonography

This is another non-invasive tool that is used to look at lesions at the back part of your eyeball. This is also an important tool in distinguishing ODD from papilloedema.  The conditions differ in their signal responses to ultrasonography. ODD maintains a high signal intensity, whereas papilloedema is associated with a decrease in signal intensity.  

Clinical examination and symptoms

Trained ophthalmologists can use these various tools either by themselves or in conjunction with each other to look at your eye in closer detail and determine if you have ODD. Some of the signs they look for include:

An elevated optic disc

The optic disc (also referred to as the optic nerve head) is located at the back of your eye. It plays a vital role in sending signals to the brain. If you have ODD, the disc can appear higher up than normal. 

Indistinct and irregular disc margins

The edges of the optic disc are unclear and uneven in shape. 

Drusen on the surface

Small, round, white or yellowish clumps are present on the surface of the nerve at the back of the eye. 

Anomalous vascular branching

The blood vessels around the optic disc have a strange twisted pattern.

Common drusen location

In ODD, these clumps tend to be found towards the side of the optic disc that is closer to your nose. 

Spontaneous venous pulsations

These are natural rhythmic movements in the veins around the eye. 

Afferent pupillary defect

The pupil does not respond properly when light is shone into the affected eye.

Treatment and management

There is no current treatment for ODD as it is associated with minimal losses to vision and a generally good prognosis. Some studies suggest ODD patients could be treated with intraocular pressure-lowering medications to stabilise the existing function of the eye and prevent potential vision loss. However, since ODD isn't associated with high intraocular pressure in the first place, there is an area of contention around using these medications for the condition specifically.⁷ 

As previously discussed, while the symptoms associated with ODD include defects to your visual field, many people with ODD will not notice the effects. They are usually only picked up through routine eye tests and many cases of ODD will not require treatment. It is important to see your healthcare provider if you have any concerns regarding your vision and any recent impairments. Keeping up to date with routine eye exams will help to keep on top of any changes to your eyes. 

Summary

ODD remains an intriguing condition. It is not associated with any concrete causes, the risk factors for developing the condition remain unclear, and there is no manifestation of any drastic symptoms. It is very common for people with ODD to not notice the changes to their visual field as such, the condition is usually associated with a good prognosis. While ODD itself is not considered serious, people with ODD may be at a higher risk of developing other more serious conditions due to deficits and abnormalities around the optic disc. Typically, ODD is diagnosed using tools such as a fundus camera, optical coherence tomography, and B-scan ultrasonography following a referral from a routine eye exam. It is important to consult your healthcare provider if you have any concerns about ODD; however, there are currently no treatments available. Some medicines that are used for glaucoma have been posited to treat ODD, but there is debate as to whether they are applicable and effective for ODD.