How To get Clear Pictures of Retinal Cameras Using Imaging Technology
Advances in retinal imaging modalities allow us to visualize posterior segment findings to a previously unmet degree. The clinical utility of these imaging techniques is constantly expanding, with new developments in machinery allowing for improvements in patient care.
Better fields of view, image clarity/detail and modes of acquisition not only help during diagnosis of retinal disorders but also during screenings and follow-ups. Well-captured retinal images allow us to identify disease severity and stage, compare follow-up visit images to documented findings, track progression of disease between visits, and screen for pathology early.
Additionally and importantly, the capture of clear retinal images allows for unambiguous communication between physicians and contributes to the education of trainees.
“A picture is worth a thousand words,” the old saying goes. It certainly pertains to the procedure of retinal photography. Imagine trying to describe the posterior pole of the eye using only a chart.
Before retinal photography came into it’s own in the 1960s, that is exactly how eyecare professionals had to document retinal pathology.
The term fundus describes the bottom or base of an organ. In eye care, fundus refers to the portion of the eye seen when looking through the pupil: the retina, macula, fovea and the optic nerve.
Retinal photography is used mainly for documentation of normal structures and ocular pathology. These photographs can be compared to the views of the fundus seen by the eyecare professional on later visits for monitoring a known condition or diagnosing a new condition based on noted changes.
Targeting for Specific Conditions
Since this procedure is non-invasive, retinal photography can be performed on most patients in the practice. Retinal cameras are designed to photograph the back of the eye through a dilated pupil (mydriatic) or a non-dilated pupil (non-mydriatic).
There are a number of ocular conditions that eye-care professionals may want to photograph. It is important for ophthalmic photographers to remember their role is to photograph a specified object. The following are examples and definitions of some of the most frequently seen conditions.
Glaucoma is defined as an optic neuropathy (damage to the optic nerve) characterized by an increase in optic disc cupping and damage to the retinal nerve fiber layer. This is often in the presence of increased intraocular pressure.
When photographing a glaucoma patient or a patient who has signs of glaucoma, the optic nerve is the object. To get the optic nerve centered, the patient will be directed to look to a fixation target. Some practitioners prefer to have the optic nerves photographed in stereo.
Taking an optic nerve head photo, moving the patient fixation over, and taking another photograph achieve this. The photos are printed and placed side-by-side and viewed through special lenses to make the optic nerve heads appear in 3D.
Depending on your practice, you should be able to photograph the majority of your patients using a non-mydriatic camera.
Diabetes is a leading cause of blindness in adult patients in the United States. Diabetic retinopathy can be found in patients with type-1 or type-2 diabetes.
The four stages of diabetic retinopathy include:
- Mild non-proliferative– In this stage, small balloon-like swelling in the blood vessels of the retina occur, also known as micro-aneurysms.
- Moderate non-proliferative– As the disease progresses, some retinal vessels become blocked.
- Severe non-proliferative-More blood vessels are blocked, depriving areas of the retina of a blood supply. New blood vessel growth occurs in these areas due to the lack of a blood supply (neo-vascularization).
- Proliferative Retinopathy.When the patient has this fourth stage of retinopathy, the new blood vessels (neovascularization) that have grown into the retina are abnormal and fragile. They grow along the retina and along the surface of the clear, vitreous gel that fills the inside of the eye.
By themselves, these blood vessels do not cause symptoms or vision loss. However, they have thin, fragile walls. If they leak blood, severe vision loss and even blindness can result.
When screening for diabetic retinopathy, the entire posterior pole is the object. There may also be areas in the peripheral retina that need to be photographed. Managing patient fixation is extremely important when photographing these patients. Patient dilation is usually required.
The area of the retina that provides patients with their central vision is known as the macula. The fovea is at the very center of the macula. This area holds the highest number of cones, which provide patients with sharp central vision and color vision.
When we test a patient’s visual acuity, we are measuring it at the fovea. Macular degeneration occurs when this area becomes damaged, typically in patients in their 50s or older.
There are two types of macular degeneration, dry and wet, or exudative. With dry, the most common form, the cells in the macula break down and begin to expire. Patients with this type of macular edema may be unaware they have it.
They may only notice blurred or poorer vision. Wet AMD occurs when there is blood vessel growth beneath the macula area and those blood vessels leak or break, causing the patient to have very poor central vision.
The area photographed in these patients is the macula. The macula is located temporal to the optic nerve and appears to be redder than the rest of the retina. With AMD, the macula may appear mottled or may have hemorrhages.
Since these patients have decreased central vision, they may have difficulty viewing the internal fixation target. Be prepared to have them view an external target for better photographs.
Severely nearsighted (high myopia) patients may also benefit from retinal photography. A patient with myopia may have a longer axial length in their eye. This may cause damage (stretching) of the retina near the optic nerve.
Patients who have a nevus, also called melanocytes (pigmented cells) in an area of the retina, may need photographs for documentation. It is important that the practitioner has described the location of the nevus on the retina. It is not uncommon for a nevus to be very prominent when looking through a binocular indirect ophthalmoscope, but very difficult to see with the retinal camera.
Working With the Patient
Remember, the role of the ophthalmic photographer is to photograph, not diagnose. If, while photographing a patient’s retina, a different pathology is noted, bring it to the attention of the doctor.
No matter how experienced you are, it is not your role to diagnose or discuss pathology and treatment with the patient.
Be certain to explain the procedure to the patient. Patients must understand and follow instructions regarding target, fixation, when to blink, and sitting still. Retinal photography is just as susceptible distortion due to movement as regular photography.
Patient positioning is an important part of all procedures. Make sure the patient is comfortable with her chin resting in the chin cup and that her forehead touching the forehead rest. Align the patient’s temporal canthus (the outer edge of the eye/eyelids) with the marking on the patient headrest.
This will help keep the camera in range of the area to be photographed, making changes during the procedure less necessary.
Look Out for Common Artifacts
A retinal photograph should be focused, evenly illuminated and colorful. Artifacts can occur when the photographer is inexperienced. Digital photography allows the photographer instantaneous feedback on photo quality. Some common artifacts are:
You will see white streaks in the upper and/or lower portion of the photo if a patient’s eyelashes interfere. Using your free hand, retract the upper and lower lids, moving the lashes out of the way.
A bluish haze around the edges of the photo indicates the camera is too far away from the eye. A reflection in the center of the image means the camera is too close. An orange haze on either side of the photo means the camera is off to the side. Move the camera in the opposite direction.
Limitations of Retinal Cameras
Spots or streaks indicate a dirty lens on the camera. Clean the lens according to the manufacturer guidelines.
Be sure to replace the lens cap after each patient. Also, pull the camera all the way back when switching from the right eye to the left to keep from brushing against the patient’s nose, causing a smudge on the lens.
It is important to understand the limitations of the retinal camera. If a patient has corneal edema, cataracts, or other media opacities, the photograph may be compromised. Corneal disruption that can occur from procedures like Goldmann applanation tonometry or gonioscopy or the viscous solutions that are used to perform them may distort photos.
Once the photos are taken, they may be saved to the computerized camera, printed for a paper chart, or networked to the office’s EHR.