Retinal Diagnostics & Testing
Because the retina is a small lining of tissue located along the back wall of the eye, monitoring retina health and diagnosing conditions requires a dilated eye exam. To get a full glimpse into the state of the retina’s health, retina specialists also use several different imaging techniques that help to identify the presence, severity, and location of retinal abnormalities.
Dilated Retinal Eye Exam
Dilated eye exams help retina specialists see the back by making it possible for more light to shine inside of the eye than normal. Before beginning retinal diagnostic testing procedures, dilating eye drops are applied to the eye to keep the pupil open.
Normally, the pupil, which is the black hole located at the center of the iris that allows light to travel towards the retina, appears smaller when in the presence of light and larger when in low-light or dark settings. Although the pupil appears to grow or shrink depending on the amount of light, it’s the iris (the colored portion of the eye) that controls expansion and contraction. When an ophthalmologist shines a light into the eye without dilating them, the pupil naturally shrinks. The dilating eye drops help to keep them open so that the doctor can evaluate the retina, macula, and optic nerve.
After dilating eye drops have been applied to the eyes, it can take up to 30 minutes for the pupils to become fully dilated. While the eyes are dilated, vision can appear fuzzy or blurry. Many patients also report feeling extra sensitive to light or having trouble focusing on fine details. The dilating effects of the eye drops typically last for approximately 4 to 6 hours, so it’s strongly recommended that patients arrange for someone to drive them to and from their exam.
Amsler Grid Testing
Retina problems often have a significant impact on a patient’s central visual field. One of the simplest ways to tell if a patient is experiencing disruptions in their central vision is with the use of an Amsler Grid. The Amsler Grid consists of a white background with evenly spaced black lines organized into a grid. At the center of the grid is a black dot.
Testing one eye at a time, patients are instructed to focus on the black dot. As the patient focuses on the dot, they take note of any abnormalities they notice in the lines of the grid, such as lines disappearing or appearing wavy. The Amsler Grid is particularly useful in identifying signs of macular abnormalities and can be used to diagnose or monitor conditions such as age-related macular degeneration (AMD) and macular puckers.
Not only are Amsler Grids used in-office by retina specialists, but they are also available for patients to use at home. This is a great way for patients to monitor their vision on a daily basis so that they can keep on top of any significant changes to their central vision.
Retinal Imaging Diagnostics & Testing
During a retinal diagnostic exam, several imaging tests may be performed. These imaging tests are often crucial in the diagnosis and management of many retinal, macular, and vitreal diseases.
Fundus Photography
Fundus photography involves using a specialized camera combined with a microscope to capture images of the retina and the eye’s interior structures, including the retinal vascular system, the optic nerve, and more. This form of diagnostic photography yields full-color, high-definition images, which play a crucial role in the retina specialist’s ability to evaluate retina health.
Fluorescein and Indocyanine Green (ICG) Angiography
Fluorescein and ICG angiograms are both used to observe the retinal vascular system. Before photographing the eye, patients are given light-sensitive dye, which is administered intravenously through the arm. The dye flows through the bloodstream to the eye so that it can highlight the blood vessels of the eye. The retina is then photographed with the eye’s blood vessels on full display. This type of imaging technique is especially useful for any condition where neovascularization is possible, such as diabetic retinopathy, wet AMD, and retinal vein occlusion.
The main difference between fluorescein and ICG angiography is the type of dye used. The dye used in fluorescein angiography is better for observing the retinal blood vessels, while the dye used in ICG angiography is better for monitoring the choroidal blood vessels.
Fundus Autofluorescence
Fundus autofluorescence is an imaging technique that does not require the use of dye to capture an image of the retinal vascular system. Instead, it relies on a fluorescent material known as lipofuscin. Lipofuscin is a byproduct consisting of oxidized proteins and lipids that accumulates in the retinal pigment epithelium as we get older. When exposed to light, lipofuscin emits a yellowish-green light. The light is captured and recorded to create an image of the retina.
Optical Coherence Tomography (OCT)
OCT is a non-invasive imaging technique that captures high-resolution, cross-sectional images of the retina. OCT technology works by using low-coherence light to create two- and three-dimensional images of the eye’s inner structure. It is frequently used in the diagnosis of many retinal and macular conditions, including AMD, diabetic retinopathy, vitreous traction, macular hole, macular edema, macular pucker, and central serous retinopathy. It can also be used to observe and monitor optic nerve conditions.
B Scan Ultrasonography
B scan ultrasonography is a painless, non-invasive diagnostic tool that relies on high-frequency sound waves to capture images of the eye. It can be used to evaluate the retina, vitreous, lens, and choroid. It is performed using a transducer probe that transmits the sound waves. The probe is placed against the sclera (the white part of the eye) and transmits the sound signals. The sound waves hit the various structures inside the eye and bounce back to the transducer probe as an echo, which then converts the sound into electrical signals. The electrical signals are reconfigured into an image, which can be seen on a monitor. Although the sound used in B scan ultrasonography can penetrate through tissue, it cannot be heard by human ears.