A fundus photo is a specialized image of the back of the eye, offering a detailed view of its internal structures. This non-invasive imaging technique serves as a diagnostic and monitoring tool in ophthalmology. It provides a permanent record that eye care specialists can use to assess various conditions.
What a Fundus Photo Captures
A fundus photo captures specific anatomical structures at the back of the eye, known as the fundus. These include the optic disc, also referred to as the optic nerve head, where the optic nerve exits the eye. The retina, a light-sensitive tissue lining the back of the eye, is also clearly visible. The image also shows the intricate network of retinal blood vessels, which supply blood to the retina. This digital imaging process uses a specialized fundus camera to capture these components.
How Glaucoma Appears
Glaucoma, a condition characterized by damage to the optic nerve, presents distinct visual signs on a fundus photo.
Optic Disc Cupping
One of the most noticeable changes is optic disc cupping, which refers to the enlargement and deepening of the central cup within the optic nerve head. In glaucoma, the cup appears to expand and deepen due to the progressive loss of retinal ganglion cells and their axons, leading to a posterior bending of the lamina cribrosa. This often results in an increased cup-to-disc (C/D) ratio, where the cup occupies a larger proportion of the optic disc area. While a specific C/D ratio alone does not diagnose glaucoma, a ratio of 0.6 or greater can be suspicious, especially when considering the overall size of the optic nerve.
Neuroretinal Rim Thinning
Accompanying cupping is neuroretinal rim thinning, which is the loss of the healthy, pink tissue surrounding the optic cup. This rim, which contains the nerve fibers, typically appears thickest inferiorly, followed by superiorly, nasally, and then temporally in a healthy eye; however, in glaucoma, the inferior and superior rims are often affected first, leading to thinning in these regions. Focal or diffuse thinning of this rim can be observed, sometimes appearing as a “notching” where a specific area of the rim becomes significantly narrower. Such thinning indicates damage to the nerve fibers at these specific locations.
Retinal Nerve Fiber Layer (RNFL) Defects
Another sign of glaucoma is the appearance of retinal nerve fiber layer (RNFL) defects. In a healthy eye, the RNFL appears as faint, parallel striations fanning out from the optic nerve head. As nerve fibers are lost in glaucoma, these striations become less distinct, and defects may appear as darker areas or wedges, indicating localized or diffuse thinning of this layer.
Disc Hemorrhages
Small, splinter-shaped or flame-shaped hemorrhages on or near the optic disc, known as disc hemorrhages, are also a potential sign associated with glaucoma. These hemorrhages are typically small, with feathered ends, and often oriented perpendicular to the disc margin. They tend to occur in areas of existing damage, such as where the neuroretinal rim is notched or an RNFL defect is present. The presence of such hemorrhages may signal an increased risk of disease progression.
Undergoing the Examination
Upon arrival, eye drops are typically administered to dilate, or widen, the pupils. This dilation is performed to allow the ophthalmologist a clearer and more expansive view of the back of the eye, though it temporarily causes blurred vision and increased sensitivity to light. The effects of these drops usually last for a few hours.
Once the pupils are adequately dilated, the patient is asked to sit comfortably in front of a specialized fundus camera. The patient positions their chin on a chin rest and their forehead against a bar, ensuring stability during the imaging process. The eye care specialist then aligns the camera with the patient’s eye, focusing on the internal structures. During the procedure, brief flashes of light occur as the camera captures images of the retina, optic disc, and blood vessels. The process is quick, typically lasting only a few minutes, and is considered non-invasive and painless.
Tracking Glaucoma Over Time
Fundus photos are valuable for initial diagnosis and monitoring glaucoma progression over time. By taking serial fundus photographs at different appointments, ophthalmologists can create a chronological record of the optic nerve and retinal nerve fiber layer’s appearance. This allows for direct comparison of images captured months or years apart, revealing subtle changes that might indicate disease progression.
The ability to compare images from different time points helps eye care professionals assess the effectiveness of ongoing treatment strategies. If the optic nerve or nerve fiber layer shows signs of deterioration despite treatment, it may prompt an adjustment in medication or other interventions. These photographs establish a baseline appearance of the optic nerve, against which all future images are compared, making it easier to identify even slight changes in the optic disc or nerve fiber layer. This long-term tracking helps manage glaucoma to preserve vision.