The ophthalmoscope is a handheld instrument used to examine the internal structures of the eye, specifically the posterior segment known as the fundus. This examination, called ophthalmoscopy or funduscopy, visualizes the retina, the optic nerve head, and the retinal blood vessels. Observing these structures offers a non-invasive window into the body’s microcirculation and neurological health, making the fundus exam a valuable part of comprehensive physical assessments.
Preparing for the Examination
The initial step in preparing for a fundus examination involves controlling the ambient light in the room, which should be dimmed or darkened completely. Reducing the light level encourages the patient’s pupil to naturally dilate, providing a larger window through which to view the structures at the back of the eye. A larger pupil significantly enhances the contrast and the field of view, thereby making the examination process more efficient and thorough.
Proper positioning of both the examiner and the patient is important for the procedure. The patient should focus their gaze straight ahead at a fixed, distant object to minimize eye movement and keep the eye in a neutral position. The examiner should position themselves comfortably, typically sitting or standing at the same height as the patient, to allow for a steady approach toward the eye.
The ophthalmoscope must be configured correctly for the examination. The aperture setting should be selected based on the size of the patient’s pupil; a medium or small spot of light is appropriate for an undilated pupil. The diopter wheel should be initially set to zero, or adjusted to compensate for the examiner’s own refractive error. This initial setting allows the examiner to begin the approach from a distance with a relatively clear focus.
The examiner should adhere to the “right-right, left-left” principle: use the right eye and right hand for the patient’s right eye, and the left eye and left hand for the patient’s left eye. This technique ensures the examiner’s head remains clear of the patient’s nose, allowing the closest possible approach. If the pupil remains too small for an adequate view, mydriatic eye drops may be used to pharmacologically dilate the pupil.
Mastering the Examination Technique
The examination begins from a distance of about 12 to 15 inches (30 to 50 cm) away from the patient, with the light beam directed toward the pupil. At this distance, the examiner should look through the sight hole of the ophthalmoscope to locate the red reflex. This reflex confirms that the light is correctly aimed through the patient’s pupil and is illuminating the fundus.
While maintaining the red reflex in view, the examiner must move closer to the patient’s eye, ensuring the ophthalmoscope remains in line with the patient’s visual axis. The goal is to get within 1 to 2 inches (3 to 5 cm) of the patient’s cornea. The index finger should remain on the edge of the diopter wheel to allow for immediate focusing adjustments during the approach.
Once the examiner is close to the eye, the view will initially be blurry due to the combined refractive errors of both the patient and the examiner. The diopter wheel must be rotated to bring the retinal structures into sharp focus; adjust the wheel until a clear retinal blood vessel is observed. If the examiner is nearsighted, they will rotate the wheel toward the minus (red) numbers, and if farsighted, toward the plus (green) numbers.
The systematic exploration of the fundus should begin by focusing on the retinal periphery before moving toward the more central structures. If the optic disc is not immediately visible, the examiner can locate a retinal vessel and follow its path backward until it converges with the disc. To examine the entire fundus, the patient should be asked to look in various directions, which brings different areas of the retina into the examiner’s field of view.
Recognizing a Healthy Fundus
A successful fundus examination culminates in the clear visualization of a normal, healthy fundus, which presents distinct characteristics. The optic disc, where the optic nerve enters the eye, should appear round or slightly oval and have a pinkish-orange color. Its margins, or borders, should be distinct and sharply demarcated from the surrounding retina.
The center of the disc contains a pale depression called the optic cup, and in a healthy eye, the ratio of the cup’s diameter to the disc’s diameter is typically small, often around 0.35 or less. The retinal vessels radiating from the optic disc should appear clear, with arteries being slightly narrower and brighter red than the darker, wider veins. The eye is the only location in the body where microcirculation can be directly observed in this manner.
The macula, located temporal to the optic disc, is responsible for sharp, detailed central vision and appears as a small, slightly darker area of the retina. The central-most pit of the macula is the fovea, which may exhibit a small, bright pinpoint of reflected light known as the foveal light reflex. The healthy retina maintains a uniform reddish hue, and the overall view should be crisp, indicating clear media throughout the eye.