Overview of Fundus Camera
Fundus photography is the process of taking a picture of the back of the eye, specifically an area called the retina, using a special camera. This type of photography is helpful for diagnosing and treating various eye diseases. The photograph is taken by illuminating the retina and capturing the light that it reflects back through the pupil, which is the central part of the eye that lets in light.
Jackman and Webster were the first to publish pictures of the retina back in 1886. The first fundus camera that could be bought commercially was made available by Carl Zeiss in 1926. A significant improvement was made by Hansell and Beeson, who added an electronic flash tube that allowed light to be directed through the pupil.
Over time, there have been some major improvements in how these photographs are taken. The images have become sharper, cameras can now take these photos without the need to dilate the pupil, and some cameras can even track the movement of the pupil. Now, you can even take a picture of the retina using a smartphone. More recently, cameras that can capture a wider view of the fundus of the eye have been developed. Also, artificial intelligence is now being used in both online and offline photography to help improve retinal imaging.
Anatomy and Physiology of Fundus Camera
The retina is the part of the eye that turns light into electrical signals for the brain to interpret, allowing us to see objects. However, taking images of the retina can be challenging because it needs to be lit up and viewed at the same time through the small opening known as the pupil.
Additionally, the retina does not reflect much light. Therefore, the light that bounces back from the retina is less than the combined light from the systems used to light up and take images of the retina. To capture images of the retina, a tool called a fundus camera is used. This device works by using indirect ophthalmoscopy, a method that avoids any reflections.
Typically, fundus cameras light up the retina through the edge of the pupil and take the image from the center of the pupil. This reduces unwanted overlapping of light reflections, resulting in a clearer picture of the retina.
Why do People Need Fundus Camera
A fundus camera is a specialized device that is used by eye doctors to examine and photograph the back part of the eye, also called the fundus. This includes the main parts: retina, optic disc, macula, and fovea. It’s an important device because it helps in finding diseases that affect those areas of the eyes. Here, we will look at why a fundus camera may be used along with the different eye conditions it can help diagnose:
The camera is frequently used to detect diseases that affect the vitreous (a transparent gel that fills the eye) and retina (the layer at the back of the eye that helps us see). It can detect conditions like:
- Diabetic Retinopathy: This is a diabetes complication that affects eyes causing damage to the blood vessels of the light-sensitive tissue at the back of the eye (retina)
- Age-related macular degeneration: A condition which blurs the sharp, central vision needed for “straight-ahead” activities such as reading, sewing, and driving.
- Retinal vascular occlusions: These are blockages in the blood vessels of your retina
- Retinal dystrophies: These are a group of inherited disorders that affects the photoreceptor cells, which capture and process light
- Retinopathy of prematurity: An eye problem that happens to premature babies who have been given oxygen treatments
- Tumors of the eye, vascular lesions: Abnormal growths or conditions related to the blood vessels in the eyes
- Complications from surgery in the front part of the eye to treat conditions like cataracts, which can include dropped lenses or dropped intraocular lens
- Macular pathologies like a macular hole (a small break in the macula, the part of your eye responsible for detailed, central vision), epiretinal membrane (a thin, transparent layer that forms over the macula), and macular edema (swelling or thickness in the macula)
- Retinal detachment: This is a serious condition where the retina separates from the back of the eye
- Vitreous abnormalities like vitreous hemorrhage (bleed in the clear gel that fills the center of the eye), vitreous cyst, and asteroid hyalosis (a condition that leads to small white opacities in the vitreous)
The camera also helps in diagnosing Glaucoma which happens due to damage to the optic nerve. Specific conditions that can occur are:
- Optic disc damage from glaucoma
- Retinal nerve fiber layer damage from glaucoma
It is also useful in detecting conditions that affect the uvea, the middle layer of the eye. These conditions include:
- Posterior uveitis characterized by inflammation of the back part of the uvea and can cause blurriness, dark, floating spots in the vision, eye pain, redness, and sensitivity to light
- Intermediate uveitis which usually affects the vitreous and the peripheral part of the retina
Further, it can help in discerning a condition related to vision and the nervous system (neuro-ophthalmology). For example, it can detect problems in the optic nerve, such as:
- Anterior ischemic optic neuropathy: the blood flow to your optic nerve at the back of the eye is blocked
- Optic atrophy: the dying back or “withering” of the optic nerve fibers which leads to a loss of some or most of the vision in that eye
- Morning glory syndrome: a rare congenital anomaly of the optic disc
Lastly, it’s used for eye conditions that affect the front portion of the eye and its surrounding structure, the ocular adnexa.
When a Person Should Avoid Fundus Camera
There are no specific reasons which absolutely prevent fundus imaging from being done on a person. Fundus imaging is a way for doctors to take pictures of the back of your eye.
However, there are certain conditions that can make the procedure challenging:
- People with certain bone and muscle diseases might find it hard to keep their chin in the chin rest which is required for the procedure.
- People who have a powerful sensitivity to light (known as severe photophobia), especially after an eye injury, might experience involuntary closure of the eyes (blepharospasm) and increased tear production. This can make it hard for the doctor to take a clear picture.
Equipment used for Fundus Camera
A fundus camera is a specialized device made up of multiple lenses and a camera, much like a high-tech version of an old-fashioned camera obscura. It works by harnessing the mechanics of a medical tool called an indirect ophthalmoscope. Think of it as a very complex, medical-grade camera designed to take pictures of the back part of your eye.
Want to know how it works? Just like any regular camera, the fundus camera needs light. The light from the camera’s lamp is directed onto a round mirror and then sent through a set of filters onto another mirror. From there, the light hits a series of lenses. However, there’s a special mask in the top lens which shapes the light beam into a donut shape. This donut-shaped beam then hits yet another mirror that has a hole in the center. The reflection leaves the camera system through the objective lens and enters your eye through the cornea. This special process takes a photo of the inside of your eye.
When the illuminated rays around the edge of your pupil and the image at the center of your pupil are perfectly aligned, the image exits the center of the pupil, i.e., through the unilluminated part of the donut of light. This image then passes through the central hole of the mirror as mentioned above, through special lenses for correcting astigmatism and diopter, and finally, reaches the camera system.
Essentially, it’s a complex process where light is manipulated through multiple mirrors and lenses to project a picture of the inside of your eye onto a camera.
Various brands produce fundus cameras like iCam, 3nethra, digital retinography system, EasyScan, TRCNW8Fplus, Visucam, Nonmyd7, and Canon CR-2.
There have been many advancements over time in the fundus camera technology including wide-field and ultra-widefield cameras, which essentially take wider images of the eye’s interior. The wider the field of view, the more of the eye’s interior can be seen in a single image – you can think of it like using a wide-angle setting on a conventional camera.
Lastly, the camera systems are categorized based on whether they need any physical contact with the eyes or not, the field of area they cover, imaging method, and their advantages and disadvantages. Some of them are the Equator-plus camera, RetCam, Optos® camera, Heidelberg Spectralis with the Staurenghi lens, and Clarus® 500.
Who is needed to perform Fundus Camera?
Fundus photography is a special process that takes a picture of the back of your eye, including the important pieces like your retina. This can be done by eye doctors, such as an ophthalmologist (a doctor who specializes in the medical and surgical care of the eyes) or an optometrist (a medical professional who can examine your eyes for both health and vision problems). Others who can do this are healthcare workers, mid-level eye care practitioners, or someone who has been trained specially to take pictures of the eye. This test is used to keep check on the health of your eye and spot any potential issues.
Preparing for Fundus Camera
Before starting the procedure to take pictures of the back of your eye (the fundus), your doctor will explain what will happen and why it’s necessary. It’s important to keep everything clean, so they’ll wipe down the camera parts that you will be in contact with, such as the chin rest and forehead rest, using an alcohol swab. If you wear glasses, you’ll need to take them off before the procedure starts. You will be asked to sit and place your chin and forehead into rests to keep your head still during the procedure. Most of the time, eye doctors need to widen (dilate) your pupils for the best possible image without any distractions or obstructions.
How is Fundus Camera performed
Let’s talk about how your doctor takes a detailed picture of your eye using a special camera. This process can help them check for any issues or changes in the back part of your eye, where the retina is located. The retina is an area on the back of your eye that senses light and sends signals to your brain so you can see.
Your doctor will take a picture of one eye at a time. First, they’ll line up a circle that appears on their screen with your iris (the colored part of your eye) and the pupil (the black center). They then adjust the camera’s height to align three white dots they see on their screen. This helps them know the camera is correctly positioned.
Next, they focus on your retina. They’ll ask you to look at a green light, and they’ll move the camera around to make sure they can see everything clearly. If something doesn’t look quite right, they might adjust the camera closer or further away from your eye.
Some cameras have an indicator, which shows up as two vertical lines, that helps them achieve a good focus on the retina. When these lines line up properly and the retina looks clear in their viewfinders, they know they have a good focus and they can take the picture. Pushing a button captures the image.
If you wear glasses or contacts to correct your vision, the person taking the photograph will need to adjust their lens as well before taking the picture to make sure the image is clear. If areas closer to the front of the eye need to be in focus, a special lens is used. For an area further back in the eye, like the retina, a different lens might be used. People with very strong prescription glasses might need special adjustments to the camera before an image can be taken.
During the COVID-19 pandemic, doctors taught students how to do this process using online platforms, which proved very useful.
Lastly, Stereophotography is a technique where two photographs are taken, one from the right and one from the left, which can then be viewed together to create a three-dimensional effect. This can help doctors better understand the structure and health of your eye.
Possible Complications of Fundus Camera
Fundus cameras are used for eye exams and they don’t typically cause problems because they don’t require any surgery or invasive procedures. But, there is a small risk that an infection like conjunctivitis (a contagious eye disease) could spread from one patient to another if the fundus camera is not properly cleaned between uses.
Also, some people might find the strong light from the camera to be uncomfortable, especially if they’re particularly sensitive to light, a condition known as photophobia.
Sometimes, when taking photos of the back of your eye (the fundus), certain issues (called artifacts) can happen:
* If you see an orange or bright line at the edge of the photo, this is usually because your pupil isn’t wide enough and the light from the camera is reflecting off your iris (the colored part of your eye). To fix this, the operator can adjust the position of the camera so that the light goes through your pupil without hitting your iris.
* Eyelashes can create a sort of foggy veil over some parts of the picture. In such a case, your eyelids should be held open so that your lashes don’t block or distort the light.
* If the camera is too close or too far from your eye, the picture may look blurry and lack detail. The camera needs to be at just the right distance from your eye to capture a clear, detailed image of your fundus.
If you see a spot in the same spot on different photos, it may be because something has smeared or touched the lens of the camera. This will generally get better once the camera lens is cleaned.
What Else Should I Know About Fundus Camera?
Fundus cameras take pictures of the back of your eye (the ‘fundus’), which is useful for spotting, educating patients about, and tracking different eye conditions such as diabetic retinopathy (DR), age-related macular degeneration (ARMD), retinal vascular disorders, retinopathy of prematurity (ROP), and glaucoma.
Standard tabletop fundus cameras give a 50-degree view of the back of your eye, allowing doctors to spot any problems. There are also wide and ultra-wide field fundus cameras that provide an even larger view of the back of your eyes and can detect problems beyond the middle of your eye. These cameras are particularly useful in detecting diabetic retinopathy, which when found in the further reaches of your eye, can be a strong indicator of future disease progression.
There’s a particular type of camera (called a RetCam) that’s portable and can be used for babies undergoing screening for a specific eye condition (ROP) that can cause blindness. These cameras can even be used in rural or remote areas.
Technical advances in fundus cameras are shaping the future of eye care. Big data, machine learning, and artificial intelligence are improving patient care. These advanced technologies are integrated into fundus cameras for early and accurate detection of diseases like DR. For instance, using fundus photography along with other information such as your age, deepness of the front part of your eye, and planned surgery details, can predict the risk of your eye changing after refractive surgery.
Moreover, fundus photographs can predict the presence of white matter hyperintensities, which are areas of high intensity on types of brain scans, indicative of abnormalities. Therefore, fundus photographs prove to be an efficient tool for early detection of several diseases in their preliminary stages, helping to initiate treatment early.
Combining fundus photography with another type of eye imaging called optical coherence tomography (OCT) has been successful in improving glaucoma screening and diagnosing associated high degrees of nearsightedness in patients with retinopathy. Handheld fundus cameras and smartphone-based fundus imaging tools are becoming more popular and are very useful for procedures like teleophthalmology – consulting with a doctor over the phone about eye issues.
However, while smartphone-based cameras are able to detect the presence or absence of ROP disease, they still cannot identify the severity and specific areas of the disease. Therefore, while emerging technologies hold promise, further improvements are necessary for effective remote management of eye diseases.
