From the Research
The large aperture on the ophthalmoscope is used to examine the optic disc and retinal vessels. This aperture provides the widest field of view and the brightest illumination, allowing for optimal visualization of these important fundus structures. When performing fundoscopy, the examiner should select the large aperture setting (typically indicated by a large circle on the aperture dial) and approach the patient's eye at approximately a 15-degree angle from the temporal side. The large aperture allows sufficient light to enter the eye and illuminate the fundus while providing an adequate viewing area to assess the optic disc margins, cup-to-disc ratio, and the course and caliber of retinal vessels. This is important for detecting abnormalities such as papilledema, optic atrophy, arteriovenous nicking, or retinal hemorrhages. While smaller apertures are useful for other purposes like examining through undilated pupils or focusing on small lesions, the large aperture remains the standard choice for routine examination of the optic disc and retinal vasculature.
Some studies have investigated the relationship between retinal vessel caliber and optic disc characteristics, such as the study by 1, which found that smaller optic discs were associated with narrower retinal arterioles and venules. However, these studies do not provide guidance on the aperture setting for ophthalmoscopy. The key consideration is to use the large aperture to provide the best possible view of the optic disc and retinal vessels, as this is essential for detecting abnormalities and monitoring disease progression.
In terms of specific techniques, the examiner should use the large aperture setting and adjust the focus to optimize the view of the optic disc and retinal vessels. The use of multiple en-face images, as described in the study by 2, may also be helpful in certain cases, such as optic disc swelling. However, this is not directly relevant to the choice of aperture setting for routine ophthalmoscopy.
Overall, the large aperture on the ophthalmoscope is the best choice for examining the optic disc and retinal vessels, due to its ability to provide a wide field of view and bright illumination. This allows for optimal visualization of these important fundus structures and facilitates the detection of abnormalities.