Overview of Ocular Ultrasound
Ocular ultrasound is a useful tool for doctors when dealing with patients who visit the emergency room due to sudden loss of vision, eye injuries, headaches, or worries about increased pressure within the skull. This method has several advantages in assessing these health conditions.
Anatomy and Physiology of Ocular Ultrasound
To perform ocular ultrasound, which is a type of scan for the eye, a medical professional needs to understand the structure of the eyeball and its surrounding areas.
Within the eye socket, there are fat and muscles around the globe (the eyeball itself). The globe is made up of the sclera, uvea, and retina, which are filled with a watery substance (aqueous humor) and a thicker gel (vitreous humor).
The sclera is the outermost layer of the eye and acts as a protective barrier that surrounds the entire eyeball. Think of it like a strong shell around the globe. This layer actually continues back to connect with the shielding around the optic nerve, which is the nerve leading to the back of the eyeball.
Underneath the sclera is the uvea, which includes the iris (the colored part of the eye), the ciliary body, and the choroid plexus. The iris has a hole in the middle, called the pupil, and the ciliary body connects the iris to the ciliary muscle. This setup forms divisions inside the eye. The lens of the eye is just behind the iris. The choroid, which sits between the sclera and retinal pigment layer, provides vital blood supply to the eye and is connected to the lens through zonular fibers (the threads that hold the lens in place).
The innermost layer of the eyeball is the retina, which contains photoreceptors that react to light, a ganglion cell layer, and the retinal pigment epithelium layer that attaches to the choroid. The retina is only attached to the optic disc (where the optic nerve enters the eye) and the ora serrata (the jagged edge where the retina stops). The rest of the retina stays in place because of the pressure inside the eye. There are two key parts of the retina: the optic disc, and the macula, which is the thinnest portion of the retina.
The main blood vessels of the eye are the central retinal artery, which comes from the ophthalmic artery (a main artery supplying the eye), and the central retinal vein. The optic nerve sends sensory data from the eye to the brain. These three parts — the central retinal artery, central retinal vein, and the optic nerve — are encapsulated within a sheath that contains cerebrospinal fluid (fluid found in the brain and spine) and is directly linked to the space filled with this fluid.
Why do People Need Ocular Ultrasound
There are several conditions that can cause vision loss, such as issues with the eye’s retinal and vitreous detachment, a hemorrhage in the vitreous of the eye, central retinal artery occlusion, increased pressure inside the skull, trauma causing a foreign body to enter the eye, lens dislocation, rupture of the eyeball, accumulation of blood behind the eye, consensual pupillary response, and retinal detachment.
One common cause of vision loss is retinal and vitreous detachment. This can result in symptoms such as seeing “flashes” or “floaters”, or experiencing partial or complete vision loss. When a doctor examines your eye using an ultrasound, a floating membrane or flap can be seen if the retina has detached. A retinal detachment is attached to your optic nerve and the fringe (ora serrata) of your retina. If your vitreous, a gel-like substance that fills your eye, detaches, it doesn’t attach to your optic disc and it doesn’t reflect as much sound during an ultrasound.
A vitreous hemorrhage, which is when blood enters the vitreous of your eye, looks like different material mixed together (heterogeneous matter) inside your eye on an ultrasound. If you move your eye, this can swirl around which is referred to as a “snow globe” effect. This can also occur due to an injury.
Central Retinal Artery Occlusion causes painless, sudden vision loss. Ultrasounds may show a bright spot – called a hyperechoic spot – behind your eye. The doctor will then confirm this condition by showing a lack of blood flow in the affected artery using color Doppler ultrasound.
If you have a severe headache, it could be due to an increase in the pressure inside your skull (intracranial pressure). With an ultrasound, they can see that the optic nerve expands and the optic disc pops out into the vitreous chamber, a condition known as papilledema.
Objects like metal, glass, or wood can enter the eye during an eye injury. These foreign bodies can be seen in an ultrasound, although a suspected ruptured eyeball may halt the ultrasound process. Another type of injury can cause the lens, which is normally positioned behind the iris, to show up in the vitreous chamber. In the worst case scenario, the eye can rupture, referred to as a globe rupture, observed as a mixture of blood and vitreous in the back of the eye in an ultrasound. An injury might also lead to a retrobulbar hematoma, which is when blood accumulates behind the eye and can cause pain, increased pressure inside the eye, and stretching of the optic nerve. This condition is an emergency.
In cases where the pressure inside the skull has increased, an ultrasound can measure the diameter of the optic nerve sheath to monitor the condition. Additionally, if there’s severe swelling around the eye that makes it difficult to examine your pupils’ reaction to light, you can use an ultrasound to view the other eye’s response to light when light is shone into the affected eye.
Lastly, a retinal detachment could occur because of an injury and can be seen the same way as described earlier.
When a Person Should Avoid Ocular Ultrasound
If doctors believe that there might be a problem with the eye, like it being ruptured or burst, they shouldn’t do an eye ultrasound. An ultrasound uses sound waves to create images of the inside of the body. However, they’re not safe to do if the eye might be damaged. If any signs suggesting the eye might be ruptured are seen during the ultrasound, it should be stopped immediately.
Equipment used for Ocular Ultrasound
An eye ultrasound, also known as ocular ultrasound, should be conducted with a piece of equipment called a high-frequency linear probe. This high-tech device helps doctors to see detailed images inside your eye. Interestingly, many ultrasound machines come equipped with a specific setting designed just for eye examinations.
Preparing for Ocular Ultrasound
For the test, you’ll need an ultrasound machine with a specific tool called a linear probe, some ultrasound gel, and a certain type of clear plastic film, often named Tegaderm, is required. Clean versions of petroleum jelly, antibiotic cream, or eye ointment can be helpful but they are not essential for the test.
How is Ocular Ultrasound performed
You might need some ointment on your closed eyelid and lashes. This helps to minimize air getting trapped in the eye. Then, a clear plastic film is carefully put on your closed eye ensuring no air gets trapped beneath it. If there is any trapped air, it might disturb the examination. Then a large amount of a substance called ultrasound gel is put on top of the plastic film. There should be enough gel so the ultrasound probe (a tool that captures images of the inside of your body) just takes a rest on it. This prevents putting too much pressure on the eye.
The doctor’s hand will be lightly resting on the bridge of your nose to keep the probe steady, and your eye will be examined in two different directions – up-down and left-right. When the probe is placed horizontally, the doctor scans your eye from top to bottom. Then, with the probe in the same position, you will be asked to look up and down continuously for a few seconds.
Next, in another angle called the sagittal plane (think of it as vertical), your eye will be scanned from right to left. The probe stays in place, while you move your eyes from right to left. These scans allow the provider to take a thorough look inside of your eye.
Possible Complications of Ocular Ultrasound
Except for the unlikely chance of eye damage in the case of a ruptured eyeball, using ultrasound on the eyes has few risks for patients. When it’s done properly, this procedure shouldn’t cause a lot of discomfort.
What Else Should I Know About Ocular Ultrasound?
When it comes to examining deeper parts of the eye, such as through a dilated eye exam or a slit lamp exam (an eye exam where the doctor uses a high-intensity light source to illuminate the interior of your eye), these methods can be challenging. They require quite a bit of experience before healthcare providers can efficiently and confidently use these techniques.
Noninvasive options such as CT scans and MRIs can also be used to examine the eye and the area surrounding it (the globe and orbit). However, these methods come with their own potential drawbacks such as exposure to radiation, delays in receiving care, and high costs.
Typically, doctors working in emergency medicine would have to do a procedure called a lumbar puncture to evaluate the pressure inside the skull (intracranial pressure). This procedure involves placing a needle in the lower part of the spine to collect fluid, which takes time and can pose risks to the patient.
In many cases, an alternative to these tests is ultrasound. Ultrasound is easy to use, affordable, doesn’t involve radiation, and can be used to take images at the patient’s bedside, providing a more convenient and less invasive option in some cases.